Weather

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fxus62 kgsp 281833 
afdgsp 


Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
233 PM EDT Thursday Aug 28 2008 


Synopsis... 
a weak frontal boundary will slowly approach the forecast area from 
the northwest through the first part of the weekend. On 
Sunday...high pressure will begin to build along the eastern 
Seaboard...then remain in place through the middle of next week. 


&& 


Near term /through Friday/... 
weak and ill defined surface low pressure center over the Carolinas 
may finally wash out overnight...but weak upper level low will 
remain overhead through Friday. As such...there really will not be 
much in the way of an air mass change for the next 24 hours. Rich 
low level moisture will remain in place with light wind which should 
allow areas of fog to develop after midnight. Kept forecast closer 
to the warmer met guidance for low temperature tonight in light of the high 
dewpoint. On Friday...a weak easterly flow should redevelop which 
will keep the low level moisture in place. Forcing is minimal even 
with the remnant of the upper low overhead...but there should be 
enough instability to allow for widely scattered showers...perhaps 
more near the Blue Ridge. Kept high temperature on the cool side of 
guidance figuring that some of the insolation would go toward 
evaporation of high soil moisture. 


&& 


Short term /Friday night through Sunday/... 
as of 150 PM EDT Thursday...at least isolated convection should 
linger into the evening hours on Friday...as the models indicate 
instability should linger after sunset...and the overall synoptic 
pattern will remain favorable for convection due to a weakness in 
the middle-level ridge. A strong SW trough moving across southeast 
Canada/New England will drive a frontal boundary into the area on 
Saturday. With the lingering weakness in the upper ridge allowing 
for relatively cool middle-level temperatures...and rather high values of 
low-level moisture...respectable instability should develop across 
the area Sat afternoon. At least scattered diurnal convection can be 
expected along the front. We will generally stick to low chance probability of precipitation 
for now...but I wouldn/T be at all surprised if probability of precipitation need to be 
increased in later packages. 


Although the front is expected to be east of the area on Sunday... 
Post-frontal easterly flow will allow for a continued fetch of 
moisture off the Atlantic. This will provide a favorable environment 
for another round of diurnal convection on Sunday...although 
coverage shouldn/T be quite as high as it will be Saturday. 


&& 


Long term /Sunday night through Thursday/... 
as of 215 PM Thursday...overall things look pretty quiet for the 
medium range. The GFS and the European model (ecmwf) are in reasonable agreement for 
the upper pattern over the eastern Continental U.S. With both keeping the area 
under the influence of strong ridge through the end of the forecast 
period. However...they handle the two tropical systems quite 
differently. The European model (ecmwf) take Gustav through the central Gulf Coast 
and wraps it around the large ac centered over the Ohio 
Valley...keeping the effects of Gustav well west of our area. The 
GFS does not allow Gustav to make any northward progress from the 
Gulf Coast instead deflecting it off to the west along the western 
Gulf Coast. With ts Hanna...the GFS fails to depict the storm at all 
while the European model (ecmwf) brings it across the Bahamas and over Cuba by the 
latter part of next week. At any rate...it does not appear at this 
time that either system will have much of an effect on the forecast area 
through Thursday. 


Basically a dry forecast in place through Thursday as the upper ridge 
builds overhead and a surface high dominates the eastern Seaboard. 
Temperatures run close to...if not slightly above climatology norms for early 
September. 


&& 


Aviation /19z Thursday through Tuesday/... 
weak surface low pressure over the southern Appalachians is doing its 
best to hold a low cloud bank over the Blue Ridge/foothills of NC. 
In these situations...without significant downslope or mixing of dry 
air from above...we have to wait for the sun to melt away the clouds 
from the edge...which means that khky is usually the last to break 
out. Even if that does happen by late afternoon...the low clouds 
will tend to fill back in sometime later in the evening. In the mean 
time...there remains considerable low level moisture across the 
area...which should allow new convective clouds to form in areas 
that manage to break out. Temperature/dewpt spreads suggest cloud bases 
somewhere near the upper end of MVFR...so that will be included 
until the time of maximum heating...afterward a VFR ceiling is included 
at least temporarily. See no reason to doubt guidance with fog 
formation late tonight...given the dry air aloft and low level 
moisture with a very light wind. The visibility could be IFR in many 
spots...but will be limited to MVFR for now except at kavl. The 
clouds/fog should have an easier time burning off Friday morning 
without the weak low present...so look for an earlier transition to 
VFR. 


Outlook...early morning fog/stratus is possible the next few days 
which would mean periodic conditions MVFR or worse mainly centered 
around daybreak...with slight to low chance of mainly diurnal 
convection each day through Monday. 


&& 


Gsp watches/warnings/advisories... 
Georgia...none. 
NC...none. 
SC...none. 


&& 


$$ 
Synopsis...bsh 
near term...PM 
short term...jdl 
long term...bsh 
aviation...PM