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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 02:21 PM

Good morning again. I hope you enjoyed the weekend, that was a NICE example of summer weather! We have another weak front draped over the northwest corner of the state marching gently to the east.  This will bring in just a slightly drier bit of air into the state, but nothing shocking or cold. 

Winds, though, are light and variable around the entire region (hence, not much of an effect as the front goes by). Dew points are in the 60's across much of western PA behind the front (with temperatures in the 60's), and very soupy and high (mid 70's in the southeast and Philadelphia area).     [the key to what the colors of the stations mean is at the very bottom of this page]

That satellite picture shows a band of cirrus stretching west to east across the state associated with some lift in the atmosphere under the jet stream (see below) and some ripples of cool air aloft that are traveling along in the flow (also seen below). 

These, mostly weak, showers are sliding to the east.  They will, for now, stay to the north of Philadelphia, but as they approach, the cool air aloft helping them to form may make them expand in coverage as there will be more moisture (the mid 70's dew points mentioned above) to feed them. 

The jet stream can be seen below on the 500mb map (the winds blow from left to right along the black lines).  Where the lines come together, the winds are the strongest.  The jet stream is labeled as where the winds are blowing the strongest.  This passes over our state!  The purple lines show ripples in this flow caused by bubbles of cold air moving along (called short waves in meteorology speak).  These bubbles of cold air kick off showers on their right side as they move (they help air to lift). 

Because of the moisture, the jet stream, and the proximity of the weak front, the severe storms prediction center has issued a slight chance of severe weather for this afternoon (when surface heating is at a maximum) over the southern counties of PA including our fair city. Keep an eye to the skies and an ear to the radio after 2-3pm today. 

The next chance of clouds besides a random afternoon shower or two in the afternoons will be Wednesday night through Thursday morning when moisture from tropical storm Bill (now approaching the Louisiana coast) will slide by to our south.  The next map shows the core of the moisture way down in North Carolina. 

 It's time to settle in and adjust to summer.  The normal steamy, hot, afternoon sprinkle pattern is not far from settling in.  But it wouldn't be home if it didn't do that in the summer - right?

Meteorologist  John Ensworth

Surface Station sky cover color key: