579 
fxus62 krah 151911 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
310 PM EDT Monday Mar 15 2010 


Synopsis... 
upper level low pressure off of the middle Atlantic coast will move 
slowly east...farther into the open Atlantic...on Tuesday. A 
gradual warming trend takes place for the middle and end of the week. 


&& 


Near term /through tonight/... 
as of 220 PM Monday... 


Water vapor imagery continues to show a modestly-strong middle-level 
shortwave moving south toward central North Carolina. Scattered 
showers continue to hold together with the shortwave and a surface 
trough...both of which will pass through central North Carolina 
during the evening. The latest guidance suggests little change from 
morning thinking...in that better moisture and lift occur northeast 
early this evening...with precipitable water values near 0.75 inch... 
and a combination of weak 850mb convergence and diffluence aloft. By 
06z...850mb Theta-E values fall quickly...and k indices fall as well. 
With subsidence behind the shortwave...along with diminishing 
moisture...expect the threat of measurable precipitation to diminish 
quickly by 02z or so...again with the focus of this northeast. NAM 
and GFS bufr soundings suggest mainly VFR...broken stratocu for the 
overnight hours...courtesy of shallow...high moisture between 850mb 
and 925mb...and a decent inversion around 800mb. Was tempted to 
forecast mins a category above the consensus of MOS overnight...but 
the bufr soundings do show a period or two...especially central and 
west...of possible reduction in the moisture in the shallow layer 
before it returns again late tonight and early Tuesday. As such... 
forecast lows near the warmer MOS...in this case the mav...at or 
just above 40. 


&& 


Short term /Tuesday and Tuesday night/... 
as of 220 PM Monday... 


Overall subsidence is in place Tuesday and Tuesday night...with 
confluence aloft...and limited moisture except in the shallow layer 
between about 850mb and 925mb. As the middle-levels are dry on both the 
NAM and the GFS...potential for any precipitation appears small. 
However...the sharp inversion around 800mb remains in place into 
Tuesday night...which will make it difficult for clouds to fully mix 
out in a deep...north-to-northeast flow. Farthest from the marine 
influence...the southwest Piedmont should have...on average...partly 
sunny conditions. The northwest Piedmont is expected to be partly to 
mostly cloudy. The entire western Piedmont should be mainly mostly 
cloudy Tuesday night as the low-level moisture retreats west. 
Central and east...a few breaks in the clouds are anticipated...with 
the fewest breaks northeast...for a mostly cloudy day on average. 
Eventually...both the GFS and the NAM suggest low-level drying takes 
place from the northeast Tuesday night...with the progress of the 
drying slower on the GFS...which should bring at least partly cloudy 
conditions by the overnight hours. Any high-level clouds west of a 
building upper ridge...and the approach of a 105kt 300mb jet late 
Tuesday night...should only start to move into the southwest 
Piedmont late. Was tempted to forecast maxes a category below 
guidance...but...again...any brief period of sun this time of year 
can make a big difference in warmth. Leaned toward the cooler 
daytime values of the met MOS for highs...which will make the day 
unseasonably cool due to the clouds...and the warmer lows of the mav 
MOS for Tuesday night. 


&& 


Long term /Wednesday through Sunday/... 
as of 310 PM Sunday... 


Models all indicate low level moisture scouring from northeast to 
southwest by Wednesday morning as the upper level low departs 
further into the Atlantic. A pair of shortwave troughs...will 
quickly reload the mean East Coast trough leading to periods of 
cloudiness for the latter half of the week. The lead shortwave 
currently over the desert SW will track along the Gulf Coast before 
lifting and shearing further along the southeast coast....as the second 
wave dives south out through the Central Plains to the Gulf Coast. 
As the aforementioned shortwave dive through the southeast states...best 
low level convergence remains to our south from the Savannah River 
basin region to the Carolina coast. With not much moisture 
transport into the County Warning Area and models showing generally flat isentropic 
flow...have kept the forecast dry. Expect a fair amount of jet 
induced cirrus Wednesday which...if opaque..may offset warming from 
the relaxed northerly flow. Have adjusted highs for thickest cloud 
cover in the south and best warming in the northeast...with 
generally uniform highs around 60. Overnight lows in the upper 30s 
to around 40. 


Upper level trough axis formed by the phasing of the aforementioned 
waves will slide east of the area on Thursday...with cloud cover 
slowly decreasing from west to east. Some recovery in low level 
thicknesses to around 1350m...with further warming by Friday and 
Saturday as a shortwave ridge builds overhead and low level 
southwesterly flow develops. Expect highs to climb from the middle 60s 
Thursday to upper 60s and lower 70s by Saturday. Overnight lows 
also progressively warmer from the upper 30s to middle and upper 40s. 


Medium range models depict a deep upper trough over the center part 
of the country progressing east to the Tennessee Valley region by 
Sunday morning. Confidence is a little low right now in terms of 
timing and impact...with the European model (ecmwf) showing more of a split flow with 
a shortwave disturbance becoming negatively tilted and lift across 
the County Warning Area Sunday. The GFS on the other hand has an upper low with 
lifting into the Great Lakes with a cold frontal passage later Sunday night. 
The European model (ecmwf) is slightly more preferred...though not enough to support 
more than chance probability of precipitation on Sunday. 


&& 


Aviation /18z Monday through Saturday/... 
as of 220 PM Monday... 


VFR conditions will be the rule through the evening...with numerous 
areas of MVFR ceilings developing late tonight and continuing 
Tuesday morning. Gusty surface winds will diminish this evening... 
with a few gusts in the teens kts expected with initial mixing 
Tuesday morning. Winds will gradually veer from the northwest to 
northerly during the night and early Tuesday. Winds aloft tonight 
should increase to near 30kt from the north around 2500ft above ground level. Any 
isolated to scattered showers toward krwi and kctz will diminish by 
06z. 


MVFR ceilings will improve to VFR conditions overnight Tuesday as 
ceilings rise and clouds are expected to become more scattered. 
Beyond Tuesday night...VFR conditions are expected. Winds will be 
relatively light compared to conditions of this afternoon and 
eventually become southwesterly by late in the week as surface high 
pressure moves offshore. 


&& 




Rah watches/warnings/advisories... 
none. 


&& 


$$ 


Synopsis...Smith 
near term...djf 
short term...djf 
long term...Smith 
aviation...djf 

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