SPC AC 210040

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0640 PM CST Wed Nov 20 2024

   Valid 210100Z - 211200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Severe thunderstorms are not expected tonight; although, a few
   strong storms may be noted along the immediate Washington/Oregon
   Coast this evening.

   ...01z Update...

   Strong upper low off the BC/WA coast should gradually fill tonight
   as it occludes offshore. As a result, mid-level heights will
   gradually rise through sunrise, and onshore flow should weaken.
   Until then, a few longer-lived showers/supercells developed about
   100mi offshore and are now moving inland, especially over northwest
   Pacific County WA. This convection was aided by marine-influenced
   buoyancy, but this activity will quickly weaken as it encounters a
   poor air mass inland. Some near-term risk for gusty winds, and
   perhaps an offshore water spout, exist for the next few hours.
   However, severe threat does not appear to be enough to warrant
   severe probabilities overnight.

   Downstream across the middle Atlantic, strong height falls will
   spread across this region (180m in 12hr) ahead of a pronounced upper
   low shifting southeast across the Great Lakes. A plume of modest
   0-3km lapse rates developed across the Ohio Valley earlier this
   afternoon which appeared to aid shallow convection across eastern OH
   into western PA, where some localized damaging winds were noted.
   However, this convection has spread well east of this steeper plume
   and poor low-level lapse rates downstream do not support robust
   updrafts overnight.

   ..Darrow.. 11/21/2024

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