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Area forecast discussion 
National Weather Service Raleigh NC 
300 am EDT Monday Mar 15 2010 


Synopsis... 
a strong upper low will meander off the middle-Atlantic coast today 
before finally moving out into the Atlantic waters on Tuesday. As 
this weather system moves away... high pressure will gradually build 
in from the west... bringing dry weather through middle week. 


&& 


Near term /through tonight/... 
as of 250 am Monday... 


Upper low will meander over off the Delaware-Maryland-Virginia coast today and tonight 
before finally moving southeast towards Bermuda on Tuesday. 


The sheared vorticity lobe currently over the area will slide 
south and east of the area later this morning. In its wake... 
models show significant clearing/scattering of stubborn middle cloud 
deck through the first half of the day...before the combination of 
surface heating... lingering moisture at 850-700 mb... and weak 
surface troughing across NC is likely to lead to scattered to broken 
flat convective clouds for the latter half of the day. Peak afternoon 
mixing should allow for some of the 25kt wind at the top of the mixed 
layer to reach the surface...so expect a breezy afternoon with northwest 
winds of 15-25 miles per hour. As far as temperatures...not really sure why MOS 
statistical guidance is showing such a warm up today...as we 
actually have some weak cold air advection ongoing throughout the day low-level 
thicknesses falling after 18z. Local temperature scheme is closer to the 
cooler met statistical guidance. Afternoon high around 60 northwest 
to middle 60s southeast. 


Models are rather insistent that maritime moisture will get pulled 
southward across the eastern half of the forecast area this evening 
and overnight as the low pressure area makes a turn southward towards 
Bermuda. So expect a east to west gradient with clouds...with mostly 
cloudy east to partly cloudy/fair west. Lows near 40 northwest to 
lower 40s elsewhere. 


&& 


Short term /Tuesday through Thursday night/... 
as of 240 am Monday... 


Tuesday and Tuesday night... 
southwest extension of the upper low that has persisted across the east 
Continental U.S. For the past 4 days or so pivots east on Tuesday. This results 
in a backing and relaxing of the upper flow and a modest increase in 
500 mb heights on Tuesday and Tuesday night. Low level flow remains 
northeasterly though... and this which will transport a cooler and 
slightly more moist air mass into the region. Expect varied amounts 
of cloud cover given the NE flow with moisture persisting in the 
lowest 8kft below an intensifying inversion. Moisture is not very 
deep and forcing for ascent is lacking so precipitation is note 
expected. High temperatures in the middle 50s on Tuesday will be several degrees 
cooler then normal given the NE flow cloud cover. Low temperatures on Tuesday 
night will range in the upper 30s to lower 40s. 


Wednesday through Thursday night... 
brief rise in upper heights stops on Wednesday as closed low over the 
Desert Southwest at the beginning of the week moves east...weakens 
and opens up. As this disturbance moves into the northwest Gulf of Mexico 
on Wednesday...a disturbance in the northern stream drops south into the 
Missouri Valley. As these system try to phase...a positively tilted 
upper trough axis develops across the central or eastern Carolinas by 
around 12z Thursday. Low level flow remains primarily northerly 
across the southeast and the Gulf of Mexico which will obviously 
limit the amount of moisture available to the system. Nwp guidance 
is coming into better agreement with the overall pattern and 
confidence in the development of the upper trough and perhaps a close 
low is increasing. But given the lack of moisture transport...the 
likely placement of the trough axis across the eastern Carolinas and 
a surprisingly stable profile on Thursday suggests limited precipitation 
chances. Will increase the degree of cloud cover and knock temperatures 
back a degree or too but keep forecast dry for now. -Blaes 


&& 


Long term /Friday through Sunday/... 
as of 300 am Sunday... 


Friday through Saturday night...short wavelength upper trough off the 
Carolina coast on Friday pushes east allowing short wave ridging to 
develop on Friday night. Broad southwesterly flow develops on 
Saturday and persists into early Sunday as next trough in the northern 
stream approaches from the west. Mainly clear skies expected on 
Friday night with some increase in high clouds arriving by Saturday 
and Saturday night. This pattern suggest a notable warming trend 
with temperatures reaching the upper 60s and lower 70s by Sat. 


Sunday and Sunday night...guidance fairly consistent in bringing a 
northern stream trough across the region on Sunday. Details and timing 
of this feature are varied as is expected this far out. 14/12z European model (ecmwf) 
and 15/00z Canadian forecast the upper trough and attendant cold front to 
arrive early in the day on Sunday while the 15/00z GFS holds precipitation 
off until late in the day. The European model (ecmwf) closes off a low over the 
southern Appalachians with better forcing while the GFS pushes the 
best forcing further north. Current forecast includes a 30 pop on 
sun and have no reason to adjust this now. But timing and other 
details will likely evolve over the coming week. With increased 
cloudiness and a chance of precipitation...maximum temperatures on sun should be a few 
degrees cooler then Sat. -Blaes 
&& 


Aviation /06z Monday through Saturday/... 
as of 200 am Monday... 


VFR conditions through the 24 hour taf period. 


Upper low will meander off the Delaware-Maryland-Virginia coast today. Channeled 
vorticity axis currently over the region will continue to generate weak 
lift with scattered sprinkles and ceilings between 5 to 8 kft. 
This shortwave energy will slip south and east of the area between 
12 to 15z. Subsidence behind this shortwave energy should translate 
into partial clearing late this morning. By the afternoon...March 
sunshine should support a fairly expansive cumulus field as middle-level 
moisture lingers in vicinity of of the upper low. Breezy northwest winds will 
develop by the afternoon as well...with gusts near 25kts expected. 


The gustiness will diminish during the evening...but pressure 
gradient remains tight enough to support a steady 5 to 10kt wind 
from the north overnight. Model soundings show MVFR ceilings 
developing late tonight by daybreak Tuesday as the northerly winds 
draw some Atlantic maritime moisture south into the area as the 
offshore low takes a turn to the south. 


VFR ceilings return for Tuesday as drier air moves into the region. 
A series of upper level disturbances/lows will approach the area by 
middle week. However at this time impacts will be marginal with only 
some clouds expected as this time. Northerly flow will gradually 
shift to easterly as the week progresses and winds should remain 
fairly light (5-10 kts) with minimal gusting. 


&& 




Rah watches/warnings/advisories... 
none. 


&& 


$$ 


Synopsis...cbl/Hartfield 
near term...cbl/Hartfield 
short term...blaes 
long term...blaes 
aviation...cbl 

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