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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 02:25 PM
Good weekend to you! We have fairly nice (a bit drier) and seasonal weather for this weekend. The temperatures this morning are in the upper 70's and lower 80's (the red numbers) across the state, Philadelphia is at 83 already, but the dew points are only in the mid 50's out west and lower 60's around Philadelphia. This means the west winds behind yesterday's warm front are firmly here. The winds on this map are uniformly from the west and southwest everywhere nearby. The 'cool' front has passed.
The upper air map (the 500mb map below shows winds as they are moving along in the atmosphere about 1/2 the way up - pressure wise- which is at about 18,000 feet) shows a big trough just to our west. This means there is cooler air aloft than there normally is.
The satellite picture shows the effect of this cooler air with the formation of a vast cumulus field across most of Pennsylvania and up into New York state. Other than that, it's clear around Philadelphia.
This morning radar for the region shows a few showers popping up in Ohio and into West Virginia, but that's it for the north east (ok there are sprinkles going on near Niagara Falls).
On the surface map, you can see the front is past us and out to sea (almost). The area circled in orange is the bottom of the trough on the 500mb map (above) and where the only showers are happening (here and on the radar just above). This area of rising air will approach the state giving us the small chance of scattered showers that is called for in the forecast.
By 2pm today, that area of weak lift and a few showers enters far western Pennsylvania...
And is a bit closer to us by 2am tonight (Sunday morning).
There is more east coast rain to our south by 8am Sunday, but still nothing large scale or wet right near Philadelphia.
And if the forecasters and models are correct, the rain skirts us briefly and more clear skies and fairly dry air continues to move in from the west (with the approach of the High pressure system in northeast Illinois).
The bottom line is... what you see is what you get today.
Have a GREAT weekend and I'll be here on Monday.
Meteorologist John Ensworth
Surface Station sky cover color key:
Flight category definitions:| Category | Ceiling | Visibility | |
|---|---|---|---|
| Low Instrument Flight Rules LIFR* (magenta circle) |
below 500 feet AGL | and/or | less than 1 mile |
| Instrument Flight Rules IFR (red circle) |
500 to below 1,000 feet AGL | and/or | 1 mile to less than 3 miles |
| Marginal Visual Flight Rules MVFR (blue circle) |
1,000 to 3,000 feet AGL | and/or | 3 to 5 miles |
| Visual Flight Rules VFR+ (green circle) |
greater than 3,000 feet AGL | and | greater than 5 miles |
| *By definition, IFR is ceiling less than 1,000 feet
AGL and/or visibility less than 3 miles while LIFR
is a sub-category of IFR. +By definition, VFR is ceiling greater than or equal to 1,000 feet AGL and visibility greater than or equal to 3 miles while MVFR is a sub-category of VFR. |
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