SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0151 PM CST Tue Nov 24 2020

Valid 242000Z - 251200Z


Severe thunderstorms are expected from the Texas Panhandle into
Oklahoma through this evening. More isolated severe storms are
possible overnight from northeast Texas into Arkansas.  Large hail
and damaging winds will be the main threats, along with a couple of

...20z Update - Southern Plains/Ark-La-Tex...

Only minor adjustment have been made to the 10% general thunderstorm
line across parts of the Plains based on latest trends and CAMs
guidance. Otherwise, the ongoing outlook is on track. Strong
thunderstorms have developed across parts of the OK/TX Panhandles
this afternoon where temperatures have warmed into the 60s and
MLCAPE has increased to around 500 J/kg near and east of current
convection. Additional storms are expected to develop with time as
the surface low and cold front develop eastward toward western OK
over the next couple of hours. Large hail, damaging gusts, and a
tornado or two still appear possible through this evening across the
Slight risk area. Most recently, 1 inch hail has been reported with
storms in Beaver County, OK. For more details, reference MCD 1807.

..Leitman.. 11/24/2020

.PREV DISCUSSION... /ISSUED 1027 AM CST Tue Nov 24 2020/

...Parts of the southern Plains to the Ark-La-Tex through tonight...

A midlevel shortwave trough over NM this morning will progress
eastward to northwest TX and western OK by late evening, and then
continue northeastward to MO/AR by the end of the period.  The
midlevel trough will be preceded by a surface cyclone that will
develop eastward from the TX Panhandle this afternoon to western OK
this evening, and then northeastward to MO overnight.  A narrow
corridor of mid-upper 50s boundary-layer dewpoints will return
northward to the east of a dryline, where a few cloud breaks could
allow pockets of surface heating as far north as west central or
northwest OK by mid-late afternoon.  

Storm development appears probable by mid afternoon in the TX
Panhandle near the triple point, and storms will subsequently spread
eastward into west central and northwest OK late this
afternoon/evening, generally along and north of I-40.  Deep-layer
shear will support supercells, but rather modest low-level shear and
substantial forcing for ascent in the left-exit region of the
mid-upper jet suggest that some upscale growth into clusters or line
segments is also probable.  Thus, there will be some threat for a
tornado or two relatively early in the convective evolution across
northwest OK, in proximity to the surface boundaries and where
low-level lapse rates/CAPE will be largest.  Isolated very large
hail will be a threat with supercells given steep lapse rates and
500 mb temperatures colder than -17 C, and damaging winds will
become more of a concern this evening as convection grows upscale.

A separate zone of convection is expected overnight from northeast
TX into southeast OK and western AR, both in pre-frontal warm
advection and along the cold front as it encounters richer low-level
moisture and weakening convective inhibition.  Convection will
likely remain elevated near and north of I-40, with more
surface-based convection closer to northeast TX.  Vertical shear
will be strong in this corridor, but there will be a tendency for
the stronger forcing for ascent to begin passing north of the more
unstable warm sector late in the period.  Overall, isolated severe
storms may occur overnight from northeast TX into AR, but it is
still not clear that a more concentrated severe threat will evolve
in this corridor, so low severe probabilities will be maintained in
this update.

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