600 
fxus61 kphi 300708 cca 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
310 am EDT Sat Aug 30 2008 


Synopsis... 
a cold front over the Great Lakes will move through the region 
tonight. A high pressure system will then build into the 
Appalachians for the rest of the Holiday weekend. A blocking 
weather pattern is forecast to develop. The high pressure system is 
expected to move little through most of the upcoming work week. 


&& 


Near term /through today/... 
the WRF-nmm initialization was better than the GFS with the 00z 
model package. Its position on Gustav was better than the GFS which 
looked too far to the S or southeast. The GFS did better with the 
initialization than the WRF-nmm with Hanna and a had a quite 
different solution toward the end of our deterministic forecast. 
Please refer to the TPC bulletins for further information on both 
tropical systems. 


Getting back to today, the forecast models continue pretty steady 
state about our weather. The Theta-E advt and conv came a 
little bit later than we originally thought and precipitation developed and 
is lingering into the night. The best Theta-E advt should be through by 
morning and only low chance probability of precipitation will be carried early. In addition to 
the shras, low clouds and even some fog has formed. Model forecast 
soundings are expecting them to slowly lift or dissipate during the 
morning. We will continue to carry some patchy fog in the higher terrain. 


Then our County Warning Area is left in a more humid air mass with an approaching 
cold front to provide a trigger. The surface flow is complicated a bit 
by low pressure moving southeast of our County Warning Area plus the winds below 10k are pretty 
light. Model forecast soundings are giving our County Warning Area about 1500j of cape 
along with total totals in the middle 40s. Slightly more robust than 
yesterday and even the middle level lapse rates are a little stronger, 
around 5.5c/km. County Warning Area remains in the entire region of the h2.5 jet and 
flow aloft looks diffluent. All factors point to keeping in chance 
probability of precipitation and in this instance siding with the higher Eta model MOS probability of precipitation. Not 
going higher than chance at this time because the front's timing is getting 
slower, plus there is no strong short wave at this time to help increase the 
organizational aspect of the thunderstorms and rain showers. Lastly the Theta-E conv and advt 
is forecast to be over by the morning. While a Theta-E ridge is 
forecast to remain over Delaware and NJ, its not expected to get juicier, 
which is easy to follow as the above boundary layer winds are quite 
light. The drop of Theta-E with height is forecast to occur above 15k, 
so pulse severe does not look likely. One can hardly ever say never, 
but right now it looks like "sps" type thunderstorms and rain showers. 


GFS MOS looks too lofty given we do not have as much daylight and we 
are going to lose some of the sunshine this morning because of the 
low clouds. 


&& 


Short term /6 PM tonight through Sunday night/... 
because of the slower cfp, we did extend precipitation chances throughout our 
County Warning Area during this evening and we might have to extend it deeper into 
"tonight" for the southern part of our County Warning Area if this trend continues. 
We will let the day crew see how much precipitation falls if it will become 
necessary to add patchy fog. Thinking guidance may be too low with 
min temperatures tonight in spite of their tight clustering because of the 
slower trend and we will nudge them higher. 


The rest of the Holiday weekend should continue on a better note. 
Not much moisture forecast to be available on Sunday and even 
farther to the south, the forecast soundings should be capped. Weak 
cold air advection expected Sunday, nonetheless the higher GFS MOS looks better 
this day. Without the cold air advection full sun macros from both models are 
giving the coastal plain around 90. Clear night for Sunday night. 
Have greater confidence about MOS min temperatures because of light winds 
and expected sky cover. 




&& 


Long term /Monday through Friday/... 
this time frame is still expected to be dominated by a surface high 
sliding across the region in response to an amplifying upper-level 
ridge. It appears the uncertainty that was more pronounced regarding 
an upper-level low to our east has decreased due to additional model 
guidance agreement. The latest model guidance has not changed much 
from 24 hours ago, in that they continue to advertise a 
building/expanding ridge across the eastern United States. The 
change in the latest GFS is that it weakens the ridge faster. 
Forecast models have often been overdoing forecast ridging in the 
medium range across lower Canada and the northestern conus, so this is one 
trend that will have to be followed. 


Based on the above, an expansive area of high pressure will be 
located over the eastern Great Lakes and sliding eastward on Labor 
Day. This will allow our entire area to be under a general northerly 
flow, and the surface flow may try and shift to the northeast or 
east, especially along the coast as the gradient looks fairly weak. 
MOS guidance looks a bit too high on Monday as forecast 850mb temperatures 
are more a by-product of subsidence than advection. 


This extensive area of high pressure at the surface is expected to 
be reinforced as the upper-level ridge remains close through 
Wednesday. Given the consensus of the building upper-level ridge, 
this is expected to toss an increasingly warmer air mass into our 
region. The only possible fly in the ointment is perhaps some 
onshore flow that could reduce maximum temperatures and also introduce more 
clouds. Right now the forecast location and proximity to the high 
favors more of a possible effect from an onshore flow in Delaware and New Jersey 
but less of an effect of additional clouds. Either way, that should 
be rather short lived as ridging quickly builds eastward. 850 mb 
temperatures are forecast to near +18c in the middle of the week. 
If some models are correct, some areas may start September with a 
heat wave /highs 90 degrees or higher for 3 or more consecutive 
days/. 


During Thursday and Friday, the surface high may start breaking down 
as the upper ridge could begin to be knocked down as some troughing 
pushes into the Midwest. Since high pressure is anticipated to be 
the main weather feature through the period, we opted to maintain a 
dry forecast. Overall, we did not deviate to much from HPC guidance, 
however some blending of 12z mosguide data was introduced in some 
fields mainly for collaborative purposes. The surface dew points may 
mix out during the afternoon's of Monday and Tuesday, and the 
mosguide data better reflected this. The overall surface flow looks 
weak, therefore a sea breeze may occur each afternoon. 


The latest GFS run stalls Hanna farther to the east and then moves 
her northward faster. At this time this run is a northward and eastward 
outlier with respect to to its ensemble members and also the other medium range 
models which still take her farther to the west or southwest before 
starting any northward turn. Please refer to TPC bulletins for 
official forecasts. 


That is all for now. Thanks to the surrounding offices/HPC for the 
collaboration. Have a good one! 


&& 


Aviation /07z Saturday through Wednesday/... 
the lowest conditions will be across the taf sites through the first 
part of the morning. Lower ceilings and patchy fog are across the region 
as of 2 am. The marine flow will decrease this morning and then 
swing around to west this morning and then northwest behind a cold front 
which will cross the region this evening. The pace of the front has 
slowed a bit, so a small chance for showers or maybe a thunderstorm 
exist for the afternoon during the peak heating time. I have 
introduced some vcsh and cumulonimbus groups for the 18z to 00z time frame. 


Outlook...great flying weather Sunday through much of the upcoming 
week. 


&& 


Marine... 
light winds across the waters early this morning will remain fairly 
light most of the day as only weak weather systems will affect the 
waters. A front will cross the waters tonight and a decent northerly 
flow will follow it for Sunday. Waves should be around 3 feet along 
the coastal waters today and bump up to 4 feet on Sunday. A Small Craft Advisory flag 
is not anticipated behind the front but a few gusts in the 20 to 25 
knots range are possible for a few hours Sunday morning for the coastal 
waters. 


Fair weather will be over the waters much of the upcoming week. 
Swells with Hanna may begin to affect our area toward the end of the 
week. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...none. 


&& 


$$ 
Synopsis...gigi 
near term...gigi 
short term...gorse 
long term...gigi/gorse/HPC 
aviation...O'Hara 
marine...O'Hara 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)