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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: 04/12/2004 09:29 AM
 

Good Afternoon Philadelphia!   

    I'm glad to announce that these discussions will continue until at least the middle of May (off and on).

    I'm REALLY busy teaching three places at once (and creating one class from scratch), so as long as I miss handfuls
of days, I'll have the server space needed to stretch it to one year.  

In short:  Rain showers have started and will get heavier and more continuous over the next 48hours, then things break up and stay cool. . 

 In long: The visible satellite image (showing reflective/bright things, like clouds and snow, as white, and dark things like ground and ocean, as black) shows thing clouds to the north and thicker clouds moving in from the south and west.  

But it takes the infrared satellite view (showing cold cloud tops and blue and warm surfaces like the ground and ocean as red) shows the coldest clouds are to our southwest and west still.  This is where the deepest convection is...

AND that's where the rain is.  Neat!

The next few days' forecast starts with the upper air pattern.  The air here on the 500mb map is blowing mainly west to east across the continent at about 18,000 feet parallel to the dark black lines.  The troughs of lower heights are marked with red dashed lines.  You can see two troughs almost phased into one over the central US.  These merging will give the region to the right, in the red circle, additional lift and squeeze MORE moisture out in the form of rain. 

By Tuesday night, 6pm, we see one BIG trough phased over the eastern US (and yet another to the north not quite in line). 

What this looks like at the surface is, currently, a low sits to the right of the split trough and rain is spreading just now into Pennsylvania. 

For Monday night/Tuesday morning the low heads straight for us with a giant shield of rain with it. 

Then by Tuesday night, the low is sitting in Ohio (northbound) and HEAVY rain is pouring down to the east of it's frontal system dumping on Philadelphia. 

Is this shaping up to be another spring like last year?  Who can know...

I'll see you again Tuesday if I can.

Meteorologist  John Ensworth

Surface Station sky cover color key: