Areas affected…The Colorado front range to portions of southeast
Wyoming
Concerning…Severe potential…Watch possible
Valid 211851Z – 212045Z
Probability of Watch Issuance…40 percent
SUMMARY…Thunderstorms will develop/intensify through early
afternoon and pose a threat for severe hail and brief severe wind
gusts. The potential coverage of the threat, and hence the need for
a Severe Thunderstorm Watch, is uncertain.
DISCUSSION…Strong heating and an approaching weak mid-upper-level
low are contributing to deepening cumulus and initial thunderstorm
development over the Colorado and Wyoming high terrain. A moist and
modifying continental polar air mass has pushed up to the foothills,
creating an environment supportive of thunderstorms that varies
little with latitude from the Raton Mesa northward to the Laramie
Mountains. By early afternoon, forecast soundings suggest this
environment will consist of 1500-2500 J/kg of MLCAPE (higher toward
the Mountains) with little convective inhibition, moderate
straight-line vertical wind shear confined mostly in the 1-4 km
layer (supportive of multicell to some transient supercell
structures), and DCAPE of 1200-1500 J/kg.
Given storm rotation and steep low-to-mid level lapse rates, severe
hail is the main threat with these storms, but brief severe wind
gusts are possible in the stronger downdrafts. Moderate low-level
southeasterly upslope flow combined with relatively weak
west-northwesterly to westerly flow at 500-300 mb suggests a slow
south to southeast motion to the cells, thus limiting the eastward
extent of the threat. The main uncertainty concerning the need for
a Severe Thunderstorm Watch is the coverage of the hail/wind threat.
The coverage of storms that mature and move into the foothills will
be monitored in the next hour or so to better determine if a Watch
will be needed.
..Coniglio/Guyer.. 08/21/2019
…Please see www.spc.noaa.gov for graphic product…
ATTN…WFO…PUB…BOU…CYS…RIW…
LAT…LON 42860625 42760567 41960518 40150447 39820440 38480387
37790355 37460341 37110354 37050408 37090466 37430506
38260552 39540598 40280617 41270651 42560648 42860625