Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 170531
SWODY2
SPC AC 170530

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 PM CST Sat Feb 16 2019

Valid 181200Z - 191200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk of severe thunderstorms appears negligible across the U.S.
Monday through Monday night.

...Discussion...
Models continue to indicate that one branch of split westerlies
emanating from the mid-latitude Pacific will undergo at least some
amplification across the U.S. during this period.  Within the base
of larger-scale mid-level troughing inland of the Pacific coast,
another in a series of digging short wave impulses is forecast to
progress across the Southwestern international border area, before
gradually turning eastward/northeastward toward the southern U.S.
High Plains by late Monday night.

Downstream, it appears that short wave ridging within the
mid-latitude westerlies will build in phase with the subtropical
stream, across the lower Plains into the lower Ohio and Tennessee
Valleys.  This is on the northwestern periphery of a subtropical
ridge centered near/east of the Bahamas, which is forecast to remain
prominent through this period.

Models indicate that increasing mid-level confluence, between the
building ridge and a digging trough within a branch of westerlies to
the north, will support the southeastward development of a center of
expansive cold surface ridging across the northern Plains through
southern portions of the Great Lakes region.  Along the
quasi-stationary shallow southwestern periphery of this air mass, it
appears that a warming and moistening southerly return flow off the
western Gulf of Mexico will contribute to a gradual erosion of this
air mass near coastal areas.

Farther inland, as the return flow strengthens Monday night
(including to 30-50 kt around 850 mb), an east-west zone of
steepening isentropic ascent, near the leading edge of the more
substantive elevated moisture return, is expected to become the
focus for increasing thunderstorm development.  It appears that this
may be associated with CAPE on the order of 250-500 J/kg, though
continuing elevated moisture return and steepening mid-level lapse
rates may contribute to increasing CAPE in its wake (to its  south).
However, the higher potential instability may coincide with
increasing mid-level inhibition associated with warming aloft.  As a
result, while some hail may be possible in the stronger storms, the
potential for severe hail currently seems negligible.

...MAXIMUM RISK BY HAZARD...
Tornado:  <2%     - None
Wind:     <5%     - None
Hail:     <5%     - None

..Kerr.. 02/17/2019

$$


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