ACUS01 KWNS 191242
SWODY1
SPC AC 191241

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0741 AM CDT Mon Aug 19 2024

Valid 191300Z - 201200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
WESTERN INTO NORTH-CENTRAL MONTANA...EASTERN MONTANA...AND EASTERN COLORADO...

...SUMMARY...
Scattered severe thunderstorms are possible across portions of
Montana and eastern Colorado during the afternoon and evening.
Large hail and severe gusts are the primary hazards.

...Synopsis...
Water-vapor imagery this morning shows a mid- to upper-level ridge
situated over the south-central High Plains northward through the
northern Great Plains.  A mid-level trough is over the East and a
mid-level low and associated trough are over the eastern Pacific to
the west of the Pacific Northwest.

...Portions of the central and northern Rockies/High Plains...
Broad 40+ kt southwesterly 500 mb flow will overspread portions of
the central into the northern Rockies as an impulse embedded in the
West Coast mid-level trough grazes the region.  Isolated to
scattered thunderstorms are forecast across Montana with locally
greater thunderstorm coverage forecast over western into
north-central MT this afternoon and evening, and separately over
portions of eastern Montana.  Richer moisture is evident in morning
surface analysis across eastern MT where lower 60s F surface
dewpoints are present with mid 50s farther west near the I-15
corridor.  Consequently, greater buoyancy is expected later this
afternoon over eastern MT with 2000+ J/kg MLCAPE possible with
750-1250 J/kg farther west.  Given the deep boundary layer and
corresponding steep lapse rates in both areas, severe gusts are
possible with the more intense cells and clusters, especially if a
linear cluster can evolve near the Rocky Mtn Front and push
northeastward into the High Plains.  Elsewhere, isolated instances
of hail/wind may accompany the stronger thunderstorms from the
eastern Great Basin northward into ID/WY.

...Eastern Colorado...
Moist upslope flow during peak surface heating will result in
thunderstorm initiation off of the higher terrain.  Surface
dewpoints in the low 60s F beneath 7.5-8 C/km mid-level lapse rates
will support over 2000 J/kg MLCAPE.  Modest veering and
strengthening of the vertical wind profile will contribute to 30-40
kts of effective bulk shear and modestly elongated hodographs. Some
of the stronger multicells and transient supercells may yield a risk
for large hail and severe gusts beginning mid afternoon through the
early evening.

...North Carolina into the Northeast...
At least scattered thunderstorms will develop amid weak vertical
wind shear this afternoon ahead of a cold front.  Pulse cellular and
occasional multicells are the expected storm mode. Rich low-level
moisture preceding the front will contribute to 1000-2000 J/kg
MLCAPE, which may support a few strong, potentially damaging gusts
with some of the stronger storms.

...North Florida...
A couple of strong thunderstorms may develop along the trailing
portion of a cold front by afternoon. Similar to the Northeast, rich
low-level moisture will promote 2000-3000 J/kg MLCAPE, fostering wet
downburst/strong wind gust potential with pulse single cells and
multicells.

...Sabine River Valley...
Ongoing clusters of weak thunderstorms moving southward on the
backside of the Eastern U.S. mid-level trough will likely continue
southward through the Sabine River Valley today.  Although the 12
UTC Lake Charles raob is characterized as only weakly unstable,
additional heating will result in moderate destabilization by
midday.  A localized wind-damage risk may accompany the stronger
outflow surges before this activity moves into the northwest Gulf.

..Smith/Mosier.. 08/19/2024

$$
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