669 
fxus62 krah 231738 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
1238 PM EST Monday Nov 23 2009 


Synopsis... 
a low pressure system off the South Carolina coast will continue to 
slowly move north along the East Coast today. Rain will taper off to 
mainly drizzle by this afternoon...with high pressure and a cool 
airmass remaining over our area through middle week. 


&& 


Near term /through tonight/... 
as of 945 am Monday... 


12z observation analysis shows a 1036mb surface high over Maine...with a 
ridge of high pressure extending to the southwest through the 
Carolinas. An upper low is lifting NE through the Tennessee Valley 
region...with weak low pressure just off the South Carolina coast. 
Radar trends over the past few hours have shown a decrease in both 
precipitation coverage and intensity across central North Carolina. 
Am expecting mostly drizzle to continue through the afternoon hours 
as drier air aloft continues to move northward across the southeast 
US and isentropic lift slowly decreases. Therefore...have trended 
probability of precipitation downward through the afternoon...especially across the southern 
County Warning Area. Temperatures will not increase much today due to the cad wedge 
air mass in place...however did increase temperatures just a couple of 
degrees...especially across the eastern County Warning Area...as precipitation coverage is 
expected to decrease slightly quicker than previously thought. -Krr 


Lingering patchy drizzle should for the most part come to an end 
after midnight tonight as weak lift associated with a 925mb front 
shifts north into Virginia. A saturated boundary layer will lead to fog 
development on the cool side of The Wedge boundary...which should 
encompass most of the County Warning Area. A light breeze in the pressure gradient 
on the back side of the passing coastal low...which is expected to 
be off the Delaware-Maryland-Virginia by midnight...should keep widespread dense fog 
from developing...but if winds settle to near calm...fog could 
become more dense. Lows 46 to 50. 


&& 


Short term /Tuesday through Wednesday/... 
as of 300 am Monday 


Even with the parent high influence well removed from our area...The 
Wedge airmass is likely to persist through Tuesday...and possibly 
into Wednesday with no significant air mass change and weak thermal 
advection. Model soundings agree more on the persist left over cad 
stable layer for Tuesday...but other than a nagging pocket or two of 
drizzle in the morning...Tuesday should be dry but overcast and cool 
with highs low to middle 50s. 


For Wednesday....an upper level low lifting into the Midwest will 
send a relatively dry front toward the western slopes of the 
Appalachians. The front stays west of the mountains on 
Wednesday...but increasing DPVA with the upper trough spins up a 
surface low along the coastal baroclinic zone...which then lifts 
northeast parallel to coast. Even though models (most notably the 
gfs) produce some light quantitative precipitation forecast over eastern NC...it looks like the 
effects of the low will be too far east for mention of pop at the 
moment. Also...highs are tricky on Wednesday due to the possibility 
of the lingering wedge air mass. With the surface front remaining 
west of the area...low clouds may hold for at least part of the day 
on Wednesday...at least until the boundary layer becomes a little 
more stirred between the two systems mentioned above...which would 
finally allow for more mixing. Have trimmed back highs a couple 
degrees given more indication of lingering low level moisture by 
most recent forecast soundings. Highs 60 to 64. 


&& 


Long term /Wednesday night through Sunday/... 
as of 300 am Monday 


A strong upper level wave will be dropping out of the Midwest into 
the upper Mississippi Valley Wednesday night as a weak inverted 
surface trough lingers off the Carolina coast. As the upper low 
moves through the Ohio Valley a deepening low develops over the Middle 
Atlantic States... which lifts toward New England Friday evening. 
This will leave west to northwest flow over North Carolina into 
Sunday as weak Midwest upper ridging drifts toward the Atlantic 
Seaboard. 


Will keep this period dry. A risk for trace rainfall Friday 
afternoon in instability showers. But the air mass looks too dry to 
expect measurable rainfall. 


Friday looks breezy... with west winds 15 miles per hour and gusts over thirty 
as mixing heights approach 6000 feet during the afternoon to tap 
winds of thirty to forty knots at the top of this layer. 


Afternoon highs in the middle 60s Thursday... then middle 50s into Sunday. 
Overnight lows in the middle 40s Wednesday night... falling into the 
low to middle 30s for Friday and Saturday nights. 


&& 


Aviation /18z Monday through Friday/... 
as of 1230 PM Monday... 


LIFR to IFR ceilings are expected through the taf period as low 
pressure off the Carolina coast continues to pump in Atlantic 
moisture. Light rain across the region is beginning to transition 
to drizzle and this widespread drizzle is expected to persist 
through the early evening hours. Overnight...areas of fog and light 
drizzle will maintain IFR/LIFR conditions through at least the middle 
morning hours on Tuesday. 


Cad wedge will likely persist across central NC through a good 
portion of the period...resulting in a persistent period of MVFR/IFR 
conditions with periods of fog/light drizzle through Tuesday and 
possibly Wednesday. Some improvement is possible on Wednesday or Thursday as a cold 
front approaches the region and the increasing pressure gradient 
will result in breezy/gusty conditions by the end of the period. 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 


Synopsis...krr/Smith 
near term...krr/Smith 
short term...Smith 
aviation...krr