820
ACUS01 KWNS 201253
SWODY1
SPC AC 201252

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0752 AM CDT Sat Jul 20 2024

Valid 201300Z - 211200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE SOUTHEAST AND CENTRAL TO SOUTHERN HIGH PLAINS...

...SUMMARY...
Strong to isolated severe thunderstorms are possible over parts of
the Southeast and central to southern High Plains, mainly from
mid-afternoon to evening.

...Synopsis...
The large-scale pattern in mid/upper levels will continue to feature
longwave troughing over eastern North America, and ridging in the
West.  The latter will be anchored by an anticyclone -- now centered
over AZ -- that will retrograde slowly northwestward through the
period.  This process -- and a broad field of minor shortwaves and
vorticity lobes in northerly/northwesterly flow -- will contribute
to net height falls over much of the central CONUS.  A downstream
shortwave trough was evident in moisture-channel imagery from the
lower Ohio Valley southwestward across western TN to eastern LA.
This perturbation should move eastward across the Tennessee Valley
region through midday, then over parts of GA and the Carolinas
through this evening.

The 11Z surface map showed a weak, quasistationary frontal zone from
southern VA across eastern TN, western MS, central LA, and
south-central TX.  Except where locally reconfigured by convection,
this frontal zone should remain quasistationary, while gradually
losing definition.  A lee trough -- drawn from western MT to western
SD and western KS, should remain nearly in place through the day,
with slight shifts possible in late afternoon toward strongly heated
areas.

...Southeast...
Widely scattered to scattered thunderstorms should form and move
northeastward over the area this afternoon, as large-scale lift
ahead of the approaching trough spreads atop a richly moist,
strongly heated, weakly capped boundary layer.  Damaging to isolated
severe gusts are possible.  Some of the activity may aggregate into
loosely organized clusters that maximize damage potential locally.
Somewhat enhanced mid/upper flow will contribute to spotty
effective-shear magnitudes of 30-35 kt, aiding in organization of
some of this activity.  The inflow layer will be characterized by
surface dewpoints commonly in the low-mid 70s F and favorable lapse
rates from surface heating beneath a deep troposphere.  As such, and
despite the lack of large mid/upper-level lapse rates, a deeply
buoyant preconvective profile should take shape, with peak MLCAPE in
the 2000-3000 J/kg range over the Low Country/coastal plain, and
1500-2500 J/kg across the Piedmont.

...Central/southern High Plains...
Isolated to scattered thunderstorms are expected to develop this
afternoon along the Front Range/Sangre de Cristo corridor from
southeastern WY to NM, as well as over the Raton Mesa, near the lee
trough, and along leftover outflow/differential-heating boundaries
from prior overnight/morning convection.  Isolated severe gusts and
hail are possible.

This activity will be moving into a generally less-buoyant airmass
than the previous day, thanks to extensive prior convection and
outflow over much of the region.  Nevertheless, sufficient diurnal
heating and residual boundary-layer moisture are expected to support
both well-mixed subcloud layers and enough CAPE for deep convection.
Though outflow-driven forward propagation may contribute to erratic
storm motions locally, a general southeastward to southward
translation is forecast, given the ambient midlevel winds. Although
strong directional shear is expected, forecast soundings indicate
much of this will be in the form of backing with height instead of
veering, and with weak low/middle-level winds limiting vertical bulk
shear.  Peak afternoon MLCAPE of 1000-1500 J/kg is possible near an
irregularly defined moist axis extending from the eastern Panhandles
and southwestern KS northeastward, and over eastern CO.  Buoyancy
will diminish atop a drier, more deeply mixed layer westward toward
the mountains.  Overall, convection should diminish in coverage and
intensity throughout the evening.

..Edwards/Broyles.. 07/20/2024

$$