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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 02:37 PM
 

Good Morning Philadelphia!  

The server this page resides on is still down today... so no one will be able to see it live.  I'll, again, quickly recap what is happening, and wait for the big diagnosis for the day when the power is back on!

The front to our east has washed out and is no longer really visible, except for a bunch of rain and showers flowing northward up the east coast.  The other player is the very slow moving front to our west. The low north of the Great Lakes hasn't moved much in five days.  South winds have brought a ton of moisture over our area and showers and rain fire up every afternoon and every time a short wave (a bubble of cold air aloft) passes.   Some places in the state have now seen 6" of the predicted 2 feet possible over this 5-7 day period beginning middle last week. Yikes.  Watch the rivers. 

The visible satellite picture shows you the clouds as you would see them from space with your eyes.  Thick clouds look white.  Dark water looks dark.  The skies are partly cloudy except where the showers and thunderstorm waves are operating. 

To tell which clouds are worth watching, we use the Infrared Satellite view which shows us the temperature as seen by IR sensors from space.  The thunderstorms have high clouds that are very cold.  They are colored blue on this view. 

The main weather maker is the big trough (marked in red) in the upper air flow.  This is the path the air is taking at about 18,000 feet above sea level.  We, being now located on the right side of the big trough, are in the place where the atmosphere likes to rise.  With new moisture continually flowing northward ahead of the Low in the lakes (air goes counterclockwise around a Low pressure system) the rising motion is making storms likely and numerous.  

The bubbles of cool air, or short waves, are smaller versions of the big trough.  They move through the air flow and are marked in blue.  Each time one passes, you can expect more showers on the right side of them as well. 

The radar this afternoon shows many small lines of storms moving around.  We had one of these lines go through the city earlier today. Look at the location of the most numerous showers and where the blue marked short waves are above.  Also compare the location of the storms below with the infrared satellite view above.  These maps really work together!

Rainfall over the last day has been summed up by the NWS Doppler Radar.  Most places have received at least a trace of rain, with swaths in the 1 to 2 inch amounts.  And the pattern isn't expected to fall apart for a number of days more!

As the front oozes eastward, it will help showers and storms to form as well.  The Severe Storms Forecast Office is predicting a slight risk of some of those storms getting severe tomorrow.  Wow, what an exciting summer!

By Tuesday afternoon, we see that little has changed.  The front is only marginally closer, and rain and showers are expected anywhere and everywhere. 

Forty eight hours out, Wednesday morning 8am, the front may be past us but still in the area.  The rain and showers should continue.  

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

Until then, keep looking up and stay dry!

Meteorologist  John Ensworth

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