SPC AC 240647

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0147 AM CDT Sun Sep 24 2017

   Valid 261200Z - 271200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The severe threat across most of the country should remain very
   sparse Wednesday.

   ...Synopsis...
   A persistent longwave trough across the western states will finally
   break down as a substantial, yet shorter-length mid-level trough
   migrates east toward the Upper Mississippi Valley.  Farther
   southwest, models suggest that the remnant portion of the trough
   over the western Great Basin will evolve into a closed low.  Height
   rises will be noted downstream of this closed low across the
   southern Plains as a ridge strengthens some over the Lower
   Mississippi River Valley - and modest strengthening of mid-level
   flow should occur across western New Mexico and vicinity.

   At the surface, a cold front will continue to migrate southward
   across the southern Plains and extend from near the Big Bend of
   Texas northeastward to central Missouri and on to another weak low
   located near the Upper Peninsula of Michigan early Wednesday
   evening.  A modified maritime airmass will remain in place ahead of
   the front and foster isolated to scattered convective development
   throughout the day, with peak coverage occurring during the
   afternoon and early evening.  Overall, the lack of strong deep shear
   and marginal mid-level lapse rates will keep any severe risk to a
   minimum - although areas of New Mexico may experience a low risk of
   hail and gusty winds Wednesday afternoon.

   ...Southern into western New Mexico...
   Easterly low-level trajectories will advect moisture into the higher
   terrain of the southern Rockies, fostering the development of a few
   storms in that area during the afternoon hours.  These storms may be
   enhanced by the presence of the mid-level cut-off low just west of
   the area, and ~7 deg C/km mid-level lapse rates may combine with
   just enough deep shear to provide a risk of hail and gusty winds. 
   Marginal (5%) severe probabilities may be needed in later outlooks
   if models remain consistent in depicting this low hail/wind risk -
   which may end up being closely tied to the evolution of the closed
   mid-level low over the Southwest.

   ..Cook.. 09/24/2017

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