129 
fxus61 kakq 182010 
afdakq 


Area forecast discussion 
National Weather Service Wakefield Virginia 
410 PM EDT Friday Jul 18 2008 


Synopsis... 
high pressure drifts off the middle Atlantic coast this 
evening...remaining just off the coast through the weekend. 
Meanwhile...weak low pressure currently off the Georgia coast will 
slowly move northeast this weekend. 


&& 


Near term /until 6 am Saturday morning/... 
turning out to be another warm and clear day today across Virginia with 
high pressure centered over the Delaware-Maryland-Virginia. A weak low pressure system 
is currently located off the central coast of Georgia (south of savannah) 
and this will be the main variable in the forecast for our area through 
the short term. It is in an area favorable for further development and 
the hurricane center has upgraded the probability for tropopause cyclone 
development to high (gt 50%)...thinking that it could become a depression 
tonight or tomorrow. Due to the fact that a broad ridge dominates 
the southeastern US for the next few periods however...there isn't 
anything to move this system anytime soon...so will not be a factor 
for US in the near term. 


Continued S flow tonight on the west side of the high will warm 
things up even further...with lows about 3-7 degrees higher than 
last night. Dew points also a bit higher and while the areas in the southeast 
that saw dense fog this morning will have slightly more cloud cover 
tonight than they did this morning...have still included some patchy 
fog in the zones for mostly coastal/southeast locations where dew points are 
expected to be close to 70 degrees. 


&& 


Short term /6 am Saturday morning through Monday night/... 
Saturday will start out relatively clear but with increasing 
moisture...should see increasing clouds throughout the day across 
the area. This should keep temperatures a few degrees below today's highs. 
The exact mvmt of the low up the coast tomorrow is a little 
uncertain right now as the GFS has really sped its movement up while 
the NAM and European model (ecmwf) still take it a bit more slowly (ecmwf still the 
slowest). Some discrepancies on exact track as well as far as how 
far off the coast it stays. Have maintained slight chance/low end 
chance probability of precipitation for the southern third of the area Sat afternoon...but not 
holding out much hope for any sig rain. Will mostly be just spotty 
rain showers maybe a ts or two that pop up during maximum heating hours. 


With a cloudy night expected Sat night (at least for southeast/east portions 
of the area) temperatures will continue to remain quite warm overnight 
(around 70 inland...lower to middle 70s southeast sections). Generally went 
close to the NAM for mvmt/position of low this weekend which would 
bring the low up to just off the central NC coast by Sun 
morning/midday. Did bump up probability of precipitation slightly on Sunday from straight 
NAM probability of precipitation to account for the fact that the ridge offshore may keep 
the low closer to the coast than what the NAM is indicating. Best 
shot for rain with this system would be during the day Sunday as the 
low mvs east of the coast...but still no more than 40% probability of precipitation 
warranted at this time. Knocked highs down a good 5 degrees for southeast 
portions of the area on Sunday with sig cloud cover however. 


On Monday...the low will be at least pushing offshore away from the 
area (even with the slowest European model (ecmwf) soln) but a front will be moving 
through in the afternoon/late evening time frame (again dependent on exact 
position of the low and if it could slow the front's progression 
down at all). Such a weak front though and most of the energy 
remains well north so no more than slight chance probability of precipitation at this point 
for Monday. 


&& 


Long term /Tuesday through Friday/... 
long term period characterized by warm...humid and rather unsettled 
conditions...primary forecast challenge was in diagnosing precipitation chances. 


Deepening low exits (slowly) to the northeast to begin the 
period...a weak cold frontal boundary will continue to edge its way 
into the region from the west. GFS is far more aggressive in pushing 
the front offshore...with the Euro seemingly much less progressive. 
As with the past few fropas...have trouble believing front will be as 
quick as prognosticated by the operational GFS. As a result...tried to 
depict front getting hung up a bit across our S County Warning Area through 
midweek...with some diurnally driven thunderstorms possible through the period. 
Temperatures should remain quite warm...though edged maxima downward given 
high cloud cover and very moist airmass. 


&& 


Aviation /20z Friday through Wednesday/... 
high pressure remains in control of our weather this evening...with clear 
skies and light winds continuing. Although slightly more cloud cover 
is expected over the ecg area early in the morning...temperatures and dew 
points will again be close and winds will be light so fog is again a 
possibility. The models are not picking up on the chance of dense 
fog...but they didn't this morning either...so while for now will 
go with VFR conds in the ecg taf...and will continue to monitor 
for the possibility of IFR conds overnight through sunrise. 


Low pressure off the coastal Carolinas...and increasing moisture over 
the area may result in widely scattered precipitation and occasional lowering of 
AVN conditions late Sat through early Tuesday...especially for ecg and 
possibly orf. 


&& 


Marine... 
biggest feature of note continues to be an area of low pressure that 
continues to spin off the Georgia coast. NHC now showing high potential 
for further development with this system...with this feature 
potentially becoming a T.D. Later tonight or early Sat. Erred closer to a 
NAM blend for this forecast package...as this model has trended 
slower and farther offshore with this system. That said...forecast 
is a very tricky one at this time...and will need to continue monitoring 
Sat/model trends and change grids accordingly as needed. 


S/southeast winds around a large area of high pressure centered offshore will 
continue through the weekend (5 to 10 knots at night and at or below 15 knots during 
the day). Seas will remain between 2 to 3 feet through Sat...with waves 
of 1 to 2 feet in the Bay/snd....with seas building to 3 to 4 feet range 
as low pressure to the south slowly pushes northward. Deepening low 
looks to push away from the area by midweek..with weak high pressure 
building in from the west. 


Moderate rip risk appears likely to continue for tomorrow for the 
Maryland/VA/NC beaches with lingering east swell. 


&& 


Akq watches/warnings/advisories... 
Maryland...none. 
NC...none. 
Virginia...none. 
Marine...none. 


&& 


$$ 
Synopsis...jym 
near term...jym 
short term...jym 
long term...mam 
aviation...baj 
marine...mam 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)