980723 - Severe weather often occurs a day or two after frontal passage in
Colorado and today proved to be no exception as high dewpoints and deep
moisture were present over eastern Colorado.  By noontime it became evident
that the Denver Convergence Vorticity Zone (DCVZ) would establish itself
later in the day.  Earlier missions had demonstrated that during periods of
shallow moisture the DCVZ would manifest itself as a dry line.  Our intent
was to collect transect data of the DCVZ during a period of deep moisture.
We also wanted to test a hypothesis that landspouts are more likely to form
if both sides of the DCVZ are moist.

Our target area was just east of Byers, Colorado, where the DCVZ crossed
US36 - the same area we operated in last week.  A rapidly growing Cb was
located at the intersection of the DCVZ and US36.  How convenient!  A
circulation at cloud base was present as we approached the cloud and soon
thereafter a nearly transparent dust column became visible.  The two mobile
mesonets did multiple transects along a north-south road ahead of the
approaching landspout.  As the weak tornadic circulation approached the
road, both mobile mesonets carefully positioned themselves to collect
proximity data.  After the vortex crossed the road, both mesonets resumed
their north-south transects collecting data behind the circulation.  We
intercepted this circulation again on another north-south road one mile to
the east.  This weak tornado lasted for 13 minutes.

A second cloud base swirl was quickly forming to the southwest and moments
later another landspout formed.  This circulation was multi-vortex in 
nature and the strength of the ground circulation was much stronger than 
the first, so a greater distance was maintained as the circulation crossed 
the road.  As before, both mesonets collected data ahead and behind the
tornadic circulation which lasted 7 minutes.  Neither tornado produced a
prominent dust cloud or a funnel cloud.