WINTER WEATHER UPDATE – FRIDAY

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Winter Weather Update Fri 5 PM
Another quick update. This afternoon’s NAM and GFS show a faster storm onset. Precipitation starts about between 3-5pm Saturday afternoon. It’s likely to start as snow, with 1, possibly 3 inches before a rapid changeover to sleet and then rain.

Heavy rain by early evening Saturday. (Freezing rain likely far northwest in Allentown up until midnight.) Rain tapers in the morning Sunday as temperatures plummet and winds pick up. Minimal accumulation expected in the immediate PHL area when all is said and done.

Temperatures are forecast to drop from 49 (GFS) or 42 (NAM NBM) to 30 by 1 PM, then falling further during the afternoon to 20 by 7 PM and single digits at night. Windy conditions may dry some open roadways, reducing icing, but standing areas of water or draining areas from the side of roadways will freeze.

The next model runs come out between 9 PM (NAM) and 10:45 (GFS). I’ll update before 11 PM.

Winter Weather Update Fri 10 AM
A quick update. This morning’s NAM shows a faster storm onset. Precipitation starts about 4pm Saturday. A very fast changeover to sleet and then rain. Freezing rain possible far northwest. Heavy rain by early evening Saturday. Rain tapers in the morning Sunday as temperatures plummet and winds pick up. Minimal accumulation expected in the immediate PHL area when all is said and done.

NAM accumulations
NAM forecast total accumulations by Sunday noon.

Last night’s models did very well with the light snow that should be ending within the next hour.

Here’s the latest on the Saturday to Sunday storm. For Philadelphia and its immediate suburbs, a total storm QPF is about 1.95 inches water. Most of this precipitation will be rain, but the beginning and end of the storm will have snow or mixed precipitation.

Based on the latest 06Z run of the NAM and GFS models (1AM last night), the NAM is holding off much of the precipitation until temperatures rise enough when the precipitation begins towards evening. Temperatures in all levels of the atmosphere will minimally support snow, so between 5 and 7 PM Saturday, expect some light snow rapidly mixing with sleet and rain and then all rain by 9 PM. In the far northwestern suburbs, an extended period of sleet and freezing rain may be occur and areas near Allentown may remain a frozen mix until midnight.

The GFS also has the atmosphere warming, but it has more precipitation starting somewhat earlier in the late afternoon, with greater mixed precipitation accumulating before the changeover to rain about 9 PM.

The Arctic front moves through about daybreak Sunday. Temperatures plummet from about 40 at 7 AM to 28 at 1 PM and 17 by 7 PM. Little moisture is left with this drop in temperatures. A change back to snow is expected Sunday morning, but accumulations in the immediate PHL area and surround suburbs will be minimal Sunday, according to latest models.

Stay tuned for more updates. We’ll be in better range for specifics tonight and tomorrow morning.

2 thoughts on “WINTER WEATHER UPDATE – FRIDAY”

    1. That’s an excellent question and will depend on several things that I will discuss in greater detail on an upcoming post. Basically, it depends on temperature and drying effects of wind. Temperatures will drop from the 40s (NAM) or near 50 (GFS) to about 30 by 1 PM and near 20 by 7 PM. Any falling precipitation will freeze, but the models have the precip cutting off as the cold air moves in. High winds can dry areas on roadways during the daylight hours. But any draining areas or ponding areas will freeze over during the afternoon. So it’s a tough call.

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