907
ACUS48 KWNS 190850
SWOD48
SPC AC 190849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Tue Aug 19 2025

Valid 221200Z - 271200Z

...DISCUSSION...
...Friday/Day 4 to Sunday/Day 6...
On Friday, a mid-level shortwave trough and an associated cold front
is forecast to move into the upper Mississippi Valley. An axis of
moderate instability will likely develop by afternoon ahead of the
front from the western Great Lakes southwestward into the mid
Missouri Valley. Due to limited large-scale ascent, convective
coverage near the instability axis is expected to be very isolated.
A marginal risk will be possible with cells that develop close
enough to the instability axis.

On Saturday, the front is forecast to move through the Great Lakes
region, extending southward into the central Plains. Instability
will again develop ahead of the front, but convective initiation
should remain isolated due to a lack of large-scale ascent. The area
with the greatest potential for a marginal severe threat would be
over the central Great Lakes ahead of a shortwave trough.

The shortwave trough is forecast to amplify over the Great Lakes
region on Sunday, as the cold front advances through the lower Great
Lakes and Ohio Valley. Instability will increase during the day
ahead of the front over the central Appalachians with scattered
thunderstorms developing during the afternoon. Deep-layer shear
should be strong enough for an isolated wind-damage threat, mainly
in areas where instability is stronger.

...Monday/Day 7 and Tuesday/Day 8...
A cold front is forecast to advance towards the Eastern Seaboard on
Monday. Scattered thunderstorms will be possible Monday afternoon
ahead of the front from New England southward into the Mid-Atlantic.
Although moderate deep-layer shear is forecast, instability should
remain weak, suggesting any severe threat will be marginal. Although
uncertainty is substantial at this extended range, the models keep a
relatively dry post-frontal airmass over much of the central and
eastern U.S on Tuesday. Along the southern periphery of this
airmass, isolated thunderstorms will be possible in the southern
Plains and Ark-La-Tex Tuesday afternoon. However, weak instability
is expected to limit severe threat potential.

..Broyles.. 08/19/2025