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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 02:39 PM
 

Good Morning Philadelphia!  

[The server this page resides on continues to be down today... so no one will be able to see this live.  I'll, again, quickly recap what is happening, and wait for the big diagnosis to return when the power is back on!  Update, the UPS is out and one was ordered Thursday. Yikes. ]

There are just a few scattered showers around the area, but this generally unsettled, showery pattern is going to remain over the area through the weekend...until a BIG change comes in the weather next week.  Did you feel you were missing summer?  Well, here it comes with a vengance. 

We missed everything but a sprinkle, but across the region, up to 2 inches (Doppler radar measured) in localized spots.  This will be the nature of the rainfall without a strong cold front boundary to our west to act as a focusing mechanism (with the warmest moistest air sitting on us). 

That old dead cold front is nothing more than a bit of low pressure and weakly converging air at the surface. There is a hint of a Low over Philadelphia and a bunch of fog in the cooler moist air to our west.  The heavier rain showers are still off ahead of the 'front' over us.  With this boundary overhead (including the low pressure center), the afternoon heating (and short waves again) may kick off a few, locally heavy, rain showers. 

The skies are still cloudy (as you can see on the visible satellite), keeping temperatures down.  Which clouds are associated with the showers?

To find out, we look at the Infrared Satellite view and 'see' the temperatures of the first things the satellite sees.  The ground is the hottest stuff (reds), clouds are cool (yellows/ greens) , and stronger shower cloud tops are very cold (and high in the atmosphere = blue).  The circled area is the area of higher colder clouds associated with the washed out frontal boundary and low pressure system overhead. 

The upper air map looks almost identical to what is has for the last two weeks.  To see more about it, go back to the archives and explore! The big trough (that is keeping us sort of cool and very cloudy and sometimes showery) is marked in red, and the little ripples of cool air aloft that can kick off showers are marked in blue.  The right side of any dip on the map is the place to look for rising air and a chance of showers  (our whole state!).

Looking towards Sunday morning, we see the same as we have seen for 10 days.  Showers possible near the trough on the east coast. 

Now we'll just concentrate on the upper air flow and watch the change that is coming!  Sunday night 8pm has the trough still in place...and the chance of showers continues. 

By Tuesday morning, 8am, we see the CHANGE!  The trough is getting more shallow and pulling out to the north east.  A weak trough is left in it's place... but not for long. 

Wednesday morning, we see the trough tilted and much less 'what it was' marked in blue.  It is leaving.  The ridge (high pressure, higher temperatures and dry weather is found under a ridge) is marked in green and is moving out from the central US. 

Then BOOM! On Friday morning we see the ridge ON US.  Very hot, dry weather and light winds (with returning high humidity) is the story.  As the week goes on, it will get hotter and more summer like.  Prepare yourself... after all, it is August now! (This would also be a good time for a tropical system to threaten the eastern US. We'll watch that here as well.)

I'll be connected via modem for the next 5 days (and the server will still be down until about the time I get back from vacation).

Hopefully the servers will be working soon and I'll be able to post live again. 

Until then, keep looking up and stay dry!

Meteorologist  John Ensworth

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