Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Wed Jun 21 2023 08:42:21

ACUS48 KWNS 210842
SWOD48
SPC AC 210840

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0340 AM CDT Wed Jun 21 2023

Valid 241200Z - 291200Z

....DISCUSSION...
....Day 4/Sat -- Mid-MO Valley Vicinity...

A shortwave upper trough will spread east from the northern/central
Plains to the Upper Midwest vicinity on Saturday. This will bring a
belt of enhanced west/southwesterly flow over the region. 30-40 kt
850-700 mb flow is forecast beneath a 45-55 kt 500 mb jet. At the
surface, a corridor of mid/upper 60s F dewpoints will spread
northward from eastern NE and IA through the eastern Dakotas and MN.
Stronger height falls are expected after 21z, and surface
cyclogenesis will strengthen during the late afternoon into evening
across eastern SD. This will aid in increasing southeasterly
low-level flow and strengthening vertical shear, supporting
organized severe convection. Initial supercells appear possible,
with upscale development during the evening/nighttime hours as the
low-level jet increases. All severe hazards are expected as
convection develops east/southeast across the region.

....Days 5-6/Sun-Mon -- Mid-MS/OH Valleys toward the Mid-Atlantic...

The upper shortwave trough over the Mid-MO Valley early Sunday will
shift east over the upper Great Lakes and the Mid-MS Valley by
Monday morning. On Monday, the trough will deepen over the Midwest,
and become oriented from Lower MI toward the Southeast states.
Severe potential will likely develop over parts of the Mid-MS/OH
Valleys toward the Mid-Atlantic during this time, as enhanced
southwesterly mid/upper flow overspreads a moist/unstable airmass.
Severe-area delineation will likely be needed at some point.
However, uncertainty in timing of the upper trough, and the track of
a surface low/cold front, as well as multiple rounds of possible
convection, are resulting in too much uncertainty at this time to
hone in on specific corridors of 15 percent or greater coverage of
severe at this time.

....Days 7-8/Tue-Wed...

Late in the forecast period, an upper ridge is expected to be
centered over the Plains. A weak upper trough will exist over the
western states while the eastern trough pivots east/northeast toward
the Atlantic coast. Thunderstorm potential will cover much of the
Atlantic coast states in relation to the upper trough, and some
areas of strong to severe convection may develop, though confidence
is too low to include probabilities at this time.

...Leitman.. 06/21/2023

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