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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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    Sun, 25 Feb 2007

    Winter Storm Update- Sun PM
    Latest NAM-WRF just became available....

    The worst part of the 'storm' has already occurred. For the balance of the night, another 0.25 inches of water will fall, first as snow, then sleet about midnight and then back to snow before daybreak. Much of the storm will be over by rush hour. Expect another inch or or accumulation in the city. Not much ice or freezing rain expected, just sleet and snow.

    posted: Feb 25 2007 at 9:15 pm

    [/weather/feb07] permanent link

    Winter Storm Update- Sun Early Afternoon
    See my earlier forecast.

    The latest GFS available shows a somewhat colder model solution with perhaps more sleet and snow and less freezing rain. The GFS agrees with the earlier NAM model, with a total QPF value of 0.65 inches water falling, mostly during the later afternoon and evening hours.

    Temperatures hover near freezing (31-33) through the storm for the general Philadelphia area. The models differ slightly with the temperatures at 5000 and 7000 feet, which determines the snow/sleet/rain combination. Both models have temperatures aloft not supporting snow by midnight; the latest GFS has a change back to snow around daybreak, while the NAM is a bit later.

    The moisture aloft has almost reached us by 1:20 PM, so snow may start before my previous timeframe of 3 PM. Base on the cold temperatures of the latest GFS, I'm raising the accumulations to 2-4 slushy inches on grassy areas by Monday morning for Philadelphia, and back to 4-6 inches north and west.

    What should concern us most is the travel conditions Monday morning. Once daylight hours occur, icing will melt on the roadways this time of year: solar insolation is very strong this time of year, even with clouds. So leaving for work a bit later will probably be doable, even if there's a 2-4 inch accumulation of snow and sleet off road.

    Next NAM-WRF model output will become available about 9:00 PM tonight. I'll update around that time.

    posted: Feb 25 2007 at 1:26 pm

    [/weather/feb07] permanent link

    Winter Storm Update- Sun AM
    The models continue to advertise a mixed precipitation event, starting later this afternoon. However there have been some trends apparent since last night. Here they are:

    1. The actual low temperatures last night were higher than previously predicted. Temperatures are starting very close to freezing, unlike the storm on Valentines day.

    2. The model's QPF values, the amount of water falling, has decreased somewhat over recent model runs and is significantly less than the Valentines day storm.

    3. The storm is coming from the west, with less development expected along the coastline.

    4. The ground surface temperatures are not as cold as the last storm.

    Towards icing problems, the storm will be occurring during the night time hours.

    Taking into account these factors, we may luck out and the amount of icing could be significantly less than our recent last storm. Put another way, I think we may get more wet conditions than ice in the immediate Philadelphia area and whatever falls (wet snow, sleet, rain) will be hitting marginally freezing surfaces. (Conditions in the normally colder western/northern suburbs will be much worse.)

    Sun 2/25: Bright skies very early, then becoming cloudy with a mix of wet snow and sleet starting between 3-6 PM, changing to freezing rain and plain rain in Philadelphia. About 1 inch slush accumulation on roadways in the immediate Philadelphia area. Driving conditions in Philadelphia will be passable Monday morning, but areas to the north and west will be difficult.

    posted: Feb 25 2007 at 8:45 am

    [/weather/feb07] 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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