Links to subsections in this chapter:
This is the unofficial, WWW version of the VORTEX-95 Operations Plan. It may differ from the published operations plan which is available by 15 March from the National Severe Storms Laboratory.
The VORTEX-95 Field Experiment will be conducted in a very different manner from storm intercept projects of the past. All field resources will be focused on only one storm at a time. The goal is to obtain datasets sufficiently comprehensive that all of the hypotheses can be adequately evaluated. It is of great interest to discover why some supercell storms do not produce tornadoes. For this reason, and the difficult logistics of moving more than 15 field teams, we likely will remain with supercell storms that are not tornadic until they have weakened or changed structure and are no longer supercells. Every field team will conduct very specific scientific data gathering missions (
" Team Descriptions and Missions" ). Traditional " storm chasing" (where all teams maneuver for prime photography positions near the tornado, and often move from one storm to another) will not be permitted.The remainder of this chapter describes an
" experiment matrix" that will be used to coordinate VORTEX activities. The rows represent stages of storm development, with additional rows for pre-storm and post-storm activities. The columns represent four types of storms: LP, Classic, and HP supercells, and landspout-producing storms. The first three are subdivided into fast-moving and slowly-moving categories.
The stage of storm development (rows) will be assessed by the Field Coordinator (FC) during field operations. The type of storm and motion will be assessed through visual and radar observations if a storm is in progress, or will be assigned based on the operational forecast prior to storm development. As the type of storm, motion, or stage of development changes, all participants will be informed by the FC via radio broadcast or personal briefing (the NOC will be informed via telephone). A new activity will be announced, as determined by the entry in the Experiment Matrix. All participants can then determine their new missions by referring to the descriptions of the activity and team missions found in
" Team Descriptions and Missions" . These mission descriptions for a given activity will be referred to as " activity cards" ; each team will find a laminated set of activity cards for their particular team in the back of the OP notebook in their vehicle.
The classification of storm type (HP, Classic, LP, or landspout) is somewhat subjective. On many supercell days, storms may proceed from LP to Classic, and even to HP, during their life cycles. In general, we do not anticipate landspout tornadoes in environments supportive of supercells, and vice versa. For the sake of experiment selection and coordination, storms will be classified as LP if there is little or no precipitation visible below the updraft cloud base. If there is more extensive precipitation, but the center of rotation or wall cloud is not completely wrapped in rain, the storm will be classified as a Classic supercell. If it is completely enshrouded and largely obscured by rain, it will be classified as HP. Some storms will transition back and forth between HP and Classic; typically these storms produce multiple tornadoes in a cyclic fashion.
Several comments must be made here regarding non-supercell scenarios. On many days with large CAPE and helicity, the lid is strong and no storms form at all. It is often a fine line between having supercells and clear skies. In general, the teams will stay in the projected storm initiation area " Slow" scenarios) or well ahead of the initiation area " Fast" scenarios) until an hour or two before sunset. On other occasions, supercells will be forecast, but multicellular storms with significant cold pools will form instead. On these days, we will perform experiments aimed at determining why multicellular storms formed when supercells were expected, but we will minimize our expenditure of resources and attempt to stay near the system in case the storms evolve into supercells.
We are subcategorizing storms based on motion because intercept strategies are quite different when storms are slow moving compared to fast moving. Experience shows that if a storm is moving faster than about 30 m.p.h., most road networks do not allow for intercept teams to stay with the storm. In VORTEX, we will be attempting to coordinate the activities of about 15 vehicles around a target storm, so we will arbitrarily set the breakpoint between fast and slow at 25 m.p.h. This breakpoint speed may be adjusted as we gain experience in the field. Storms moving faster than this will be the subject of " one-shot" experiments followed by redeployment to another storm if possible; if storms move more slowly we will attempt to maneuver around them for their entire life cycles.
It is important to understand that we are presenting highly idealized descriptions and figures in this section. In the field, problems are bound to occur. Vehicles will experience logistics and mechanical problems, storm structures will be far different than the idealization, and the road networks will never permit us to have vehicles in the right spots at all times. However, the FC computer will show every vehicle's location and all available roads. This will permit us to have teams close to adequate positions much of the time, again depending on road availability and storm structure and behavior. In the following sections, each activity in the Experiment Matrix is described.In VORTEX-95, an operations decision will be made at 0900 LT. The decision will be posted immediately on the Internet using a short email message to all participants, and will be made available on a phone answering machine. Participants that do not have access to email might want to make arrangements to call another participant who does, because the phone answering machine at NSSL will be heavily utilized. The 0900 decision will be one of the following: GO, NO-GO, or STANDBY. If the status is GO, all participants should be at NSSL by 0930 LT; the ground teams will depart at 1000 LT. If the status is NO-GO, there will be no operations. A daily weather briefing/logistics debriefing will be conducted in the NSSL Main Conference Room at 0930 LT. This briefing will usually be conducted by Erik Rasmussen, but on some occasions the briefing will be conducted by one of the VORTEX forecasters or PI's. There will be a weather and operations discussion of 10-15 minutes duration, followed by a discussion (PI's and team leaders only, please) of all logistical issues and observations from previous missions. In addition to this briefing, a self-briefing workstation (maintained and served by the NOAA Storm Prediction Center) will be placed in the NSSL lobby. This will be available for use by all VORTEX participants, but priority will be given to VORTEX PI's and team leaders in that order.Only one type of STANDBY will be used: if the status is STANDBY, a final operations decision will be disseminated at 1100 LT. If the 1100 LT status is GO, participants must be at NSSL by 1130 for a 1200 departure. However, key participants, including team leaders, the aircraft and local coordinators, and PI's are encouraged to be at NSSL at 0930 for the briefing.This plan is considerably simpler than the one used in 1994. Please note that for operations there will be only two possibilities for the participants: 0930 LT arrival for a 1000 LT departure, or (if STANDBY is declared at 0900) 1130 LT arrival for a 1200 LT departure. The notification email message will contain only two items so that it can be prepared quickly. It will contain the GO/NO-GO status (or sometimes STANDBY on the 0900 message), and it will contain one line regarding the possibility of an overnight stay in the field (NO/POSSIBLE/YES). A later email message may be issued which explains the reasons for a NO-GO decision. The reasoning behind a GO decision will be explained at the daily weather briefing, and during a radio (main VHF channel) briefing at departure time.The 0900 LT operations decision will be made in the following manner. If 1200 UTC soundings, morning analyses, and the previous evening's model data indicate a good chance for severe convection within about four hours of Norman, the operations decision will probably be GO, and we will get to the field early to conduct one of the INIT experiments (these will be conducted much more formally and aggresively than in 1994). If it appears there is a reasonable chance of severe convection beyond about four hours drive time, the decision will probably be GO, and we will consider aborting and returning to base if the forecasters determine later that conditions no longer look favorable. The STANDBY decision probably will be used in three circumstances: 1) the conditions appear " marginal" and it appears there is a good chance of conserving resources by declaring a NO-GO at 1100 LT; 2) the conditions appear reasonably favorable within about four hours drive time, but there is more than one potential target area and drastically different routes would be used to reach them; or 3) the armada might need to depart for an overnight stay at a distant location for next-day operations near the fringes of the VORTEX domain. In the latter case, additional time would be required to choose the best target region.All participants should assemble at NSSL. The VORTEX cars will be in the west end of the parking area; drivers of the mobile labs and FC vehicle should get these vehicles at the NSSL maintenance facility and move them to the NSSL parking lot. Non-NSSL participants should park their private vehicles in the areas west of the NSSL parking lots (near the Doppler and SEB buildings).During PREP, participants will make sure their vehicles and equipment are ready for the day's operations, with sufficient supplies for two additional days and overnights. Vehicles must be refueled and the oil and engine should be visually inspected. Do not run auxiliary equipment (especially the VHF transceivers) without the engine running to avoid draining the vehicle battery. The team leader is responsible for going over the pre-departure checklist for the vehicle (
" Checklists"
).
Calibration checks will be performed on the mobile mesonet equipment (
See " Mobile Mesonets".
) in the parking area. The previous day's mobile mesonet data will be inspected by the Quality Assurance Manager prior to departure for gross errors using a graphing program.
This activity will commence when all preparations for field work are complete. All teams will depart from the NSSL at the same time and travel together to the target region (staying within 10-15 miles of the FC vehicle). We will stop for refueling based on the requirements of the vehicles having the lowest range capability. It is strongly recommended that all vehicles top their tanks at the refueling stops. We will attempt to refuel prior to commencing storm intercept operations. All participants should attend to personal needs during the refueling stops; it will not be feasible for vehicles to drop out of the caravan for more than a few minutes to accommodate personal needs. If vehicle maintenance problems occur, you will call a special toll-free phone number for assistance (
See " In case..."
).The travel window duration depends on the required travel time from the morning departure site to the target area. During the travel window, the NOC forecasters will be successively refining the forecast of initiation area, time, storm type, and location of first tornado occurrence. As the forecasts are refined, the route plan will be refined. If we arrive in a target area prior to TCU development, we will move to a prestorm activity (INIT1-3).
TRAVEL activities will include 6-sec mobile mesonet data collection by all teams. In addition, certain preparations for intercept experiments can be conducted in the vehicles as we move toward the target area (e.g. camera, film, documentation preparation). Briefings will be broadcast on the VHF radio as required (e.g. when new information is received from the NOC). Before every briefing or nowcast broadcast, the FC will broadcast a notification that a nowcast is about to be given so participants can prepare to take notes if they choose.
[Diagram of INIT1]
The goals of this experiment are the same regardless of whether the boundary that is expected to initiate convection is a warm front, stationary front, or dryline. We will deploy three M-CLASS teams along the boundary, to the side on which convection is expected to form (generally north of a warm or stationary front, and east of a dryline). The P-3 and the rest of the surface armada will perform transects of the boundary on a road that is roughly normal to the boundary, with longer legs toward the side of the boundary where convection is expected to form. The ELDORA will collect data using along-line legs of roughly 100 km length.In this experiment, M-CLASS teams and the ELDORA will be used gather data to study the variability along the boundary which may lead to certain locations being favored for convective development, and certain storms being favored for tornado development. In addition, surface teams and M-CLASS teams, as well as the P-3 aircraft, will be used to assess the variability across the boundary in order to understand how it propagates, how it alters the local vertical wind profile, and why it is associated with the initiation of storms.
This experiment will be conducted when a boundary is expected to play a role in the initiation of storms, regardless of the anticipated storm type. It will be conducted on a target-of-opportunity basis when the field team caravan arrives in a target area prior to the development of deep TCU. Three mobile labs will be deployed to obtain soundings at a space scale of about 30 km on the moist side of the boundary. The fourth and fifth mobile labs will be positioned in the boundary zone and toward the quiescent side of the boundary. The surface teams will make continuous box-pattern and zig-zag transects of the boundary, as directed by the FC, to measure evolution of surface conditions. Both along- and across-boundary variability in surface conditions will be assessed.
Prior to the arrival of the aircraft and surface teams at the boundary, its position will be assessed using conventional data at the NOC. A target location for the central point of the experiment will be chosen in discussions between FC and NOC, and this point should be the intersection of the boundary with a major highway oriented roughly normal to the boundary, as close as possible to the forecasted point of the initiation of severe convection. Ideally, there will be one or two nearby parallel highways (normal to the boundary) on which surface teams can operate to collect data. If the surface teams arrive first, one or two teams will be sent ahead to pinpoint the location of the dyline and report it to NOC or FC. Once this point is found, the rest of the armada will be deployed on data gathering missions. If the aircraft arrive first, the P-3 should perform its first low-level transect over the chosen target highway, and report the location of the boundary to FC or NOC.
[Diagram of INIT2]
The INIT2 experiment will be conducted whenever it is expected that storms will be initiated near the intersection of low-level boundaries, and the field armada arrives in the target area prior to the development of TCU. The goal of this experiment is to assess the nature and degree of inhomogeneities in the prestorm environment of supercells that are initiated near these fronts. Because of the thickness gradient that can persist near these boundaries, thermal wind considerations suggest that low-level vertical shear is enhanced, and thus storm-relative environmental helicity may be greater for certain storm motions on the cool side of the front compared to the warm side. Other possibly important parameters will vary across the front, such as CAPE, evaporation potential, CIN, etc.The field strategies will be very similar to those used to assess the boundary environment in INIT1, except that the emphasis will be changed to sampling all three airmasses involved. The P-3 will be used to determine the slope of the isentropic surfaces north of the front 50 km east of the dryline. The ELDORA will be used to gather wind and thermodynamic data about 100 km east of the dryline, in the " warm sector" , and in the dry air behind the dryline. The surface teams will perform transects in the area deemed most likely to contain storm initiation. As with INIT1, the first teams on site will be used to refine the location information provided by the NOC. This experiment will also be coordinated based on a center point as shown in the figure. The center point will be the intersection of a major highway with the front that features the strongest thermal contrast (e.g. the ~ east-west oriented stationary front, warm front, or outflow boundary).
[Diagram of INIT3]
INIT3 is an experiment designed to assess the characteristics of the pre-storm environment in the vicinity of a boundary that is likely to be associated with landspout-producing storms. It is felt that these storms develop near boundaries that have small density contrasts across them, and thus are vertically oriented and move very slowly. The boundaries apparently must be regions of large horizontal shear of the horizontal flow, and small vertical shear. In addition, it appears that large lapse rates immediately above the LFC are conducive to landspout-producing storms.The field strategies are designed to assess the degree of density contrast across the boundary and the amount of horizontal and vertical wind shear. The P-3 will fly a box pattern similar to the field teams'pattern mainly to assess the horizontal wind distribution.If deep clouds begin to form, the field teams must be ready to converge quickly on a target cloud in anticipation of tornadogenesis.REGROUP
The activity REGROUP will be used to bring all of the field teams into close proximity to the FC prior to a major change in field activities. For example, if the field teams have been involved in INIT1, the mobile ballooning labs may be 50 km or more away from the FC. If deep convection begins to develop, they must be brought into their correct storm-relative positions.At the beginning of REGROUP, the FC will give instructions to each field team on the route they are to take to rendezvous with the other teams. Once the sufficient level of coordination has been developed, the teams will move to a new target storm. As the target is approached, various teams will leave the caravan at different points to commence storm-relative missions. It is also possible that field operations will be terminated if no acceptable targets exist.REGROUP may also be used to re-establish field coordination if a failure in communications or logistics has caused the loss of coordination.
[Diagram of NCB-S]
If a deep towering cumulus is showing vigorous growth, and perhaps producing a small anvil cloud, and this cloud has a sufficient probability of developing into a target storm, the FC (in consultation with the NOC) may choose to commence activity NCB-S. This experiment is designed to document the early development of a CB which we hope will become a tornadic storm. NCB-S will be used if expected storm motions are less than the fast-motion threshold velocity (25 m.p.h.).In this experiment, we are especially concerned with documenting the early cloud growth, the development of precipitation, and the consequent development of gradients in equivalent potential temperature (qe) near the surface. It is possible that these gradients play a role in the development of low-level rotation.Ideally, we will obtain our first set of upper air observations during this stage of cloud development. NSSL1 will obtain an updraft sounding, and NSSL2, NSSL3, NSSL4, and NCAR will commence soundings according to one of the sounding strategies (
see storm mode
and
environment mode
) chosen by the PI's at the morning briefing. Also, we will attempt to bring the aircraft to the vicinity of this target cloud to commence pseudo-dual Doppler radar observations.The surface teams will be used as mobile mesonet " probes" in this stage. Their positions will be adjusted so that they can readily be deployed for their appropriate data gathering missions should the storm start to show rotation. If rotation or cyclonic shear are observed, we will commence the ROT-S experiments. In the
diagram
, the areas that should be sampled by each team are denoted with ellipses. These are idealizations, but the teams should attempt to sample the indicated part of the storm as thoroughly as possible. This means it's important to keep moving. Teams should not park for extended periods of time, and should never be parked at the same location.Forecasts of rapid motion require us to pursue a completely different strategy when CB development first occurs. The FC, in collaboration with the NOC, will attempt to forecast the amount of time that will pass between a cloud first becoming a CB and first producing a tornado. It will be impossible, due to logistics, to stay with a CB that is moving faster than the threshold velocity (25 m.p.h.). Thus, the field teams will move together, in a caravan to the region likely to experience tornado activity. This is why there is no activity called " NCB-R" ; instead, we will remain in the TRAVEL activity during nascent CB development in the rapid-motion scenario.It should be noted that a lot of evolution can occur during this stage as TCU and small CB's merge or dissipate. During this stage, by watching the evolution, we hopefully will be able to commit to observing the CB that eventually will become tornadic.
[Diagram of NCB-L]
In VORTEX-94 we did not have any days on which landspouts were expected. It is possible that these conditions are much more rare in the Central Plains than in the High Plains (e.g., eastern Colorado). However, it is still a priority in VORTEX to intercept a landspout because it will be very interesting to contrast the dynamics of this type of vortex with supercell tornado dynamics. If the forecast calls for landspout activity, we will commence activity NCB-L when vigorous updraft development is first observed. Landspout-producing CB's commonly show a small area of rotation in cloud base immediately prior to landspout development; this has the appearance of a swirl and may contain a small funnel cloud as well. Less often, a dust whirl below cloud base is observed before rotation in the cloud base. Because of the importance of moving to the immediate area of tornadogenesis, one of the primary missions in NCB-L will be to monitor the cloud base and surface below for any sign of rotation. The FC will request frequent observations from field teams. If a swirl or dust whirl is spotted, the FC will immediately notify the field teams to commence activity NCB-L.The other mission of the field teams during NCB-L is to document the low-level wind and thermodynamic characteristics in the vicinity of the boundary that is initiating the landspout-producing storm. It is hypothesized that these tornadoes form when an updraft passes over a pre-existing low-level whirl, which is then stretched vertically and contracted horizontally into a tornado. We hope to obtain sufficient low-level wind data to evaluate this hypothesis. Tilting of baroclinically generated horizontal vorticity also may play a role.In the
diagram
, the domains of the PROBEs are shown with ellipses. PROBE1, 6, and 7 are shown to be between the updraft and a downshear precipitation area. This assumes that upper shear is strong enough to cause separation. In NCB-L, it is quite likely that the FC will assign these teams special missions based on his display of telemetered observations. The missions will be focused on locating and documenting the mesoscale boundary, wherever it is. If precipitation does develop, these three teams will be vectored to positions to document the developing gust front and its interaction with the boundary and pehaps the landspout itself.The mobile ballooning teams will attempt to make a loosely coordinated sounding launch in a box surrounding the developing cloud. The purpose of this sounding is to assess the degree of instability and vertical vorticity in the immediate vicinity of the target cloud. The P-3 will fly a similar box pattern to obtain higher-resolution wind data and to estimate the circulation around the storm at a low level.
[Diagram of ROT-S]
This activity commences with the first observation of rotation or cyclonic shear in a developing storm, and ends with the development (actual or imminent) of the first tornado. The most important focus of this activity is to document all of the changes in the storm that lead to tornadogenesis, particularly in low levels.At the surface, many of the field teams will be used as mobile mesonets to gather data on the locations, strength, and evolution of qe gradients and associated disturbances in the low-level wind field. It is expected that these gradients and convergence/vorticity zones will sharpen with time during this activity. Two mobile mesonet missions will be particularly important and carefully coordinated. PROBE1 will maneuver in a few-kilometer diameter region near the " tip" of the precip region which is originally near or just downshear of the updraft, but propagates cyclonically around the updraft as rotation increases. PROBE4 will be kept in a position just south of the wall cloud or center of rotation to watch for, and measure, the development of strong rear-to-front storm-relative flow and drops in qe in the developing RFD.The primary objective during the ROT-S activity is to gather data that will allow us to establish why there is a mesocyclone aloft, what leads to low-level intensification of the mesocyclone, and what is the low-level evolution that leads to tornadogenesis. By contrast, the TOR-S activities are designed to assess the processes that maintain the tornado or lead to its demise. As rotation increases, the teams will be vectored closer to the storm-relative locations required to perform their missions in the TOR-S activities. The teams will be polled frequently by the FC for their positions, for their weather information, and for azimuths of important cloud and storm features.The aircraft will continue short-leg passes on the inflow side of the storm in order to monitor the evolution of the low-level mesocyclone, precipitation distribution, and associated flow fields. NSSL1 will continue to obtain updraft soundings, and NSSL2, NSSL3, NSSL4, and NCAR will be obtaining soundings according to one of the pre-designed sounding plans.
[There is no diagram of ROT-R. The official published VORTEX-95 Operations Plan contains some additional information not published in this WWW version.]
For most teams, this is not a data-collection activity. It is a continuation of the TRAVEL activity. Most of the teams will remain 30-40 km ahead of the storm in a tight caravan (within communication range of the FC). One or two of the teams (PROBE1 or PROBE8) will be selected to travel to within about 10 km of the updraft to monitor it for signs of imminent tornadogenesis, and to provide tracking triangulation to the FC. These teams will be selected in the field on the basis of mobility, availability, and communications capabilities (i.e., cell phone capability).During this activity, the FC will be in close contact with the NOC and the P-3 aircraft to monitor the storm evolution. As circulation increases, the gap between the updraft and the caravan will be decreased. Our primary objective will be to maintain the correct critical distance between the caravan and the updraft as the storm nears its tornadic phase. We want to be able to line up along a road across the storm's path once a tornado develops. We must move to the positions quickly. Thus it is important that each team be familiar with their correct storm-relative positions once we commence TOR-R. Also, the caravan should be arranged in roughly this order: FC, PROBE6, PROBE5, PROBE1, TUR1 and TUR2, CAM1, NSSL1, PROBEs 4, 2, 3, and 8, and the other M-CLASS teams. If we use this approximate order, there will be a minimum of deployment delay when we enter TOR-R. The FC will pull off to observe the storm as we commence TOR-R. Each team must note their odometer as they pass the FC, because he likely will instruct each team to drive a specific number of miles beyond the FC and await further specific deployment instructions.The strategy above should be adequate since we anticipate that we will have one opportunity to collect data on a tornadic supercell. If we wait until the tornado appears imminent, we will possibly be able to collect tornadogenesis as well as tornado dynamics data as the storm passes. Tornadoes tend to be longer lived with fast-moving classic supercells, and have longer tracks, which improves the chances of success using this strategy.
[Diagram of LANDSPOUT]
This activity commences with the sighting of cloud-base rotation, a cloud swirl, or a dust whirl, and terminates when the landspout dissipates. This activity is designed to maneuver the field teams into positions to enable them to collect tornado dynamics data, and to collect data on the behavior of any storm-scale frontal systems in the vicinity of the landspout.Experience indicates that landspouts are typically rather small and weak when they first form. For this reason, it is not necessary for teams to be unduly cautious when maneuvering below a cloud base showing signs of rotation or a swirl (in the landspout scenario!). When near or below such a feature, simply maintain a sharp lookout for dust whirls, rising tumbleweeds, etc. nearby, and be prepared to maneuver a safe distance from the developing whirl. Mature landspouts are quite capable of overturning vehicles and may start moving erratically near the end of the lives, so exercise reasonable caution.During this activity, the FC will request azimuths of the dust whirl or cloud swirl on a frequent basis from those teams that are not moving toward the vortex for data collection. The PROBE1and PROBE7 teams will attempt to track the outflow from a nearby rain core (if it exists) in order to help the FC determine when the vortex might alter its motion or behavior radically and alert the field teams. PROBE4 and PROBE6 will monitor the airmass to the immediate rear of the updraft base on both sides of the boundary. The other three mobile mesonet teams will collapse to a range of less than 5 km from the whirl if possible. The FC will direct all of the PROBEs on routes to optimize data collection. The photography, turtles, and radar teams will move close to the vortex (ranges of 1-2 km). We will attempt to position all these teams so that the vortex will move away from them should any outflow overtake it. It would be interesting to map the fields of qe and velocity in close proximity to detect a spiral patterns in the inflow, the wrapping of the boundary, etc.
[Diagram of TOR-S]
This activity commences when tornado development occurs or seems imminent in a slow-moving supercell. This activity will most likely be used for a Classic storm, but could be used for an LP or hybrid. Different experiments are planned for HP storms (HP-S and HP-R). It is designed to gather data to address the tornado dynamics hypotheses, and to assess the processes that maintain tornadoes or lead to their demise.In particular, a long-lived tornado probably requires the ongoing generation of vorticity in its inflow air, whereas shorter life cycles could perhaps be maintained simply through friction-driven near-ground convergence during the spin-down of the low-level mesocyclone. Thus, one of the important missions during the tornado is to locate and quantify the qe near-ground gradients and surface boundaries that exist in the tornado's environment. It is also vital that in-situ (turtles) and near-tornado remote-sensing (mobile radars) data be obtained during this activity.Many storms produce tornadoes in a cyclic manner, with each new tornado forming ahead of the previous one near where the surging gust front " occludes" the storm-generated forward-flank front. We are faced with the dilemma of needing to observe the process of tornado demise on one tornado at the same time that we need to observe the processes of cyclic tornadogenesis. This decision will be made " on-the-fly" by the FC. If the road network, storm motion, safety considerations, and/or already-acquired cases argue in favor of redeploying forward for cyclic tornadogenesis observations, that is what the FC will order done. If the road network or storm speed make this deployment difficult, and/or we do not have sufficient documentation of tornado demise, we will remain with the first tornado to dissipation, and then attempt to relocate for the genesis of the second subsequent tornado. Either the FC will continue the activity TOR-S centered on the ongoing tornado, ir will announce activity ROT-S centered on the new mesocyclone/wall cloud. If the latter is announced, all teams should commence ROT-S activities relative to the announced position of the wall cloud. The decision and rationale will be broadcast in the regular FC nowcasts. All field team members should be cognizant at all times of the possibility of cyclic tornadogenesis. This implies that teams ahead of an ongoing tornado must monitor cloud motions in the updraft base (including overhead!) ahead of the tornado for increasing rotation. This can be a very rapid process. Any observed rotation or dust whirls should be reported to the FC immediately.In TOR-S we will attempt to photographically document (16 mm movie film) tornadoes from two or three angles simultaneously. Through stereo photogrammetry, we should be able to retrieve the 4-D wind field; this data set will be especially thorough if the tornado is semi-transparent with many patches of dust and condensation visible. This data set will augment the Doppler velocity data obtained by the radar teams.
[Diagram of TOR-R]
Fast storm motion will make it impossible for the field teams to maneuver and successfully collect data in the same manner as in TOR-S. Thus, we will position the field teams on one road that is roughly perpendicular to the tornado path, and let the storm move over this stationary array of sensors. If the storm is rather steady (which can be assessed in post-analysis using P-3 aircraft data) as it moves across this array, we will obtain a thorough low-level mapping of meteorological parameters.Deployment will require very strong coordination. Team leaders must be very familiar with the TOR-R mission in advance. The following table shows the operational requirements for a successful TOR-R deployment, using the assumption that it takes only 10 minutes to get all vehicles into position after the activity begins, and that we desire to collect comprehensive data on a region extending at least 10 km downshear of the tornado. The " lead time required" entry is the amount of time that will elapse between the deployment decision and the tornado crossing the highway. The " lead distance required" entry shows how far ahead of the tornado, as measured along the projected path, the armada should be when the deployment decision is made. If the armada is closer than this distance, then the storm will not be thoroughly sampled in the important downshear region. If the armada is too far away, the chances that the tornado will dissipate before it passes over the deployment highway increase. As designed, the tornado must persist for 15-20 minutes beyond the time the deployment is announced, and preferrably much longer so that data is collected on a mature stage of the tornado rather than the dissipating stage. If the lead distance is more than several kilometers less than that in the table, the deployment will be cancelled because of safety concerns and the fact that very little of the storm ahead of the tornado would be sampled.During deployment, the FC will give very specific site instructions. The instructions will be relative to a known landmark the team will pass. Examples might be " 1.3 miles north of the intersection of hiway 9 and 256" , " 3.3 miles north of the FC vehicle" , " 0.6 miles beyond the river bridge" , etc. Team leaders or technicians must make clear, careful notes of the odometer and vehicle heading at various landmarks during deployment. If this is not done, it will become very difficult to position the team correctly. Guessing distances could be a lethal mistake. Teams should move to those sites as quickly as possible, stop in a location out of traffic and away from potential wind-blown hazards, with your vehicle correctly pointed into the strongest anticipated winds, and begin to carefully monitor the storm and its motion. One team member must stay near the radio in case the FC recommends that you evacuate the site for safety reasons.Safety decisions are the responsibility of the team leader. Err on the side of caution. If you must abandon a site, notify the FC and leave. The FC may be able to provide guidance. Make the decision to evacuate before conditions become too severe to safely move. The mobile labs will be arrayed from just to the right of the projected passing point of the wall cloud (NSSL1) to well to the right in the inflow (NCAR). One coordinated launch will be made prior to the passage of the storm. The CAM1 and RAD1 teams will establish a baseline for tornado movie photography. Turtles will deploy, working outward fromthe center of the projected mesocyclone path, and RAD1 team will remain to the right of the path. PROBE's 1, 5, and 6 will collect data to the left of the mesocyclone path, and PROBE's 2, 3, 4, and 7 to the right. PROBE8 will be used either for triangulation/spotting, or deployed well to the left of the storm near the edge of the precipitation. The overall sampling objective is to use the mobile mesonet to sample near the periphery of, and away from, the mesocyclone, and to use turtles to sample the mesocyclone and tornado itself.Since the mobile mesonet teams will be freed from driving and route selection concerns, they will be utilized heavily to gather azimuth data for real-time triangulation and tracking of storm features. This will help ensure the safety of the teams that are closest to the mesocyclone path.
If several tornadic cells are possible (e.g. ahead of a dryline), the armada will move as far north as feasible and target a tornadic storm in that region. After collecting data on the first storm, it is possible that there will be another target storm to the south or southwest which can be targeted if the armada moves quickly south or southeast.
[Diagram of HP-S]
For purposes of VORTEX field work, we will define an HP supercell as one with so much precipitation surrounding most of the mesocyclone that it is not possible to operate vehicles safely, and perform all data gathering missions, near the mesocyclone. Some supercells that are tending toward HP structure have heavy precipitation in the " hook echo" region around parts of the mesocyclone, but it is still possible to effectively investigate this region. In many storms, precipitation becomes so extensive that investigations are no longer feasible. However, these storms are a common and important form of supercell, and we will endeavor to obtain new knowledge of these storms. As our knowledge increases, we may discover methods to safely investigate the mesocyclone region.Once a storm becomes and HP supercell we will commence HP-S if the storm is slow-moving. In some HP storms, particularly if they evolved slowly to HP from Classic, there is a region of several miles depth to the left of the tornado and/or mesocyclone with little or no precipitation and tolerable winds. If this is the case, several of the teams with close-in missions (RAD1, CAM1, PROBE1, TUR's) will be allowed to operate in that area. If that area fills in with precipitation, these teams should abandon the storm by driving toward the left, rear part of the storm (e.g. toward the NW in an eastward-moving storm). PROBE6 will be used to monitor conditions in that part of the storm. In several HP storms, tornadoes have been clearly visible from the PROBE6 vantage point silhouetted against the bright sky of the inflow region.
All of the PROBE's will perform missions very similar to those in the activities for Classic storms. PROBE's 2 and 3 will evaluate the forward flank baroclinity. PROBE5 will make measurements in the core. PROBE7 will be deployed across a broad part of the inflow region. PROBE4 should operate in the precipitation to the right of the mesocyclone measuring the qe and winds behind the RFD gust front, and attempting to locate that gust front. PROBE4 should not drive deeply enough into the precip that they can't see the clear air to the right of the storm; further, if cyclonic winds become too strong, this team should assume it is getting too close to the tornado, and move back toward the right side of the storm.The RAD and TURTLE teams will be allowed to operate closer to the mesocyclone if their respective team leaders feel that it is safe and feasible to do so. The FC will be able to provide the usual guidance concerning roads, terrain, etc. However, with limited teams in the precipitation-filled region, it probably will not be possible to accurately triangulate and track the tornado or wall cloud.All participants should also be aware that on several HP storms, unusually strong ground-relative inflow is encountered (large area with winds strong enough to break limbs out of trees). Thus, beware of the possibility of flying debris, and blowing dust, sand, and gravel. Also, slow-moving HP supercells have been observed to cause flooding rains, so be especially cognizant of this threat. If you feel that you cannot perform your mission safely, feel free to move away from the storm and contact the FC.
[Diagram of HP-R]
Based on experiences in VORTEX-94, an experiment has been designed for the fast-moving HP scenario. We will use this strategy regardless whether the HP is tornadic or not. The primary objective is to obtain as much data as possible on these storms, without placing surface teams in the direct path of the mesocyclone or tornado. We found in VORTEX-94 that the mesocyclone associated with the fast-moving HP can produce damage of at least F1 intensity, and the mesocyclone region should be avoided by surface teams at all times.The deployment concept is modeled after TOR-R; refer to
section on TOR-R
for further details about this deployment strategy. Deployment will be done on a highway that is roughly normal to the path of the HP. The entire mesocyclone region will be sampled with turtles if they can be safely deployed. The peripheral part of the storm will be sampled by mobile mesonet units primarily deployed in stationary fashion. HP-R differs from TOR-R in the following respects. PROBE4 will be used to track the position of the RFD gust front as it approaches the deployment area. PROBE8 will also be deployed for storm tracking, and will probably be asked to provide measurements of the azimuth of the lowest part of the updraft base (often barely visible in the precipitation core). PROBE1, 5, and 6 will pass through the forward flank precipitation. After doing this, they may be directed to make short drives into the core and back out as the mesocyclone approaches the deployment area. Finally, CAM1 may be positioned to the left rear of the mesocyclone; it has occasionally been observed that tornadoes can be seen and photographed from that angle.
If supercells were anticipated but organized multicellular activity occurs, or if a supercell loses obvious signs of rotation capable of producing tornadoes, or the gust front is observed to propagate away from the main updraft, we will change to the O-C-S activity. The main goal is determine the processes that cause a storm to lose, or fail to attain, supercell characteristics. On some occasions, these storms dissipate rapidly. Is this related to stabilization in the low levels, insufficient storm-induced lift to overcome a strengthening lid, insufficient inflow to " restrain" the outflow, or changes in the environmental flow structure? On others, they tend to become part of a squall line. Is this because outflow from other storms overtakes the supercell, or does the supercell's own outflow deepen and become more dense, spreading away from the updraft and initiating a group of new updrafts; or are new storms initiated by mesoscale forcing?Because there is no way to know in advance which process(es) will lead to storm demise, it is difficult to specify a field strategy that will be adequate in all cases. Therefore, the FC will attempt to rearrange the field teams and missions according to the evolving situation. The mobile mesonet units and camera teams will be used to sample the outflow and track the gust front. The sounding teams will be used to assess the storm environment and the characteristics of the developing cold pool. Overall storm structure and evolution will be documented with the P-3 aircraft. In order to conserve resources, we will pursue this activity for about one hour. If the initial storm organization is multicellular, and it is appears possible that these storms will evolve into supercells, or that supercells will form in a nearby region, the teams will stay in the field in a standby mode.After the cessation of activities (about 1-2 hours before sunset if there is no prospect of convection, or storm demise, whichever comes first), the FC will commence the activity debrief. The teams will be moved back into a caravan and the teams will be polled via the VHF radio for reports of any technical or logistical problems they encountered, and any meteorological observations they think will be of interest to all participants. The FC will log this information. A decision will be made concerning a location for dinner and overnight accommodations. If the teams stop for dinner, debriefing and informal discussions may continue at the dinner stop, and during travel to the overnight location. After the FC completes formal polling of teams, the frequency will be made available for general conversation concerning the day's activities. For radio sanity, please observe the protocol of announcing the name of the team you are speaking to followed by the name of your team at the start of each conversation. Control your ecstasy about seeing damaging weather (others are listening to our frequency and will see the tragic side of weather events), and do not use profanity. Talk professionally. Lighthearted giddiness may be good for relieving tension, but does not make a good impression on those listening in.
When the teams return to Norman or reach another designated overnight location, they must check in logs, videotapes, movie and slide film, and removable computer media with the VORTEX field data manager (
See " Data Management".
). If the teams spend the night in the field, data will be checked in with a temporary data manager designated by the FC. If data are collected over more than one day, each day's data should be clearly labeled, segregated from the new data, and stored in a safe location. The field data manager will log each item, place an identifying number sticker on the item, on the log, and on a receipt that you will be given. Team leaders should keep these receipts. Leaders are responsible for all data until it is turned in, and if there is any question as to where data are, they will be able to demonstrate that you managed it properly.After parking the vehicles, open the trunk and switch off the mobile mesonet equipment (red button next to the red light). Then remove all gear and store it in the VORTEX headquarters shack, or safely locked in your motel room.Survey
If a VORTEX target storm produces a tornado, and turtles, radar, and/or photographic data suitable for photogrammetry are obtained, survey work must be conducted (preferably on the next day). If we are in the field overnight, appropriate survey maps will be faxed to the FC the next morning. If we return to Norman, maps will be acquired and photocopied early in the morning. In this activity, teams will be given the necessary USGS 7.5 minute and 1:100000 topographic maps. The teams will then caravan to the storm damage area and carry out the survey work. Camera teams will perform pre-photogrammetry surveys (
See " Pre-photogrammetry Surveys"
) with the assistance of the FC. Other teams will ne dispatched as needed, based on the extent of area affected by the tornado(es), to perform damage surveys (
See " Damage Surveys"
) under the direction of the team leader designated by the FC.Obviously, we may be faced with the dilemma of needing to do a survey on a day that could produce additional tornadic storms. We will make a decision based on the quality of the data collected on the tornadic storm, the perishability of the tornado damage, and the tornado likelihood and intercept potential.
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