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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: 10/30/2003 09:53 AM
 

Good Morning Philadelphia!   

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

Today's discussion will include your  Trick-or-Treat forecast!  But you have to read on down to find it.  ;-)

The BIG story nationwide (aside from an active solar weather period and fires in the west) is the switch in the upper air pattern.  This is the biggest switch since I began this page.  Very exciting.

The trough in the upper air flow (the 500mb map below shows the winds at about 18,000feet above sea level.  The winds blow parallel to the dark black lines moving mainly west to east across the US) over the east coast is departing (as marked in red) and a new massive trough is digging into the western US.  The ridge over the Great Lakes will build up and expand eastward towards us.  

The surface map shows a big huge surface High pressure system.  Remember, air moves clockwise around highs, so you would expect air to be moving in from the southwest (where it is very warm) now or soon. 

Temperatures are in the 40's this morning still (the center of the high is also the center of the coolest air).

And the winds are indeed picking up from the south out to our west (and are moving from the west to our north). 

So we have wind chills in the upper 30's this morning.  But this will be the last of the chill for a while!

With the clear skies over the east (under that high and building upper level ridge) you can see other temperature changes.  Remember the Infrared Satellite view below shows the temperature of whatever the satellite sees first.  The Gulf Stream is visible (marked with blue arrows) as much warmer ocean temperatures to our distant southeast. 

On the visible satellite view, you can't see the Gulf Stream at all, the ocean looks dark from above, but you CAN see the cumulus clouds forming in the cool air that has spread over the warm ocean.

Into the future, tonight at midnight, the high has moved a bit further east, so winds should be increasing from the southwest and temperatures will begin to warm up. 

Highs Friday will climb all the way to the lower 70's around Philadelphia...

By Trick-or-Treat time, the ridge is beginning to dominate the eastern half of the US (though the jet stream, marked in oranges, will be right overhead...meaning cold air isn't too far away to the north). 

So, when the kids are marching around the streets or going to the carnival nearby, we'll have south and southwest winds and mostly clear skies. 

Lows Saturday morning will get to the upper 40's in the city, but will only have dropped into the mid 50's by Trick-or-Treat time. 

Have a happy Halloween and I'll see you again Friday  morning.

Meteorologist  John Ensworth

Surface Station sky cover color key: