Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 051132
Area Forecast Discussion
National Weather Service Blacksburg VA
632 AM EST Mon Dec 5 2016
Upper level shortwave trough which brought light rain to the area
Sunday is moving east and off the coast. Brief clearing today in
the wake of this system will be followed by more rain tonight and
Tuesday as an area of Low pressure moves northeast from the Gulf
of Mexico. After another break in the activity on Wednesday, a
strong cold front will cross the region on Thursday.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 530 AM EST Monday...
Primary focus for wetting rain this morning will be the Tidewater
of VA/NC. Rain has ended...at least for the next 12-18 hours...for
the piedmont and mountains. Rain should also end for the
Tidewater by afternoon with partial clearing all areas today
before clouds reconvene and rain returns tonight and Tuesday.
Lull in precip today is from mid level drying in wake of passage
of an upper level short wave trough. Pooling of low level
moisture will occur along a stationary front which extends from
the Carolina Coast into the northern Gulf of Mexico, this moisture
poised to move back into the forecast area tonight as low pressure
over the western Gulf of Mexico strengthens and moves northeast
along the stationary front. Regional radars indicate widespread
rain is already occuring over southeastern TX and into LA. It is
this area of precipitation that will move northeast today,
reaching North Carolina before midnight...then spreading into the
Virginias after midnight.
Temperatures today will depend on amount of clearing that takes
place. In spite of drying in the mid levels of the atmosphere,
models indicate lingering moisture in both the low levels and
upper levels. The low level moisture is expected to get mixed out
be the brief surge of northwest downslope wind flow today, but
its questionable as to whether the upper level moisture, cirrus
level, will thin enough to permit more than a dim glint of sun.
Per this thinking, went a few degrees below MOS guidance
entertaining highs in the 40s mountains and lower to mid 50s for
areas east of the Blue Ridge.
Bigger temperature question will come into play tonight with
models taking most areas back down into the 30s. A lot will depend
on how much heating we get today and whether clouds will trap any
of that heat permitting slightly warmer readings tonight. Since
some of the models are entertaining the idea of some light wintry
precip for the VA/WV highlands, a 1 or 2 degree temperature
flucuation could make the difference between a cold rain versus
some light sleet/freezing rain for the Shenandoah valley and the
VA/WV Highlands. That said, even if those areas do test 32, any
sleet or ice accretion should be minimal, only adhering to
elevated surfaces as opposed to the ground (ground temps still too
warm to permit travel issues).
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.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
As of 430 AM EST Monday...
Model solutions have been very consistent in handling the upcoming
system for Tuesday. Expect a strong,cold wedge east of the Appalachians
to remain in place as low pressure moves out of the Mississippi delta
with strong isentropic lift and upper dynamic support from the remnant
of a closed low ejecting out of Mexico. This will bring widespread
precipitation to the region through the first part of Tuesday before
starting to taper off during the afternoon. The cold wedge will allow
for some wintry mixed precipitation mainly from Greenbrier WV and the
Alleghany Highlands southward to the higher elevations of the Blue
Ridge, though no significant accumulations of snow or sleet is expected
but a light glaze of ice is possible at the highest elevations.
High pressure will then bring precipitation to an end early Wednesday
before a strong cold front moves through early Thursday. There is not a
lot of moisture with the front so will confine any higher POPs to
upslope areas west of the Blue Ridge, and a plume ahead of the front
may generate some precipitation east of the Ridge as well. Colder air
will then rapidly move in behind the front and change precipitation
over to snow showers for upslope areas before tapering off. Any
accumulations will be quite light. Winds will also become blustery as
temperatures plummet, creating wind chills down to the single digits
west of the Ridge with teens to the east.
.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 430 PM EST Monday...
Will turn windy and much colder Friday although appears speeds still
below advisory levels with wind chills zero/single digits. Arctic
high finally builds overhead by Saturday allowing for the coldest
temps by early morning before the trough starts to lift out
allowing some moderation Saturday afternoon into Sunday in
response to return warm advection. Next weak system coming out of
the Rockies may tap enough return moisture to bring a band of
light mix to the far west by late Sunday. However without much
southern connection appears precip limited given residual dry air
and could be just clouds and spotty rain if things slow up more so
only low pops for now Sunday.
Expect highs only in the 20s mountains to 30s east under a blustery
northwest wind Friday. Lows Friday night mostly teens unless high
clouds invade more late, then warming to highs in the 30s and 40s
for the weekend.
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
As of 600 AM EST Monday...
brief drying today before rain returns tonight and tuesday.
Northern stream short wave responsible for the light rain
last night is moving east and off the coast this morning.
low cigs will linger this morning, but improve to vfr for this
Moisture will quickly return tonight. Low pressure over the
western Gulf of Mexico is progged to move northeast, rain
overspreading the region from southwest to northeast during the
overnight, reaching western NC before midnight, then into the
Virginias after midnight...and associated with widespread IFR VSBY
Winds today become northwest 5-10kts, then become light northeast
after 21Z/4PM, before increasing again during the overnight from
the southeast as the storm system approaches from the southwest.
Extended aviation discussion... Rain associated with IFR/LIFR
conditions Tuesday will be followed by partial clearing Wednesday.
This break in the weather will be followed by a cold front
Thursday, this front bringing a surge of cold air. Look for a
return of sub-VFR conditions, this time associated with snow
showers across the mountains Thursday night into early Friday.
Friday, expect a gusty day across the region with lingering
upslope cloud and snow showers between KBLF-KLWB. East of the Blue
Ridge, VFR is expected.
As of 1200 AM EST Monday...
NOAA Weather Radio, All Hazards, WZ2500 in Wythe County continues
to be off the air. Technicians will be examining the system
tomorrow to explore a possible power failure.
NOAA Weather Radio, All Hazards, WX2543 in Tazewell County went
off the air around 915 PM EST Sunday evening. The problem appears
to be related to a phone line and the telephone company has been
notified. Repair is unlikely before mid-morning Monday.