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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: 11/10/2003 09:23 AM
 

Good Afternoon Philadelphia!   

    I'm glad to announce that these discussions will continue until at least the end of November.  

In Short: Mostly clear, windy with temperatures dropping before a small warming trend starts Sunday night!.

A quick look at the upper air map, AGAIN, shows the trough that broke off in the upper air flow (shown here at roughly 18,000feet above sea level) from the west coast is now passing us and heading out into the Atlantic. There is a ridge in the northern part of the flow in the Pacific Northwest, and what is called Zonal flow across the southern US (air flowing mainly from west to east with little wiggling in it - no troughs or ridges).  Since we are behind a trough (to the left or west) you would expect clearing skies and increasing pressure. 

The surface map shows this high pressure approaching over the Great Lakes. It is a HUGE area of high pressure, and has some seriously cold air underneith it. 

Winds rotate clockwise around a High, so we have north winds (fairly stiff north winds) keeping a fresh flow of cold air moving into the state. 

But the air is dry and sinking, so cloud formation is hard.  Only the cold air picking up moisture as it flows over the still warm Great Lakes is getting moist enough to make clouds form. These are lake effect clouds streaming over western New York State and western Pennsylvania. 

Temperatures are in the 40's in Philadelphia this morning and much colder to the north. 

If you combine the wind and cold temperatures, you are feeling 30's like air cooling on exposed skin. 

The center of the coldest air is under the High center over the western Great Lakes (see the purples?!  Cold!).

So the big story will be tonight, with clear skies and cold air flowing in, we will drop into the lower 20's -actual temperatures- in the city and into the teens and single digits up on the NY state line.  Wow! This is the coldest weather yet this season. 

By Monday morning, the High center will move over Philadelphia, but it's really cold air will have moderated (been warmed by the sun on Sunday - well named- no?) and we'll start to warm up as south winds return on the back side of the High. 

Lows Monday morning will be in the mid to upper 20's in Philadelphia, the entire state will be 5-10 degrees warmer in only 24 hours. 

That's it for the weekend, soak up the sunlight that hits today and stay warm.  

 I'll see you again Monday.

Meteorologist  John Ensworth

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