Winter Weather in Virginia, December 17, 2016

Area Forecast Discussion
National Weather Service Blacksburg VA
1149 PM EST Fri Dec 16 2016

.SYNOPSIS...
Arctic high pressure over the region will shift east and offshore
overnight ahead of a complex low pressure system that will pass
well to the west over the weekend. A warm front associated with
the low will approach the region from the southwest Saturday and
pass to the north Saturday night. A trailing cold front will then
slide east across the area on Sunday, reaching the coast Sunday
night into Monday.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 850 PM EST Friday...

Satellite loops and observations show low level moisture
continuing to slowly edge up from the south as seen via lowering
cloud bases heading across the NC/VA border counties attm. However
soundings and subsequent dewpoints indicate a swath of very dry
air from the surface to 850 mb with humidity levels still below
40-50 percent in most spots. Expect this to continue to delay the
onset of much freezing drizzle or spotty freezing rain until about
midnight, mainly southeast sections where the return axis of low
level moisture under deeper warm advection aloft looks a bit
better. This supported by the latest HRRR which brings a lobe of
light precip into the southeast counties, mainly from MTV to LYH
and points east in the next few hours, while other solutions
including the RAP/HRRRX show much less until late over the
northwest where deeper moisture will reside by daybreak.
Therefore already cut back on pops early on espcly north before
going with mostly chance pops all sections into the early morning
hours which may be generous.

Although the RNK evening sounding remains below freezing aloft,
ongoing very strong warm advection aloft should quickly develop a
larger warm nose above per GSO raob, with this warming reaching
the surface on Saturday. Thus leaving out any snow/sleet mention as
still appears the best chance will be for very low QPF light
icing over the southeast, and far northwest with perhaps only
spotty if any in between. Southwest winds may also be an issue
toward daybreak on the ridges as the inversion lowers and the
depth of the warm air increases. However appears given such a
deep/cold airmass to scour out that will have less chance of
mixing down except over the far west where added a mention to the
HWO into Saturday. Otherwise updated temps to reflect a bit colder
start to initialize but already seeing some slight rises which
should increase overnight with a nondiurnal curve on track.

Previous discussion as of 348 PM EST Friday...

Sprawling high pressure area over eastern Virginia extends a
ridge back from it into the southern Appalachians. Temperatures
remain quite chilly with readings mainly in the 20s, and the low-
level airmass remains extremely dry as seen in current dewpoints
and this morning's 12z RNK/GSO RAOBs. Those conditions will set
the stage for light wintry weather tonight with light ice
accretions producing some impact for our area. Hence, freezing
rain advisories have been issued for most of our counties except
for Smyth and Tazewell in Virginia.

For tonight into early morning Saturday...strong southwesterly
warm advection takes place aloft on 850 mb winds nearing 50 knots,
with 850 mb temperatures pushing above +3C by the time
precipitation starts and will only continue to rise aloft as the
overnight and early morning progresses. Via the top- down
methodology, +3C is usually sufficient to fully melt any light
precipitation that falls, but will only re-freeze in the shallow
cold air (temps in the 20s to around 30). I stuck mainly with the
GFS thermal profiles. Given how dry the airmass is, freezing
rain/freezing drizzle will probably be fairly intermittent and not
steady. In fact icing amounts are barely a couple hundreths and
feel in most cases will be a trace; as such, PoPs were kept low.
But the impact will be the same, and that is mainly for slippery
roads and sidewalks overnight tonight. Surface temperatures warm
above freezing earliest in Smyth and Tazewell counties and the
duration of any freezing precipitation is limited. Elsewhere,
surface temperatures project to rise above freezing into the early
Saturday morning hours. After collaboration with surrounding
offices, the freezing rain advisory begins at 7 pm for northwest
NC and the VA foothills and southside, and at 10 pm for the rest
of the advisory area. The overall message, however, is that
precipitation amounts will be very light but should result in
slippery roadways and sidewalks.

Regarding winds...Southwesterly winds stand to increase as well and
should get gusty across the higher summits; but even in these areas
wind speeds should stay below Advisory criteria.

Temperatures tonight are largely non-diurnal and given the
retreating modified Arctic airmass, the low has already been met in
a few places. But lows temps in the 20s will rise to the upper 20s
to low 30s by morning, except mid 30s in the Mountain Empire.

As is typically the case in leftover cold air damming scenarios, the
question becomes for late morning Saturday into Saturday afternoon
on how quickly does the lingering "cool" air get scoured out, which
should have an influence mainly on the high temperature forecast for
Saturday. Given that there isn't rain falling into the airmass and
the strength of southwesterly wind fields, temperatures should warm
into the upper 40s east of the Blue Ridge as the CAD erodes. The 850
mb temps would support higher values but I sided a little on the
colder end of guidance owing to likely persistent overcast. West
of the Blue Ridge, temps should warm into the mid 50s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 348 PM EST Friday...

A sharp upper level trough will push a surface wave across the Ohio
Valley Saturday night to New England on Sunday. The eastward
movement of the front will be slow, stalling across the southern
Ohio Valley into the Tennessee Valley Saturday night, then finally
moving across the southern Appalachains on Sunday. A secondary
surface wave develops along the front Sunday afternoon over the
piedmont of North Carolina. While this wave is forming, the front
and associated showers will stall over the area. By late Sunday
evening, both the front and showers will move out of Southside VA.
Rainfall amounts Sunday will range from a quarter to half /0.25-
0.50/ of an inch. The front will continue to move slowly to the
coast Sunday night and Monday. High pressure will follow the front,
then remains over the region through the better part of next week.

We can expect a wide range in temperatures Sunday with cold air
banked up against the western slopes of SE WV/SW WV while the east
remains in the warm sector. Temperatures will range from the lower
40s across the Greenbrier Valley to near 60F in Southside VA. With
the cold front south of the forecast area Monday, high temperatures
will be 10F cooler than normal ranging between 30F to 40F.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 348 PM EST Friday...

High pressure remain over the region into Wednesday night.
Temperatures will moderate each day with Monday being 10F below
normal and around 5F above by Wednesday. The northern and southern
jet streams remains out of phase with most of next week being warmer
than normal and dry. The next chance for widespread rain may not
come until next weekend.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
As of 1140 PM EST Friday...

Cloud bases will continue to lower overnight, reaching overall
MVFR levels after midnight, and perhaps areas of IFR across
southern sections including the Blue Ridge during the early
morning hours. This in response to deepening warm advection aloft
on a very strong southwest jet interacting with increasing
moisture advection. This could also result in spotty freezing rain
or freezing drizzle, mainly around KDAN and across the northwest
near KLWB during the early morning hours. However confidence quite
low given so much dry air in place and model tendency espcly the
Nam in bringing return low level moisture too far west. Thus
trending toward the drier GFS and latest HRRR in only including a
precip mention at the two above sites late for now.

Warming temperatures should allow for any residual freezing
rain/drizzle to transition to a cold rain by mid-morning Saturday,
with only very light icing amounts possible. A period of IFR may
also occur early Saturday espcly at sites along/east of the Blue
Ridge where a lobe of low level moisture will swing up from the
south early on before exiting. However MVFR ceilings will persist
through much of the rest of the TAF period, with possible periods
of VFR along the KBLF-KBCB-KROA corridor where could end up in a
small dry slot between deeper moisture to the northwest, and low
clouds to the south/east. Expect most rainfall to taper off by
afternoon with only spotty showers possible over the northwest for
the most part during Saturday afternoon.

Winds will begin to steadily increase aloft this evening and
eventually near the surface by early Saturday. However the speeds
will increase faster aloft and support a period of potential low
level wind shear after midnight, with the exception of KBLF where
should see enough surface gustiness to preclude any LLWS mention.
Surface winds begin light southeast but veer to south and
increase to 5-15 kts by Saturday, with gusts to 30+ kts perhaps
developing at KBLF Saturday morning.

Extended aviation discussion...

Although rainfall will be limited Saturday night ahead of the cold
front approaching from the west, still expecting overall MVFR cigs
overnight with ocnl IFR possible where patchy fog/stratus take
shape.

Deterioriating conditions will occur from west to east on Sunday
as the surface cold front drives east with ana front type precip
trailing the boundary much of the day. This should bring
widespread MVFR/IFR cigs/vsbys to the mountains for most of Sunday
with cigs/vsbys lowering across the east as the rain arrives by
afternoon. The rain may change to a mix or wet snow before ending
across KLWB/KBLF later Sunday with perhaps some of this making out
to the Blue Ridge locations by evening just as the rain ends. MVFR
ceilings and visibilities are likely in the mountains Sunday night
within the post frontal northwest flow regime overnight.

Conditions will improve for Monday through midweek as dry high
pressure builds into the Mid Atlantic region.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Freezing Rain Advisory until 9 AM EST Saturday for VAZ010>020-
     022>024-032>035-043>047-058-059.
NC...Freezing Rain Advisory until 9 AM EST Saturday for NCZ001>006-
     018>020.
WV...Freezing Rain Advisory until 9 AM EST Saturday for WVZ042>044-
     507-508.

&&

SYNOPSIS...AL/JH
NEAR TERM...AL/JH
SHORT TERM...RCS
LONG TERM...RCS
AVIATION...AL/AMS/JH

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BLACKSBURG VA
1034 PM EST FRI DEC 16 2016

NCZ001>006-018>020-VAZ015>017-032-033-043-044-058-180345-
ASHE-ALLEGHANY NC-SURRY-STOKES-ROCKINGHAM-CASWELL-WATAUGA-WILKES-
YADKIN-GRAYSON-CARROLL-FLOYD-PATRICK-FRANKLIN-HENRY-PITTSYLVANIA-
HALIFAX-
1034 PM EST FRI DEC 16 2016

...FREEZING RAIN ADVISORY IN EFFECT UNTIL 9 AM EST SATURDAY...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL NORTH
CAROLINA...NORTHWEST NORTH CAROLINA...SOUTH CENTRAL
VIRGINIA...SOUTHWEST VIRGINIA AND WEST CENTRAL VIRGINIA.

.DAY ONE...TONIGHT.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FREEZING RAIN ADVISORY.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FREEZING RAIN ADVISORY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

VAZ010>014-018>020-022>024-034-035-045>047-059-WVZ044-507-180345-
BLAND-GILES-WYTHE-PULASKI-MONTGOMERY-CRAIG-ALLEGHANY VA-BATH-ROANOKE-
BOTETOURT-ROCKBRIDGE-BEDFORD-AMHERST-CAMPBELL-APPOMATTOX-BUCKINGHAM-
CHARLOTTE-MONROE-EASTERN GREENBRIER-
1034 PM EST FRI DEC 16 2016

...FREEZING RAIN ADVISORY IN EFFECT UNTIL 9 AM EST SATURDAY...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL VIRGINIA...SOUTH
CENTRAL VIRGINIA...SOUTHWEST VIRGINIA...WEST CENTRAL VIRGINIA AND
SOUTHEAST WEST VIRGINIA.

.DAY ONE...TONIGHT.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FREEZING RAIN ADVISORY.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FREEZING RAIN ADVISORY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

VAZ007-009-180345-
TAZEWELL-SMYTH-
1034 PM EST FRI DEC 16 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWEST VIRGINIA.

.DAY ONE...TONIGHT.

PATCHY FREEZING RAIN OR FREEZING DRIZZLE COULD LEAD TO SPOTTY
LIGHT ICING ON ELEVATED SURFACES LATE TONIGHT. IN
ADDITION...SOUTHERLY WINDS COULD GUST TO AROUND 45 MPH ALONG THE
HIGHER RIDGES OVERNIGHT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

SOUTHERLY WINDS COULD GUST TO 45 MPH ALONG THE RIDGES ON SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

WVZ042-043-508-180345-
MERCER-SUMMERS-WESTERN GREENBRIER-
1034 PM EST FRI DEC 16 2016

...FREEZING RAIN ADVISORY IN EFFECT UNTIL 9 AM EST SATURDAY...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST WEST VIRGINIA.

.DAY ONE...TONIGHT.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FREEZING RAIN ADVISORY.

IN ADDITION...SOUTHERLY WINDS COULD GUST TO AROUND 45 MPH ALONG
THE HIGHER RIDGES OVERNIGHT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FREEZING RAIN ADVISORY.

SOUTH TO SOUTHWEST WINDS COULD CONTINUE TO GUST TO AROUND 45 MPH
ALONG THE HIGHER RIDGES THROUGH MIDDAY SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.