Friday Night's Snow Forecast
Friday's snow event is a minor event in the region. We're dealing with a cool front that is moving into a retreating cold air mass. This front will have a fair bit of moisture associated with it (with 1/4-1/3" of liquid moisture possible along the frontal boundary) but won't bring much in the way of cold air behind it. Precipitation will be moving into this retreating cold air mass during the early evening hours. While temperatures aloft will not warm above freezing, surface winds from the southwest will be warming the lower levels of the atmosphere, which will limit the potential for snowfall around Philadelphia assuming we get enough sunshine here tomorrow before clouds move in around noontime or shortly after that.
What is going for the front in terms of snowfall is that temperatures are forecast to be close to freezing tomorrow afternoon across the region. While not the most optimal for snow, the marginal environment in the atmosphere will allow for some snowflakes to mix in with rainfall across the city, with a chance for accumulating snows Friday night north of the city as temperatures north of the city will be closer to freezing. The atmosphere in Philadelphia, at least as the GFS is concerned, is showing air above freezing in the bottom 2000' of the atmosphere. The NAM's "warm layer" is a bit shallower and only is about 1500' in thickness. "Warm air" has typically rushed in faster in the atmosphere than at the surface so we may see temperatures aloft that may be a touch warmer than forecast in the models. This could keep snowfall totals on the lower side.
Update, 7 AM: Having looked at model guidance, temperatures, and updated surface conditions throughout the Midwest, I think it's a smart call to increase snowfall totals in some areas. I have moved the coating to one inch area south to include Philadelphia, Wilmington, and parts of South Jersey (see the map above). The coating accumulations should be on cars and grassy surfaces for the most part. If you are north of the Pennsylvania Turnpike or Interstate 195, snowfall should accumulate to 1-2" in the Philadelphia burbs across to Trenton and New York City. Snow will change to or mix with rain from south to north, including Philadelphia and the suburbs to the north, before ending late tonight.
Farther north, the Lehigh Valley should get 2-3" of snow, with 2-4" of snow across the New York City north/west burbs. The Poconos should get between three and five inches of snow from tonight's cold front.
The thought as of this evening is to forecast little in the way of accumulations for Center City and the Airport, with the Roxborough, Mount Airy, and other parts of Norther Philadelphia above the Boulevard with the potential for a coating to an inch of snowfall. Bucks and Delaware County have been split roughly along Route 1, with areas south of that seeing very little in the way of accumulations and areas north of Route 1 seeing coating to an inch. The Lehigh Valley should see a general 1-2" snowfall, with 2-4" possible across the I-80 corridor in Pennsylvania, including the Poconos.
Snow and rain showers should move out of the city early Saturday morning, with the bulk of precipitation falling overnight. Travel impacts should be minimal except for the potential of some snow shower activity falling during the evening hours on Friday, generally after the PM Rush Hour.
What is going for the front in terms of snowfall is that temperatures are forecast to be close to freezing tomorrow afternoon across the region. While not the most optimal for snow, the marginal environment in the atmosphere will allow for some snowflakes to mix in with rainfall across the city, with a chance for accumulating snows Friday night north of the city as temperatures north of the city will be closer to freezing. The atmosphere in Philadelphia, at least as the GFS is concerned, is showing air above freezing in the bottom 2000' of the atmosphere. The NAM's "warm layer" is a bit shallower and only is about 1500' in thickness. "Warm air" has typically rushed in faster in the atmosphere than at the surface so we may see temperatures aloft that may be a touch warmer than forecast in the models. This could keep snowfall totals on the lower side.
Update, 7 AM: Having looked at model guidance, temperatures, and updated surface conditions throughout the Midwest, I think it's a smart call to increase snowfall totals in some areas. I have moved the coating to one inch area south to include Philadelphia, Wilmington, and parts of South Jersey (see the map above). The coating accumulations should be on cars and grassy surfaces for the most part. If you are north of the Pennsylvania Turnpike or Interstate 195, snowfall should accumulate to 1-2" in the Philadelphia burbs across to Trenton and New York City. Snow will change to or mix with rain from south to north, including Philadelphia and the suburbs to the north, before ending late tonight.Farther north, the Lehigh Valley should get 2-3" of snow, with 2-4" of snow across the New York City north/west burbs. The Poconos should get between three and five inches of snow from tonight's cold front.
Snow and rain showers should move out of the city early Saturday morning, with the bulk of precipitation falling overnight. Travel impacts should be minimal except for the potential of some snow shower activity falling during the evening hours on Friday, generally after the PM Rush Hour.Tags:
