398 
fxus61 krnk 301053 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
653 am EDT Sat Aug 30 2008 


Synopsis... 
a weak cold front will approach the area from the north late this 
afternoon...and then move slowly through the area tonight. By 
Sunday night...strong high pressure will be building down the East 
Coast bringing drier and cooler air into the region Monday and 
Tuesday. 


&& 


Near term /through tonight/... 
weak high pressure remains over the forecast area...with a weak 
cold front west of the mountains in the Ohio Valley...and deeper 
moisture south and east of the area. Dense fog has developed along 
the New River in SW Virginia and southeast WV...so I have included in the 
weather grids through 1000 am. Water vapor shows a weak...nearly 
stationary upper low over SC this morning...with what looks like a wave 
rotating northward towards NC. Thinking is that this weak feature 
may help initiate scattered thunderstorms this afternoon- though most associated with 
the upper low may be southeast of the forecast area. 
Otherwise...there is not much forcing for thunderstorm development this 
afternoon...despite a moderately unstable airmass. Low level southeast 
flow provides some weak convergence along the Blue Ridge early in 
the afternoon...while the appchng fnt will also provide some 
convergence in southeast WV. By late afternoon...models generally show 
scattered convection across the County Warning Area. With little or no forcing to 
focus on...I have put in low chance probability of precipitation across the County Warning Area. For high 
temperatures...I have undercut mav MOS guidance as it has been too 
warm...and I expect a bit more clouds this afternoon along with 
the southeast flow to hold highs down some. 


Heading into tonight...model soundings show enough instability 
that showers/thunderstorms could keep going well into the evening. With 
the weak surface fnt finally moving into the area overnight as 
well...I thought it a good idea to keep some chance probability of precipitation along and 
east of the Blue Ridge in the deeper moisture through 06z. I taper 
off the probability of precipitation west to east toward morning. Overnight lows will 
likely be higher than MOS guidance with plenty of clouds- 
especially along and east of the Blue Ridge...so I used MOS 
guidance and then raised them a few degrees. 


&& 


Short term /Sunday through Sunday night/... 
cold front should be south of the County Warning Area by Sunday morning...but both 
NAM and GFS show plenty of low level moisture in the northeast to 
east flow during the day Sunday- particularly in the southern County Warning Area. Model 
soundings show enough instability in the afternoon for a few 
showers or thunderstorms to develop. Best chance should be along the Blue 
Ridge in the easterly flow...and in the deeper moisture in the southern 
County Warning Area...so I have chance probability of precipitation along the Blue Ridge in far SW Virginia and northwest 
NC with slight chance elsewhere. High temperatures Sunday will be tricky 
depending on the amount of sky cover. Models generally are too 
warm in the east with a strong high pressure ridging down the East 
Coast...so I undercut MOS a few degrees in the east and stayed 
close to MOS elsewhere. By Sunday night...the low level flow is 
more east to southeast...and it is a good pattern for a lot of 
clouds and light precipitation along the Blue Ridge. However...guidance 
probability of precipitation are very low...so I have just added in slight chance probability of precipitation with a 
narrow band of low chance probability of precipitation along the Blue Ridge in SW Virginia and northwest 
NC for now. Stayed close to MOS lows Sunday night. 


&& 


Long term /Monday through Friday/... 
upper ridge will build over the Great Lakes and spill 
southeast...allowing heat to build over parts of the Ohio Valley. 
A wedge develops on Monday...but models are rather dry with it. 
However...both the NAM/GFS are cranking a little quantitative precipitation forecast early 
Monday...if this verifies it will be cloudy and cooler along the 
Blue Ridge than current forecast suggests. Something to Ponder 
with future packages. Models typically do a poor job with such a 
thin layer of higher relative humidity close to the ground this far 
out...especially with a few disturbances arriving off the coastal 
plain. 850 mb adjustment with +14c and a good east wind under at 
least partly cloudy skies would suggest the cooler met numbers are 
best. No changes after day 3. 


&& 


Aviation /12z Saturday through Wednesday/... 
light fog and stratus is scattered across the area early this 
morning...but does not appear to be very thick. Only locations 
right along the New River seem to have dense fog. Most of the 
stratus extends from the Roanoke and southern Shenandoah valleys 
eastward into the lyh/Appomattox areas. Think the startus and fog 
will lift most places by 14z. 


Weak cold front currently across the Ohio Valley early this 
morning has made little eastward progress. Northern section of the 
front will sag southward rest of today...and the front will be 
appchng northern sections of the County Warning Area this afternoon. Is looking like 
the best chance for showers/thunderstorms will be in the lwb area...but I 
am expecting scattered convection to develop across the County Warning Area...so I 
have included a vicinity shower period at Alabama taf sites. If storms 
develop...they will be slow movers and could cause restrictions as 
low as IFR. 


Overnight...looks like goo conditions again for fog/stratus 
development as drier air behind the front does not move in until 
later Sunday. Fog formation will depend the most on sky cover. 
Feel like western areas will see the least sky cover...so I put 
fog in at blf...and took lwb down to LIFR after 08z. 


Any fog/stratus that develops may hang in longer on Sunday as 
there will be a light northeast to easterly flow during the day. 
By Sunday afternoon...there may be enough heating for scattered 
showers/tstms- best chance will be from roa southwest along the 
Blue Ridge. Sunday night the flow becomes more east to 
southeast...and with a moist boundary layer...I expect low clouds 
and fog to devleop along and east of the Blue Ridge. This will 
likely affect roa...lyh and possibly Dan. After Sunday night...with 
the exception of Mountain Valley fog during the overnights...VFR 
conditions will prevail Monday and into the middle of next 
week...high pressure building across the middle Atlantic region. 


&& 


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


&& 


$$ 
Synopsis...jj 
near term...jj 
short term...jj 
long term...kk/km 
aviation...jj/km 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)