173 
fxus61 kphi 071941 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
340 PM EDT sun Sep 7 2008 


Synopsis... 
a weak high pressure system will build over the region tonight and 
off the coast Monday. A cold front will move in from the Great Lakes 
and cross the region Tuesday night. Another high pressure system 
will then build in from the Great Lakes Wednesday and Thursday 
before moving off the coast Friday. A pair of cold fronts will 
approach from the west late Friday night and again for late in the 
day on Sunday. 


&& 


Near term /through tonight/... 
the GFS initialization was better down toward Ike while the WRF-nmm 
initialization looked better toward US. But the WRF-nmm had a slow 
bias with Hanna and its cold front passage timing is slower than most of the other 
models except for its sref Brethren. This forecast pkg is going to side 
with the faster GFS and thus a slightly faster cold front passage on Tuesday. 


A much quieter night expected throughout our County Warning Area. The cloudiness west 
of our County Warning Area is forecast to lift northeastward tonight and miss our 
County Warning Area. Now that it has rained, we did add some patchy fog for tonight 
in the interior valleys as winds overall should be light and skies 
mainly clear. Not much of a spread between GFS and Eta model MOS and we 
will follow as they look good based on current dew points. 


&& 


Short term /Monday through Tuesday night/... 
forecast soundings remain quite dry for Monday and the mostly sunny 
forecast will be continued. The full sun macros by both models are 
siding with the warmer GFS MOS. 


Even following the faster GFS, there is forecast warm air advection and low level Theta 
east advt to arrive before dawn on Tuesday. A question as to whether or 
not there will be enough moisture or too much dry air for precipitation to reach 
the ground. At this time we introduced a slight chance northwest of the i95 corridor 
where the forecast warm air advection is the strongest. 


Tuesday still looking like it could be a severe weather day across 
our County Warning Area. We would have raised that level a notch higher if the 
negative tilt trough was forecast to move through our County Warning Area instead to our 
north. So in typical fashion the greatest forecast instability (se) is 
not coincidental with the proximity to the low level jet and entrance region 
to the h2.5 jet aloft (n). The GFS slightly faster timing would favor 
the southeastern half of our County Warning Area (in spite of better kinematics n), while 
the WRF-nmm would favor any part of our County Warning Area. The GFS instability 
parameters are inflated because of forecast dewpoints in excess of 70f. 
Even a toned down version of the WRF-nmm would support convection 
with the possibility of some severe storms as the current swody3 has. 
Days are getting shorter, so the window of opportunity Narrows if 
warm air advection induced clouds are present. GFS MOS assumes full sun while Eta model 
MOS assumes low clouds all day. Reality preceding a cold front usually 
resides closer to GFS MOS where there should be sufficient breaks to 
bring maximum temperatures close to those levels. 


With the faster GFS solution plus the progressively earlier sunsets, 
we continued to emphasize the evening hours for the higher probability of precipitation as 
the front nears and then crosses our County Warning Area. 


&& 


Long term /Wednesday through Sunday/... 
our County Warning Area will remain within the general zonal flow across the 
northern Continental U.S. Throughout this period as we wait to see where Ike 
GOES toward the end of this deterministic forecast period. The front 
should be south of our County Warning Area by Wednesday morning and two cool and dry 
days are expected on Wednesday and Thursday. The caveat will be the orientation 
of the high which might bring in some SC from the ocean with our southern 
County Warning Area having the great chance. The next low pressure system is 
forecast to reach the Great Lakes on Friday. The chances and trend 
of some warm air advection induced precipitation to occur Thursday night appear 
diminished. The next cold front should move through our County Warning Area Friday 
night or early Saturday. The air mass behind this front is not 
anticipated to be as refreshing as the midweek one. Stab forecasts 
support the continued mention of thunder. Another cold front is then 
forecast to approach the region on Sunday. This one might eventually 
entrain Ike itself or at the least some of the tropical connection 
moisture associated with Ike. Please refer to products by the TPC 
for official forecast information. 


&& 


Aviation /20z Sunday through Friday/... 
as Hanna continues to move away from the area, high pressure with 
much drier air has moved in. Nothing more than a few fair weather cumulus 
today and these will disappear by sunset. The high pressure will 
control our weather into Tuesday. Expect clear skies tonight. May be 
some light fog with MVFR visibilities in the pre-dawn hours in the most 
susceptable areas where winds drop off and ground moisture remains 
from yesterdays rains, but, for the most part, VFR conditions will 
prevail. Only some fair weather clouds expected Monday. A frontal 
system will move in with another possibility of showers and 
thunderstorms Tuesday into Tuesday night. High pressure with VFR 
weather is expected again Wednesday and Thursday. 


&& 


Marine... 
small craft advisories were extended into the afternoon for seas. 
Even though wave heights well off shore are still running 5 to 
almost 6 ft, they have transitioned into 13 to 14 second long 
period swells. With a diminishing trend forecast, see no reason 
to continue the advisory. High pressure will keep winds and waves 
below Small Craft Advisory criteria into Tuesday or Tuesday night. 
A cold frontal passage is forecast for Tuesday night. High pressure 
pushing in behind the front is expected to bring north to NE winds on 
Wednesday and that may push winds and/or seas to near Small Craft 
Advisory criteria. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory until 11 am EDT this morning for 
anz450>455. 


&& 


$$ 


Synopsis...gigi 
near term...gigi 
short term...gigi 
long term...gigi 
aviation...rpw 
marine...rpw 
rip currents...rpw