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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: 12/11/2003 12:47 PM
 

Good Morning Philadelphia!   

    I'm glad to announce that these discussions will continue until at least the end of this Year!. 
    I have the necessary server space.

In short:  Clouds are still thick, and the 'warm-up' and snow  melt has happened.  
Another shot of  snow or sleet  is probable at the end of the weekend.  

 In long: The rainfall came and widespread 1" and locally 2" of liquid water hit this time killing almost all the snow. It's misting and chilly and overcast out there this early afternoon. Yuck.  Mud is the rule.  

Because of the snowmelt and rain, the National Weather Service has issued a Flash Flood Warning for Philadelphia and areas west and north of the city (as shown in this map).  The text of the warning is included below. 

... Minor flooding has occurred...

Snow melt has caused significant rises along rivers and stream in the counties of Montgomery and Philadelphia. Rainfall amounts up to around two inches will continue to cause minor flooding.

In Montgomery County, minor flooding will occur on the lower reaches of the Manatawny creek near Pottstown and on the East Branch of the Perkiomen creek.

Minor flooding is also likely in areas of poor drainage and along other smaller streams and creeks in the two counties.

The rain is moving out to the northeast and...

Checking for snow shows light snow and snow/rain mix happening out west, nothing severe or heavy at this time. 

The Low that brought this rain and warm air is still sitting almost ON Philadelphia this mid-day...

And winds across southern Pennsylvania are picking up from the west as it passes (air is still coming from the east in northern New Jersey and New York.

And though there are freezing temperatures in the lakes, we are still in the upper 40's and low 50's in the eastern part of the state. Wild weather - no?

The visible satellite picture shows a tongue of clearing just nosing towards Philadelphia, but more low clouds are filling in from the west on top of the cold air filtering in behind the departing front.  In the circled area you can see a changeover between one kind of cloud (low and smooth) and another kind of cloud (high and choppy) to the east.  How do I know the difference?  You need to use the next view - the Infrared Satellite image...

The Infrared Satellite view shows the temperature of the thing the satellite first sees (ground if clear, clouds if cloudy).  Blues are very cold and reds are very warm. The highest clouds are in a colder part of the atmosphere (it gets colder as you rise in the lower later of the atmosphere) and the clouds way up there are made of ice crystals.  They are colored blue and are high clouds (labeled).  The clouds over central Pennsylvania are colored an orange so are closer to the ground (they are warmer, like the ground) so they are low clouds.  You can see the mass of colder air flooding in from the west with the low clouds out there as a middle-yellow color. 

Into the Near Future:

The system is slowly pulling away by tonight 7pm and showers are still possible in Philadelphia with snow in the higher elevations out west. 

For Friday morning, the precipitation in Pennsylvania is limited to Lake Effect stuff forming as air circulates around the Low to our northeast blowing from the northwest and the High to our distant  west blowing from the northwest across the warm lakes.  Some snow and rain will fall out there based on elevation. 

Then by  Friday night, the High is moving closer and the Low is off way up into eastern Canada (they didn't mark it, but it is in the center of the concentric white circles of equal barometric pressure.  The Lake Effect snow /rain continues out west.

Our next storm for the end of the weekend is taking shape in Oklahoma and Texas.  More on this Friday and Saturday. 

Stay warm and dry and watch out for flooding, and I'll see you here again tomorrow!

Meteorologist  John Ensworth

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