Back To Home
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
Good Morning Philadelphia!
Skies are clearing and drier, cooler air is in place. The forecast is right on from yesterday except the chance of rain is even a bit lower than I called for. The front is well to our south and hardly influencing us at all (just some high clouds are streaming by).
Here you can see the front between Virginia and N. Carolina with north winds rotating around the High pressure system over northern Illinois.
On the wind map, you can see the nice, light, north winds over Pennsylvania and Philadelphia.
This is bringing in the mid to upper 70's temperature air. (It is a bit warmer near the shore because of a slight downslope warming. When air sinks, even going downhill, it compresses and warms.)
The dew point map shows how wet the air is (how much water vapor there is in the air). Mid 50's or low 60's dew points is quite dry for this time of year (wet if it were winter, but nice for summer!).
The red line on the 500mb map below shows the trough in the upper level air flow. This is the flow of air around a big pool of cool air aloft that is allowing the surface temperatures to be so low.
And for the next two days, the front is sitting to our south and waves in the upper air flow will ripple over it making new batches of rain, but all that activity is missing us.
By early morning Wednesday, there is still little change.
By Wednesday night, the front is a bit further south and we are still in the clear. The air will warm a bit each day since the sun is pouring in, but we won't have to worry about rain again until the end of the week when the next front (again out on the northern plains) swings our way.
It is a nice, straightforward forecasting day. Enjoy this weather.
Until then, keep looking up!
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. |
|||