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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: 12/05/2003 09:30 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.

In short:  Everything wintry and nasty is hitting and will continue to hit Philadelphia through Saturday night. You have a Winter Storm Warning for the city for the next 36 hours and could see nearly a foot of snow and ice in places in or near the city. This is a dangerous winter weather situation.  Watch the watches and warnings that will be issued via radio and TV. 

 In long: I'll start to day with the words of the National Weather Service.  Snow is falling and is going to continue to fall.  We are under a winter strom warning.  The text of the warning is in 'loud voice' caps below.  

...WINTER STORM WARNING IN EFFECT INTO THIS AFTERNOON...
....WINTER STORM WATCH IN EFFECT FOR LATE TONIGHT THROUGH SATURDAY NIGHT... 
SNOW INTO THIS AFTERNOON IS EXPECTED TO ACCUMULATE FOUR TO EIGHT INCHES BEFORE CHANGING TO RAIN OR MIXED PRECIPITATION DURING THIS AFTERNOON. THE MORNING COMMUTE WILL BE TREACHEROUS, AND PEOPLE SHOULD ALLOW EXTRA TIME TO REACH THEIR DESTINATIONS. PERIODIC RAIN FROM THIS AFTERNOON INTO THIS EVENING IS EXPECTED TO TURN BACK TO SNOW LATE TONIGHT, WITH A FRESH ONE TO TWO INCHES FORECAST BY DAYBREAK. AN ADDITIONAL TWO TO FOUR INCHES OF SNOW MAY FALL ON SATURDAY BEFORE ENDING ON SATURDAY NIGHT. REMEMBER THAT A WINTER STORM WARNING IS ISSUED WHEN SEVERE WINTER WEATHER IS CONSIDERED IMMINENT. FUTURE DRIVING AND WALKING CONDITIONS WILL BECOME DANGEROUS. PEOPLE SHOULD REMAIN INDOORS UNLESS TRAVEL IS ABSOLUTELY NECESSARY. STAY TUNED TO LOCAL MEDIA OR NOAA WEATHER RADIO FOR UPDATES ON THIS WEATHER EVENT. ALSO, REMEMBER THAT A WINTER STORM WATCH IS ISSUED WHEN SEVERE WINTER WEATHER IS POSSIBLE, BUT NOT IMMINENT. AT THE TIME, THERE IS A POTENTIAL FOR SIGNIFICANT SNOW ACCUMULATIONS FROM LATE TONIGHT INTO SATURDAY NIGHT. FUTURE DRIVING AND WALKING CONDITIONS MAY BECOME HAZARDOUS, SO IT IS IMPORTANT TO MONITOR THE LATEST FORECASTS, AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS.

And the official forecast calls for a possible range of snowfall from 8 inches to 15 inches around and within the city (and more out west!). 

ZONE FORECAST PRODUCT...UPDATED NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 730 AM EST FRI DEC 5 2003 
PAZ071-052300- UPDATED PHILADELPHIA PA- 730 AM EST FRI DEC 5 2003
 WINTER STORM WARNING INTO THIS AFTERNOON
 WINTER STORM WATCH FOR LATE TONIGHT THROUGH SATURDAY NIGHT 
TODAY SNOW...HEAVY AT TIMES...CHANGING TO RAIN BY EARLY AFTERNOON. SNOW ACCUMULATIONS OF 4 TO 8 INCHES BEFORE THE CHANGEOVER. HIGHS IN THE UPPER 30S. EAST WINDS 10 TO 15 MPH. 
TONIGHT CLOUDY AND BRISK. PERIODS OF RAIN CHANGING BACK TO SNOW LATE TONIGHT. SNOW ACCUMULATIONS OF 1 TO 2 INCHES BY MORNING. LOWS IN THE MID 30S. NORTHEAST WINDS 15 TO 25 MPH. 
SATURDAY CLOUDY AND WINDY WITH SNOW. TOTAL SNOW ACCUMULATIONS OF 3 TO 6 INCHES BY EVENING. HIGHS IN THE UPPER 30S. NORTHEAST WINDS 20 TO 30 MPH. 
SATURDAY NIGHT MOSTLY CLOUDY AND WINDY WITH A 60 PERCENT CHANCE OF SNOW SHOWERS. LOWS IN THE MID 20S. SUNDAY PARTLY SUNNY AND WINDY. HIGHS IN THE UPPER 30S.

The surface map shows the coastal low forming as expected off the Carolina coast, and the low over the Ohio Valley, and the shunt of moisture from the ocean is headed inland where it is lifted and cooled AND where cold air is already in place. 

From the Weather Channel, we are right inside the band of snow now. (Duh!)

The straight reflectivity map shows ice and heavier rain just to our east.  Melting ice in falling precipitation shows up as EXTRA reflective to radar and can be over represented sometimes. 

Looking at the radar combined with the temperature structure of the atmosphere, we are on the ice/snow edge this late morning. There is a LOT of heavy precipitation falling across the state. 

The cold air mentioned above is shown here.  We have temperatures just about AT 32F down to the southern edge of the state (and colder north). 

Air cycling around the Low to our south is coming in from the east northeast (a Noreaster?)...

Giving us wind chills in the 20's F this morning. Oh brrrr. 

As mentioned yesterday, Tropical Storm Odette is moving north-ish out of the tropics, BUT seems to be slated to curve more out to sea than northward where it could feed MORE moisture and energy into our winter storm. That may not matter when we already are getting about a foot of snow, but it can make you feel better (who wants 2 feet of snow?!).

So let's look at the switch from snow to rain and back again that will happen through Sunday morning from the National Weather Service. 

By 7am this morning, we were receiving moderate to heavy snow. 

By 1pm, we will have warmed enough to maybe switch back to rain for a while.  That will keep accumulations down!

By Saturday 7am, the snow is on the increase all around us and is moving back into the city overnight as temperatures drop again. 

Then by 1pm, the next push of cold air slides under the system and snow easily pushes to the sea and we are in solid heavy falling snow. 

By Saturday 7pm, the snow continues with little break. 

And snow continues through 1am Sunday morning!!!

Then the system moves off the coast by 7am Sunday and only the higher elevations out west will be giving the slacking winds the lift needed to squeeze out some more snow. 

Get some groceries and keep the warm blankets on hand in case winds and ice take down the power. 

Stay warm and dry and I'll see you again tomorrow morning.

Meteorologist  John Ensworth

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