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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: 10/18/2003 09:03 PM
Good Evening Philadelphia!
I'm glad to announce that these discussions will continue until at least the end of November.
First off... LEAVES! The cool temperatures are kicking the trees into winter mode, and the leaves are changing fast. The peak of leaf color now dominates most of the state and will reach Philadelphia early this week. Get the cameras out and start taking pictures!
Those cool temperatures this evening include upper 40's in Philadelphia at the current hour. This is a reflection of the *still present* east coast trough that you'll see below.
Winds are light, but it's cool enough that any breeze will chill you some more. It feels like lower 40's out there now.
We are mostly cloudy this evening ahead of the warm front that you'll see in a moment...
And this same front is kicking off light showers that are staying north of the city this evening.
The major player in the weather is the big dip in the wind flow at 18,000 feet above sea level (as seen on the 500mb map below). This thinner atmosphere is denser and colder and ripples are traveling over the big ridge out west and moving surface reinforcing cool air towards us time and time again.
You can see the warm front on the current surface map and the Low driving it up in the Lakes.
Looking into the future, tonight at 2am, the trough will be a bit further to the east.
And the low will be moving southeast in that flow towards central PA.
Sunday at 2pm, the trough is even further tilted to the east...
And the low is sitting on Philadelphia with a chance of showers mainly to our northeast (but some clouds and showers will wander through).
Sunday night 7pm, and the ridge over the body of the US has expanded toward us.
And the low moves off shore, with a chance of some showers wrapping around the low still giving us a chance of rain.
Then Monday morning 8am, you can see a new dip forming in the ridge over the central Plains.
A high (behind the current Low and front) slides down over Pennsylvania as that new trough in the ridge over Montana begins to move another front south and east across the US. Wait for this one for the middle of the week.
So stay dry and warm as best as you can...
And I'll see you Monday morning!
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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