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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 02:30 PM
Welcome back! Are you ready for your vacation weekend? We have a change from yesterday's forecast...watch out for a batch of shows to pass sometime Saturday afternoon through Sunday morning. Don't leave the rain gear and tarp home of you are going camping.
Also, left over from yesterday we now know where the remains of "Bill" went. The ETA had rain hitting much of the state and the GFS switched and had the rain skirt most except for the southeast corner (where we are sitting).
Looking at the WSR-88D Doppler Radar rainfall totals, we see
that...
the GFS won! One inch rains hit much of the area south of Philadelphia
while our fair city got about a tenth to a quarter inch.
This morning's surface map shows the low center still over central Virginia with no huge areas of coordinated rainfall. The front you can see out in the northern plains may help kick off showers here Saturday night... more on that in a bit.
The radar view this morning shows just a few showers to our east. We only have a few sprinkles around the city.
The surface observations this morning show that things are already hot and moist, atmospherically. The red numbers on the upper left are the current temperature, the green numbers are dew point. The flags sticking into the station circles are wind direction blowing from the feathers to the station circle. Winds across southeast PA are still circulating around the old circulation center of T.S. Bill and are coming out of the east. Mid to Upper 60 dew points is a very moist atmosphere. This is, as the NWS forecasters have said among themselves, going to be a good old fashioned, hot and humid 4th of July break.
Aside from wandering showers, the biggest chance of rain hits Saturday night either side of 8pm as a frontal initiated batch of thunderstorms (that might organize as what is called an MCS - Mesoscale Convective System - a big bunch of thunderstorms that help one another live longer) slides over Pennsylvania.
Looking ahead to the entire weekend (thanks to the Weather Channel) we see the showery remains of T.S. Bill still sitting to our south and east. There is a chance of showers later today as the surface heats up by afternoon. Friday (the 4th) should be dry, warm and humid. Saturday brings our chance of showers/thunderstorms, mainly in the evening for the Philadelphia area, then Sunday looks dry again.
Take a break and have fun! Hey! You could catch up on that tan you've been waiting for!
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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