886 
fxus61 krnk 120444 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
1144 PM EST Thursday Mar 11 2010 


Synopsis... 
complex low pressure system over the eastern U.S. Will affect our area 
the next few days...bringing periods of showers and possibly 
thunderstorms. 


&& 


Near term /through Friday/... 
main axis of heavier rain with embedded convective elements 
continues to slide slowly NE across the eastern/northern portions 
of the County Warning Area this evening. With much of the heaviest rainfall 
remaining confined to areas along/east of the Blue Ridge where ffg 
is higher not expecting much of a flood threat. However have seen 
totals of nearly three quarters of an inch near/east of the Blue 
Ridge with overall a quarter inch or less elswhere although rates 
mainly less than .40/hour. Infrared pics continue to show the back edge 
of the deeper colder cloud tops shifting east ahead of the middle 
level dry punch leaving low clouds and very -ra over the SW at this time. 
Latest NAM and espcly the local WRF seem to have a good handle on 
the current precipitation coverage and gradually shift the best corridor 
of signficant lift into the NE zones by midnight where it lingers 
until about daybreak to some degree. Thus keeping highest Cat probability of precipitation 
NE third overnight with tapering of coverage to more -dz as relative humidity 
Shallows and the low level flow turns more easterly. This in 
conjunction with very saturated 00z radiosonde observations and light upslope southeast 
flow suggests the likelihood of pretty widespread dz/fog as the 
rain ends so beefed up coverage espcly after midnight. Expect 
temperatures to only drop a few more degrees at most given saturation so 
bumped up a Cat or so in spots mainly southeast where lows 55-60. Otherwise 
lows upper 40s to middle 50s. 


Previous discussion below... 


Expecting a period of rain showers this evening and overnight as southeast 
flow in the low levels persists as low pressure wave movess along the 
SC coast. Rainfall amounts are not expected to be an issue...but 
could see up to a quarter inch along the Blue Ridge and points 
east...with less in the west. Friday will see the area wedged in 
across the northeast with a warm front moving north into NC by 
afternoon. A triple point expected to move over the Tennessee Valley into 
SW Virginia by late in the day. This will be a Focal Point for 
thunderstorm development ahead of the upper low in the middle 
Mississippi Valley. At this time...think there will be a lull in rainfall 
Friday morning...except in the east as the winds remain off the 
Atlantic in the moist easterly flow keeping showers around...but 
nothing in the moderate to heavy range. 


Temperatures will be mild tonight with cloud cover and rain showers. 
Fog will form as the rain tapers off overnight...and could see some 
dense fog if we clear enough...but not anticipating that 
at this time...except possibly over the Blue Ridge. 


Friday...temperatures are tricky and will depend on if sunshine breaks out. 
Seems that in the northern County Warning Area...insitu cad holds longer...but will keep 
highs close to mav guidance. 


As for Hydro concerns...will remain with a Flood Watch as is...and 
will monitor stream levels in southeast WV and other places as the showers 
move across this evening. Appears the main threat for flooding will 
be after the near term period. 


&& 


Short term /Friday night through Sunday night/... 
the upper level low located in western Iowa is prognosticated to approach 
the area firday night with the heaviest rain falling in the 
overnight hours in the mountain Empire of virignia...south through 
the northern North Carolina mountains. HPC guidance suggests over an 
inch of rain along the southern section of the Blue Ridge and west 
Friday night. This heavy rain will then transition east northeast as 
the upper low moves across the forecast area early Saturday. Lifted 
indices show a range from -2 to 4 across the southern areas. Have 
isolated thunderstorms mention through late evening with rain heavy 
at times. 


As northwest flow begins on the back side of the low...the upslope 
component will kick in. This will allow for precipitation to become 
maximized over southeast West Virginia then tapering off farther 
east. 


Slightly cooler air will advect into the forecast area over the 
weekend dropping low temperatures back into the low to middle 30s. 
However...they should stay above freezing both Saturday and Sunday 
night. This may result in rain mixing with some snow in the higher 
elevations but expect the predominant precipitation will be rain. 


Maximum temperatures will range in the upper 40s west to lower 60s east 
through the weekend. 


&& 


Long term /Monday through Thursday/... 
for the medium range leaned towards hpcguide which favored the European model (ecmwf) 
over the slower UKMET...GFS and Canadian. 


A large area of low pressure off the East Coast will continue to 
move northeast into the Atlantic Ocean Monday. As the storm moves 
away...northwest flow with upslope rain/snow showers in the west 
will continue Monday into Tuesday. A vorticity lobe will rotate around 
the main low and enhance upslope component on Monday. Then...it 
appears that the available moisture starts to thin around 12z 
Tuesday. High pressure will build across our area from the Ohio 
Valley Tuesday night into Thursday. In general...kept temperatures 
on the cooler side early next week then moderate a little by the end 
of the week. 


&& 


Aviation /06z Friday through Tuesday/... 
clusters of light to moderate showers persist mainly just east of 
the Blue Ridge at this time and expect at least a couple more hours before 
things taper off during the early morning hours. However some 
potential for an axis of rain showers to persist across the NE as low pressure 
along the coast links into the relative humidity axis. Even as the precipitation 
tapers...high confidence of seeing ceilings and visibilities lower further 
with widespread IFR/occasional LIFR after midnight aided by deepening 
easterly flow into the developing wedge. This should also help 
prompt widespread drizzle and fog overnight with these very poor 
flying conditions under IFR conditions possibly hanging across 
most locations into Friday afternoon per saturated BUFKIT radiosonde observations. 
Kblf on the western periphery of The Wedge may break out into MVFR 
pending the strength of the southeast flow into the area. 


There is moderate to high confidence of showers and isolated 
thunderstorms moving in from the SW by Friday evening...or at 
least a band of low topped/elevated heavier rain showers moving overtop 
The Wedge during the night. This should keep ceilings and visibilities in the 
IFR to MVFR range into Friday night although ceilings may improve at 
times if the more convective nature precipitation can mix out some of the 
lower ceilings. The heavy showers should end Saturday morning with a 
return to MVFR/VFR conditions expected...however scattered 
convective showers are likely Saturday through Sunday...with 
ceilings and visibilities falling back into the MVFR/IFR range 
during these showers. Looks like low clouds and spotty -ra may 
keep at least MVFR conditions going into Monday with some slow 
improvement to VFR on Tuesday. 


&& 


Hydrology... 
continuing to monitor the possibility of flooding due to combined 
snow melt/heavy rainfall scenario late this week. Main heavy rain 
threat will be coming in Friday evening into Saturday morning with 
thunderstorms potentially bringing a higher rainfall rate into the 
mountains. Potential exists for isolated flash flooding if the 
thunderstorms are slow moving...but not expect that to be the case. 


Still looks like river flooding is possible along the Greenbrier 
River this weekend...and over the upper James basin. 


&& 


Rnk watches/warnings/advisories... 
Virginia...none. 
NC...none. 
WV...Flood Watch through Saturday afternoon for wvz043>045. 


&& 


$$ 
Synopsis...ams/wp 
near term...jh/wp 
short term...reb 
long term...kk 
aviation...ams/jh/mc 
hydrology... 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)