Weather

580 
fxus62 krah 111955 cca 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
302 PM EDT Sat Oct 11 2008 


Synopsis...surface high pressure will build south down the Atlantic 
Seaboard from New England through the day...bringing drier air to 
the region this evening into Sunday. Temperatures will gradually 
warm to well above normal during the early part of next week. 


&& 


Near term /through tonight/... 
as of 250 PM... 


Rest of today: per 12z upper air data... heights aloft have 
continued to rise over the Ohio Valley and middle Atlantic region. 
Drier air courtesy of the building ridge will continue to shunt 
southward the well-defined upper low and associated moist easterly 
fetch of moisture from the Atlantic through tonight. However... 
before this fully occurs... occasional light rain or sprinkles will 
be possible over the southern coastal plain and eastern sandhills 
this afternoon... with dry conditions prevailing elsewhere. 


Tonight: any threat of rain should be to our south by this 
evening... as we become increasingly dominated by the subsident and 
drying ridge to our north. The current shield of cirrus is expected 
to move little tonight... though the low and middle level cloud cover 
below is expected to succumb to deep layer subsidence beneath the 
building ridge aloft. This deep layer drying was already evident at 
12z this morning at kgso... where observed dewpoint depressions of 
33 and 47 at 700 mb and 500 mb... respectively... were present. Despite the 
deep layer drying... the 12z models continue to indicate the 
potential for the onshore advection of marine stratus or 
stratocumulus in northeast flow late tonight... beneath the 
developing subsidence inversion aloft. While latest satellite 
imagery does reveal some stratocumulus and inferred low level 
moisture off the northeastern North Carolina this afternoon... 
confidence of this moisture resulting in low cloud cover over 
central North Carolina tonight is low. Will advertise a range of 
51 under mostly clear skies northwest to 60 southeast under partly 
to mostly cloudy skies southeast. -Mws 


&& 


Short term /Sunday through Monday/... 
as of 250 PM... 


The deep layer ridge will continue to expand from the Ohio Valley to 
the middle Atlantic region through the period... and result in dry and 
generally mostly clear conditions with moderating temperatures 
during the period. Low level thicknesses are forecast to increase 
from the 1380 to 1385 meter range Sunday to 1390-1395 meters on 
Monday. This should translate to high temperatures in the upper 
70s to near 80 Sunday... to 79 t0 82 degrees on Monday. Lows 
Sunday morning upper 40s northwest to middle 50s southeast... as the 
surface high settles over the central Appalachians. -Mws 


&& 


Long term /Monday night through Friday/... 
as of 250 PM... 


Have elected to introduce a chance for rain Thursday night. Front 
approaching central North Carolina late Thursday with majority of 
its dynamics to our north... and what little there is over North 
Carolina occurring below 850 millibars. Timing of this feature has 
slowed several hours from previous runs and this is typical for 
systems this far out in time...and timing may slip further. 
Current trend would suggest rain chances in the south Friday 
morning. However due to the potential weakness of the event and 
uncertain timing... will confine rain to one period of the 
forecast. 


Other than the potential rain event listed above... the forecast 
is mainly a temperature forecast. High pressure both surface and 
aloft early in the period persists into Wednesday... with flow 
aloft increasing and becoming west Wednesday night. Temperatures 
look to be up to ten degrees above normal... but falling short of 
record highs... Tuesday night through Thursday night. Temperatures 
Thursday night may yet be too cool if the current front timing 
holds... as models tend to fail to catch enough of the warm 
advection ahead of a cold front. 


With flow aloft not turning significantly to the northwest until 
Friday afternoon... and current surface high forecast to be broad 
and relatively weak... have Friday temperatures and beyond a bit 
above GFS model numerical guidance. 


&& 


Aviation /19z Saturday through Thursday/... 
as of 225 PM Saturday... 


A deep layer ridge will continue to expand from the Ohio Valley to 
the middle Atlantic region through the period. Drier air courtesy of 
the building ridge will continue to shunt southward the well-defined 
upper low and associated moist easterly fetch of moisture from the 
Atlantic through tonight. However... before this fully occurs... 
occasional MVFR ceilings will be possible at Fay and rwi (and 
perhaps briefly at rdu) this afternoon... with VFR conditions 
expected at gso and int. Northeasterly surface winds are expected to 
range from 10 to 15 knots... with gusts to around 20 knots this 
afternoon... as downward momentum transport from a Stout (~30 knots) 
low level jet (llj) continues through sunset. The gustiness should 
subside and sustained winds will fall into 5 to 10 knot range once 
the nocturnal inversion sets up this evening. Have maintained low level wind shear 
only at Fay overnight... since they will be in closest proximity 
to the forecast low level jet axis. However... the surface stirring 
overnight should lessen the potential for abrupt wind speed 
changes with height in the lowest 2000 feet... thereby mitigating 
the threat of low level wind shear. 


Forecast soundings and cross sections indicate the potential for 
the onshore advection of marine stratus or stratocumulus in 
northeast flow late tonight... beneath the developing subsidence 
inversion aloft. While latest satellite imagery does reveal some 
stratocumulus and inferred low level moisture east of the Outer 
Banks this afternoon... confidence of this moisture resulting in 
IFR/mfvr ceilings at central North Carolina terminals tonight is 
low. Have accordingly only included a brief period of MVFR/IFR 
ceilings from rdu eastward around daybreak. If the low cloud cover 
indeed develops... ceilings could remain MVFR until scattering out 
and lifting midday Sunday. 


Clear skies and light winds may allow for shallow radiation fog 
development and resultant MVFR/IFR visibilities early Monday 
morning. Otherwise... VFR conditions will prevail. -Mws 


&& 


Climate... 


Record highs for Tuesday October 14: 
rdu - 86 (1985) 
gso - 85 (1975) 


Record highs for Wednesday October 15: 
rdu - 88 (1985) 
gso - 87 (1985) 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 


Near term...mws 
short term...mws 
aviation...mws 
climate...Hartfield 

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