583 
fxus61 krnk 051150 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
750 am EDT Sat Jul 5 2008 


Synopsis... 
a stationary front is over the area. This front will be the focus 
for showers and thunderstorms through the weekend. High pressure 
will build over the area early next week...followed by another 
front...which will approach the area from the northwest on Wednesday. 


&& 


Near term /through tonight/... 
surface front has stalled just north of the area...blocked by the 
Bermuda high over the western Atlantic. A trough of low pressure 
in the upper levels of the atmosphere was progressing across the 
Great Lake and Ohio Valley. It appears this upper level feature is 
going to deepen today...evolving into a weak closed cutoff low 
over the eastern Ohio Valley. What this suggests is that our weather 
will become unsettled and stay that way through the weekend as 
as moisture gets transported northward around the subtropical 
ridge and into the upper level trough...right over the 
midatlantic region. This is good news...since it will provide the 
area with an opportunity to partake in some much needed rainfall. 
The downside to this is not everybody will get the rain...but the 
folks that do may experience some locally heavy rain. 


Precipitable waters  are forecast to be 1.5 inches or higher through the weekend and 
may eclipse 2.0 inches east of the mountains across the Piedmont 
and into the Tidewater areas. This will increase the rain 
efficiency with potential for several inches of rain underneath 
the thunderstorm cores. With the forecast closed low to our 
northwest...a situation could develop where this upper level 
feature causes thunderstorms to train over the same area...and 
flooding would not be out of the relm of possibility. At this time will 
refrain from any sort of flood headlines per ongoing drought and 
low stream levels. 


Severe weather potential appears limited due to cloud debris which will 
limit solar insolation today. Still not out of the question to get 
some large thunderstorm cores where waterloading results in strong 
downdraft winds. Ill-defined baroclinic zone - stationary front to 
our north may help focus moisture such that storms become 
organized into clusters...but again I think the greater threat 
from all of this will be the heavy rainfall...instead of the wind. 


High temperatures today will depend on how much sun can materialize 
through the considerable cloud cover. That said...see no reason 
to differ from mav MOS. 


&& 


Short term /Sunday through Sunday night/... 
upper level trough will drift ever so slowly across the middle 
Atlantic region. Low level convergence will be best along and east 
of the Blue Ridge to place highest chance probability of precipitation in the Piedmont. 
Dry air intrusion and afternoon heating may produce isolated 
severe storms in southeast WV with the threat being more in the 
way of wind. If everything GOES as planned...the rain and upper 
level trough will be along the East Coast by Monday morning with 
relatively dry air filtering in to the region. 


With a saturated atmosphere...overnight lows will be muggy and above 
normal by 3-5f. Sundays temperature should run about normal with 
clouds and rain in the the area. Areas lucky enough to see breaks in 
the clouds will pop up a few degrees above normal. 


&& 


Long term /Monday through Friday/... 
weak ridging aloft and relatively dry air in the region...chance of 
showers are minimal Monday with an isolated storm popping up in the 
mountains. Monday afternoon into Tuesday night...flow becomes 
southerly bringing hot and humid conditions back into the region. 
Typical scattered diurnal convection can be expected during this 
time. 


Wednesday through Friday forecast will be a challenge and is 
dependant on a cold front moving through the region. Current 
projected day of the frontal passage is Wednesday. However...upper 
level ridge stretched from the Texas Gulf Coast to Bermuda may slow 
down this front and possibly stalling it over the area until 
Thursday or may be Friday. If medium range models are 
correct...frontal convection will start in the mountains Wednesday 
afternoon and move to the Piedmont in the evening. Weak high 
pressure will build into the region for Thursday and Friday. With 
uncertainty in the forecast...will keep probability of precipitation low for now. 


Tropical Storm Bertha may also play a role in the forecast late next 
week/end. All indications should keep this tropical storm tracking east 
of Bermuda. But there is always one outlier model that tracks the 
storm closer to the East Coast to keep an eye on it. The European model (ecmwf) model 
is the outlier and brings the storm west of Bermuda but remains off 
the Carolina coast. Bertha is still in the eastern Atlantic and is 
at least 8-10 day from even threatening the East Coast...if it does 
track that far. 


Temperatures next week will moderate to above normal until the front 
passes. 


&& 


Aviation /12z Saturday through Wednesday/... 
check all active airmets and sigmets for convection...IFR and 
mountain obscurations today. Cluster of showers and thunderstorms 
was moving away from the lyh and Dan airports at 11z. Conditions 
will improve to VFR by 14z. 


Thunderstorms will become more widespread with heating this 
afternoon. In between areas of showers and thunderstorms...ceilings 
and visibilities are likely to be VFR...with some periods of MVFR/IFR in 
the west. 


Tonight and Sunday will also be active with showers and 
thunderstorms as the upper support remain just to our west. A 
drying trend is forecast for Monday and Tuesday...then another 
front will approach increasing the potential for showers 
Wednesday. 


&& 


Rnk watches/warnings/advisories... 
Virginia...none. 
NC...none. 
WV...none. 


&& 


$$ 
Synopsis...PM 
near term...PM 
short term...PM 
long term...rcs 
aviation...ams/PM