495 
fxus61 kphi 181517 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
1120 am EDT Friday Jul 18 2008 


Synopsis... 
high pressure stretching from the western Atlantic to the Tennessee 
Valley today will move gradually eastward Saturday. A frontal 
boundary may remain just north of our area Sunday, but low pressure 
could become persistent along the middle Atlantic coast early next 
week. High pressure may settle over the region late next week. 


&& 


Near term /until 6 PM this evening/... 
there was some cirrus overhead late this morning, mainly over New 
Jersey. Also, some cumulus was beginning to develop over the 
Poconos. 


There should continue to be a good amount of sunshine this afternoon 
throughout eastern Pennsylvania, New Jersey, Delaware and 
northeastern Maryland. With an upper level short wave expected to 
move across upstate New York this afternoon, we will keep the slight 
chance probability of precipitation for the northern section of our forecast area. 


As of 1100 am, the temperature forecast for this afternoon looked to 
be on target, as did the excessive heat warning. Temperature 
readings were already up to 90 degrees in parts of Philadelphia and 
in parts of southern New Jersey. 


&& 


Short term /6 PM this evening through Saturday night/... 
any leftover convection north should play out this evening. 


Otherwise, another hot day is in store for Saturday as the air 
mass will be similar. However, dew points are likely to be/remain 
a little bit higher. As a result, the excessive heat warning will 
naturally be continued through Saturday. As for temperatures, the 
mav MOS guidance was shaved by a few degrees as it has tended to 
run warm in previous hot spells. Therefore, the forecast high 
temperatures are closer to the met and FWC guidance. 


&& 


Long term /Sunday through Thursday/... 
the northeast-southwest front appears to hang just north of our 
area Sunday at least on the GFS, while other guidance wants to 
shoot it into our area. The excessive heat watch was of course 
continued, with a lack of confidence on sunday's maxes. Speaking 
of the GFS, it depicts prevailing low pressure setting up Monday 
and continuing mostly into Thursday. It could spell a period of 
unsettled, warm, and humid conditions, with scattered to broken 
(and mainly diurnally-modulated) convection. With low confidence, 
probability of precipitation were kept in the chance range each day. Unfortunately, it 
will sound like a broken record and perhaps seem like worse 
weather is being forecast than actually occurs, but until we 
actually move into next week and achieve higher confidence in 
model solutions, that's about all that can be done at this point. 


Temperatures will probably step down a bit with more clouds and 
convection by early next week, but it will still be quite warm to 
hot, and likely humid. Perhaps the mex offers some relief in 
forecasting normal highs by Thursday, albeit with high chance 
probability of precipitation. 


&& 


Aviation /15z Friday through Tuesday/... 
the NAM BUFKIT soundings show a cap that persists through the day. 
Admittedly, the cap is weak. Also, the energy moving by to our north 
today carries a surface low, a surface trough and a trailing front. By 
06z Sat, there is weak low-level frontogenesis in our northwestern 
zones associated with the trough. That would suggest perhaps some 
convection in the northwest toward dusk. Would prefer not to put 
that in at this time, as it has the feeling of forecasting the 
previous event into today, so will keep any convection out of the 
taf sites for now. Subsequent tafs for ridge and/or Abe may revisit 
this. 


Winds above the surface today are a little bit stronger than 
yesterday, so the exceptions to forecasting the mainly southwest 
return flow once we begin to mix will be at Acy /sea breeze/ and ilg 
/Bay breeze/. 


Outlook... 
mainly VFR conditions are anticipated through Tuesday. However, 
visibility restrictions are possible in the early morning hours each 
day, and there is the potential for mainly afternoon and evening 
showers and thunderstorms on Sunday, Monday and Tuesday, and perhaps 
Saturday in the northwest with a weak surface front making some 
progress toward US. 


&& 


Marine... 
long period swells of 10 to 11 seconds continue at the buoys this 
morning, and wave heights remain in the 2 to 4 feet range. This with 
Bertha out at 55w longitude. At this point, will carry the swells in 
the first period and update once a few consecutive observations 
indicate they are gone. Until then, they should continue to cause 
rough conditions in and around the inlets along the coasts of New 
Jersey and Delaware. 


High pressure anchored off the middle-Atlantic coast will influence the 
region over the weekend, and perhaps into the early part of the new 
week. A caveat to this would be the aforementioned surface 
boundaries. Am not forecasting them into our waters, but they look 
to get close enough to tighten the gradient between themselves and 
the surface high. At this time, will continue to forecast conditions 
to remain below Small Craft Advisory criteria through the period, 
but will push the envelope a little. 


A slow moving area of low pressure off the southeast coast 
may pass off Cape Hatteras Monday or Tuesday if the 00z NAM/12z 
European model (ecmwf) are correct. 


&& 


Rip currents... 
with the long period swells hanging tough, will go for another day 
of moderate risk of rip currents. 


&& 


Phi watches/warnings/advisories... 
PA...excessive heat warning from noon today to 8 PM EDT Saturday 
for paz067>071. 
Excessive heat watch from Saturday evening through Sunday 
evening for paz067>071. 
New Jersey...excessive heat warning from noon today to 8 PM EDT Saturday 
for njz015-017>019. 
Excessive heat watch from Saturday evening through Sunday 
evening for njz015-017>019. 
Delaware...excessive heat warning from noon today to 8 PM EDT Saturday 
for dez001. 
Excessive heat watch from Saturday evening through Sunday 
evening for dez001. 
Maryland...none. 
Marine...none. 


&& 


$$ 


Near term...iovino 
aviation...delisi 
marine...delisi 
rip currents...delisi 

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