Valid 191200Z – 201200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MID MISSISSIPPI AND LOWER OHIO VALLEY REGION…
Severe thunderstorms are expected from the lower Missouri Valley and
Ozarks vicinity into the middle Mississippi and lower Ohio Valleys.
Damaging gusts, isolated large hail and tornadoes are possible.
Early-morning satellite imagery depicts a well-defined upper trough
over AZ lifting northeast in line with latest model guidance. Strong
500mb speed max within the base of the trough over northern Mexico
is forecast to translate into the TX Panhandle by 12z, then into MO
by late afternoon before ejecting into lower MI during the overnight
hours. In response to this feature, lee surface low over eastern CO
will track to near FNB by late afternoon, then into northern lower
Latest short-range model guidance suggests boundary-layer moisture
will advance north across KS/MO into southeast NE/IA ahead of the
surface low where lower 60s dew points appear possible by peak
heating. Latest thinking is a corridor of strong low-level heating
should develop across the southern High Plains-KS-southwest IA. This
should allow surface temperatures to warm into the upper 60s/70F
which will result in MLCAPE values at least 1500 J/kg. Thunderstorms
are expected to develop within exit region of the upper jet by 18z
across southern NE then track/develop east ahead of the surface low.
Forecast soundings support supercells and very large hail may
accompany this activity. While low-level flow will be veered
immediately ahead of the low, a tornado or two can not be ruled out
in this flow regime.
Farther south, considerable amount of convection is currently
ongoing (0530z) across the southern Plains. This activity should
propagate downstream into eastern OK/MO by sunrise. It’s not
entirely clear how severe this activity will be at the start of the
period, but strong shear and adequate moisture/buoyancy suggest
locally damaging winds and some tornado threat will be noted at 12z.
With the strongest zone of large-scale forcing for ascent expected
to spread to the north of this region, southern extent of organized
deep convection may orient itself along a corridor from northern
AR-southeast-MO-southern IL-southern IN along northern extent of
higher-quality boundary-layer moisture. It appears upper 60s surface
dew points will advance as far north as southeast MO/western KY.
While forecast lapse rates will not be that steep, very strong shear
and higher-PW air mass should prove sufficient for damaging wind and
a tornado threat with organized line segments and embedded