Temperatures have dropped significantly over the past 18 hours after storms in western PA prompted tornado warnings near Pittsburgh on Wednesday evening. We’re now shifting into winter weather mode, with everything from the first flakes of the season to up to three feet of snow in PA by Friday.

A coastal low pressure system has developed moving into Southeast New York State Friday morning and then into eastern PA Friday afternoon. That placement allows cold air to move in behind the center, which in this case will be southwest of the low pressure. This puts most of Pennsylvania in the crosshairs due to snow accumulation.

The heaviest snowfall will occur at higher altitudes, in mountainous areas above 1500 meters. The amount of snow will decrease significantly as you move into the valleys where temperatures are above freezing and slopes are common (warmer temperatures, less precipitation downwind of the mountains), namely in places like the Wyoming Valley and much of the Central Susquehanna River Valley.

Latest timing for winter storm

The rain will change to snow in the northeastern part of the state during the late evening hours of Thursday. The changeover will occur up to about 2,500 feet in elevation, with locations lower than Wilkes-Barre and Williamsport seeing a mix of rain and snow into the early hours of Friday morning. Below is the Hi-Res NAM model for Thursday 9:00 PM.

Snow will fall in most places near and north of I-80 between 3 a.m. and 4 a.m. Friday. Snowfall will be heaviest in the northern Poconos, north and east of Scranton, at this time Friday morning. The heavy snow bands will move southwest as the upper level lows move differently than the usual coastal surface lows we see in the winter.

Travel will be very difficult in the northern PA mountains by then. Speed ​​limits have been reduced to 45 mph on I-81 and I-84 in Northeastern Pennsylvania for this storm, and we recommend avoiding travel early Friday morning in the higher elevations outside the Wyoming Valley. Here is the future Hi-Res NAM radar for Friday 3am.

Friday morning’s commute will be ugly across the Appalachians, with snow expected in most areas north of I-76 between 6 and 7 a.m. Friday. Road impacts from the snow will be minimal below 750 feet, which includes most valleys in the state.

Snow will continue to move south Friday morning as low pressure approaches the state. Southern PA Valleys may start out as rain briefly before changing to snow as moderate precipitation moves in. Below is the future high-resolution NAM radar for Friday 7am.

Late Friday morning, as low pressure approaches, snow will spread across the state. Temperatures will be around 30 degrees in most places, with only elevations above 600 meters at or below freezing. Snow is likely to accumulate only on the grassy plains in the lowlands. Here is the future radar for Friday 11am.

This is a long lasting storm, as you may have noticed! Snow is expected to fall heavily in the Laurel Highlands beginning Friday afternoon and into the evening. Meanwhile, snow on the lower plateau in Western PA will likely change to rain by then.

While in Central and Eastern PA moderate precipitation rates will result in continued snowfall, areas with lighter precipitation will likely see rain. Below you can see the future radar for Friday 4:00 PM.

LAST CALL SNOWFALL FORECAST FOR THURSDAY NIGHT – FRIDAY

Area A: Snowfall of 8 – 12″ expected. Roads will be impassable Friday morning, causing work and school closures. Heavy snow and strong winds can cause sporadic power outages due to fallen trees on power lines.

Area B: Snowfall of 4 – 8″ expected. Roads will become covered in snow, likely leading to work and school closures. Isolated power outages are possible.

Area C: Expected snowfall of 2 – 4″. The roads are likely covered in snow or mud. Work and school delays or cancellations possible.

Area D: Snowfall of 1 – 2″ expected on grassy surfaces. Roads are likely to remain wet, and during times of snow, muddy conditions may develop on untreated surfaces.

Area E: Accumulation of snowfall less than an inch is expected on grass surfaces only.

Area F: Rain is expected from start to finish.

Don’t forget to share this forecast with friends and family who will be affected!