SPC AC 210045
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0745 PM CDT Mon Aug 20 2018
Valid 210100Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING
ACROSS THE MID SOUTH REGION...
Thunderstorms may continue to pose a risk for damaging wind gusts
and perhaps an additional tornado or two this evening across the Mid
...01Z Outlook Update...
A lower/mid tropospheric speed maximum (on the order of 30-40+ kt)
appears to be propagating around the southern through eastern
periphery of larger-scale troughing gradually turning eastward
across the middle Mississippi Valley. This is contributing to
moderately large deep layer shear across much of the Mid South
region, where seasonably high boundary layer moisture is supporting
moderate to large CAPE (2000-3000+ J/kg). While the lack of both
colder air aloft and steeper lower/mid tropospheric lapse rates
appears to be inhibiting severe weather potential, given the current
modest strength of the synoptic system, the environment still has
been supportive of thunderstorm activity accompanied by some severe
weather. This may linger into the 03-04Z time frame, before
boundary layer instability wanes with the loss of daytime heating.
Otherwise, scattered thunderstorm activity lingers within the warm
sector across the lower Ohio Valley into parts of the Upper Midwest.
Localized strong surface gusts and perhaps a tornado may still not
be out of the question this evening, but severe weather potential in
general appears to be in the process of diminishing.
Across the Southwest, light southeasterly flow, around the
southwestern periphery of a mid-level subtropical high centered near
the Arizona/New Mexico border, is contributing to a slow westward
propagation of thunderstorms off the higher terrain of southeastern
Arizona. As this continues, a hot and deeply mixed boundary layer
at lower elevations may remain supportive of isolated strong
downbursts into the 03-05Z time frame.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0600Z