Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Jul 23 2024 08:48:04

ACUS48 KWNS 230847
SWOD48
SPC AC 230846

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Tue Jul 23 2024

Valid 261200Z - 311200Z

....DISCUSSION...
Upper ridging will spread across parts of the Plains and eastern
states, while the subtropical high develops westward over the
southern tier of the U.S. during the Day 4-8/Fri-Tue period. This
will suppress severe thunderstorm potential for much of the CONUS.
The exception will be a potentially more active period for parts of
the northern Plains into the Upper Midwest due to a series of upper
shortwave troughs migrating across the Canadian Prairies and parts
of the northern Plains/Upper Midwest through the forecast period.

Surface high pressure over the Great Lakes and periodic surface low
development over the northern High Plains will maintain a baroclinic
zone over the Upper Midwest. As a result, southerly low-level flow
will keep a seasonally moist airmass in place across the eastern
Dakotas and Mid-MO Valley east to the Mid/Upper MS Valley. Some
severe thunderstorm potential could develop around Day 4 Fri as the
first upper shortwave trough moves across the Canadian Prairies.
However, stronger vertical shear and large scale ascent will be
focused north of the international border. Another weaker, but
further south shortwave trough will traverse the northern Plains
vicinity on Day 6/Sun before a somewhat stronger wave migrates
through westerly flow toward Day 8/Tue.

While various forecast guidance generally depicts this more
progressive northern stream pattern, details in timing of each wave,
as well as differences in the strength of the central U.S. upper
ridge/subtropical high vary greatly. As a result, confidence is too
low to include 15 percent probabilities at this time.

...Leitman.. 07/23/2024

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