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000
ACUS01 KWNS 161244
SWODY1
SPC AC 161242

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0742 AM CDT Tue Apr 16 2024

Valid 161300Z - 171200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
IOWA...NORTHERN MISSOURI...AND NORTHWESTERN ILLINOIS...

...SUMMARY...
Scattered severe thunderstorms appear likely today, centered mostly
over northern Missouri, Iowa, and northwestern Illinois. Large hail,
damaging winds, and tornadoes should occur in this corridor. More
isolated activity could develop as far south as the Ozarks of
northern Arkansas.

...Synopsis...
An upper trough/low over the central Plains this morning will
continue to eject east-northeastward across the mid MO Valley and
Upper Midwest through tonight. A 70-90 kt mid-level jet will
overspread parts of the Midwest through the day, contributing to
substantial deep-layer shear and thunderstorm organization. At the
surface, a 990 mb low over central NE will likewise develop
east-northeastward through the day in tandem with the upper wave. A
warm front should lift northward across parts of the Midwest, with
generally low to mid 60s surface dewpoints present across the warm
sector as far south as the Ozarks. A composite Pacific cold
front/dryline will move quickly eastward from the southern/central
Plains into the mid Ms Valley by this evening. This boundary should
stall across the southern Plains, and may begin to lift northward
late tonight.

...Midwest/Mid Mississippi Valley...
A large area of showers and thunderstorms is ongoing this morning
from parts of eastern KS/NE/SD into IA. Much of this activity across
the central Plains is being driven by large-scale ascent associated
with the ejecting upper trough/low, along with strong warm/moist
advection with a 40-50 kt southerly low-level jet. As this
convection continues to spread eastward this morning in tandem with
the migrating low-level jet axis, it will probably become more
elevated, especially as it moves into northern MO and IA and a less
unstable airmass to the north of the warm front. Still, an isolated
severe threat may persist in the short term with these
thunderstorms. The effect of this early-day convection on robust
destabilization in its wake along/ahead of the cold front remains a
concern and potentially limiting factor for additional severe
thunderstorm development this afternoon. Even so, most guidance,
including multiple recent runs of the RAP, shows a narrow corridor
of weak to moderate instability developing along/south of the warm
front in IA, and ahead of the cold front sweeping eastward across
MO/IA. This re-destabilization should be aided by a pocket of steep
mid-level lapse rates and cold temperatures aloft on the southeast
side of the upper trough/low.

Assuming that low to mid 60s surface dewpoints and modest daytime
heating can aid in this instability actually materializing, then a
risk for supercells should exist over parts of IA, northern MO, and
northwestern IL. Both low-level and deep-layer shear appear strong
enough for supercells. Steep lapse rates will aid in hail
production, with some chance for 2+ inch diameter stones with the
more robust cores. Tornadoes will also be a concern, as the enhanced
boundary-layer flow and enlarged/curved hodographs associated with a
the low-level jet will aid in updraft rotation. The best tornado
potential will probably be focused along/near the warm front in IA,
where the greatest low-level shear is forecast. Here, a strong
tornado appears possible. Isolated to scattered damaging winds may
also occur.

Farther south into the Ozarks and Mid-South, the potential for
severe thunderstorms appears more conditional. Various NAM/RAP
forecast soundings exhibit generally poor lapse rates, with at least
weak inhibition through much of the period. Given these regions
displacement from the upper trough/low to the north, it remains
unclear how robust updrafts will be in a more marginal low/mid-level
lapse rate environment. Still, have maintained the Slight Risk into
parts of the lower MS Valley, but convection may struggle to
intensify this afternoon/evening.

..Gleason/Grams.. 04/16/2024

$$