435 
fxus62 krah 282349 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
749 PM EDT Thursday Aug 28 2008 


Synopsis... 
a surface trough coupled with a moist air mass will result in 
scattered showers and thunderstorms each afternoon through 
Sunday. 


&& 


Near term /through tonight/... 
as of 230 PM... 


Moist and moderately unstable air mass continues to reside over a 
large swath of central NC. Most of the scattered convection through 
1830z has occurred over the northern coastal plain. A weak upper 
level trough seen in water vapor imagery may provide enough lift to 
initiate additional convection farther west over the 
Piedmont...especially near a temperature discontinuity area that 
exists between rdu and gso. Main threat from convection will be from 
slow moving heavy downpours that may lead to localized flooding. 


While middle/upper levels of atmosphere have dried out significantly 
since last night. Air mass below 8000ft still very moist. Partial 
clearing this evening may lead to the development of widespread fog. 
Due to recent spat of heavy rain...potential for areas of dense fog 
to develop. Confidence not high enough to issue a dense fog advisory 
at this time but will mention areas of dense fog in forecast text. 
Min temperatures basically in the 65-70 degree range. 


&& 


Short term /Friday through Saturday night/... 
as of 230 PM Thursday... 


The unsettled weather pattern continues through the period. 


The upper level cyclonic vortex currently digging across upstate Georgia 
atmosphere is prognosticated by short term models to stall out in vicinity of the Carolinas 
through Saturday...as it becomes left behind by the main belt of 
westerlies moving north through the Great Lakes. Meanwhile...an 
inverted surface low pressure trough will remain draped across the 
coastal plains with moist Theta-E ridge extending the area. 
Low-level thicknesses support moderating highs into the 87 to 91 
range...with really only exceptions occurring in the northwest Piedmont on 
Friday...where dissipation of any dense fog could be slow to burn 
off. Thus...expect strong afternoon heating to supply steep 
low-level lapse rates. Convective available potential energy is 
prognosticated to reach between 2000 to 2500 j/kg both afternoons. Will 
keep probability of precipitation in the 20 to 30 percent range...with highest probability of precipitation in the 
east....maintaining isolated probability of precipitation overnight Friday night. 


Channeled shortwave shear axis moves across the area Sunday 
morning...along the the tail end of a shortwave trough pushing 
through the southeastern candida. This will push a cold front 
through the area sometime during the day on Sunday. Models continue 
to indicate anafrontal precipitation across central NC during the day on 
Sunday. Gfsbfr soundings keep precipitable waters  in the 1.7 to 1... of 
normal...with a continuation of moderate to high instability 
from US 1 east. Will have scattered probability of precipitation east...slight chance west. 


&& 


Long term /Sunday through Wednesday/... 
as 230 PM Thursday... 


Anomalously strong long wave ridging builds east through the 
middle-Atlantic region and down the eastern Seaboard through midweek. 
Surface ridge will extend south into central NC from the northeast... 
with Labor Day marking the arrival of drier...tranquil conditions 
for quite some time. Forecast temperatures for all of next week look 
to fall well in the normal range. Highs in the middle to upper 80s. 
Lows in the middle to upper 60s. 


During the mean time...the crazy active tropics will be closely 
monitored over the next several days. A pivotal feature that will 
impact Hannah is whether the long wave trough exiting the East Coast 
picks up the tropical cyclone. Otherwise...the eventual paths/tracks 
of both tropical cyclone Gustav and Hanna...will be greatly 
influenced by the aforementioned strong subtropical ridge(including 
it's eventual demise)....as Gustav and quite possibly Hannah...will 
be suppressed south of the anticyclone. The official NHC track for 
Gustav has it making landfall along the northern Gulf Coast...with 
Hannah being a threat to the southeastern US as well. 


&& 


Aviation /00z Friday through Tuesday/... 
as of 745 PM Thursday... 


VFR conditions prevail at all taf sites this evening...but that is 
expected to change through the course of the night. Scattered 
convection occurring over the northeast Piedmont and coastal plain 
should diminish over the next few hours with the loss of 
instability....leaving the rest of the night precipitation free across 
central North Carolina. The evening hours will see mainly clear 
skies and light winds. Water vapor imagery shows that the middle and 
upper levels of the atmosphere have dried out significantly since 
yesterday and this should aid in good radiational cooling 
conditions. With all of the rain that occurred over the past 24-48 
hours...ground level moisture is quite high. This sets the stage for 
the development of low stratus and fog overnight across all of 
central North Carolina. IFR conditions likely to develop at all 
terminals sometime after 06z...with LIFR conditions possible at 
rdu/Fay/rwi where dewpoints in the low 70s will assist in the 
formation of dense fog. 


Low stratus and fog should lift around 14z Friday with VFR 
conditions prevailing for the rest of the day. Convective chances do 
not appear too high tomorrow...however the best chances for diurnal 
convection will occur over eastern North Carolina in association 
with the best deep layer moisture and weak low level convergence 
along an ill defined surface trough. Coverage not expected to be high 
enough to include any convective mention at any of the terminals. 


Will continue to see a chance of afternoon convection through Sunday 
as surface trough and marginally moist air mass lingers over the 
region. High pressure nosing south Monday should lead to an extended 
period of VFR conditions. 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...wss 
near term...wss 
short term...cbl 
long term...cbl 
aviation...jfb/wss