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SPC Convective Outlook

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 Forecast Discussion

ACUS01 KWNS 220531
SPC AC 220530

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 PM CST Wed Feb 21 2018

Valid 221200Z - 231200Z


A few strong thunderstorms are possible today through tonight,
mainly across parts of the southern Plains.  However, the risk for
severe storms still appears negligible.

It appears that positively tilted, large-scale mid/upper troughing
will be maintained across the West today, as another significant
short wave trough digs southeast of the Pacific Northwest, toward
the southern Great Basin.  A preceding short wave is already in the
process of accelerating northeast of the lower Colorado Valley. 
Models indicate that it will continue across the Four Corners region
early today, and through the mid Missouri Valley into the Upper
Midwest by late tonight.

Forcing for ascent associated with the lead feature is expected to
remain well to the west and north of a sharp surface frontal zone
now stalled across the Cumberland Plateau through the lower
Mississippi Valley and Texas Gulf coast region.  Models are
suggestive that some erosion of the shallow leading (southeastern)
edge of the cold surface-based air mass is possible from portions of
southeast Texas into the lower Ohio Valley, beneath anticyclonic
mid-level flow on the northwestern periphery of persistent strong
subtropical ridging centered off the south Atlantic coast.  However,
generally weak mid-level lapse rates and forcing for ascent are
expected to limit potential for appreciable boundary layer
destabilization and vigorous thunderstorm development.

Highest thunderstorm probabilities seem likely to remain focused
above the residual cold surface-based air to the north of the
frontal zone, from portions of the southern Plains northeastward
toward the Ozark Plateau.  One wave of thunderstorm activity may
form in association with forcing accompanying the aforementioned
impulse emerging from the Southwest, spreading across and northeast
of the Red River Valley this afternoon.  Another wave of
thunderstorm activity appears possible late tonight, near and
southeast of the Texas Hill Country into northeast Texas.  This
latter convection is expected to be supported by low-level warm
advection downstream of the primary short wave digging into the
Great Basin, and perhaps forcing associated with an impulse within
the subtropical stream.  This may occur in the presence of at least
somewhat more substantive steepening of mid-level lapse rates than
with the earlier convection.  However, it remains unclear whether
mid-level destabilization will be sufficient to support an
appreciable severe hail risk.  Given the late night (end of period)
timing, less than 5 percent severe probabilities will be maintained
for now.

..Kerr/Leitman.. 02/22/2018