825 
fxus61 kphi 200927 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
527 am EDT sun Jul 20 2008 


Synopsis... 
high pressure located over the Atlantic will continue to influence 
our region today. Tropical Storm Cristobal should pass well to 
our southeast on Monday. Meanwhile, a cold front dropping down 
from the northwest is forecast to move slowly into the region on 
Monday and then stall nearby. 


&& 


Near term /until 6 PM this evening/... 
Sat pictures and an observer indicate some dense fog along the coast 
early this morning. As the tempertures rise, we expect that to 
dissipate. 


Most dynamic forcing in the way of a middle-level short wave and 
upper jet is expected to remain north of the area today, although 
thermodynamically, caps look weaker than they did yesterday, 
especially northwest. European model (ecmwf) MUCAPES look most impressive north and 
west, and stat guidance probability of precipitation are fairly low, but the storm 
prediciton center has placed a bit more than the northern half of 
our area under a slight risk of severe thunderstorms this 
afternoon and evening. Given what we're seeing, we're staying 
close to the stat guidance probability of precipitation and we haven't enhanced the 
wording in the text product, but we have split out our north to 
mention the possibility of damaging winds and large hail in the 
severe weather potential statement. 


Regarding the heat, the European model (ecmwf) is making it as hot today as it was 
yesterday, and the dew points that should mix down from above the 
surface aren't quite as low as they were yesterday. We continue 
the excessive heat warning for highly urbanized areas of the 
Delaware valley. 


&& 


Short term /6 PM this evening through Tuesday night/... 
the NAM is much too slow lifting Cristobal northeast from its 
present location, and that contaminates what happens upstream in 
its forecast. A 00z GFS/European model (ecmwf) compromise slowly brings the surface 
front into our area on Monday and then stalls it near or over US. 
The two models have some differences on how much of a focus the 
front will be for precip, with the GFS being wetter tonight and 
Monday. Both seem to agree on only minor activity Monday night 
into Tuesday, after which they agree on developing some wave along 
the front for Tuesday night and giving US a bit more action then. 
We've basically split the difference between the two in this 
uncertain pattern. 


Am a little uncomfortable with nothing out for the urbanized areas 
regarding the heat after this evening, since two out of three 
stat guidance packages (mav, fwc) are going with phl Monday maximum 
temperatures in the middle 90s and afternoon dew points in the upper 60s. 
However, with the front nearby, will let the day shift assess 
this. We've gone a bit under the FWC and mav forecast on temps, 
thereby dropping heat indices into the middle 90s. It's not exactly 
going to feel a lot better on Monday than it will today. After 
that, we've split the difference on the stat guidance packages in 
the short term, again leaning toward compromise and continuity in 
an uncertain pattern. 




&& 


Long term /Tuesday night through Saturday/... 
a frontal boundary may remain stalled off the coast through much of 
the period. While there could be a reduced chance for precipitation 
during the middle week period, an area of low pressure may ride along 
the boundary late in the week, increasing the potential for showers 
and thunderstorms, especially in the central and southern parts of 
our forecast area. 


&& 


Aviation /09z Sunday through Thursday/... 
scattered middle and high clouds, and maybe a few stratocumulus north 
and west, are forecast for this morning. Also, there will be a few 
spots which drop to marginal VFR in fog and haze toward and around 
sunrise. Kabe was already 4 miles in haze at 06z. With copious low 
level moisture, patchy dense fog had formed along the southeastern 
New Jersey coast. Kacy could be on the periphery of this action, so 
it was dropped to 3 miles in a tempo group for a few hours toward 
sunrise. 


Otherwise, high pressure is mainly centered well to our southeast 
and this will maintain a southwesterly flow of very warm and hot air 
across our area today. After the patchy morning fog and haze, 
conditions should be VFR today. The northwestern taf sites will be 
on the edge of the middle level clouds, so a bit more cloud cover was 
added for kabe and krdg. BUFKIT and a few current observations show 
this at the 12 to 15 thousand foot level. Scattered clouds were 
added for the other taf sites until after dark, when sky cover was 
increased to broken in view of the GFS MOS guidance. The chance of 
convection developing still seems fairly low today, however a 
boundary gradually approaching from the west may be able to provide 
enough focus when combined with the heat, humidity and terrain. For 
now, a cumulonimbus mention was included after 18z only for kabe and krdg. The 
surface winds are expected to be from the southwest and increase 
through the morning hours. The wind should tend to back somewhat to 
the south, especially at kacy, kmiv, and even kilg during the 
afternoon. 


Outlook... 
a cold front is forecast to move gradually across the region Monday. 
Ahead of this, scattered diurnally-forced (mainly afternoon and 
evening) thunderstorms will be possible. The front is expected to 
stall probably along the coast Monday night, and linger through 
Thursday. This could provide for at least marginal VFR conditions at 
times. 


&& 


Marine... 
conditions are forecast to remain below Small Craft Advisory 
criteria at least through early next week. 


Swells from Bertha were decreasing as that distant storm was moving 
even further away, but a reversal to an increase in swells is 
expected as Tropical Storm Cristobal, located off the Carolinas, 
moves by well to the east of the New Jersey and Delaware coasts 
Monday night. The swells from Cristobal could start to arrive later 
tonight or by Monday, and continue into early next week. Meanwhile, 
a cold front from the northwest should move into the area Monday 
night and become stationary along the coast through the middle of 
the week. In addition, wavewatch is predicting 5 foot seas by 
Tuesday evening as the gradient increases; that may or may not pan 
out, but with an increased south-southwest flow, that will have to 
be watched. There is also a slight chance for an afternoon 
thunderstorm over the northern coastal waters today, and isolated to 
scattered convection over most of the area this coming week. 


Rip currents... 
the threat of rip currents will be diminished somewhat today as 
compared with the past dew days, as the period of the swells has 
moved to slightly lower numbers. With some slight residual effect, 
the slightly onshore flow, and it being a Sunday, it was decided to 
say low approaching moderate for New Jersey for the rip current risk 
for today. For Delaware, the rip current risk was kept in the low 
range today. 


However, the swells are expected to redevelop a longer period again 
in response to Tropical Storm Cristobal, which was east of the 
Carolina coast. Cristobal is expected to head toward the northeast 
and well east of the New Jersey and Delaware coasts Monday night. 
This may bring a consequent increase in the rip current risk to the 
area starting late tonight or Monday, and persisting into early or 
even the middle portion of the coming week. 


&& 


Phi watches/warnings/advisories... 
PA...excessive heat warning until 8 PM EDT this evening for 
paz067>071. 
New Jersey...excessive heat warning until 8 PM EDT this evening for njz015- 
017>019. 
Delaware...excessive heat warning until 8 PM EDT this evening for dez001. 
Maryland...none. 
Marine...none. 


&& 


$$ 
Synopsis...delisi 
near term...delisi 
short term...delisi 
long term...iovino 
aviation... 
marine... 

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