Weather

591 
fxus62 krah 071737 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
125 PM EDT sun Sep 7 2008 


Synopsis... 


Weak high pressure over the Ohio Valley will shift east over our 
region tonight and Monday. A weak surface trough will linger over 
southeastern NC tonight before dissipating Monday. A cold front will 
approach NC from the northwest late Tuesday... then move south through 
central NC Tuesday night and Wednesday. 
&& 


Near term /through tonight/... 
as of 100 PM EDT Sunday... 


Weak surface high pressure is edging into central North Carolina 
today. This weak low level flow is slowly advecting drier air in 
from the north and northwest. We have much drier air aloft with a 
strong cap over the County warning forecast area. This cap is weaker in the southeast in the 
vicinity of a surface trough and most abundant low level moisture...but 
the cap will be strengthening today. As such...a slight chance of 
afternoon convection looks possible in the southern coastal plain. 
The thin layer of middle level moisture will be mixing out and only a 
scattered cumulus field as we approach maximum heating will allow for mostly 
sunny. Highs on track to reach 88-92 across the area. 


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 130 PM Sunday... 


The weak surface trough will linger near kfay to kgsb through the 
evening. An isolated shower will be possible this evening near the 
boundary. Otherwise... weak high pressure over the Ohio Valley will 
build east over western NC tonight. With nearly calm winds and 
generally clear skies expected overnight... MVFR fog is expected to 
develop between 06z-09z... mainly from krdu eastward. LIFR to IFR 
fog is expected between 09z-12z at krdu/kfay and krwi. MVFR fog is 
possible in the kint/kgso areas between 09z-12z. The fog will 
rapidly lift between 12z-13z Monday... with VFR conditions expected 
13z-24z. 


A surface high will continue to extend over NC from the Atlantic 
Monday night. MVFR fog (potentially IFR again at krwi)... with light 
winds and generally fair skies. 


A cold front will approach the area late Tuesday... moving south of 
the area by Wednesday evening. There will be a chance of mainly 
afternoon and evening showers and thunderstorms late Tuesday into 
the kint/kgso areas... spreading elsewhere on Wednesday. 


After the front pushes south Wednesday night... strong high pressure 
over New England is expected to build into NC from the north. This 
should bring a moist NE flow off the Atlantic... with MVFR ceilings. 
&& 


Rah watches/warnings/advisories... 
none. 


&& 


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

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