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The Story Behind the Weather - By Forecaster John Ensworth M.S. - 

The Discussion of Weather Events Daily for Philadelphia and Pennsylvania

 Last updated: 12/15/2003 11:01 PM
 

Good Morning Philadelphia!   

    I'm glad to announce that these discussions will continue until at least the end of this Year!. 
    I have the necessary server space.  

BUT I may have to switch to an approximately every-other-day schedule as Christmas year-end work piles up.  I'll do my best to stick with ya! 

In short:  Skies are mostly clear and temperatures are warmer than they have been.  Snow sits to our northwest but not in the city. Rain is coming for Tuesday and some Snow for Thursday, then clearing again for the weekend.  

 In long: The snow pack map  shows up to 6" (and maybe more) of snow in much of the state, but nothing near home. 

The storm that dumped that snow over the weekend (as we floated along the freezing line but stuck to rain most of the time) is almost off the map to the northeast.  The NEXT system is cranking hard (with strong winds and dust in the belt between the dry line (purple line) and the front (blue and red line). 

Temperatures here are chilly (mainly due to the snow to our NW) and are hovering near freezing this evening, but 40's and 50's are visible out west in the southern Ohio Valley and Mississippi Valley.

Those warm temperatures (coming to a Philadelphia near you) are roaring northward on the south winds you can see even now beginning to hit western Pennsylvania. This wind is eating up the snow dropped by earlier storms out on the Plains. 

The Infrared Satellie view (showing warm surfaces in red -usually clear skies and warm ocean or ground temperatures; cold surfaces in blue - usually cloud tops high in the atmosphere with blues often being ice) shows the clear skies over Philadelphia and the cold land temperatures as compared to the Ocean.  Any east winds that kick up will be warm!

We are under the influence of a ridge in the 500mb map. The sinking air on the right side of a Ridge produces clear skies and calm conditions. The next system heading out of Oklahoma is associated with the deep trough labeled in Red below.  Lots of energy and a narrow slam of cold air in this system. 

(This map shows the winds at about 18,000 feet above mean seal level as they blow west to east over the US.) 

Into the Future, you can see that by 1pm Tuesday, the storm has two low centers and snow over the lake and we are getting a strong south wind. 

By Tuesday 7pm, the system is barely shifted eastward.  We still have warm south winds whistling through the city. 

Wednesday 7am, rain hits Philadelphia as the northern front brings cold air towards us and the southern Low pulls up moisture for the rain (and later snow). The two are working together to mess up the middle of the week!

By Thursday morning, the 500mb map shows a deep trough over the eastern US bringing down COLD air again. 

On the back side of the departing low, we get northeast winds again and snow falling in the cold air. Yuck. 

And finally, just to keep an eye on the snow possibilites for a White Chrismas... the nearest snow still seems to remain confined to New York state.  That's not too far a drive - no?

And I'll be back here either Tuesday PM or Wednesday morning.  I'll do my best but the Christmas Season is what it is...busy!

Meteorologist  John Ensworth

Surface Station sky cover color key: