962
ACUS48 KWNS 210906
SWOD48
SPC AC 210904

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0404 AM CDT Tue May 21 2024

Valid 241200Z - 291200Z

...DISCUSSION...
...Day 4/Fri - Mid MS Valley/Upper Great Lakes vicinity...

An upper shortwave trough over the northern Plains will pivot
northeast across the Upper Midwest on Friday. At the surface, low
pressure will develop northward across MN/WI and a trailing cold
front will push east, becoming positioned from WI to central OK/MO
by Saturday morning. Some severe potential is possible ahead of the
front from the Mid-MS Valley into the Great Lakes vicinity. However,
ongoing convection early Friday and large-scale ascent lifting
northeast of the region with time is resulting in uncertainty.
Severe probabilities will likely be needed in subsequent outlooks as
mesoscale details become better resolved, but confidence is too low
to delineate an unconditional 15 percent probability at this time.

...Day 5/Sat - Southern Plains to the Ozarks vicinity...

Low-amplitude west/southwest mid/upper flow is forecast across the
southern Plains to the Mid-South vicinity for much of the diurnal
period on Saturday. By 00z, forecast guidance suggests a shortwave
trough will eject from the southern Rockies into the southern
Plains, and eventually impinging on the Ozarks/Mid-South area by
Sunday morning. A very moist and unstable airmass is forecast over
the southern Plains vicinity ahead of this feature as a surface warm
front lifts northward through the day. Increasing ascent may not
arrive until after 00-03z, limiting convective initiation until the
nighttime hours. If storms can develop during the day across
portions of OK/TX, all hazards severe potential will exist.
Otherwise, thunderstorm potential may be more likely during the
evening/overnight from north TX into southeast OK and AR as
large-scale ascent increases and a 65-75 kt 500 mb jet overspreads
the region. The north and west bounds of severe potential are a bit
uncertain, so this area may shift in subsequent outlooks.

...Day 6/Sun - Ozarks to the Lower OH and TN Valleys...

An upper shortwave trough will progress across the region on Sunday.
Forecast guidance depicts a 50-60 kt southwesterly 700 mb jet
overspreading the region during the day. Meanwhile, a surface low
will intensify over MO/IL, shifting northeast along the OH River
through the period. A very moist and unstable airmass is depicted
ahead of the low and attendant south/southeastward-progressing cold
front. Intense severe thunderstorms will likely accompany this
system. Consistency among deterministic guidance, favorable synoptic
pattern, as well as CSU/NSSL ML output, support introduction of 15
percent probabilities for Sunday.

...Days 7-8/Mon-Tue...

Spread among forecast guidance increases substantially by the end of
the forecast period. However, a pattern shift by Day 8/Tue appears
possible, with an amplified upper ridge potentially building over
the western half of the CONUS. Overall, predictability is too low to
delineate areas of severe potential across the eastern half of the
CONUS.

..Leitman.. 05/21/2024