Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Jun 16 2023 08:25:54

ACUS48 KWNS 160825
SWOD48
SPC AC 160824

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0324 AM CDT Fri Jun 16 2023

Valid 191200Z - 241200Z

....DISCUSSION...
The overall pattern during the Day 4-8/Mon-Fri period is expected to
be characterized by a large, persistent western U.S. upper trough,
an upper ridge building across the Plains and Upper Midwest, and a
weak upper anticyclone persisting across the Southeast vicinity.
Strong storms may be ongoing Day 4/Mon morning across parts of the
central Gulf Coast vicinity as a continuation of convection from the
Day 3/Sun period. Given uncertainty in how Day 3 convection will
evolve, and how far south/east it may track if a fast-moving
convective complex develops, 15% severe probabilities will not be
introduced at this time, though may be needed in subsequent
outlooks.

Beyond Day 4, the building upper ridge across the Plains/Upper
Midwest will effectively shut down the strong southern-stream flow
that has persisted across the southern tier of the U.S. for the past
week. Strong southwesterly mid/upper flow will develop ahead of the
western upper trough across parts of the central/northern High
Plains on Day 5/Tue. Southerly low-level flow will transport 60s F
dewpoints into the northward ahead of a surface low over eastern MT.
Moderate to strong destabilization will occur given strong heating
of the moist airmass from western NE into the western Dakotas.
However, strength of vertical shear is uncertain (strong shear may
be focused more northward into Canada) and capping may limit overall
thunderstorm potential. Trends will be monitor for possible risk
areas in the coming days.

By Day 6-8/Wed-Fri stronger deep-layer southwesterlies will remain
confined to parts of the western U.S. and displaced from deeper
boundary-layer moisture/instability. Thunderstorm activity is
expected across the central and northern Plains given abundant
low-level moisture, and plenty of instability, on the western flank
of the upper ridge. However, generally weak shear and a lack of
consequential large-scale ascent leads to low predictability for
organized severe potential.

...Leitman.. 06/16/2023

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