ACUS01 KWNS 221250
SWODY1
SPC AC 221248

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Mon Jul 22 2024

Valid 221300Z - 231200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE MID-ATLANTIC REGION...AS WELL AS WESTERN ARIZONA TO THE LOWER
COLORADO RIVER VALLEY...

...SUMMARY...
Isolated severe thunderstorms will be possible today over portions
of the mid-Atlantic region, as well as western Arizona to the lower
Colorado River Valley.

...Synopsis...
The basic mid/upper-level pattern will continue to feature mean
ridging over the western CONUS, and broad but mostly weak cyclonic
flow around a trough extending from the Upper Great Lakes
southwestward over south TX.  However, the northern part of the
western ridging -- over western Canada and the northern Rockies --
will break down as:
1.  A large cyclone moves eastward from the Gulf of Alaska, and
2.  A strong shortwave trough in the cyclone's southeastern quadrant
pivots northeastward from the Pacific across western/northern Wa to
southern BC this evening and tonight.

Downstream, broadly difluent and weak, mostly northerly to
northwesterly flow will cover the central CONUS.  A shortwave trough
-- apparent in moisture-channel imagery moving into northern MN and
northeastern ND from Canada -- will pivot eastward across western
Lake Superior, northern WI and parts of Upper MI today.  Isolated to
scattered showers and multicell thunderstorms may produce small hail
and strong gusts ahead of this feature, over areas surrounding
western Lake Superior; however, weak deep-layer flow/shear should
preclude an organized threat.  Meanwhile, another shortwave trough
-- initially over parts of IL/MO -- should drift eastward over IL,
while weakening.  Weak perturbations apparent over eastern parts of
KY/TN, and over MS and western TN, will eject northeastward over the
southern Appalachians.

The 11Z surface analysis showed a wavy, quasistationary frontal zone
from a weak low near MEM to near SHV, DAL, ABI, PRS and ELP.  A warm
front was drawn from the low across middle/eastern TN, southern WV,
northern VA, NJ, and Long Island Sound.  The warm front should drift
farther northward in some areas and become stationary in others,
while the western boundary segment slowly experiences frontolysis
over the southern Plains to Mid-South.

...Portions of VA/NC...
Widely scattered to scattered thunderstorms should form south of the
front -- near outflow and differential-heating boundaries as well as
a weak surface trough -- and move east-northeastward to
northeastward over the outlook area through the afternoon.  Once
ongoing clouds/precip exit the area, diurnal heating/destabilization
will act in concert with rich low-level moisture (surface dewpoints
in the 70s F, PW exceeding 2 inches, mean mixing ratios near or
above 17 g/kg) to offset modest mid/upper-level lapse rates and
yield favorable buoyancy.  MLCAPE around 1500-2500 J/kg should
become common, with isolated strong/damaging gusts possible in the
most intense, water-loaded downdrafts.  With modest flow but
well-curved low-level hodographs, and around 35 kt effective-shear
magnitude ahead of the ejecting weak shortwave trough(s), and
potential for boundary-storm interactions, a tornado may occur as
well.

...Western AZ/lower Colorado River Valley...
Widely scattered to scattered thunderstorms should form this
afternoon over the western parts of the higher terrain in
north-central/northwestern AZ and migrate southwestward to lower
desert regions in western parts of the state -- perhaps lasting long
enough to cross parts of the lower Colorado River Valley.  Activity
should form over well-heated higher elevations with sufficient
moisture to sustain the most vigorous convection for at least a
couple hours after it moves southwestward to lower deserts, deeply
mixed boundary layers with hot surface temperatures and large DCAPE
will favor isolated severe downbursts.  A deep (700-300 mb and
sometimes higher) layer of modest (5-20 kt) northerly to
northeasterly flow generally is progged across the region, within
the mid/upper anticyclone and southeast of the high.  This will
encourage preferential southward to southwestward motion of both
active convection and resulting outflow pools.

..Edwards/Broyles.. 07/22/2024

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