Freezing rain to bring travel issues for parts of Pittsburgh area Friday | First Alert Weather
An ice storm warning has been issued until 7 a.m. Saturday for Somerset, Westmoreland (ridges), Indiana, Armstrong, Clarion, Jefferson, Forest, and Venango counties.
A weather advisory includes Allegheny, Beaver, and Washington until 3 p.m. Friday, and a winter weather advisory includes Preston, Fayette, Westmoreland, Butler, Lawrence, and Mercer counties until 1 a.m. Saturday.
First Alert: Friday Ice storm for parts of Pittsburgh viewing area; monitoring next Monday as well.
These advisories expire based on the time when temperatures are most likely to be safely above freezing, and or precipitation has ended.
We are still on track for a mixed bag of precipitation to move on Friday morning between 8 a.m. to 12 p.m. Not much has changed from previous discussions regarding precipitation type expectations. The initial wave will likely begin with a period of sleet and perhaps a few flakes, then transition to freezing rain and rain as the depth of warm air in the atmosphere expands with an approaching surface low-pressure pressure.
Over the last 12-24 hours, there has been a slight northward nudge in the expected track of the surface low, which raises confidence that a majority of the Pittsburgh metro will only have a brief window for freezing rain before switching over to rain by mid-afternoon Friday. Ice amounts will range from a glaze upwards to a few hundredths of an inch, with no tree or powerline damage expected. An untreated surface may be slippery for a couple of hours, but temperatures are likely to warm above freezing.
Farther north toward Highway 422/I-80, this is where temperatures will be below freezing much of the day, supporting a longer duration of freezing rain and sleet, and ice accumulation. Ice amounts upward of 0.25"-0.4" are likely here, and this may cause minor damage to trees and power lines.
Any untreated surfaces will be coated in ice, including roadways, which will make for difficult travel. Some locations along the I-80 corridor, especially east of I-79, may stay below freezing for the entire duration of the event. The same can be said for the Laurel Highlands, especially the eastward slopes and valleys that are more likely to hold onto the shallow, subfreezing layer of air due to cold air damming.
Areas southwest of Pittsburgh are expected to receive all rain, and locations where the surface warm front passes, afternoon and evening temperatures will reach the low to mid-50s.
This system will exit on Saturday, leaving us with a mostly cloudy and seasonable day with highs generally in the upper 30s to low 40s. Another strong storm system will organize to the west on Sunday and force a warm front into the region Sunday morning and early afternoon.
Temperatures will reach the low-to-mid-50s late in the day Sunday and possibly some locations near 60°F before the cold front passes Sunday night into Monday morning.
Widespread rain and possibly some thunderstorms are expected with this system. This system will have a fairly high amount of atmospheric moisture by December standards, so heavy rainfall is possible spots.
Temperatures will quickly fall behind the front through the day on Monday, with rain changing to snow. Monday's setup could possibly involve a flash freeze if temperatures drop fast enough, and relative humidity remains elevated behind the front.