281 
fxus62 krah 181807 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
207 PM EDT Thursday Mar 18 2010 


Synopsis... 


An upper level low will move slowly off the Carolina coast today. 
High pressure will build in from the west Friday and linger overhead 
Saturday bringing warm and dry conditions. 


&& 


Near term /through tonight/... 
as of 1010 am Thursday... 


Expect the middle-upper level cyclone over SC this morning... which has 
deepened around 20 meters in the last 12 hours per 12z radiosonde observation data... 
to become increasingly stacked today atop a weak surface low about 
250 miles south of hse. In the meantime... the combination of weak 
warm air advection/isentropic upglide and forcing for ascent courtesy of an 
attending middle-upper trough axis that extended northeastward across 
NC... should maintain widespread cloudiness and virga mainly between 
6 and 10 thousand feet... and spotty light rain or sprinkles mainly along 
and southeast of a line from near Rocky Mount to Raleigh to 
Wadesboro today. Expect the best chance of any measurable 
precipitation will be over the sandhills and southern coastal 
plain... where ceilings are lower and the sub-cloud layer is 
resultantly shallower/moister and more supportive of precipitation 
reaching the ground... per 12z gso/mhx radiosonde observation comparisons. Given the 
current and only slowly eroding/eastward departing cloud cover... 
expect temperatures to follow an atypical climatology distribution... with 
middle 60s northwest to perhaps only upper 50s southeast. 


Tonight...upper level low and attendant surface low move farther 
offshore. Diffluent flow in the middle layers over central NC should 
lead to decreasing cloudiness around or shortly after sunset. 
Previous forecast of min temperatures slightly cooler than MOS appears more 
correct based on trends expected today. Min temperatures near 40 north to 
lower 40s southeast. 


&& 


Short term /Friday through Saturday/... 
as of 255 am Thursday... 


Expect warm and dry conditions this period as ridging near 
surface and aloft build into central NC from the SW. Afternoon low 
level thickness projected to be in the middle/upper 1360s. Weak northerly 
flow Friday will temper air mass moderation somewhat so have trended 
maximum temperatures to the cooler end of MOS guidance Friday. Surface ridge 
overhead Friday night will cause clear/calm conditions...allowing 
near surface air mass to realize full cooling potential. 


On Saturday...surface ridge edges east. With return SW flow 
developing...low level warm air advection will boost afternoon temperatures 
well into the 70s. Thickness with full sun support maximum temperatures near 70 
to the lower 70s. Adjusting for SW flow yields maximum temperatures in the middle 
70s most locales. 


&& 


Long term /Saturday night through Wednesday/... 
as of 245 am Thursday... 


The 17/12z European model (ecmwf) and 18/00z GFS came in with very good agreement 
with regards to the next storm system that will affect central North 
Carolina by the end of the weekend. A deep upper trough that is 
prognosticated to cut off over the the south central US by late Saturday 
will move east and eventually track over the middle Atlantic by late 
Sunday into Monday. This will push a cold front across the forecast 
area overnight on Sunday. Many uncertainties still remain with the 
exact impacts of this system...especially with regards to the 
convective/thunder potential. A relatively strong 850mb jet as well 
as good southerly flow ahead of this system will result in decent 
moisture returning to the region...which will increase the 
instability. However...the current timing has the system moving 
through overnight on Sunday which would then limit the convective 
potential. Also...the most recent model runs show the trough 
remaining positively tilted to neutral at best as it moves across 
the forecast area. Nevertheless...being we are still four days out 
this will have to monitored closely. 


Temperatures on Sunday are going to be highly dependent on the arrival of 
the clouds/rain...but with the slower movement of the system...still 
am expecting the upper 60s (further west due to more cloud cover) to 
lower 70s further south and east. Behind the front...high pressure 
quickly builds in from the west by early Tuesday. Near to slightly 
below normal temperatures are expected for early next week before climbing 
back to near 70 degrees again by the middle of the week. 


&& 


Aviation /18z Thursday through Tuesday/... 
as of 205 PM Thursday... 


Expect mainly scattered to broken middle level cloudiness between 6 and 10 
thousand feet (lowest and densest over the sandhills and coastal plain 
from Fay to gsb)... to gradually dissipate and shift east 
southeastward through tonight... as the middle-upper level low and 
accompanying lift over the Carolinas this afternoon gradually drifts 
offshore. Skies should accordingly become sky clear late tonight... and 
persist through Friday. 


The slow eastward drift of an attending surface low pressure 
system centered a couple hundred miles south southeast of hse will 
cause light generally northeasterly winds this afternoon to back to 
northwesterly or become variable and still light tonight and Friday. 
Dry and subsident ridging -- most pronounced in the middle levels -- 
will dominate and maintain VFR conditions through the weekend. 
Expect IFR conditions... heavy showers... and windy conditions when 
a storm system affects the region Sunday night through Monday. 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 


Synopsis...wss 
near term...mws/wss 
short term...wss 
long term...krr 
aviation...mws