711 
fxus61 kphi 200757 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
257 am EST Thursday Nov 20 2008 


Synopsis... 
a weak area of low pressure from the Great Lakes region will track 
over the region late tonight and off the coast Friday. Cold Canadian 
high pressure will then build toward our area Friday night into 
the weekend. A cold front is then forecast to move through the 
from the west Monday night or early Tuesday. 


&& 


Near term /until 6 PM this evening/... 
forecast soundings from both the WRF and the GFS show clouds will 
remain over the region today as they remain trapped under an 
inversion aloft this morning. The lower levels of the atmosphere 
go adiabatic this afternoon. This should maintain the clouds in 
most areas, however, the mixing could allow the clouds to 
dissipate a bit late in the day. With the clouds and cold air, 
there will be a continuing threat of snow showers or flurries to 
the north/west of phl. The airmass wont be quite a cold today as 
yesterday with the main limiting fact the clouds. The mav temperatures 
continue to look a bit high, but seem better than they were 
yesterday at this time. 


&& 


Short term /6 PM this evening through 6 PM Friday/... 
a weak area of low pressure will cross the area early Friday 
morning. Model soundings show the best moisture forecast to be around 
the i95 corredor with light snow or flurries possibly beginning 
around midnight from phl westward and toward daybreak in Monmouth 
County New Jersey. This moisture is mostly below 10 thousand feet on the 
soundings but both the WRF and the GFS and is due to isentropic 
lift aloft associated with a short wave moving through the region. 
Model soundings also indicate that all precipitation would be in the form 
of snow if it develops. Even the blyr looks cold enough to support 
snow. 


Snow amounts should generally total an inch or less from Cecil 
County Maryland/Chester County PA eastnortheast through Monmouth and 
ocean counties in New Jersey. Also, the Friday morning rush should could 
see slippery areas from any snow that would fall. Since amounts 
are relatively low, no headlines will be issued with the package. 


Over Delaware-Maryland-Virginia and from ridge-Abe-smq northward, isentropic lift is 
weaker, so precipitation probability of precipitation are lower than near the phl metropolitan area. 


Forecast temperatures are based on model soundings with some adjustment 
toward the mav guidance. 


&& 


Long term /Friday night through Wednesday/... 
the axis of the upper trough will move off to the east Friday night. 
This will allow a very large high pressure system, to build in 
for the weekend. Saturday looks to be the colder of the 2 weekend 
days, as there will still be some northerly flow ahead of the 
building high. By Sunday, the high is pretty much overhead. Both 
days look dry. 


The area of high pressure will move to the east later Sunday, and 
there will be a return flow in advance of the next system. 


A low pressure system is forecast to move southeastward from central Canada on 
Monday. A War front will move through ahead of this system, 
followed by a cold front Monday night or early Tuesday. This low 
looks to bring our best chance of precipitation in the next week. 
Fortunately, most, if not all of the precipitation is ahead of the cold front 
and should be rain in most areas, with the exception of the northern and 
western areas. 


A cold 500 mb trough then establishes itself over the area on Wednesday, 
but things appear dry attm, as high pressure starts to build in, 
just in time for the Holiday travel period. The European model (ecmwf) solution does 
present an interesting scenario as we move into the lead-up to the 
Thanksgiving Holiday. It brings the cold front through like the other 
mdls, but then it lingers the trof, GOES negative tilted and develops a 
coastal low. Obviously, a lot can and will change with the model 
solutions between now and then, so it will be interesting to see if the 
European model (ecmwf) is picking up on something before the other models (which is 
often the case), or if the European model (ecmwf) is putting out a Turkey of a forecast. 


&& 


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


Series of short waves continue to rotate around the upper level low 
to our north. The current wave is associated with surface low 
pressure dropping down from the eastern Great Lakes. The low will 
remain weak and give US plenty of low and middle clouds today but not 
much in the way of precipitation. The clouds will become scattered 
at times late today, especially southern and eastern sections. The 
next short wave will usher in colder air and another batch of 
moisture late tonight into Friday. Expect SC ceilings by around midnight 
tonight. Some light snow or snow showers are possible late tonight 
into Friday, possibly reducing conditions to MVFR at times. 


Outlook... 
high pressure pushing in from the west will bring clearing Friday 
night and provide fair weather with VFR conditions through the 
weekend. 


&& 


Marine... 
low pressure over the Canadian Maritimes is continuing to move off 
to the northeast. Winds and waves have dropped below Small Craft 
Advisory criteria, so our waters are advisory free this morning. 
These relatively tranquil conditions will be short lived through 
tonight. A weak clipper system and reinforcing cold front will cross 
the waters today into tonight. Offshore cyclogenesis is expected 
along the cold front on Friday, thanks to another shot of energy 
rotating around the upper low to our north. Winds and seas will be 
increasing Friday, probably reaching advisory criteria in the 
afternoon. Will raise small craft advisories on all our waters at 
noon Friday and continue through Friday night. Later shifts may 
need to extend the advisory if conditions warrant. Wind gusts 
could approach gale force for a few hours Friday evening. The 
pressure gradient between a large high pressure system pushing in 
from the west and the intensifying low pulling off to our east will 
be slow to weaken. Wind gusts of advisory strength may continue 
into Saturday before relaxing late Saturday or Saturday night as 
the high reaches our area. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory from 12 PM Friday to 6 am EST Saturday 
for anz430-431-450>455. 


&& 


$$ 
Synopsis...stauber 
near term...stauber 
short term...stauber 
long term...nierenberg 
aviation...rpw 
marine...rpw 

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