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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