Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 250730

Area Forecast Discussion
National Weather Service Blacksburg VA
230 AM EST Sat Nov 25 2017

High pressure will give way to a cold front that will cross the
region from the west later today into this evening. High pressure
follows the front overnight and should remain in control of our
weather for much of next week. The potential exists for another
cold front to cross the area by Friday.

As of 230 AM EST Saturday...

Fast upper split flow will continue across the region with the next
in a series of 500 mb trofs crossing the area this evening and
overnight. This will propel the next mainly dry cold front through
the region later today followed by another quick surge of colder air
into the overnight hours. Models show some increase in moisture
ahead of the boundary by this afternoon but lack much lift within
the warm but overall dry column. May see a sprinkle or light shower
just ahead of the front across the far west but appears most showers
if any will be mainly post frontal upslope aided over the northwest
into tonight. Thus based on guidance consensus have trimmed back
pops over the west today to mainly isolated and basically across the
southeast West Va counties for a rain to snow shower mix overnight.
Hard to see much coverage going east of the mountains per strong
westerly downslope so leaving elsewhere dry with mainly increasing
clouds today.

Will be mild for late November and turning breezy given warm
advection ahead of the front today. Degree of cloudiness the key in
just how warm readings might go espcly east but appears low/mid 60s
east and 55-60 west. Post frontal 850 mb northwest jet to kick in
overnight behind the front with decent pressure rises on top of a
lowering inversion. This should allow for gusty surface northwest
winds as the axis of cold advection works into the mountains before
stalling. Latest Bufkit/local scheme numbers remain below advisory
levels so overall a blustery/colder overnight with a few mountain
flurries/snow showers possible with clearing skies out east. Did
bump up lows given weak cold advection and mixing which should keep
most in the 30s if not around 40 Piedmont.

As of 210 AM EST Friday...

Sunday morning the few remaining upslope clouds in the far west and
the gusty ridge top winds will both diminish quickly during the
morning for clear skies and only light northwest breezes by
afternoon as the surface high moves into the western Appalachains.
This period is then dominated by dry high pressure with mainly clear
skies, light winds, and significant diurnal temperature swings
similar to the end of Thanksgiving week. Went middle of the road on
guidance Sunday for highs given there is still weak cold advection
going on, but warm side on Monday with high nearly right overhead.
While all guidance has lows Tues morning a few deg warmer than Mon
morning as weak southwest flow aloft brings dew points back up
slightly, am not so sure about this out east given that guidance has
been way too warm under similar conditions with good radiational
cooling. Difference is that dew points may be a little higher by
Monday night compared to these last couple of nights. May still have
to eventually go a little lower for Tues morning lows out east

As of 110 PM EDT Friday...

Operational ECMWF and GFS and the ensembles were in fairly good
agreement with the overall pattern Tuesday and Wednesday. Pattern
remains progressive and weak upper ridging moves across the central
and eastern United States. Seeing typical bias with the slower ECMWF
and faster GFS with a closed low that moves out of the Pacific and
into the southwest United States by Tuesday. Bases more on the ECMWF
timing this feature will reach the Mid Atlantic region around
Thursday. Bigger spread in the guidance for the timing and location
of synoptic features on Thursday and Friday.

Warm air advection and west surface to low level wind on Tuesday so
maximum temperatures will be near or slightly above normal depending
on cloud cover.

As of 1230 AM EST Saturday...

VFR conditions with just high clouds all sites through this
morning. A weak cold front will move through the region late
today. A sprinkle is not out of the question at BLF and LWB with
upslope just behind the front this afternoon into tonight, with
at least a brief period of MVFR ceilings most likely at BLF.
All other TAF sites will remain VFR and dry. Primary impact of
this front will be to increase west to northwest winds behind it
with gusts 15-20 kts and even higher over ridges. These winds
will slowly begin to weaken overnight.

Extended Discussion...

VFR conditions continue into much of next week with high
pressure building back in from Sunday through mid week. The
next potential chance for sub-VFR conditions is not until late
Thursday at the earliest.




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