SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1133 PM CST Mon Nov 23 2020

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS...

...SUMMARY...
Severe thunderstorms are possible late afternoon Tuesday into
Tuesday night across portions of the southern/central Plains,
Ozarks, Mid-South, and lower Mississippi Valley.  Large hail and
severe gusts are the primary hazards.

...Central/Southern Plains to Lower MS Valley...

Strong mid-level vort with an accompanying 90kt+ speed max are
digging into the lower CO River Valley at 0530z. This feature will
shift east into southern NM by 18z then into the southern High
Plains by late afternoon. 120m 12hr height falls, along with a
focused exit region of the aforementioned jet, suggest convection
will develop by early afternoon along the front over the western
OK/TX Panhandle region. Forecast soundings suggest the strongest
boundary-layer heating will be noted across this region, and despite
the relatively dry boundary layer, profiles exhibit more than
adequate instability for surface-based convection along the front.
RAP forecast sounding for DHT exhibits ~900 J/kg SBCAPE with steep
lapse rates and -22C at 500mb. Hail production should be efficient
with this activity, although it may be initially sub-severe.

Late-evening surface data suggests mid 50s surface dew points are
advancing north across the Edwards Plateau and this moisture plume
should return across western OK prior to the main convective
development. While large-scale forcing for ascent should ultimately
lead to more organized line segments downstream, initial activity
across the far northeastern TX Panhandle into northwestern OK should
be supercellular in nature. This early activity could certainly
produce very large hail before the convective mode is disrupted.
Prior to this disruption, a few brief tornadoes are also possible.
As large-scale forcing spreads across western OK, a more organized
band of storms should evolve then propagate east with an attendant
hail/wind threat. Given that the LLJ will be focused into northeast
OK/Ozark Plateau region, the primary corridor for organized
convection should spread north of I-40 across OK into this region.

Farther south, it's not entirely clear how active the warm sector
will be prior to the cold frontal passage across northeast TX into
western AR. HRRR is the most aggressive high res model in generating
discrete storms in the warm sector by 25/00z, then along the front
as it advances into this more moist air mass. However, stronger
forcing will remain north of this region and there is reason to
believe convection may be a bit more isolated across this region.
Will maintain MRGL Risk across this area due to uncertainty in storm
coverage/intensity.

..Darrow/Squitieri.. 11/24/2020

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