SPC AC 100533

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1233 AM CDT Tue Sep 10 2024

   Valid 101200Z - 111200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE LA
   COAST...

   ...SUMMARY...
   Some tornado threat associated with Tropical Cyclone Francine may
   approach the Louisiana Coast by early Wednesday morning.

   ...Synopsis...
   A shortwave trough is expected to be off the Northeast Coast early
   Tuesday morning, with continued eastward progression into the
   northern Atlantic expected thereafter. A relatively zonal pattern is
   anticipated west of this shortwave trough across the majority of the
   CONUS throughout much of the period. A low-amplitude shortwave
   trough is forecast to move within this zonal flow across the
   northern Plains and the Upper Midwest, but with minimal pattern
   amplification. Some amplification is expected late Tuesday/early
   Wednesday across the Pacific Northwest, ahead of a strong shortwave
   trough approaching the coast.

   Surface pattern early Tuesday will feature high pressure centered
   over the central Appalachians and covering much of the OH Valley.
   This ridging is expected to gradually shift eastward/northeastward
   throughout the period. Surface troughing associated with the
   northern Plains shortwave trough will extend across the central
   Dakotas early Tuesday, before then shifting eastward throughout the
   day. Farther south across the northwest Gulf of Mexico, TC Francine
   is expected to reach hurricane strength while gradually progressing
   northeastward.

   ...TC Francine - LA Coast...
   Rainbands from Francine will likely spread across the northwest Gulf
   Coast throughout the day, but the stronger flow will remain
   displaced south throughout much of the period. Beginning around 06Z,
   the stronger flow may be far enough north to influence any deeper
   updrafts that develop along the LA Coast, with an attendant risk for
   brief tornadoes.

   ...Upper Midwest...
   Moderate low-level moisture, characterized by surface dewpoints in
   the upper 50s/low 60s, is expected across the region Tuesday
   afternoon ahead of the approaching shortwave trough and associated
   surface trough. Steep mid-level lapse rates will aid in the
   development of strong buoyancy across the region, supporting a
   conditional severe-thunderstorm risk. However, despite moderate
   low-level moisture and strong daytime heating, warm mid-level
   temperatures are forecast to keep capping in place, precluding
   afternoon thunderstorm development. 

   ...Elsewhere...
   Afternoon thunderstorms are expected again across the eastern Great
   Basin and northern/central Rockies, where orographic effects and
   modest large-scale ascent will combine with modest moisture and
   buoyancy to support thunderstorm development. Increasing
   thunderstorm potential is anticipated late Tuesday into early
   Wednesday across the Pacific Northwest ahead of the approaching
   shortwave trough.

   ..Mosier/Lyons.. 09/10/2024

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z