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Area forecast discussion 
National Weather Service Raleigh NC 
1000 PM EDT Wednesday Oct 15 2008 


Synopsis... 
high pressure over the southeast states will continue to bring very 
warm temperatures to the area through Thursday. A strong cold front 
will move south through the area Thursday night through Friday 
morning...causing a steep drop in temperatures and bringing a 
good chance of rain early in the weekend. 


&& 


Near term /through tonight/... 
as of 1000 PM Wednesday... 


Only minor updates to the forecast necessary this evening. Main 
problem appears to be the approach of high clouds racing out ahead 
of the approaching storm system...whose cold front extends from 
northern Indiana southwest to Texas...and low temperatures. The strong 
ridge over the southeast US has deflected any cloud cover to the north of 
the County Warning Area thus far...which allowed maximum temperatures to reach into the middle 80s 
earlier today under nearly full sun. High clouds are currently 
moving east over the western slopes of the Appalachians...and as the 
upper level ridge continues to deamplify...expect these clouds to 
drift across the northern County Warning Area overnight as upper level streamlines 
become increasing west to east. The cirrus does not appear to be 
extremely dense per latest infrared...and therefore should not hinder low 
temperatures terribly much. Instead...low temperatures will likely be affected 
more by low level moisture that did not completely mix out today. 
Dew points are as much as 4-6 degrees higher this evening than 
forecast...in the low to middle 60s from Burlington/Asheboro eastward. 
While model soundings indicate some stirring and mixing just above 
the surface over tonight...and dewpoints falling a few 
degrees...have bumped up low temperatures a degree or two...especially in 
the east...to reflect higher dewpoints. -Smith 


After sunset...expect light/variable winds to go calm or 
near calm as the nocturnal inversion quickly sets up. Excellent 
conditions for radiational cooling will continue tonight (as in the 
previous few nights). However...due to airmass modification that has 
occurred throughout the week (we've been warming each day underneath 
the strong ridge aloft)...and perhaps a light southwest breeze (3-5 
knots) developing by sunrise as the pressure gradient begins to 
tighten in advance of an approaching pre-frontal trough...expect 
lows to be a few degrees warmer than the previous few mornings...in 
the middle/upper 50s. -Vincent 


&& 


Short term /Thursday through Thursday night/... 
as of 1000 PM Wednesday... 


High temperatures look to be on track on Thursday...possibly a degree or 
two cooler in the west depending on advancement of a lowering cloud 
deck. Gso 1000-850mb thickness at 00z was 1405m...which was well 
forecast. Higher thicknesses forecast by models tomorrow...and 850 
streamlines become more westerly...but cloud cover should mitigate 
warming. Continuing highs right at record values of 85 (gso and 
rdu). -Smith 


Expect middle/upper level cloud cover to increase from the west 
throughout the day Thursday ahead of a surface cold front that will 
be progressing east into the Tennessee/Ohio valleys during the afternoon 
hours. A pre-frontal surface trough will move into central NC by 
early afternoon...and low/middle level cloud cover will begin to 
markedly increase from the west behind this feature after 
sunset...with broken or overcast conditions expected everywhere by 
sunrise Friday morning. Although the surface cold front will 
initially be approaching from the west...due to the high terrain in 
western NC...the cold front will actually push through the 
relatively lower terrain in WV/Virginia and approach central NC from the 
north overnight...with the GFS/NAM showing the boundary near the 
NC/Virginia border by sunrise Friday morning. 


High temperatures on Thursday will be similar to today with 1000-850mb 
thicknesses prognosticated to be around 1410 meters during the afternoon. 
Temperatures may be a degree or two cooler in western portions of the 
forecast area where there should be more middle/upper level cloud cover 
during the peak heating hours. Will show highs ranging from 84-87f. 
Low temperatures Friday morning are expected to be a few degrees warmer 
than Thursday morning given overcast skies...however...there is some 
uncertainty in northern portions of central NC...depending on the 
progress of the cold front moving south toward the area...and 
whether or not there is any isolated shower activity associated/west it. At 
this time will show lows ranging from 59f north to 63f South. 


West/regard to precipitation...have decided to keep a slight chance (20%) of 
showers in northern portions of the area...with a low chance (30%) 
directly along the NC/Virginia border in The Triad. Forecast soundings show 
precipitable water values increasing to 1.25-1.75" by sunrise Friday morning... 
which is about 200% of normal for this time of year. This abnormally 
moist atmosphere combined with low level convergence along the cold 
front approaching the area from the north may lead to the 
development of isolated to scattered shower activity. Both the 12z GFS/NAM 
model runs generate light quantitative precipitation forecast (< 0.10") between midnight and sunrise 
Friday morning...although primarily along/north of the Virginia border. As 
such...the best chances for shower activity will remain north of 
central NC in southern Virginia. -Vincent 


&& 


Long term /Friday through Tuesday/... 
as of 330 PM Wednesday... 


The 12z/15 October models were in general agreement in a weaker 
and more progressive middle and upper level trough development over 
the Appalachians into the southeast and Middle Atlantic States Fri-Sat. This 
trend began with the 00z and 06z runs last night... and continued 
with the 12z run today. The strongest 500 mb height falls are 
expected late Friday into early Saturday... as the upper trough 
amplifies overhead with increasing middle level positive vorticity 
advection and as the right entrance region of the strengthening 120 
knots upper jet shifts over central/eastern NC. The best chance of rain 
appears to be Friday into early Saturday... with likely pop favored 
in the west Friday into Friday night... and in the east late Friday 
into early Saturday. The likely pop for rain will transition to 
chance pop for light rain and drizzle from northwest to southeast Friday night and 
early Saturday. 


The quantitative precipitation forecast storm totals are expected to range from 0.25 to 0.50 across 
the region Friday-early Saturday. The higher totals are expected across 
the southeastern zones (near 0.50). 


The met statistical guidance was preferred over the mav guidance 
especially with the temperatures Friday-Saturday. Since the surface 
boundary is expected to be over the southern sections 12z Friday... 
much cooler air will push across central NC during the day Friday. 
The clouds and increasing chance of rain should aid in the cooling 
process. Highs should occur in the morning Friday... with temperatures 
falling into the 50s north and central during the day. The low level 
NE moist flow will keep a low overcast in place for many areas into 
Saturday morning... with a gradual clearing expected Saturday 
afternoon. Lows Saturday should remain in the lower to middle 50s due 
to all the clouds... with some upper 40s possible north. 


Strong cold air advection will continue Saturday and with the variable amounts of 
cloudiness in the afternoon... highs will remain chilly. Expect 
upper 50s to middle 60s north to southeast with a NE flow at 10-20 miles per hour. Any 
pop should be early in the day (chance) and in the southeast zones. 


For Saturday night through tuesday: ridging will build in from the 
north with the chilly surface high expected to move overhead Monday 
morning. Skies should become mostly clear Saturday night... with 
some lingering clouds over the southeast zones early. Lows will dip into 
the 40s. Highs Sunday with light winds and sunny skies should be in 
the 65-70 range. Lows Sunday night 38-45. 


The surface high should gradually modify Monday under middle level 
height rises... and low level thicknesses rebound close to normal 
Monday. Will continue to advertise highs returning to the 70s 
Monday... with plenty of sunshine. 


It appears another surface cold front will arrive Tuesday... pushed 
by another strong surface high that will build from the Great Lakes 
toward our region Tue-Thu. Expect dry and mild Tuesday... then much 
cooler again middle week. 
&& 


Aviation /00z Thursday through Monday/... 
as of 815 PM Wednesday... 


An area of high pressure over the southeast U.S. Will provide clear and 
calm conditions across central NC overnight. The area of high 
pressure will drift south Thursday. The clockwise flow around the 
high will advect middle and high level moisture into the region after 
daybreak. This will be evident by an increasing and thickening of 
high level clouds...especially after 16z Thursday. Near a surface winds 
will be SW between 7-10kts. 


A cold front will approach and cross central NC from the north-northwest late 
Thursday night into Friday. This frontal system will concentrate moisture in 
the lower levels of the atmosphere resulting in MVFR ceilings across 
the north by Friday morning...and across the south by Friday 
afternoon. IFR ceilings are probable by Friday night a cool NE flow 
becomes established in the lowest 3000ft. Will likely see areas of 
rain or rain showers will the frontal system...especially Friday 
afternoon into Friday night. 


As the frontal system lifts east-NE out of the region...expect ceilings 
to gradually lift above MVFR criteria. Expect a return to VFR 
conditions Saturday night...persisting into Monday. 




&& 


Climate... 


Record highs for Thursday October 16: 
rdu - 85 (1989) 
gso - 85 (1953) 


Record high minimum temperatures for Friday October 17: 
rdu - 66 (1947) 
gso - 67 (1947) 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 


Synopsis...Badgett 
near term...Vincent/Smith 
short term...Vincent/Smith 
long term...Badgett 
aviation...wss 
climate...Badgett 

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