Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 281914

Area Forecast Discussion
National Weather Service Blacksburg VA
314 PM EDT Tue Mar 28 2017

A cold front will slide east across the region early this
evening before exiting offshore overnight. High pressure then works
in from the north later tonight into Thursday behind the front.
Another storm system moves in from the southwest with showers
and storms by the end of the week.

As of 250 PM EDT Tuesday...

Surface cold front remains just west of the mountains this afternoon
with a preceding surface trough heading into eastern sections, in
turn helping to spark overall shallow convection under the exiting
cold pool aloft over far eastern sections attm. Expecting the front
to finally jump east by early this evening as the residual cold pool
exits allowing a somewhat deeper/drier northwest trajectory to
develop after sunset. This should bring an end to most eastern
showers by early this evening followed by a brief period of upslope
clouds/spotty showers mainly northwest sections through early
tonight. Upper heights begin to build in the wake of the front
overnight with surface high pressure slowly starting to nose in from
the north by morning. Thus expecting some clearing espcly Blue Ridge
east overnight with more filling in of low clouds mountains later
tonight. Expect this along with only weak cool advection to keep
lows mostly in the 45-50 range west to low/mid 50s east with some
patchy dense fog around espcly valleys and out east where
heavier rain has occurred.

High to the north will slowly evolve into more of a wedge formation
east of the mountains later Wednesday as it builds well to the
north. Expect weak sinking motion along with dry air aloft and weak
northwest flow to initially allow more sun to develop during the
morning before trajectories become a bit more northeast during the
afternoon. This may set up a weak convergence zone just east of the
mountains where clouds may fill in with heating during the afternoon
so boosting clouds a bit. Cant totally rule out a sprinkle or light
shower as well but too iffy to include much mention at this point.
Otherwise temps dependent upon the amount of insolation before
clouds reform so stayed on the low end of Mos which gives 60s
mountains to lower 70s southeast.

As of 300 PM EDT Tuesday...

Surface high pressure over southeastern Canada will wedge south down
the east coast Wednesday night. This wedge is relatively shallow,
roughly 2kft feet thick, and will remain mainly along and east of
the Blue Ridge into Friday morning. This wedge may bleed just west
of the Blue Ridge, into the New River Valley and Alleghany Highlands
Wednesday night but will likely erode during the day Thursday.
Stratus clouds will accompany this wedge and as the flow becomes
southeasterly Thursday morning, light rain/drizzle/fog is possible
across eastern slopes of the North Carolina High Country and Grayson
Highlands. Southeasterly flow is expected along the south-central
Virginia Blue Ridge going into the afternoon and evening to spread
light precipitation northward.

A once strong low pressure system coming out of the Rockies early
this week will track slowly eastward over the Midwest. A weak short
wave ejected out ahead of this low will increase rainfall rates
across the mountains Thursday evening. This wave will likely erode
any wedge environment over the mountains. Rain moving east of the
Blue Ridge and over the foothills Thursday night may enhance the
wedge some. However, rain will be relative warm to keep enhancements

The upper level low will open as it tracks over the Ohio-Tenn
Valleys Thursday night. A stronger ejected short wave is expected to
track from the southern Appalachians and along the Blue Ridge Friday
morning. This wave also appears to track along the western wedge
boundary. High rainfall rates and mixing will erode what is left of
the wedge through the day Friday. The upper level trough swings over
the region Friday afternoon and evening pushing heaviest
precipitation east. Some scattered mountain showers are expected
with the passing of the trough/cool pool with all rain ending by

Overnight lows Wednesday night will fall into the mid to upper 40s.
With a wedge in play and light rain forecasted, temperatures
Thursday will only warm into the lower 50s. Areas outside of the
wedge, such as Bluefield and Richlands, could see temperatures in
the lower to mid 60s. Winds remain southeasterly and the atmosphere
saturated. Temperatures may fall some during the evening then rise
through the early morning hours as the wedge erodes. With the
removal of the wedge Friday and despite copious amounts of rain
falling, temperatures should manage to recover into the low to mid
60s by the end of the day.

As of 300 PM EDT Tuesday...

Surface high pressure builds over the region Saturday, however drier
air does not enter the area until Saturday night. Lingering theta-E
ridge will likely result in a good amount of fair weather cumulus
clouds over the area, becoming clear in the evening. Conditions
remain dry into Monday morning, then we wait on the next system
tracking across Texas to the Tennessee Valley Tuesday. Precipitation
pattern may be similar to Thursday-Friday`s event with light rain
over a weak wedge followed by short waves from an upper level
low/trough to our west.

Temperatures Saturday will be near normal with above normal
temperatures Sunday. Temperatures cool down Monday with rain falling
into a wedge. Tuesday will be wet with slightly above normal
temperatures as wedge erodes.

As of 1245 PM EDT Tuesday...

Bands/pockets of showers continue to develop and push east
across the mountains under the upper cold pool aloft seen
passing across the region early this afternoon. Lower cigs and
vsbys within the vicinity of this rainfall will continue to
bring periods of sub-VFR mainly across the mountain locations
through at least mid afternoon, with perhaps some deeper
convection over the east prior to early this evening. Thus
thinking best thunder threat mainly from KROA east to KLYH/KDAN
so keeping in VCTS mention at these spots given isolated nature.
Will also see upslope lower cigs redevelop around KBLF late
including patchy dense fog at KBCB/KLWB and perhaps KLYH/KDAN
which could bring periods of MVFR to IFR overnight.

Cold front associated with the upper low will finally work
through the region this evening allowing clearing to develop as
deeper northwest flow develops. However MVFR bkn cigs seem
likely at KBLF this evening into the overnight, and perhaps at
KLWB/KBCB with northwest flow taking shape, and some spillover
of low clouds late.

High pressure slowly builds in from the north on Wednesday with
a low level wedge of cooler air developing east of the mountains.
Should see some drying under the increasing subsidence but also
some uncertainty with the degree of residual cloud cover given
heating and flow turning light northerly. This suggests that
KBLF may stay sub-VFR into Wednesday morning with perhaps low
end VFR cigs possible elsewhere by the end of the valid TAF

Extended Aviation Discussion...

High pressure continues to build in from the north Wednesday
night into Thursday with the next storm system moving in the
Mississippi Valley Thursday night into Friday. A threat for
sub- VFR cigs appears likely as the high wedges southwest Wed
night into Thursday for most sites bringing widespread low cigs
and possible light precip. The highest probability of rain will
be on Friday along with sub- VFR cigs/vsbys with the showers.
Post-frontal northwest flow sub- VFR into Saturday mountains
with gusty northwest winds possible.




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