Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
348 PM CDT Wed Jul 15 2020
.MESOSCALE DISCUSSION...
348 PM CDT
Watching an impressively wound-up convectively-enhanced Mesoscale
Convective Vortex lifting northeastward out of Central Illinois
this afternoon. This feature seems to have been born out of
convection last night across the Texas and Oklahoma Panhandles.
Typically the more well-developed MCV`s carry with them a flow
enhancement, and that certainly seems to be the case here.
Lincoln`s special 17z sounding sampled 50-60 kts of flow in the
550-400 mb layer, and this is supporting effectively deep layer
shear values of about 50 kts into our southern counties. While
overall instability values aren`t high (likely due to somewhat
pronounced mid-level warming noted on the aforementioned
sounding), recent objective SPC mesoanalysis depicts a corridor of
150 to nearly 200 J/kg of 0-3 km MLCAPE, more than sufficient in
concert with the elevated shear values to locally augment low and
mid- level updraft accelerations. It is thus not a surprise to see
an established supercell northwest of Bloomington.
The concern locally here is that even in the face of limited
instability from a typical sense (read: MLCAPE), a hodograph run
using KILX`s radar and the rather deviant storm motion on the
right-motion vector and breezy southeast winds yields 0-3 km SRH
values nearing 400-450 m2/s2. As a result, we did recently
coordinate a small/targeted tornado watch for our far southwestern
counties to highlight this localized threat developing over the
next few hours. Corridor of localized damaging wind gusts and some
hail threat will also exist in this region, although the limit on
the hail potential should be capped a bit by the muted mid-level
lapse rates. The severe threat will likely have a harder time
building too much farther northwest than I-55 given the expansive
and persistent cloud cover today holding temperatures down, but
peeks of sunshine south and east of there may help locally boost
the severe potential through this afternoon and into the evening.
Finally, we are still monitoring at least a localized flash flood
threat into the evening as rather slow storm motions and at least
some potential for a bit of training will be possible within a
richly-moist atmosphere. Already seeing some 2-3" rainfall amounts
out of the storms upstream. Greatest signal for this potential is
across roughly the southeastern half of the CWA.
Carlaw