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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: 12/30/2003 07:30 PM
Good Morning Philadelphia!
I'm glad to announce that these
discussions will continue until at least the end of January!
I
have the necessary server space (especially with missed days!).
In short: Now skies have
cleared, we'll see a warm-up through the week until a relatively warm rain hits
for Saturday and Sunday.
In long: The current snow pack had retreated north with the warm temperatures and rainfall.
The latest storm (as of 7am today) dropped only about a quarter inch of water across the state (these are not the final rainfall amounts... the storm was still effecting the east coast through the morning. )
That front is off the shore and the wrap around precipitation is FAR less than suggested by the model run yesterday. The winds are decreasing and there isn't any precipitation in the state.
The coded rainfall/snowfall radar map confirms how quiet and even lacking the expected Lake Effect precipitation (which CAN be snow, rain or just clouds).
So the warm up begins. The upper level map (the 500mb map shows the airflow at about 18,000 feet above sea level as it blows mainly west to east across the continent parallel to the dark black lines) shows a ridge over the east coast by 7am Thursday Jan 1st. Ridges (northward humps in the flow) are associated with high pressure, sinking air, cloud free skies and warmer temperatures.
By 7am Friday, we are still under a broad flat ridge...more warm mostly clear skies.
Then by 7am Saturday, a trough digs into the central (and mountain) states. We, being on the right side of a trough start to see the weather get bad. (Note the ridge axis is now off the coast to our east).
At this same time, the surface map shows precipitation beginning to spread into the state.
And by 7am Sunday, even MORE rain develops and moves in. Nasty weekend coming!
So long from, now, the mountains of central Arizona. After the New Year on Friday and we'll see how the weekend storms look then!
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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