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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 02:34 PM
Good Afternoon Philadelphia!
The big story is... enjoy the nice relatively cool dry air today...because will be GONE soon.
We have a high pressure system sliding in behind the front to our distant south bringing in nice weather...
With cooler air aloft and nice sun warmed August ground, we are getting daytime cumulus across the region and...
...even a few showers where the moisture is deeper near the ocean.
But looking over the rainfall in the last day, there has been very little, and only in very isolated locations...none of them Philadelphia.
The temperatures are a bit below normal across the region. But you can see the extreme heat lurking to our west and southwest. It poised for a full invasion. RUN !!! Ok, don't run, just prepare to keep your cool.
The dew point (a measurement of the actual amount of water in the air...higher dew point = more actual water vapor) is low behind this front as well, but the steam is off where the heat is lurking to our west and southwest and south.
The path of air at halfway up in the atmosphere (about 18,000 feet) by pressure, shows a trough over our heads (giving us the cooler air) just before it pulls away. Heat and doom are building to our west under the big ridge.
On Tuesday morning, the trough is a bit further east, the ridge is approaching, and the trough over the Rockies is fading out...
The High center is over our heads with a slight chance of showers as surface moisture flows under the cool air aloft.
For Tuesday afternoon, we see the HEAT approaching and building out west.
For Wednesday AM, the trough is gone and the ridge is taking over the US.
A HOT high pressure system is now to our west. The rain is not approaching.
And by Wednesday afternoon, the temperatures are a good 10-15 degrees warmer than they are now. Yikes.
Then Thursday morning shows the ridge sitting on us.
And heat is entrenched. Keep the AC running!
By Friday AM, there is a hint that a new trough is forming to our west. This 'might' bring a new front down and cut off the heat before it becomes a heat wave.
As long as this atmosphere keeps progressing like it is, we won't get stuck with any one kind of weather, be it wet, cool, steamy or hot.
I'll see you tomorrow!
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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