Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 101132
Area Forecast Discussion
National Weather Service Blacksburg VA
632 AM EST Sat Dec 10 2016
High pressure will build east across the Mid-Atlantic region
today before sliding to the coast tonight and then offshore on
Sunday. The associated cold airmass will remain over the area
through early Sunday before moderating. A cold front will approach
the region late Sunday night before working east through the area
later Monday into Monday night.
.NEAR TERM /THROUGH TONIGHT/...
As of 245 AM EST Saturday...
Overall mainly a temperature forecast today into tonight as surface
high pressure slides overhead this afternoon and to the coast overnight.
Lingering upper trough along with passing weak shortwave energy may act
to keep upslope low clouds/flurries across the far west this morning
before drying and weakening westerly flow helps diminish clouds this
afternoon. However 850 temperatures will be slow to warm in the wake of
another impulse aloft, with most guidance now giving only 20s to lower
30s mountains, with somewhat warmer upper 30s/low 40s east per weak
downslope. Some high clouds could also mix in and with the low sun
angle suspect the colder side of guidance best. Thus lowered highs a
little espcly west closer to the latest Euro Mos. Otherwise mainly
sunny but still cold under diminishing winds.
Warm advection aloft will develop behind the exiting ridge overnight
with the main axis of lift taking shape to the northwest along a weak
warm front aloft and within strong upper zonal flow. Appears most of
this deep moisture will stay to the north with the upper jet helping to
shear an axis of mid/high clouds eastward across mainly the northern
half of the region through daybreak per most model humidity fields.
However southward extent and thickness of the canopy to likely
play into how low temps could go given residual very dry dewpoints
in place. Think also likely to see some spots plummet early on
before steadying out under the clouds and at elevation where
return southwest flow will start to mix down late. Therefore
running on the colder side of Mos valleys and southern sections
per better radiational cooling while leaning a bit warmer north
but still teens to low/mid 20s under intervals of clouds at this
.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
As of 433 AM EST Saturday...
Broad surface anticyclone across the eastern seaboard, with
ridging extending back westward to the Alleghany Mountains early
Sunday, in a low-amplitude quasi-zonal mid-level flow regime.
Ridging gradually shifts eastward into early Sunday evening. The
daytime hours stand to be mostly sunny with veered/southerly
return allowing for 850 mb temps to rise to -1 to +2C, supporting
highs in the upper 30s to mid/upper 40s.
Our weather then turns more active Sunday night and into a good
part of Monday as a cold front moves across the region, associated
with a developing winter storm affecting the northeast US. Strength
of warm advection increases markedly Sunday night ahead of the
cold front as low- level southwest flow increases to near 50 kts.
Strongly non-diurnal temperature trend with a brief period of
radiational cooling where lows in the 30s are more likely to
occur. Surface temperatures then stand to steadily rise through
most of the overnight hours. Most of the global models and the NAM
bring in some light QPF overnight Sunday; further inspection of
BUFKIT soundings off the GFS/NAM reveal an unsaturated cloud- ice
layer with all the RH in the -3 or warmer isothermal level. Via
the top-down methodology, feel that any precip into the overnight
is largely drizzle. A brief period of patchy freezing drizzle and
potential for slippery roads/sidewalks are possible where surface
temperatures are initially near or below freezing, particularly in
the Alleghany Highlands and in the elevated terrain in the
southern New River Valley and the VA/NC border on I-77. But
temperatures should warm above freezing rather quickly so the
period of freezing drizzle is limited. As the column saturates we
should see steady light to at times moderate rain associated with
the front`s passage Monday with PoPs in the Categorical range
before PoPs diminish down to slight chance behind the front Monday
night. QPF amounts range from about a quarter to a half inch.
Mondays highs should be well into the 40s to mid/upper 50s highest
out in the Virginia piedmont and southside areas.
For Tuesday, there`s some sizable differences apparent between
the GFS and ECMWF as far as how far south the baroclinic zone
associated with the cold front`s trailing edge makes it into
North Carolina. The ECMWF pushes the front barely into the central
NC piedmont and western mountains and would allow for some precip
to overrun the frontal zone later Tuesday; while the GFS advances
the front southward further enough to keep our area dry. Since the
east-west front will essentially parallel the mid-level flow
aloft, thinking closer to the slower ECMWF idea and maintained
idea of Chance-level PoPs for mainly light rain Tuesday (mixing
with wet snow in the Alleghany Highlands into Tuesday night). I
also chose to keep highs cooler Tuesday than otherwise with more
cloud cover - in the 40s with lows in the 30s. If the GFS proves
correct, highs could be a few degrees warmer and lows cooler.
.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 433 AM EST Saturday...
Strong isentropic lift will develop over an in-situ wedge as a complex
low approaches from the southwest. There may be some p-type issues at
the higher elevations with the initial surge of warm air advection
into the first part of Wednesday. However, a significant surge of
cold air will start moving in during the day Wednesday behind the
departing low and transition precipitation to snow, especially in
upslope areas west of the Blue Ridge. There may also be some
freezing issues as the cold air arrives on blustery winds and
interacts with wet surfaces Wednesday night. Lingering snow
showers west of the Ridge will dissipate as cold high pressure
builds in through the end of the workweek.
Temperatures will generally exhibit a cooling trend for most of next
week with highs on Tuesday well above normal, falling to well below
normal by Thursday.
.AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 1132 PM EST Friday...
Upslope cloudiness should keep KBLF/KLWB and perhaps KBCB in MVFR
to ocnl IFR at times through about mid morning before clouds
diminish. Otherwise once the clouds fade, expecting widespread VFR
through the period with high pressure building in from the west
into this evening. Swath of mid/high clouds likely to skirt across
central and northern sections overnight but still should see cigs
remain above 8-10K feet into Sunday.
Extended aviation discussion...
Next weather system to follow will be a cold front, models
suggesting a Sunday Night arrival which will likely produce sub-
VFR conditions at times, and possibly wintry mix in the mountains.
The cold front crosses the area Monday with continued threat of
showers and sub-VFR at times, then somewhat of a break Monday
night and maybe Tuesday, with another system arriving midweek
with more precip, and more than likely sub-VFR at times.
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