LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1236 AM CDT Sat May 20 2023
Valid 201200Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE SOUTHEAST...LOWER RIO GRANDE VALLEY OF TEXAS...SOUTHERN NEW
MEXICO REGION...AND INTERIOR OREGON AND WASHINGTON...
...SUMMARY...
Strong to isolated severe thunderstorms are possible Saturday across
much of the Southeast, lower Rio Grande Valley in Texas, southern
New Mexico region, and parts of central Oregon and Washington.
...Discussion...
Seasonally weak mid-level flow regime continues across much of the
CONUS. Even so, modest 500mb flow is expected across the
mid-South/northern Gulf States due to an upper trough digging
southeast across the Great Lakes. This flow regime will encourage a
surface front to advance into middle TN-northern AL-central MS/LA by
18z, with subsequent movement toward the central Gulf Coast by the
end of the period. Early this morning, scattered convection persists
across much of eastern AR, immediately ahead of the aforementioned
surface front. This activity may persist into the pre-dawn hours
then possibly increase in areal coverage/intensity by mid day as
buoyancy improves due to low-level heating. Forecast soundings
exhibit modest instability but poor lapse rates. While mid-level
flow should increase during the day, it's not clear how intense this
convection will ultimately be due to weak lapse rates. Some
organization is possible, along with a few weak supercells. Will
maintain MRGL Risk at this time due to instability issues. Isolated
damaging winds/hail are the expected threats.
Trailing front has surged into south-central TX. The majority of
convection remains post-frontal and should gradually propagate
toward the international border early in the period. Latest model
guidance suggests the strongest boundary-layer heating will be west
of the Rio Grande, thus the primary concern for robust updrafts will
initially be over northeast Mexico. Some of this activity may spread
into the lower Rio Grande Valley of deep south TX later in the day.
Gusty winds and isolated severe hail are possible.
Upstream, easterly low-level component will strengthen across far
west TX into southwestern NM. Strong boundary-layer heating will
contribute to instability and isolated-scattered convection should
easily develop across this region as temperatures warm through the
mid 70s. Gusty winds/marginally severe hail are the primary
concerns.
Strong surface heating east of the Cascades, along the western
periphery of an upper ridge, will contribute to steep surface-3km
lapse rates later this afternoon. Isolated convection should once
again develop over interior WA/OR by mid-late afternoon. This
activity will not be strongly sheared, but adequate flow should
contribute to some organization. Gusty winds/hail are the primary
concerns with this late afternoon/evening convection.
..Darrow/Thornton.. 05/20/2023
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