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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 02:36 PM
Good Afternoon Philadelphia!
Did you enjoy your weekend taste of Fall? Here comes a longer taste of Summer.
Skies are clear (very clear) around Philadelphia this afternoon...
With a cold front back in Canada, there is little but the high pressure to our south that matters on the Surface Map. Air moves around a High pressure clockwise, so we would expect west winds (pretty much parallel and a bit outward from the high - to the white line drawn around the high. This white line is a isobar... a line of equal barometric pressure. Drawing these lines allows meteorologists to see the pattern of high and low pressure across the nation).
Temperatures are already in the low 80's early this afternoon with really scary hot air (near 100 F) to our west.
Dew points out there are also high, meaning there is a lot of actual water vapor in the air. Our weekend cool front is history. With more moisture coming, we'll see more haze and have our clothes stick to us more! Yuck.
The winds spell out the bad news. Winds are going clockwise around the high to our south. This is pumping that hot humid air from the Mississippi and Ohio valleys our way.
The upper air map shows a GIANT ridge across the entire US. This is a HUGE area of mainly high pressure and sinking warming air. Amazing. This is summer. And it is coming.
The GFS 500mb map (the winds 18,00 feet above sea level- as in the map just
above) forecast for Tuesday morning shows the big ridge being squashed a bit
over us.
The front is kicking off storms in the Great Lakes and western Pennsylvania.
The Severe Storms Prediction Center is showing a Slight risk of sever weather there - in the western half of the state. We just have a chance of storms popping up around us ahead of that front. Hot steamy air is pouring in!
To see that air, look at the Tuesday night forecast temperatures from the GFS model. Good heat is getting close again.
Wednesday morning, the trough (according to the GFS model) is beginning to dig to our north, but a ridge exists to our south. Which will effect us more? The GFS thinks the trough will... so it is predicting the front coming into our area.
The front hasn't moved much, and the storms are most likely east-west in the western part of the state.
Thursday morning, the trough is pulling off to the east, and the ridge is moving in again. If it cools at all Tue/Wed, it will warm up again.
And chances of rain drop to near zero.
The mid 80's to low 90's will be back Thursday night.
Overall, I can't discount a chance of a storm now and then, and the heat will be on and off this week. Next weekend might be the return of even more heat.
I'll see you again tomorrow... enjoy the weather!
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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