Weather

402 
fxus62 krah 070801 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
400 am EDT sun Sep 7 2008 


Synopsis...a weak surface trough will linger over the sandhills and 
coastal plain today...possibly triggering isolated thunderstorms 
this afternoon. Weak high pressure will reside over the area Monday. 


&& 


Near term /through tonight/... 
as of 310 am EDT Sunday... 


Rather moist air mass still exist across majority of central NC 
as evident of precipitation water values that range from 1.3 inches in 
the northwest to 1.7/1.8 inches in the coastal plain. Some concern that 
fog with pockets of dense fog could occur by daybreak. 
However...appears that there may be enough middle level cloudiness 
to create less than favorable radiational cooling conditions. Will 
mention patchy fog but may omit mention of dense fog. 


Water vapor imagery depicts a weak middle level short wave lifting across 
Georgia and upstate SC. This feature prognosticated to cross our area this 
afternoon. Best moisture and instability prognosticated to lie across our 
far S-southeast counties in vicinity of a lingering surface trough. Will 
maintain a slight chance pop in this region with probability of precipitation less than 15 
percent elsewhere. Thicknesses this afternoon are about 10-15m 
above normal. With at least partly sunny skies expected...should 
see afternoon temperatures in the upper 80s/lower 90s. 


Tonight...expect mostly clear to partly cloudy skies. Residual 
ground moisture from recent heavy rain may lead to formation of 
fog which may be dense in spots. Min temperatures mainly in the 65-70 
degree range. 




&& 


Short term /Monday through Tuesday night/... 
as of 330am Sunday... 


On Monday...850-700mb ridge axis across forecast area Monday 
morning shifts east Monday afternoon evening. As ridge moves east 
in the afternoon...return flow commences with some weak confluence 
noted in the far south which coincides with a shear axis aloft 
that migrates north from SC. Air mass expected to be moderately 
unstable with lifted indices around minus 4 and precipitation water 
values around 1.5-1.7 inches. This type of airmass should support 
isolated convection anywhere in the forecast area but expect 
better chance for isolated convection over the southern and 
western counties. Thicknesses remain about 10m warmer than 
normal...supporting maximum temperatures once again well into the 80s to 
around 90. 


Moist and marginally unstable air mass will linger over region 
Tuesday. Approach of a better defined short wave crossing the lower Ohio 
Valley will enhance low level southerly flow over our region. 
Approach of this middle level feature will likely increase threat for 
convection...especially late in the day over the northwest and overnight 
Tuesday night over most of the region. Better upper divergence 
occurs after 00z Wednesday across the north while 850mb confluence 
increases Tuesday night into Wednesday with approach of 850mb trough. 
This supports previous forecast of precipitation chances Tuesday night. 


Increase in cloudiness and a bit more convective coverage suggest 
maximum temperatures Tuesday should be a few degrees cooler. Maximum temperatures 
middle/upper 80s. Min temperatures Tuesday night in the 60s to around 70. 




&& 


Long term /Wednesday through Saturday/... 
as 330 am Sunday... 
both the GFS and ec have actually shown good run-to-run continuity 
in regards to a back-door cold frontal passage on Wednesday...which 
then quickly attempts to morph into a short-lived hybrid cad 
Wednesday night/Thursday as a weak parent high(< 1030 mb)centered 
over New York/PA extends south down the eastern slopes of the 
Appalachians. Front stalls out along the coast as the expansive 
subtropical ridge extends over the southeast Continental U.S.. as Ike tracks 
west across Cuba...south of the the expansive ridge...a 
tropical plume of moisture surges north towards the Carolina coast 
Wednesday night and into Thursday. Models indicate overrunning 
precipitation breaks out across central NC...in the cool/stable stable 
sector on Thursday as low-level southeasterly onshore flow expands northwest 
over the area. The GFS is more robust with precipitation and lift as the 
GFS indicates better upper level support with entrance region of 
upper jet hugging the coast. The latest GFS and ec suggest high 
temperatures on Thursday...some 15 to 20 degrees below normal...with 
northern/northwest areas remaining in the 60s. With the upper ridge still 
over the southeast...overall lift should be weak...suggesting 
quantitative precipitation forecast/precipitation will be very light or possibly even drizzle. 


It should be noted that central NC is entering in one of two 
climatologically favored times of year for cad events...so it 
appears mother nature is right on cue. Lowered thursday's high one 
category...but further more significant changes will be needed if 
current depiction holds true. 


Instability returns on Friday as the damming high moves east and 
offshore...with the encroachment of a cold front on Saturday. 


&& 


Aviation /07z Sunday through Thursday/... 
as of 145 am Sunday... 


Main aviation impact/concern(s) for this forecast...is whether we 
will see pockets of dense fog develop this morning. Nocturnal 
boundary layer moisture remains very high from the widespread heavy 
rainfall received over the past 24 hours from Hanna. While skies are 
currently mostly clear across the area...forecast soundings suggest 
a period of broken ceilings at or above 6kft are possible across the 
areas of the forecast area this morning...as a subtle middle-level 
short wave trough passes through the area. Latest infrared imagery and metar 
observations does indeed show some clouds spreading into the area 
from the south. Additionally...drier air is forecast to spread into 
the area from the northwest as a weak surface trough advances east into the 
central NC. Models indicate that the boundary stalls out...never 
making it into the coastal plain region...keeping dewpoints in the 
lower 70s. At this moment...it is a tough call determining how much 
of an impact the aforementioned cloud cover will impeded radiational 
cooling and just how far east the drier air will spread. Will keep 
with previous forecast...indicating the greatest likelihood for 
dense IFR fog across the east (fay and rwi) where the higher 
dewpoints are. 


Conditions after 13-14z Sunday morning will improve to VFR with 
light and variable winds. High pressure will take control of the 
area weather late Sunday into Monday. 


A back-door cold front will approach the area late Tuesday/early 
Wednesday...moving south of the area by Wednesday evening. The 
frontal passage will lead to a chance for scattered rain showers 
with MVFR to IFR ceilings. 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


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

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)