SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0155 PM CST Fri Jan 29 2021

Valid 292000Z - 301200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Weak thunderstorm development remains possible across parts of the
Southwest into Great Basin late this afternoon and evening, with
weak thunderstorms also possible across parts of the south central
Great Plains overnight.

...20Z Outlook Update...
Some adjustments to the categorical (10 percent probability)
thunderstorm line have been made to account for the progression of
the synoptic features, and latest trends concerning ongoing
destabilization.

Large-scale mid-level troughing, including a significant
smaller-scale impulse just now in the process of advancing inland of
the southern California coast, may be accelerating
east-northeastward a bit farther north than generally indicated by
prior model output.

Beneath a lead smaller-scale impulse, weak boundary-layer
destabilization is occurring, northward across portions of
southern/eastern Nevada.  This is contributing to deepening
convective development, in an environment where thermodynamic
profiles may become marginally conducive to lightning for a few
hours late this afternoon.

Otherwise, as the more significant trailing impulse progresses
inland, it appears that the onset of mid-level warming may
contribute to diminishing risk for thunderstorms near southern
California coastal areas as early as 22-23Z.  The extent of the risk
for thunderstorms eastward across the lower Colorado Valley into
Arizona is becoming more unclear due to at least some offset of the
diurnal heating cycle with the arrival of the stronger mid-level
cooling/forcing for ascent.  However, at least isolated thunderstorm
development still appears possible by this evening.

Farther east, precipitation associated with moistening and
large-scale ascent above an elevated mixed-layer, is stabilizing
mid-level lapse rates across parts of the Texas South
Plains/Panhandle vicinity.  However, the onset of mid-level cooling
and strengthening lower/mid tropospheric forcing for ascent may
contribute to weak thunderstorm development toward the 03-06Z time
frame, before spreading northeastward overnight.

..Kerr.. 01/29/2021

.PREV DISCUSSION... /ISSUED 1030 AM CST Fri Jan 29 2021/

...Southern California into Arizona...

Upper trough moving into southern CA this morning will continue into
AZ this evening. Ascent and steep mid-level lapse rates accompanying
the primary vorticity maximum are spreading into southern CA, where
isolated thunderstorms should persist this afternoon. The risk for a
few thunderstorms will spread into AZ as lapse rates steepen by late
afternoon into the evening. 

...Southern Plains region...

Steep lapse rates (7.5-8 C/km) in the 700-500 mb layer are in place
across the Southern Plains. Though low-level moisture is limited, a 
plume of mid-upper level subtropical moisture is spreading northeast
ahead of the southwestern U.S. upper trough. A few lightning flashes
remain possible today with shallow mid-level convection developing
in this plume. The primary corridor of thunderstorm development is
expected late tonight from the Texas Panhandle and northwest Texas
through western and central OK. Deeper forcing for ascent within a
strengthening warm advection regime and approach of the shortwave
trough will promote destabilization in the 700-300 mb layer, and
scattered thunderstorms will likely develop, primarily after 08Z.

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