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fxus62 krah 050702 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
302 am EDT Sat Jul 5 2008 


Synopsis... 
a moist and unsettled weather pattern will persist over central 
North Carolina through the weekend. A surface front will remain 
nearly stationary over and just north of the state through the 
weekend. Weak high pressure will build in late Monday...but 
moist air remaining in place keeps chances of mainly afternoon and 
evening showers and storms in the forecast for much of the upcoming 
work week. 


&& 


Near term /through tonight/... 
as of 3 am Saturday... 


The latest surface analysis showed a stationary front just north 
of the state...across Virginia...Kentucky...and west into northern 
Arkansas. Water vapor imagery and surface observations indicated 
good moisture over the state surface and aloft...with a middle-level 
shortwave moving east-southeast out of Illinois toward the central 
Appalachians...followed by a stronger middle-level wave moving south 
over the upper Mississippi Valley. As heights aloft decrease to our 
west as forecast by both the NAM and the GFS...deep southerly flow 
will persist over central North Carolina with at least modest 
diffluence aloft in place. 850mb and 700mb Theta-E values are 
maximized over the forecast area this afternoon...with good lift 
along and south of the surface front aided by modest low-level 
convergence but slightly increasing diffluence as the upper trough 
deepens somewhat to our west. With precipitable water values 
around two inches...a regional maximum of 0-3km shear over the 
state...and mixed layer cape around 2000j/kg as forecast by the 
NAM with slightly greater values forecast by the GFS...think 
numerous showers and thunderstorms will develop for the afternoon 
and continue at least into the evening. Although wind fields are 
not terribly weak...10-15kt on average at 850mb and 20-25kt at 500mb... 
high moisture content of the atmosphere will allow for locally 
heavy rainfall particularly if the GFS is correct with its most 
unstable cape...being near 3000j/kg in some places later in the 
day. Anticipate a diurnal decrease in precipitation coverage 
overnight but chances cannot be eliminated in the moist air mass 
with model soundings from both the NAM and the GFS showing 
potential instability continuing through the overnight hours. 
Given the degree of instability and moisture...would expect at 
least a handful of severe storms late this afternoon and into this 
evening with the potential for a high number of lightning strikes 
from any...more organized thunderstorms. Temperatures in most 
areas should remain in the 80s...with only a few lower 90s 
expected given anticipated cloud cover. Overnight lows tonight 
will be within a few degrees of 70. 


&& 


Short term /Sunday through Monday night/... 
as of 3 am Saturday... 


Not much change expected Sunday from the day Sunday. Central 
North Carolina remains in an 850mb and 700mb Theta-E ridge...with 
precipitable water values again around two inches. Good upper 
diffluence is in place once again especially in the afternoon with 
the upper trough to our west...and the NAM in particular forecasts 
a modest middle-level shortwave to pass through the forecast area. In 
addition...there is not much change noted to the available 
instability on model soundings nor with the 0-3km shear...which is 
once again maximized over central North Carolina compared to other 
locations in the region. Expected a chance of showers and 
thunderstorms in the morning to increase to numerous showers and 
thunderstorms for the afternoon...with another diurnal decrease 
anticipated overnight Sunday. Highs should be in the 80s. 


Monday...both the NAM and the GFS forecast some increase in 
surface ridging from high pressure off the coast. Shear diminishes 
some as well...however...the GFS more so than the NAM pushes 
across central North Carolina a moderately strong shortwave in the 
middle-levels during Monday afternoon. In fact...the stronger 700mb 
shortwave on the NAM over the next three days is on 
Monday...despite the NAM forecast of weaker upper diffluence as 
the trough to our west lifts out faster on that model than the GFS 
depicts. Model soundings remain unstable despite a decrease in 
Theta-E for Monday afternoon compared to expected values over the 
weekend. Overall...with the surface ridging increasing expect a 
chance of showers and thunderstorms but with a coverage less than 
what should occur during maximum heating this weekend. On Monday... 
currently would anticipate the better coverage to be toward the 
coastal plain where the available moisture would be deepest. 


&& 


Long term /Tuesday through Friday/... 
as of 3 am Saturday... 


Little change in the overall weather pattern for the middle and 
end of the work week. A moist low-level flow remains in 
place...and the latest GFS continues to show fairly unstable model 
soundings over central North Carolina through Friday with no hint 
of a middle-level cap at any time. Increased probability of precipitation slightly for 
Thursday and Friday afternoon given the apparently more moist 
GFS...and though currently do not expect any day to be a 
washout...afternoon and evening scattered showers and 
thunderstorms will remain in the forecast. The latest GFS has 
trended a little more moist toward the end of the long term period 
versus the 12z and 18z model runs. 


&& 


Aviation /06z Saturday through Wednesday/... 
as of 2 am Saturday... 


Scattered light rain will continue to move northeast through the 
eastern Piedmont... sandhills and northern coastal plain through 
the overnight hours... this could lead to a period of MVFR 
conditions... otherwise VFR conditions with cloud bases at 5 to 6 
thousand feet with higher clouds above. Residual moisture will 
lead to a chance of MVFR visibility in fog 09-13z. 


Moisture increases over the area during the afternoon with precipitation 
water approaching 2 inches... k's in excess of 30... totals 
approaching 45 and cape 1500 to about 2500 j/kg... thus we can 
expect another round of thunderstorms during the afternoon into the 
evening. Tempo groups added from 19-03z. Outside of convection 
VFR conditions should persist. 


The chance for unsettled weather will continue into the beginning of 
the upcoming week with at least scattered afternoon and evening 
showers and thunderstorms expected. 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...djf 
near term...djf 
short term...djf 
long term...djf 
aviation...rhj 

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