SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1024 AM CST Wed Nov 18 2020

Valid 181630Z - 191200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...Northwest...
As the mean mid-level trough spreads inland from the northeast
Pacific, cold advection will help steepen lapse rates to support
isolated thunderstorms outside of the immediate coast. Thunder
potential will likely maximize during the late afternoon and evening
within three corridors.

The first is across the northern Sacramento Valley where convection
is already ongoing near Redding. The presence of 51-54 F surface dew
points and weak boundary-layer heating should yield meager MLCAPE up
to about 300 J/kg. An elongated hodograph might support weak
mid-level updraft rotation in the strongest cells this afternoon,
although low-level wind fields will likely decrease and become
slightly veered as the lead shortwave impulse shifts towards eastern
OR/WA. Small hail is possible, but the narrow spatiotemporal window
for more favorable hodographs coincident with adequate
instability/ascent appears limited enough to preclude tornado/hail
probabilities. 

The leading shortwave impulse may briefly support isolated thunder
near the OR/WA/ID border area during the late afternoon in a very
marginally supportive thermodynamic environment. Otherwise, the next
primary shortwave impulse that should reach the OR coast this
evening will sustain potential for isolated thunder centered on
western OR from the coast to the Cascades.

..Grams.. 11/18/2020

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