357 
fxus61 kphi 030902 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
402 am EST Wednesday Dec 3 2008 


Synopsis... 
high pressure over the region this morning will move offshore this 
afternoon and tonight. A cold front will approach the area from 
the west tonight and move through the region Thursday. High 
pressure will return Friday into Saturday. Low pressure moving 
east-southeastward from the Great Lakes this weekend will join up 
with low pressure moving northeastward off the East Coast. 
Blustery northwest winds Sunday will bring colder air Sunday and 
into the first part of next week. High pressure will build over 
the East Coast Monday into early Tuesday...but another front is 
forecast to move in during Tuesday. 


&& 


Near term /until 6 PM this evening/... 
the stratocumulus that was over the southern zones before and 
after midnight decreased markedly during the overnight period. 
The patch that just brushed our northern zones also diminished 
rapidly before sunrise. So, except for a mention of partly cloudy 
early for the Poconos, it should be a pretty nice day for early 
December, as high pressure builds over the region and full 
sunshine, or nearly so, occurs. The airmass is fairly close to a 
normal one, temperature-wise, for the season. 


MOS guidance has been fairly consistent run to run over the past 
two days, and model to model this morning, providing higher 
confidence in highs around 40 far north to the upper 40s to near 
50 central and south. 


&& 


Short term /6 PM this evening through Thursday night/... 
protective high pressure will be slipping offshore this evening, 
and some warm advection clouds are likely to increase later on 
tonight as the cold front that will be approaching the area will 
move into western New York and western Pennsylvania by Thursday 
morning. The front looks like it will pass through our area 
Thursday afternoon, as models continue to handle the timing very 
well. With the broad upper trough well to the west, and only 
moderate forcing shown on the GFS, probabilities were kept in the 
chance category for Thursday, although the NAM offered likely; 
this seems too aggressive considering the lack of significant 
moisture. Lingering probability of precipitation were kept into Thursday evening over our 
far eastern zones, as this will blend with our neighboring 
offices. 


&& 


Long term /Friday through Tuesday/... 
the coldest air of the Young winter season will be affecting our 
area Sunday and Monday. A change in the models has occurred since 
24 hours ago...but it seems to be a change which makes sense. The 
low off the southeastern states is now brought northeastward in 
the sharpening southwesterly flow aloft, and joins forces with 
the clipper system moving out of the Great Lakes Saturday night 
and early Sunday. This was handled a bit differently 24 hours ago, 
as the clipper was the dominant system. In any case, 
intensification offshore will lead to greater cold air advection 
Sunday into Monday. This looks to be a brief incursion of Arctic 
air, as the airmass will quickly moderate by Tuesday as it gets 
rudely shoved offshore. For Saturday night and Sunday, chance rain 
or snow showers were left intact, with highest probabilities 
north over the terrain areas. 


The upper trough and related surface low will be out of the 
picture Sunday night, but with -16c at 800 hpa we may still deal 
with some instability snow showers through early Monday morning, 
especially north. Cold Arctic high pressure over the Ohio Valley 
will move across the area, and it will bring a cold sunny day for 
Monday and a very cold clear night for Monday night with excellent 
radiational conditions. As the upper wave pattern damps a bit 
Monday night, milder air will be allowed to creep into our 
southern zones later Tuesday, despite decreasing or perhaps 
minimal sunshine. Renewed upper level amplification is seen to 
take place early next week; another full-latitude upper trough and 
associated surface front looms on the northwest horizon for 
Tuesday, which promises to be a day of developing mixed 
precipitation across a good part of the region. This far out in 
time, probabilities were not raised, but if the storm takes shape 
as now advertised, probability of precipitation will need to be raised as this event 
nears. 


&& 


Aviation /08z Wednesday through Sunday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


High pressure will build into the region today and move east of the 
area tonight. As a result, tranquil conditions are in store with 
great flying weather. The wind will be west to SW becoming more SW 
during the afternoon and evening hours with speeds of 10 knots or less 
at all taf sites. There will be nothing more than some few to scattered 
cumulus around today into tonight, with clouds increasing toward the end 
of the taf period. 


Outlook...a cold front will approach the region from the west late 
Wednesday night into Thursday morning and cross the area during the 
afternoon or evening hours on Thursday. This front will bring the 
next threat of precipitation along with it, and wind will shift to 
the northwest. At this time, the precipitation looks to be all in the form of 
rain. Also, gusty winds to 30 knots are possible with the front and 
behind it Thursday night. High pressure will then build in for 
Friday. 


&& 


Marine... 
surface high pressure will be over the region today, and expect tranquil 
conditions on the area waterways. The high will move eastward tonight as 
a cold front will begin to approach the region. This front will 
move across the area on Thursday. Both wind and seas are expected 
to increase ahead of the front on Thursday and remain up behind the 
cold front passage. As the gradient tightens, wind will increase to the 25 to 30 
knots range a wind shift to the west and northwest is also expected. 


Since confidence is high on the eventual need for Small Craft Advisory flags, have 
opted to raise them for the period 04/12z to 05/00z. It is possible 
that they may be needed a few hours earlier and likely that the 
flags will need to be extended beyond 05/00z. However, since this 
is already in the third period, did not want to get too fancy and 
will let later shifts refine the time periods, if needed, based on 
later model runs. Gusty northwest winds should continue Thursday night 
as colder air moves over the region. On Friday, high pressure 
builds into the region and this should allow for a decrease in 
wind and seas. Another cold front will approach the middle-Atlantic on 
Saturday night. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory from 7 am to 7 PM EST Thursday 
for anz430- 431-450>455. 


&& 


$$ 


Synopsis.../ 
near term.../ eberwine 
short term.../ eberwine 
long term.../ eberwine 
aviation...nierenberg 
marine...nierenberg 

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