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Area forecast discussion 
National Weather Service Raleigh NC 
340 am EST Wednesday Dec 3 2008 


Synopsis... 
high pressure shifts east today allowing for moderating temperatures 
that will persist through Thursday. A cold front is then expected 
to sweep through the state Thursday night...ushering in another 
shot of colder air for Friday into the weekend. 


&& 


Near term /through tonight/... 
as of 230 am Wednesday... 


After a cold start in the 20s across all of central North Carolina 
this morning...temperatures will rebound nicely today as the surface 
high shifts east of the Carolinas. A light southerly wind will 
develop by the afternoon and thickness climb into the low 1320s. 
High temperatures expected to reach in the low to middle 50s under 
sunny skies due to shortwave ridging moving across the region. 


High cirrus begins to spread into the area tonight ahead of the 
shortwave energy ejecting out of the intermountain west. Just how 
thick this cirrus is will affect the low temperature forecast for 
tonight. In addition...the surface high gradually shifts further 
offshore overnight...meaning that at least a light south wind 
should persist for much of the night...particularly in the west 
which will be further away from the ridge axis. Therefore...think 
the lowest temperatures likely to be in the east where winds may go calm 
for a period during the first part of the night due to the 
proximity of surface ridging...and the fact the clouds will enter this 
area later in the night. Will go with lows 31 far east to 35 in 
the west. 


&& 


Short term /Thursday through Friday night/... 
as of 230 am Wednesday... 


A cold front is still prognosticated to cross through central North 
Carolina Thursday evening/night as shortwave energy over the 
Midwest begins to shear out across the Ohio Valley and northeast. 
A decent southwesterly flow develops ahead of the front during the 
daytime hours on Tuesday...helping thicknesses reach the low 
1330s northwest to near 1340 in the southeast. This should correspond to highs 
in the range of 56 northwest to 64 southeast. 20-25 knots of wind is forecast to be 
present in the mixed layer...so occasional gusts of 20-25 miles per hour 
anticipated by Thursday afternoon. 


Rain chances with the frontal passage still appear to be rather 
small. Even though we do get a southwest flow ahead of the 
front...the airmass over the Gulf is dry with dewpoints currently 
only in the lower 40s. Precipitable waters struggle to climb to 
three quarters of an inch...and this is only in a narrow area 
immediately ahead of the front. By the time the front pushes through 
Thursday night...the 850 mb flow is turning westerly in response 
to the aforementioned shortwave energy weakening and pulling away to 
the north. This leaves very little dynamics in play to help 
generate precipitation. Will maintain just slight chance probability of precipitation for 
Thursday night. 


While model guidance continues to push the surface front east of the 
region by Friday morning...the 00z NAM and GFS have delayed the 
arrival of the 850 mb front and the arrival of cold surface high 
pressure. This is in response to another shortwave diving out of 
northwest Canada and digging into the base of the longwave trough 
to our west...keeping low to middle level flow more west 
southwesterly. The GFS is the most robust with this energy...with 
the model actually showing strong enough isentropic lift in the 
285-290k layer to generate light precipitation in the coastal plain. The 
NAM does not depict this development. The latest 00z European model (ecmwf) is 
even less enthusiastic about cloud cover/precipitation chances on Friday 
as it keeps this energy further to the north. Given that the European model (ecmwf) 
has been the most consistent...will lean toward its solution. With 
this in mind...no precipitation will be mentioned for Friday. Did raise 
lows some for Friday morning as the cold air looks to come in a 
little slower. Lows 32-39. On Friday...have raised cloud cover to 
partly sunny...but not as emphatic as the GFS for now. Highs temperatures 
look to range from 45-51...likely from some increased cloud cover 
and the cooler air filtering into the region via the cold surface high 
building east. 


The surface ridge axis builds across the region Friday night... 
although the actual surface high center weakens and shifts north. 
Still...a dry airmass is deposited into the area and we should 
have mostly clear skies with light winds. Lows 26-31. 


&& 


Long term /Saturday through Tuesday/... 
as of 320 am Wednesday... 


High pressure over the area Saturday will be pushed east Saturday 
night and early Sunday as a low pressure system over the Great Lakes 
with associated upper level trough pushed east across the northeast 
Continental U.S.. while the sounding is moist and cold enough for a few flakes 
will hold off any mention at the present time. High pressure will 
once again build over the region late Sunday and Sunday night... and 
remain as the controlling weather feature through Monday night. 
Highs Saturday will range from the middle 40s in the northwest to lower 
50s in the southeast. Under variably cloudy skies Saturday night... 
lows will be in the upper 20s to lower 30s. Decreasing cloudiness 
for Sunday. Highs Sunday and Monday in the upper 40s to lower 50s. 
Clear skies Sunday night will allow for maximum radiation... lows 
will be in the 20s. 


High pressure will move offshore Monday night as a cold front 
approaches from the west. A cold front will move across central 
North Carolina during the day Tuesday... bringing with it a chance 
for rain. Lows Monday night will be in the upper 20s to lower 30s. 
As wind shift to southwest ahead of the front... highs Tuesday will 
be in the 50s. 


&& 


Aviation /07z Wednesday through Sunday/... 
as of 120 am Wednesday... 


VFR conditions expected through the taf period. Surface high 
pressure will settle just off the Carolina coast this afternoon. 
This system combined with a southwest flow allow will result in 
mostly clear skies and southerly winds at less than 10 knots. 


A nocturnal low level jet will develop over the area tonight 
resulting in southwesterly winds of 30 to 40 kts at 2000 feet. This 
translates into a concern for low level wind shear early Thursday morning with 
surface winds expected to drop to 5 knots or less. 


A cold front will move through central North Carolina Thursday 
afternoon and evening. Cloud bases will lower to between 3 and 7 
thousand feet in scattered showers. 


Otherwise VFR conditions expected through Saturday night. A storm 
system moving across the north Central/Northeast U.S. Could threaten 
our weather Sunday. 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...jfb 
near term...jfb 
short term...jfb 
long term...rhj 
aviation...rhj 

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