070 
fxus61 kphi 212030 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
330 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure will build across the northeastern states tonight 
and Sunday. The high should become centered over canada's maritime 
provinces on Sunday night, before drifting off the coast. Weak low 
pressure is forecast to develop off the southeast coast on Sunday 
night and Monday. The low is expected to track to the northeast 
and it should pass well to the east of Delaware and New Jersey on 
Tuesday. A cold front from the west expected to arrive on Thursday. 


&& 


Near term /until 6 am Sunday morning/... 
at 3:00 PM, temperatures in our region were mainly in the 50s. 
There were some readings in the 40s up in the Poconos. The sky was 
mostly sunny except for thick cirrus over parts of the Delaware-Maryland-Virginia 
and southern New Jersey. There was also a little stratocumulus 
poking down over the Pocono region. 


The cirrus should continue to drift to the east and off the 
coast. Meanwhile, some of the stratocumulus from the northwest may 
continue to overspread parts of the Pocono region into tonight. 


High pressure will continue to build into our region tonight. 
Temperatures should drop into the 35 to 45 degree range. 


&& 


Short term /6 am Sunday morning through Tuesday/... 
a strengthening high is forecast to be centered up in the Saint 
Lawrence River valley on Sunday morning. It should move to the 
Canadian Maritimes for Sunday night. 


With the high influencing our region, we are anticipating a 
mostly sunny sky for Sunday. As the center of the high moves to 
our northeast and a surface ridge builds southwestward along the 
East Coast, an onshore flow will develop. 


The 12 UTC NAM and the 12 UTC GFS both indicate an increase in 
low level moisture from the south on Sunday night. 


As a coastal low moves up from the south on Monday, the pressure 
gradient is expected to tighten. The 12 UTC NAM is a little 
stronger and closer to the coast with the low than the 12 UTC GFS 
and the 12 UTC European model (ecmwf). We will favor a compromise for the time 
being. 


As the low approaches, rain is expected to spread into our region 
from south to north on Monday. The rain should continue into 
Monday night. 


It appears as though low level moisture will linger in our region 
for Tuesday. As a result, we will maintain chance probability of precipitation. 


&& 


Long term /Tuesday night through Saturday/... 
all models agree that a significant change in the pattern occurs 
during the end of the week. We start off with a broad SW flow on 
the eastern portion of a Midwest trough on Tuesday 
night...eventually the Midwest trough moves east, but deepens as 
it heads east. The upper trough then becomes closed off as it 
moves through the region. 


This means that we have quite a bit of clouds and possible 
showers late Tuesday night and Wednesday due to moisture spreading 
over the region within the SW flow aloft. Wednesday night through 
Thanksgiving and into Thursday night, we could see rain as a 
frontal system associated with the upper trough moves through from 
the west. Then on Friday, cooler drier air arrives, but we still 
could have rain showers with the cyclonic flow aloft. Friday night 
and Saturday, it gets cold enough that some snow showers are 
possible north, but the rest of the area should be dry with 
downslope northwest flow. Also on Saturday, it should be breezy/windy 
with the northwest flow. 


HPC forecasts have the situation well in hand and in general their 
guidance has been followed. 


&& 


Aviation /21z Saturday through Thursday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, 
kilg, kmiv, kacy and surrounding areas. 


VFR conditions will continue through the entire forecast period. 
There was a fair amount of cirrus today across much of the area, 
but this should move out of the area later tonight, and provide a 
mostly clear forecast through tomorrow. The stratocumulus clouds 
to our north and west never made it to our Ara, and we are not 
expecting much at this time either. Winds are generally out of the 
northwest tonight, and will gradually switch to the north, then 
northeast tomorrow. The winds may actually begin to increase in 
the afternoon Sunday, and possibly a little gusty in some areas. 
However, winds should remain below 15 knots. There may be a brief 
period of lower visibility in fog toward morning in some isolated 
areas, but we only have it in the ridge taf at this time. 


Outlook... 
clouds will begin to lower and precipitation is expected to move 
into the area late Sunday night and could last through late 
Tuesday or Wednesday. This could bring lower ceilings and/or 
visibilities for the short term. 


&& 


Marine... 
high pressure will move to our northeast tonight into Sunday, 
while an area of low pressure develops near the Gulf states. This 
low is expected to strengthen Sunday into Monday, then move up the 
East Coast on Monday and into Tuesday. Between the high to our 
north and the low to our south, the gradient will tighten and 
northeast winds will strengthen for Sunday, Monday, then begin 
slacking on Tuesday. A persistent northeast fetch will develop, 
which is expected to increase the seas over the next several days. 
Therefore we have issued a Small Craft Advisory starting late 
Sunday and continuing through Monday afternoon. Future forecasts 
will likely need to extend the advisory. In fact, an advisory may 
be possible for basically the entire forecast period as there are 
several storm systems currently expected to impact the area 
through much of next week. We will continue to monitor the 
situation in case this comes to fruition. 


&& 


Tides/coastal flooding... 
a persistent northeast flow over the next several days could help 
to increase tide levels for Sunday, Monday, and Tuesday. Tide 
levels will have to be more than 1.5 to 2.0 feet above the 
predicted astronomical tide in order for minor tidal flooding to 
occur. Currently, the models are forecasting around 1.0 to 1.5 
feet in tidal anomalies, so minor tidal flooding is not expected 
at this time. However, if the low pressure system strengthens, the 
possibility of flooding could increase. We will continue to 
monitor the forecast for any changes. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory from 1 PM Sunday to 6 PM EST Monday for 
anz452>455. 
Small Craft Advisory from 6 PM Sunday to 6 PM EST Monday for 
anz450-451. 


&& 


$$ 


Synopsis/near term/short term...iovino 
long term...stauber 
aviation/marine...Robertson 
tides/coastal flooding...Robertson 

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