WESTERN PENNSYLVANIA — A strong cold front will pose a significant severe weather risk across western Pennsylvania this Saturday afternoon and evening, with the best timing window running from 3 PM through 9 PM. Enough instability and wind shear will be in place ahead of the front to create a potentially severe squall line capable of producing damaging wind gusts and a non-zero spin-up tornado risk. As the front pushes into central Pennsylvania it will encounter more stable air and begin falling apart, limiting the severe weather threat to the western portions of the state.
Zone 2 Faces the Greatest Threat — Pittsburgh, Erie, and Surrounding Areas
Zone 2, covering the highest risk area across western Pennsylvania, includes Pittsburgh, Erie, Meadville, Edinboro, Oil City, Mercer, Butler, Beaver, Washington, Greensburg, and Uniontown. Scattered strong to severe thunderstorms are expected across this zone during the afternoon and evening window.
The strongest storms within Zone 2 may pack wind gusts of 55 to 65 MPH, capable of downing trees, snapping power lines, and causing structural damage across affected communities. Torrential downpours and frequent lightning will accompany even the non-severe storms across this zone throughout the 3 to 9 PM window.
Zone 1 Covers Central Pennsylvania With Isolated Severe Risk
Zone 1 stretches across central Pennsylvania including DuBois, Punxsy, Clearfield, State College, Altoona, Huntingdon, Johnstown, Somerset, Bedford, Defiance, and Chambersburg. Isolated strong to severe thunderstorms are expected across this zone, with a somewhat lower threat level compared to the Zone 2 corridor further west.
Wind gusts of 50 to 60 MPH are possible with the strongest Zone 1 storms, along with torrential downpours and lightning. As the front encounters increasingly stable air pushing into central Pennsylvania, storm organization and intensity are expected to drop off compared to what is anticipated across the western zone.
Spin-Up Tornado Risk Adds to the Threat Picture
Beyond the damaging wind threat, a non-zero spin-up tornado risk exists across western Pennsylvania as the squall line pushes through during the afternoon and evening. The combination of wind shear ahead of the cold front and any embedded mesovortices within the squall line creates the potential for brief and weak tornado spin-ups across Zone 2 communities…