Subj : DAY3SVR: Marginal Risk
To   : All
From : Mike Powell
Date : Wed Sep 06 2023 06:23:00

ACUS03 KWNS 060731
SWODY3
SPC AC 060730

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Wed Sep 06 2023

Valid 081200Z - 091200Z

....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHEAST...MID-ATLANTIC...ARK-LA-TEX...AND NORTHERN HIGH
PLAINS...

....SUMMARY...
Thunderstorms, associated with a marginal severe threat, will be
possible on Friday across parts of the Northeast, Mid-Atlantic,
Ark-La-Tex and Northern High Plains.

....Northeast/Mid-Atlantic...
An upper-level trough will remain across the eastern U.S. on Friday,
from the central Great Lakes southward into the Tennessee Valley. A
cold front will move southeastward into the central and northern
Appalachians. Ahead of the front, surface dewpoints will be mostly
in the 60s F, contributing to the development of moderate
instability along an axis from the Mid-Atlantic into New England.
Due to surface heating, scattered thunderstorms are expected to
develop during the afternoon from the higher terrain of the central
and northern Appalachians eastward into the Atlantic Coastal Plains.
Although 0-6 km shear is forecast to remain near or below 30 knots
in most areas, low-level lapse rates will become steep during the
mid to late afternoon. Multicells that develop in areas where
instability becomes locally maximized may have a marginal
wind-damage threat.

....Ark-La-Tex...
An anticyclone will remain over the Desert Southwest on Friday, with
flow being from the northwest across the Ark-La-Tex and lower
Mississippi Valley. To the northeast of the high, an upper-level
trough is forecast to move southeastward across the south-central
U.S. At low-levels, southeasterly flow in the Ark-La-Tex will aid
development of an axis of maximized low-level moisture extending
from northwestern Louisiana into southeast Oklahoma. Thunderstorms,
possibly elevated in nature, could develop late Friday afternoon,
supported by large-scale ascent associated with the upper-level
trough. NAM forecast soundings near Shreveport, Louisiana late
Friday afternoon have steep mid-level lapse rates and effective
shear around 40 knots. This could be enough for marginally severe
hail.

....Northern High Plains...
An upper-level ridge is forecast to move eastward across the
northern High Plains on Friday, with west-southwesterly mid-level
flow located across much of the western U.S. At the surface, a cold
front is forecast to move southward into the northern High Plains.
Near the front, pockets of instability are forecast to develop in
response to surface heating. Isolated to scattered thunderstorms may
form across parts of the High Plains in the late afternoon,
supported by large-scale ascent associated with the upper-level
trough. NAM forecast soundings during the late afternoon in far
southeastern Montana have MLCAPE peaking in the 1200 to 1500 J/kg
range, with effective shear near 35 knots, and 700-500 mb lapse
rates around 8 C/km. This will likely be sufficient for marginally
severe hail.

...Broyles.. 09/06/2023

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