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Area forecast discussion 
National Weather Service Blacksburg Virginia
952 PM EDT Friday Jul 31 2015

high pressure will build east into the middle Atlantic region tonight.
This high center will stay over most of region this weekend. A
couple of upper disturbances may bring a few spotty showers to the
mountains late Saturday or Sunday...but the majority of our area
will stay dry.


Near term /through Saturday/...
as of 950 PM EDT Friday...

High pressure centered over Missouri will build east tonight into
Saturday. Satellite images showed a clear sky across the region.

Tonight the flow starts to back to the west as a weak upper
shortwave pivots under the broad trough across the middle Atlantic
region. Airmass is too dry to generate anything more than clouds.

The combination of light winds and some low level moisture may
produce patchy fog in the favored valleys. Leaned towards the
cooler MOS coop guidance for low temperatures tonight. Low
temperatures tonight into Saturday morning will range from around
50 degrees in the coldest deeper valleys to the lower 60s in the

High pressure will bring lower humidity again Saturday. Abundant
sunshine and light downslope wind flow will warm high temperatures
Saturday into the upper 70s in the northwest mountains to the lower


Short term /Saturday night through Monday night/...
as of 335 PM EDT Friday...

Broad upper trough will remain anchored from the James Bay area
south into the upper and lower Great Lakes Saturday night into
Monday morning...with weak surface high pressure system lingering
over the middle appalachian region.

This setup will ensure a continuation of dry weather and
relatively low dew points that will support efficient daytime
heating...with good radiational cooling at night...resulting in
marked diurnal temperature swings of around 30f.

By Monday afternoon into Monday night...approach and eventual
passage of an upstream shortwave trough diving southeast through/out
of the upper Great Lakes will bring an increase in clouds along
with a threat for widely scattered showers/thundershowers into
upslope areas of the western Blue Ridge north into the Alleghany
Highlands. However...westerly low level flow ahead of the wave should
prevent any potential for spill-over into downslope areas east of
the Blue Ridge.


Long term /Tuesday through Friday/...
as of 335 PM EDT Friday...

Energy associated with Great Lakes trough expected to be northeast of
the Blacksburg forecast area by daybreak Tuesday. Attendant cool
front will likely slow and then stall over/near the middle
appalachian and middle Atlantic region later Tuesday into Tuesday
night as trough spoke lifts northeast and away from area and as upper
flow in its wake gradually flattens to more of a zonal

East-west baroclinic zone will then become established over the
forecast area for the rest of the long-term period...with
additional upstream short waves and/or mesoscale vorticity centers
from decaying old Midwest convective complexes providing
sufficient energy/support to maintain threat for scattered
convection through the period.

Gradually rising dew points will slowly compress the diurnal
temperature curve back to around 20f as sultry airmass slowly
reestablishes itself over the area. Expect overnight lows during
the period to range from the 60s in the mountains to around 70 in
the Piedmont...with highs ranging from mainly 80s in the mountains
to Lower-Middle 90s across the Piedmont.


Aviation /02z Saturday through Wednesday/...
as of 132 PM EDT Friday...

VFR conditions expected for most areas through 00z-00z 8pm-8pm taf
time period. The exception to this rule will be some brief...late
night/early morning patchy river or Mountain Valley fog. Any that
does develop will quickly mix out by 13z/9am Saturday.

High confidence in ceilings...visibilities and winds during the
taf period.

Extended aviation forecast...
as of 132 PM EDT Friday...

Mainly VFR this weekend with high pressure in place. A few upper
disturbances may bring a few VFR ceilings to the mountains later
Saturday into Sunday. The threat of showers will be low though a
backdoor front may allow for some again later Monday or Tuesday.
With sustained winds staying light to calm at night and mainly
clear skies...the fog threat will exist in the typical predawn
hours at klwb/kbcb by early next week.


Rnk watches/warnings/advisories...


near term...ams/kk
short term...wert
long term...wert

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