240
ACUS01 KWNS 301958
SWODY1
SPC AC 301956

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0256 PM CDT Tue Apr 30 2024

Valid 302000Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN
WESTERN/CENTRAL IA TO NORTHEAST KS...

...SUMMARY...
The greatest threat for severe weather (large hail, severe gusts,
and a few tornadoes) is from western and central Iowa to
northeastern Kansas.

...20Z Update...
Main concerns with this outlook are the extent/amplitude of tornado
probabilities over the IA vicinity and MRGL versus SLGT risk across
the southern Great Plains.

Scattered thunderstorms have developed across the Mid-MO Valley
after midday soundings from OAX/TOP sampled a mean mixing ratio near
10 g/kg, within the plume of around 60 F surface dew points. Primary
uncertainty is the degree of tornado potential as these storms
spread into parts of southwest to south-central IA vicinity. A
couple long-track supercells might evolve given the favorable low to
deep-layer wind profile. But the relatively modest boundary-layer
moisture, with potential for appreciable cold pools as convection
consolidates, lowers confidence in sustaining a greater tornado
threat. The northern extent of severe potential will continue to be
modulated by weaker instability amid downstream convection currently
from central IA to eastern SD.

Non-HRRR guidance is fairly insistent on isolated to scattered
thunderstorms along the dryline, south of its triple-point
intersection with the surface cold front pushing southeast from
southwest to central KS. Across western portions of TX and OK, the
environment will be supportive of isolated large hail and localized
severe winds through about dusk. Have opted to bring the SLGT to the
agitated CU field near CSM in western OK and leave MRGL in effect
farther south.

..Grams.. 04/30/2024

.PREV DISCUSSION... /ISSUED 1129 AM CDT Tue Apr 30 2024/

...Eastern NE/Western IA/Northwest MO/Northeast KS...
Water vapor loops show a fast-moving shortwave trough and associated
mid/upper level speed max moving across the central Rockies into the
Plains.  Ahead of this trough, southerly low-level winds are
transporting moisture northward with dewpoints in the 60s now as far
north as southeast NE.  Continued daytime heating and moisture
advection will lead to a narrow corridor of moderate CAPE over
eastern NE by mid-afternoon.  A consensus of morning model guidance
indicated that thunderstorms will form in this regime, with other
intense storms developing southward along the surface cold front
into northeast KS by late afternoon.  Forecast soundings show shear
profiles favorable for supercell structures capable of very large
hail and a few tornadoes.  After dark, these storms are expected to
congeal into one or more bowing structures that will track eastward
into central IA/northern MO with a greater risk of damaging wind
gusts along with hail and perhaps tornadoes.

...Eastern KS/Western OK/Northwest TX...
The surface dryline will extend southward from northeast KS into
northwest OK and northwest TX.  Isolated intense storms are expected
from roughly Wichita northward, with decreasing confidence from
there southward.  Weak large scale forcing, rising mid level
heights, and generally warming temperatures at 700mb suggest any
storms that form along the dryline will be widely scattered.
However, large CAPE values, steep mid level lapse rates, and
sufficient vertical shear will support supercell structures capable
of all severe hazards in any storm that can form/sustain.  Will
maintain the ongoing SLGT/MRGL areas at this time, but will
reevaluate at 20z.

...NY/PA...
Strong daytime heating is occurring over areas from central NY into
central PA, where dewpoints are in the upper 50s.  Forecast
soundings suggest afternoon MLCAPE values of 500-1000 J/kg, leading
to scattered afternoon thunderstorms.  Low-level winds are
relatively weak/veered, but sufficient winds aloft and steep
low-level lapse rates could contribute to a risk of gusty/damaging
wind gusts and hail in the strongest cells this afternoon.

$$