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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: 09/14/2003 02:35 PM
 

Good Morning Philadelphia!  

    The pattern is changing rapidly now.  Buckle your seatbelts. You'll feel summer and fall over the next 5 days.

The visible satellite view shows mostly clear skies except for some morning valley/canyon fog in the state again. 

The patches of fog are colored yellow on the surface map below.  Our big cool high pressure system is moving off to the southeast and the air flow is beginning to come from the southwest. Real heat and humidity hits today.  But relief is already on the horizon, the big front arcing down over the northern plains is on it's way. 

The current radar shows the thunderstorms in Michigan being kicked up by the distant approaching front.  Nothing to be concerned with right off. 

Temperatures are slowly warming with the coolest temperatures down the Appalachians. 

Higher dew points are slipping northward as well (again avoiding the higher elevations of the mountain range for now)...

Both the warmer air and higher dew points (moisture content) are slipping in on increasing south winds (look over Indiana, Ohio etc).  

The Storm Prediction Center in Norman, OK has a Slight Risk of severe weather forecast for tomorrow for our area.  The heat, moisture, and lift associated with the front could be enough to allow severe thunderstorms to form. 

On the 500mb map (showing winds blowing mainly from west to east across the nation at about 18,000 feet), shows the ridge still on us in the east, and the trough deepening over the Great Lakes that is kicking the front down and eastward. 

The Plains heat is flowing north and east into our area for Thursday night (tonight)  just as the front is getting it's act together to our north. Tomorrow will be a big blast of summer.

Tomorrow we have the trough rapidly moving into position over our heads (and the big ridge forming in the Plains again for more heat out there). 

By Friday PM, we have heat being shuttled eastward ahead of the front.  Depending on when the front comes through (midnight Fri - Saturday is expected), Friday afternoon will be steamy and hot with thunderstorms offering the only relief. 

At that same time, showers and storms are possible state wide as the front plows into and lifts the hot moist air up. 

Saturday night, and the trough is already pulling off to the east. 

As shown with the arrows, very cool dry air will be pouring down over the east coast.  Real Fall like weather!

At that time - Saturday night - the rain is all gone to the south. 

Sunday night and the ridge is approaching from the west, the trough is definitely to our east. 

And while warm air is flowing into Minnesota again (see blue arrows), there still is a good flow of cool air down over the eastern US.  B-E-A-utiful weather  (see "Bruce Almighty" ). 

Sunday night also has no rain nearby with the front long gone down south. 

And finally, the ridge is pushing further to the east, towards us as the flow across the nation becomes very zonal (west to east flow). 

The Great Plains warm air is still flowing north and east, but cool air is still in place over us - on MONDAY!. Wow. 

And we are still in the dry, stable air behind the front... no rain. 

So if you can put up with 1.5 days of summer, you'll get a taste of fall. 

I'll see you tomorrow and stay cool!

Meteorologist  John Ensworth

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