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: 12/19/2003 09:19 AM
Good Morning Philadelphia!
I'm glad to announce that these
discussions will continue until at least the end of
this Year!.
I
have the necessary server space.
BUT I may have to switch to an approximately every-other-day schedule as Christmas year-end work piles up. I'll do my best to stick with ya!
In short: Clouds continue
with spits and waves of snow passing over the city. The Lake Effect snows
have reached their cold fingers our way. After another couple of days of
cold north east winds, things will warm up and clear.
In long: The Lake Effect snows are running the show over all the Great Lake touching states. But not ALL this snow is from the lakes...
We have another Low pressure system moving through the lakes with another shot of cold air moving in.
No matter what the map above looks like though, winds are sweeping out of the cold Canadian north and down across Philadelphia. (Remember, Lake Effect snows form when you have cold air blowing over relatively warm (unfrozen!) lakes that moisten up the cold airmass. Then the air lifts up on land, forms clouds and precipitation).
Clouds are thick over the entire region (except to our northeast). You can see the west to east sweep of clouds visually!
So cutting to the near-future chase... by 1am tomorrow morning, There will be a low in western New York (the graphics didn't include them this time <frown>). But the snows along the lake and front to our southwest continue.
Saturday 7am, little has changed except another lift zone (the trough marked in yellow- lift is caused when air converges - comes together- at the surface - in this case) sneaks past to the north.
For Saturday night, 7pm, a High pressure system begins to nose its way toward us from the southwest, but since the circulation around a High is clockwise, we still have cold air flowing over the lakes... yes more Lake Effect Snows out west (I should call them LES's for convenience in the future!).
And looking into the GFS crystal ball, the snow on Christmas Eve/Day is now confined to the Ohio valley and far northeastern New York state. Crazy no? (that is if you've been following the maps over the last week). Fear not, the weather future isn't written until it has happened!
Stay warm and, again, I'll be here every day I can as I travel for Christmas break!
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. |
|||