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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: 09/25/2003 09:11 PM
 

Good Evening Philadelphia!   

    I'm sorry to announce that these discussions will end at the end of September.  They are taking up a HUGE amount of server space.  If you REALLY want them to continue, email me.  Otherwise feel free to use the archives as teaching tools.  There are many good case studies in there - including 

The current weather story this evening is the front pressing through. It is mostly dry...mostly. The previous system cleaned out some of the water vapor in the atmosphere limiting the showers.  That is nice news!

At 7:20pm, there were showers bubbling along the front to our southwest...

At 9:50pm, the scattered storms were silently (mostly) sliding past us. 

The Chance of rain through 8pm (past) was about 40% (you can SEE a 40% chance of rain above... mostly). 

From tonight through 8am Friday, we are in the 30-40% rain chance zone (but the front is mainly past us). 

On the Infrared Satellite view (which is useful all night long, the visible satellite view needs sunlight to work) shows us the temperatures of whatever the satellite first sees from space.  Clouds are often higher in the atmosphere than the ground (except fog), and it is cooler higher in the atmosphere...so clouds are cold and are colored blue, where the warm ground is colored red.  You can see the front as the line of slightly lighter orange/red colors over all of PA and down into NW Virginia and back over Ohio.  The rest of Virginia and the states up the east coast are all redder (and warmer).  You can SEE the front with your eyes!

Our front is being pushed along by the east coast trough that is digging in and moving through right now. This map (the 500mb map) is the wind flow from (mainly) west to east across the US at about 18,000 feet above sea level.  The big dip in the east is called a trough and you would expect storms and rain on the right side of the trough (the uphill side of the air flow). 

Winds at the surface are blowing out of the west across the region behind the front...

And the combination of front and radar shows you the activity it is kicking off. The stationary fronts off the coast are probably computer errors.  Ignore those. 

Looking at the US surface temperatures, you can see the cooler blob of air in the north east (right where the 500mb trough is!) behind our front.  We have the coolest air in the nation to our NW. 

The tropics are beginning to act up again.  We have a named storm, Juan, and a new depression (sixteen) out there.

But Juan is expected to stay way out to the east and not bother us...

And T.D.16 is probably going to do the same.  We shouldn't see another Isabel in the near future. 

But we will see some more frontal rain.  For Friday 8am, we are clear and cool behind tonight's front...

Then we have a new front coming towards us Saturday 8am. 

And rain is falling Saturday night into Sunday morning around Philadelphia. 

That pushes off by Monday morning...

And Tuesday AM is nice...

Then ANOTHER front heads our way by Wednesday morning (according to the computer model called the GFS). 

Enjoy this nice weather and I'll see you tomorrow afternoon.

Meteorologist  John Ensworth

Surface Station sky cover color key: