919
ACUS03 KWNS 191941
SWODY3
SPC AC 191940

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0240 PM CDT Thu Sep 19 2024

Valid 211200Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF NM INTO
THE SOUTHERN HIGH PLAINS...PARTS OF THE UPPER MIDWEST INTO THE
CENTRAL PLAINS...CENTRAL APPALACHIANS VICINITY...

...SUMMARY...
Isolated severe thunderstorms are possible on Saturday afternoon to
early evening in New Mexico and the southern High Plains, mid
Missouri Valley to upper Mississippi Valley, and central
Appalachians region.

...Southern High Plains...
In advance of a southern-stream shortwave trough reaching the Four
Corners, a strong midlevel jet is forecast to eject over NM by early
evening Saturday. This will yield favorable deep-layer shear for
organized storms across NM into parts of northwest TX. Strengthening
large-scale ascent within a low-level warm/moist conveyor should
overspread this region by Saturday morning. This should yield
early-period convection and renders moderate uncertainty over the
degree of destabilization by afternoon.

Still, with ample boundary-layer heating to the south of early-day
activity, a plume of at least weak-surface based buoyancy should
develop. Renewed afternoon to early evening thunderstorms could
become severe. Steep mid-level lapse rates should be confined along
and west of the Sangre de Cristo Mountains, rendering further
uncertainty over the intensity and coverage of the severe threat.
The eastern extent of the threat should be limited by the confined
buoyancy plume and decreasing instability deeper into TX/OK.

...Central Plains and Lower/Mid-MO Valley to the Upper MS Valley...
A relatively complex and uncertain evolution to convective potential
remains evident on Saturday afternoon/evening. This region will
largely remain within a low-amplitude mid-level ridge. This may
flatten somewhat in between a southern-stream shortwave trough in
the Southwest and a northern-stream trough over the southern Prairie
Provinces to along the ND/MN international border. In association
with the latter wave, a surface cold front should push southeast in
the north-central states. Guidance varies with the degree of
destabilization ahead of it, and especially with the spatial extent
of afternoon/evening convection. There is sufficient confidence in
destabilization and storm coverage to introduce a 5% area from the
mid MO Valley to the upper MS Valley, though uncertainty remains
rather high.

...Parts of the Northeast/Mid Atlantic...
A low-amplitude midlevel shortwave trough is forecast to move
through northwesterly flow aloft across parts of the upper Ohio
Valley into the Mid Atlantic on Saturday. Isolated to scattered
thunderstorm development will be possible across the region during
the afternoon. Veering wind profiles within the northwesterly flow
regime will support effective shear for some storm organization,
though it remains somewhat uncertain if instability will become
sufficient to support an organized severe threat. Guidance has
trended toward somewhat greater instability and storm coverage, and
a small Marginal Risk has been included where confidence is
currently highest in some severe threat.

..Dean.. 09/19/2024

$$