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Glenn F. Schreiber DMD and Glenn Schreiber is theweatherguy writing about Philadelphia Weather [radar] [surface map] [disclaimer]
   

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  • Glenn F Schreiber
    aka "theweatherguy"

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    Fri, 04 Dec 2009

    Winter Weather Update- Fri Eve
    Latest NAM model is a bit warmer at rhe surface, keeping snow during the evening period to a slushy inch at most.

    posted: Dec 04 2009 at 9:46 pm

    [/weather/dec09] permanent link

    Winter Weather Update- Fri Afternoon
    The GFS forecast has come into agreement with the NAM model for moderate precipitation, beginning during the mid morning Saturday, and continuing into Saturday evening. The precipitation will be RAIN for most of the day, however, about 4 PM, the rain will mix with wet snow and a changeover to all snow is expected by 5 or 6 PM. That said, the NAM MOS and GFS MOS (Model Output Statistics) have the high temp about 38 and falling to near or above freezing for the afternoon and evening, which would prevent accumulation.

    The NAM FOUS data (numerical data I find useful during these sort of events) has temps that are colder, nearer to freezing.

    With the NAM cranking out so much precipitation, it is possible that 2-3 inches of snow will accumulate during the early evening hours on, 4-6 inches north and west.

    Sat 12/5: Cloudy with rain beginning about 9 AM, changing and mixing with wet snow during the afternoon and some accumulating snow by late afternoon. No accumulation at first, but accumulations possible by late afternoon. Accumulations will depend on surface temps. 2-3 inches possible, more W and NW of the city.

    Sun 12/6 Mostly sunny, breezy and cold. High 42.

    Read my most recent Fall-Winter Climate prediction here.

    Follow me on Twitter as theweatherguy for on-the-fly weather updates and observations.

    posted: Dec 04 2009 at 3:00 pm

    [/weather/dec09] permanent link

    Philadelphia Weekend Weather Forecast- Fri AM
    There remain major differences in the GFS and NAM models for Saturday afternoon.

    The NAM is wetter and somewhat milder, the GFS is drier and colder, with the storm being suppressed to our east by cold air.

    The differences remain on the order of a factor of 10 in the amount of precipitation! So expect some snow during the afternoon on Saturday, but confidence in predicting amounts is poor. This is compllicated by surface temperatures that won't be near freezing until late afternoon, so predicting actual accumulation is even more complex.

    I generally prefer the GFS model (light snow, not accumulating much) but with last Thursday night's rains, the NAM ( which is predicting 1-3 inches for Saturday) was more accurate about amounts. So it's feeling like a betting parlour with this forecast. Maybe a blend of 1 inch by mid evening will be the reality?

    Sat 12/5: Cloudy and cold with rain by afternoon, possibly starting earlier, then mixing with and changing to snow before ending early evening. Above freezing temperatures may not allow much accumulation during the afternoon, so there are many unknowns, both about the temperatures and the High 39, decreasing during the day.

    Sun 12/6 Mostly sunny, breezy and cold. High 44.

    Read my most
    recent Fall-Winter Climate prediction here.

    Follow me on Twitter as theweatherguy for on-the-fly weather updates and observations.

    posted: Dec 04 2009 at 6:10 am

    [/weather/dec09] permanent link



    Disclaimer: I am not a meteorologist and provide this information as a hobby and for entertainment (mostly my own :-) . While attempts are made to predict the weather as best as I can, use at your own risk! I am NOT responsible for any direct or indirect consequential injury/damages due to your use of these forecasts. Always check the NWS Official Forecast for your final plans.

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