SPC AC 181928

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 PM CDT Tue Aug 18 2020

   Valid 182000Z - 191200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE
   WEST TO NORTH-CENTRAL STATES...

   ...SUMMARY...
   Isolated severe wind gusts will be possible during the late
   afternoon and evening from the northern Great Basin to northern
   Rockies, Arizona to southern California, and the central High
   Plains. Isolated severe hail may also occur across the Red River
   Valley of the North.

   ...20Z Update...
   Overall forecast remains on track with no changes needed. See
   previous outlook appended below for more forecast details.

   ..Mosier.. 08/18/2020

   .PREV DISCUSSION... /ISSUED 1124 AM CDT Tue Aug 18 2020/

   ...Northern Great Basin to northern Rockies...
   A stout mid-level anticyclone will remain anchored along the NV/UT
   border. 30-40 kt 500-mb flow will persist around the periphery of
   the anticyclone from northern CA across the northern Rockies. The
   most prominent impulse embedded within this flow regime has recently
   entered western MT and will move east then southeast into the
   northern Great Plains. In its wake, pockets of strong surface
   heating from west-to-east will occur as clouds thin. This should
   support isolated to widely scattered thunderstorms by late afternoon
   initiating off the Sierras and the higher terrain of eastern OR and
   spreading east-northeast across the northern Great Basin. Inverted-v
   thermodynamic profiles beneath weak buoyancy should support a risk
   for isolated severe gusts through this evening.

   ...Red River Valley of the North to the central High Plains...
   While a conditional supercell environment will exist from eastern ND
   into a portion of western/central NE by late afternoon, convective
   development within this region appears minimal. A mid-level impulse
   is progressing south from central NE. In its wake, MLCIN appears
   likely to remain pronounced relative to the degree of boundary-layer
   moisture.

   A subtle mid-level perturbation over eastern ND may support isolated
   elevated thunderstorms across the Red River Valley during the early
   to mid-evening within a zone of weak low-level warm advection.
   Isolated severe hail would be the primary threat. Otherwise, a
   couple high-based cells may form in the NE Panhandle vicinity along
   a lee trough where MLCIN is weaker. Inverted-v thermodynamic
   profiles would favor a threat for a severe wind gust or two from any
   convection that can form and briefly propagate south near the
   NE/CO/KS border.

   ...AZ to southern CA...
   GPS and GOES PW data indicate a substantial dry intrusion pushing
   west across southeast AZ. Morning guidance indicate boundary-layer
   moisture will be lower today compared to yesterday with a distinct
   lack of buoyancy along the I-10 corridor from Tucson to Phoenix.
   This suggests the center of severe wind risk should be shifted
   westward towards the Lower CO River Valley from isolated convection
   that can emanate west off the western portion of the Mogollon Rim.
   Isolated severe wind gusts will also be possible with scattered
   storms that form along the east side of the higher terrain in
   southern CA.

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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z