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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0257 PM CDT Sat Aug 17 2024

Valid 172000Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
CASCADES AND COLUMBIA BASIN...PARTS OF UTAH...AND IN THE
OHIO/TENNESSEE VALLEYS...

...SUMMARY...
Scattered severe thunderstorms are possible through tonight in
vicinity of the Ohio Valley, Utah and the Cascades of Oregon and
Washington. Wind and isolated hail are the primary threats.

...20z Update...
The forecast remains largely on track with on minor changes. Strong
to severe storms ongoing over the OH Valley and eastern US will
remain capable of isolated damaging gusts through this evening.
Scattered severe storms are also expected to develop over the
Cascades and Columbia Basin later this afternoon and into the
overnight hours with a risk for danging winds and hail.

...Tennessee Valley and southern Appalachians....
Multiple bands and clusters of strong to occasional severe storms
are ongoing this afternoon ahead of the broad upper trough and slow
moving cold front. Recent VAD observations from HTX and MRX show a
belt of stronger mid-level flow has extend over parts of the eastern
TN Valley and Southern Appalachians supporting greater deep-layer
shear of 25-30 kt. Colocated with a hot and seasonably
moist/unstable air mass, a cluster of more organized/robust
convection being observed over part of northern AL and southern TN
may continue east/southeast into parts of northern GA and the
western Carolinas this afternoon/evening. A mix of persistent
multi-cell clusters and transient supercell structures would support
a risk for damaging winds and isolated hail. Have upgraded to level
2 categorical Slight to better account for the risk of damaging
winds with this cluster of stronger storms.

...Utah...
Ahead of a convective enhanced shortwave trough, scattered strong to
severe thunderstorms should continue this afternoon and into the
evening hours with a risk for damaging winds and occasional hail.
Confidence in the highest threat corridor remains across parts of
central UT where greater diurnal heating has allowed for moderate
destabilization. The exact eastern extent of organized convective
potential is somewhat nebulous given the limited buoyancy and
expected degree of storm coverage. However, at least some risk for
damaging gusts will be possible with high-based showers and storms
over eastern UT. Have modified the eastern edge of the level-2
Slight Risk to better reflect the potential for organized storms
with wind gust and hail potential later this afternoon. Otherwise,
see the prior discussion for additional information.

..Lyons.. 08/17/2024

.PREV DISCUSSION... /ISSUED 1121 AM CDT Sat Aug 17 2024/

...CA/OR/WA...
Morning water vapor loop shows a strong and fast-moving shortwave
trough approaching the coast of northern CA.  This feature will
rotate inland, affecting the Cascades region this afternoon and
evening.  Steep mid level lapse rates and pockets of MLCAPE of
500-1000 J/kg will aid in the development of scattered thunderstorms
by early afternoon over the mountains and coastal ranges of northern
CA, building quickly northward into southern/central OR.  Winds
aloft will be strenghtening during this period, allowing a few
supercell storm structures to likely develop.  These storms may pose
a threat of large hail and locally damaging wind gusts through the
afternoon as they track northward into WA.  Other high-based storms
capable of gusty/damaging winds may affect parts of the Columbia
Basin of northern OR/central WA as well.

...UT...
A co*pact shortwave trough over central NV will continue to rotate
around the Four-Corners upper ridge into UT today.  Considerable
coverage of afternoon thunderstorms will likely acco*pany this
system.  Winds aloft will be relatively strong, favoring
faster-moving organized multicell or occasional supercell structures
capable of damaging winds and hail.  One forecast uncertainty is the
extent of morning cloudiness and its impact on afternoon
destabilization.  Regardless, at least isolated severe storms are
expected, with some threat spreading into southwest WY by evening.

...Eastern US...
A broad upper trough will affect much of the eastern US today, with
clusters of thunderstorms from NY/PA across the Appalachians into
the Mid South.  Any of these clusters may occasionally pose a risk
of locally gusty/damaging wind gusts or hail.  However, perhaps a
more focused area of concern will extend from northern TN into
southern OH.  The axis of the mid level speed max (~40 knots) will
spread across this area during the afternoon.  CAM guidance has been
consistent on suggesting a higher confidence in a few intense cells
in this region.