SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1152 PM CST Wed Feb 24 2021

Valid 251200Z - 261200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
NORTHERN TEXAS INTO SOUTHERN ARKANSAS...NORTHERN LOUISIANA AND
CENTRAL MISSISSIPPI...

...SUMMARY...
A couple severe thunderstorms may impact a corridor across
north-central Texas through the Ark-La-Tex vicinity tonight, with a
couple instances of marginally severe hail or damaging gusts
possible.

...Synopsis...
Broad cyclonic flow aloft will dominate the upper pattern across the
CONUS through today. An embedded mid-level trough will traverse the
Southern Plains while a second trough aloft impinges on the Pacific
Northwest. Across the southern Plains into portions of the
Mid-South, a stable boundary layer will be in place for most of the
period. Nonetheless, a 35+ knot 850 mb jet is expected to develop by
late afternoon/early evening in response to the approaching upper
trough, transporting appreciable moisture northward (evident via 00Z
LCH/LIX observed soundings), beneath 6-7 C/km mid-level lapse rates,
resulting in up to 500 J/kg MUCAPE across portions of northern TX
into central MS in the 21-12Z time frame. Deep-layer ascent will be
in place to initiate elevated convection, with an 80 kt 500 mb jet
streak overspreading the region beneath the right-entrance region of
a 300 mb jet streak. Despite marginal instability, strong deep-layer
directional and speed shear may encourage storm organization and
longevity, with a couple of strong to briefly severe storms
possible.

Across the northwest U.S., meager buoyancy preceding the approach of
a mid-level trough and associated source of ascent may encourage
isolated thunderstorm development to the lee of the Cascades.
Elsewhere across the CONUS, cool and stable conditions will serve to
mitigate thunderstorm chances.

...Southern Great Plains into the lower Mississippi Valley
tonight...
Within the 21-00Z period, convective initiation is expected to occur
within a warm-air advection regime at the nose of a developing
low-level jet. Forecast soundings suggest that the southern Plains
storms will remain rooted above 850 mb given the aforementioned
stable layer. Mainly small hail is expected to be the main threat
with these storms given skinny CAPE profiles as depicted by forecast
soundings, however a couple stones over 1 inch in diameter cannot be
ruled out given the 60+ knots of effective bulk shear in place to
support updraft organization/longevity. By around 06Z, storms
tracking east towards Mississippi will encounter a moister low-level
airmass as they traverse the 850 mb jet axis. While storms are still
expected to be elevated, the availability of deeper moisture
suggests that storms may attempt to root closer to the surface,
potentially obtaining transient supercellular structure. A couple
damaging gusts may accompany the longer-lived, stronger storms that
form.

..Squitieri.. 02/25/2021

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