892 
fxus61 kphi 211306 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
806 am EST Friday Nov 21 2008 


Synopsis... 
an upper level disturbance will move through the region today and 
tonight. The disturbance will cause a low pressure to form off the 
coast and rapidly move northeast. A cold northwest wind will follow 
as high pressure builds in from the west late Saturday. 


&& 


Near term /through tonight/... 
baggy pressure pattern with weak west-east trough over our cfa with 
very light precipitation falling. We had a couple of 2 inch snow 
amounts in Berks and Montgomery counties last evening but on grassy 
surfaces. This morning, this latest burst has dropped up to around 
three inches of snow over parts of Chester County, and although 
the area tends to be dissipating as the morning continues, there 
still are areas with more than 20 dbz returns moving across the 
northern Delmarva, southeastern PA and parts of of southern New Jersey. 
Given this basically is the first accumulating snow down around 
these parts and it is falling during the morning commute, we've 
issued a Winter Weather Advisory in response. We have noted that 
grassy areas, bridges and overpasses will see the brunt of the 
accumulation, but given the time of day and the relative Novelty 
of this we will err on the side of caution. 


Zonal flow aloft will transition as trough digs south from the 
Great Lakes and moves across the region with cyclogenesis taking 
place late this afternoon off the middle Atlantic coast. Cold air 
behind the developing low will keep the chance of light rain/snow 
showers at times over a fair portion of the area this afternoon. 


Temperatures today will range from 28 north to lower 40s 
southeast. By tonight, the precipitation will be ending over the 
southern zones before midnight with skies beginning to clear. 
Overnight lows will range from 16 to 22 degrees with increasing 
northwest winds. 


&& 


Short term /Saturday through Saturday night/... 
as the low forms off the coast late tonight the trough will push 
offshore with a good blast of cold air advection at 80h. Lake effect snows will 
develop and a few snow showers may move across the northern tier 
before and shortly after daybreak on Saturday with a fresh northwest 
wind. Lows continue below the normal with highs from 27 to around 
40 degrees over the southern zones. The surface Atlantic low will 
race northeast as high pressure builds in from the west late 
Saturday night. 


Since Oct of last year, there have been around 40 cases where the 
winds have reached gale force strength along the coast. We have 
this present low center which may move away too fast to get the 
winds above gale force speeds. 


&& 


Long term /Sunday through Thursday/... 
cool crisp day on tap for Sunday as the high passes by to our south 
and we have a quick return flow to the west backing to the 
southwest as another strong short wave digs south from the Great 
Lakes with a surface front extending from the lakes to the 
northern Gulf of Mexico by Monday morning. 80h temperatures rise 
to only a plus two Monday afternoon as the front moves off the 
coast Monday night. Cold air advection quickly returns to the cfa 
with the precipitation changing over to mixed precipitation then 
all snow for late Monday night. 


The surface low will be stacked up through 500 mb over the region 
through a good part of the week before exiting to the northeast 
late Thursday night. Meanwhile, several more disturbances move 
into the southwest and Central Plains toward the end of next week. 


Temperatures remain below normal right through the end of next 
week. 


&& 


Aviation /13z Friday through Tuesday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, 
kilg, kmiv, kacy and surrounding areas. 


Short waves rotating around the upper trough to our north continue 
to supply US with plenty of low and middle level moisture. VFR conditions 
will prevail the majority of the time today, but could drop to MVFR 
and locally to IFR in snow showers and flurries. The short wave moves 
out of our area tonight allowing high pressure to push in from the 
west. Northwest winds will drop off a bit after sunset and skies will 
begin to clear. 


Outlook... 
the high pressure system pushing in from the west will provide fair 
weather with VFR conditions through the weekend and into Monday. 
Complex low pressure will drop down across the Great Lakes and 
move into our area Monday night and Tuesday. 


&& 


Marine... 
weak low pressure will ultimately develop into a fairly strong storm 
east of our waters this afternoon into tonight. This storm will 
intensify and head north reaching the Canadian Maritimes Saturday. 
Winds and seas will increase this afternoon into tonight and stay up 
through much of Saturday, before dropping off Saturday night. Will 
raise a Small Craft Advisory on our ocean waters and lower Delaware 
Bay at noon today and on the Upper Bay at 3 PM. Will carry the 
advisory until 6 PM on Delaware Bay and extend it to midnight 
Saturday night on the ocean. This will be a very close call as to 
whether or not Gale Warning criteria will be reached. I do think 
that a few gale force gusts may occur, at least for a few hours this 
evening, on our ocean waters. For now, a strong Small Craft Advisory 
will cover the situation. As the storm moves off to the northeast 
and high pressure pushes in from the west, winds and seas will 
subside. The high pressure system will provide tranquil marine 
weather Sunday into Monday. Complex low pressure dropping down 
from the Great Lakes will bring the next threat for inclement 
weather along with advisory/warning conditions late Monday through 
Tuesday. 


&& 


Phi watches/warnings/advisories... 
PA...Winter Weather Advisory until 11 am EST this morning for 
paz067-068-070-071. 
New Jersey...Winter Weather Advisory until 11 am EST this morning for 
njz016>019-021-022-027. 
Delaware...Winter Weather Advisory until 11 am EST this morning for 
dez001. 
Maryland...Winter Weather Advisory until 11 am EST this morning for 
mdz008. 
Marine...Small Craft Advisory from noon today to midnight EST Saturday 
night for anz450>455. 
Small Craft Advisory from 4 PM this afternoon to 6 PM EST 
Saturday for anz430. 
Small Craft Advisory from noon today to 6 PM EST Saturday for 
anz431. 


&& 


$$ 
Synopsis...eberwine 
near term...delisi/eberwine 
short term...eberwine 
long term...eberwine 
aviation...rpw 
marine...rpw 

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