SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0131 PM CST Tue Dec 29 2020

Valid 292000Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS CENTERED OVER
PORTIONS OF NORTHWESTERN TEXAS AND SOUTHWESTERN OKLAHOMA...

...SUMMARY...
A couple storms producing marginally severe hail are possible this
evening into early tonight across a portion of northwest Texas into
southwest Oklahoma.

...Discussion...
No changes to the ongoing outlook are necessary at this time.

..Goss.. 12/29/2020

.PREV DISCUSSION... /ISSUED 1012 AM CST Tue Dec 29 2020/

...Northwest TX and far southwest OK...
A shortwave trough just off the southern CA coast will dig southeast
and reach the southern Gulf of CA overnight, while a northern-stream
shortwave trough moves east-southeast from southern Saskatchewan to
MN. In the wake of the northern-stream wave, a cold front will surge
into the southern Great Plains this evening through the overnight. 

The northwest extent of low to mid 50s boundary-layer dew points are
already prevalent from the Permian Basin into southwest OK, and will
gradually moisten into the mid to upper 50s amid persistent surface
south-southeasterlies. By late afternoon, a dryline should take
shape across west TX, intersecting with a slow-moving
warm/quasi-stationary front near the southern TX Panhandle that
should extend northeast across western OK. The HRRR appears more
aggressive than other CAM guidance with convective development along
the dryline and front during the early evening as its parent RAP
depicts greater surface-based buoyancy than the NAM. A somewhat more
probable scenario is for convective development tonight as the High
Plains frontal surge impinges on the richer low-level moisture,
predominately rooted above the surface. Strong speed shear within
the cloud-bearing layer may prove favorable for at least transient
mid-level updraft rotation in a few cells. Weak MUCAPE and moderate
mid-level lapse rates will probably limit hail size between small to
marginally severe magnitudes.

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