387
ACUS01 KWNS 171207
SWODY1
SPC AC 171206

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0706 AM CDT Tue Sep 17 2024

Valid 171300Z - 181200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL HIGH PLAINS...

...SUMMARY...
Thunderstorms capable of severe wind gusts and isolated large hail
will be possible this afternoon and evening across parts of the
central and northern High Plains.

...High Plains/Central and Southern Rockies...
Water-vapor imagery early this morning shows a potent mid-level low
and associated trough centered over northeast NV.  This feature will
become negatively tilted and move into the High Plains late today
while the low moves east-northeast reaching southeast MT Wednesday
morning.  Strong attendant forcing for ascent will overspread the
High Plains this afternoon into the early evening with an
accompanying 50-60 kt 500-mb speed max moving into CO and eventually
western NE/SD.  In the low levels, a lee trough will sharpen with
southerly flow maintaining a fetch of seasonably adequate moisture
(50s deg F surface dewpoints) into the High Plains.

Ahead of the approaching trough, partial clearing will result in
strong surface heating this afternoon over the central High Plains.
MLCAPE is expected to peak near 1500 J/kg from eastern Colorado
northward into western Nebraska.  Initial storm activity late this
morning through the early afternoon will develop over the high
terrain of CO/northern NM and move/develop east into richer moisture
by mid-late afternoon.  The increasing large-scale ascent coupled
with heating will eventually result in numerous storms mainly in the
form of linear clusters evolving into linear bands of convection by
early evening.  The greatest combination of instability, lift
and deep-layer shear is forecast across western Nebraska and
northeast Colorado, suggesting an enhanced threat for severe wind
gusts.  Based on some of the latest CAM data, have expanded the
Slight-Risk equivalent wind probabilities farther south into
northeast NM/northwest TX Panhandle.  Some consideration was given
to expand the ENH Risk into southwestern SD, but the later timing of
storms lends enough uncertainty to preclude this change this outlook
update.

...Northern High Plains...
Ahead of the approaching mid-level low, divergent south to
south-southeasterly flow will be in place across the northern
Rockies and northern Plains.  During the afternoon, thunderstorms
will develop in the north-central Rockies and move north to
northeastward across the northern High Plains.  An axis of moderate
instability is forecast by afternoon from the Dakotas northwestward
into northeast Montana.  As large-scale ascent and moderate
deep-layer shear overspread the northern High Plains late this
afternoon and evening, organized storms will be possible.  Severe
wind gusts and isolated large hail will be the primary threats.

...Eastern Florida...
A mid-level trough will move across the eastern Gulf of Mexico
today, as an associated surface trough moves across the Florida
Peninsula. Surface dewpoints in the lower to mid 70s F, along with
surface heating will contribute to moderate instability by
afternoon. As surface temperatures warm today, scattered
thunderstorms are expected to develop along and ahead of the surface
trough.  RAP forecast soundings at 21Z in eastern Florida have
MLCAPE in the 2000 to 3000 J/kg range, with 0-6 km shear around 20
knots.  This, combined with steep low-level lapse rates could be
enough for a marginal threat for locally severe wind gusts.

..Smith/Mosier.. 09/17/2024

$$