Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 110000
Area Forecast Discussion
National Weather Service Blacksburg VA
700 PM EST Tue Jan 10 2017
Low pressure will deepen and move northeast into the Great Lakes
tonight as high pressure moves off the southeast coast. A warm front
will lift north across the region tonight into Wednesday. Another
low will form in the Rockies on Wednesday which will track northeast
through Thursday. This will result in milder temperatures and
occasional rain for our area through the end of the week.
.NEAR TERM /THROUGH WEDNESDAY/...
-- Changed Discussion --As of 657 PM EST Tuesday...Freezing rain advisory for light ice
accretion and slippery road/sidewalks for eastern Greenbrier
County in West Virginia and most of our northern tier of
Virginia counties remains valid. However with this update I did
opt to make a few changes to PoPs/Wx and hourly T`s, as well as
a rather short-lived (over next 3-5 hrs) reduction in dewpoints.
Lingering CAD/ridge continues to impart a cool and dry thermal
and moisture profile early this evening, with temperatures
hovering mainly in the mid/upper 30s with dewpoints largely in
the teens. Accordingly, 2-m wet-bulb temperatures are all below
freezing. These conditions precede strong pre-frontal warm
advection regime with composite radar revealing a solid line of
showers along a cold front now extending into eastern KY and OH.
This is currently well-handled by preponderance of CAM model
output; however, only the HRRR shows any appreciable eastward
advance along/east of the Blue Ridge overnight. So I`ve
increased PoPs for areas west of the Blue Ridge toward the
Likely/Categorical range but reduced them to some extent east.
Dewpoints do stand to surge from south to north particularly
late evening/midnight as low- level flow veers to
south/southeast and taps into higher moisture airmass now
developing over the Carolinas (Td`s observed in the mid 20s-
30s). In the near-term, however, anticipate there being some
wet-bulb cooling by a couple degrees before temperatures
steadily rise on/after midnight. While temperatures as
precipitation begins elsewhere should be mild enough for rain,
it sets the stage for areas of light freezing rain along our
northern counties. Timing of cessation of freezing rain around 1
am still appears reasonable. Still don`t feel amounts will be
anything more than a few hundreths but that is all it can take
to cause travel problems. Lows tonight should occur rather early
in the 30s before steadily rising overnight.
Previous near-term discussion issued at 332 PM follows...
Posted a freezing rain advisory across the north this evening until
1 AM Wednesday morning.
High pressure will slide east into the Atlantic ocean tonight into
Wednesday. A southwest flow on the backside of the high will push
warm air into our region. Used a non-diurnal temperature trend
tonight. As precipitation begins...there may be a brief period when
evaporative cooling as the air mass saturated lowers temperatures
but the overall trend will be steady or rising tonight into
Highres models like the HRRR and Hiresw-arw East showed the arrival
of precipitation this evening between 23Z/6PM and 03Z/10PM. There is
still enough cold air at the onset of the precipitation for freezing
rain for northern portions of forecast area including the Alleghany
Highlands, Greenbrier County, Rockbridge and Amherst counties. If
the model temperature profiles are correct, by 1 or 2 AM
temperatures across the area will be above freezing mark. Rain will
spread southeast and continue for the rest of tonight into Wednesday
morning. Any ice accumulations will be less than a tenth of an inch.
Expect areas of fog tonight where dew points rise above freezing
over the snow cover.
On Wednesday, the upper level pattern will transition to a split
flow regime with a closed low sinking over the Baja peninsula and
weak southern stream ridging over the southeast. This will keep the
Appalachians in a warm and moist southwesterly flow aloft. The warm
front will continue traveling north resulting in clouds and chance
of rain. Temperatures will be quite tricky as precipitation and
lingering snow cover will want to lock in some cool in-situ wedging
as thickness values surge. High temperatures should vary from around
40 degrees in the colder locations to the lower 50s in the southwest
-- End Changed Discussion --
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 330 PM EST Tuesday...
Noticeably milder as we head through this period with southwest flow
aloft and increasing heights. However, will see less sunshine and
some rain at times. One batch will be moving across and out of the
forecast area Wed night, as piece of energy and low level jet move
across the Central Appalachians. Best chance will be north of I-64
with less in the southeast.
Thursday will be mainly dry through frontal boundary will be
situated from Lake Erie, southwest to the southern Plains Thursday
morning and should approach the Central Appalachians by Thursday
evening. Will advertise low chance pops WV to slight chance as far
east as I-81.
Not changing much into Friday with threat of showers increasing late
Thu night into Friday with front pushing southeast to the Carolinas.
Models overall showing best lift/forcing splitting with deeper
moisture swing south into the TN valley and dynamics racing north
toward New England. May be a case where the WV mountains to NC
mountains will have the higher threat of showers while the southeast
maintains low chance.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
.AS OF 320 PM EST Tuesday...
Expect this period to stay milder than normal though strong high
moving across New England Saturday will keep it cool/damp, with sfc
front/low situated from the KY/TN area southwest to Texas. This
frontal boundary will stay in the vicinity of our area into Monday
then lift northward as a warm front into the Northeast by Tuesday as
strong upper low pushes east and north into the Plains. The
southwest flow aloft will keep the moisture streaming in and will
see temps about 10-20 degrees above normal early next week.
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --As of 657 PM EST Tuesday...
VFR conditions through the next 3 hrs with developing low-
level wind shear as southwesterly winds increase to near 45 kts.
Flight categories then start to deteriorate, with a gradual
VFR/MVFR as frontal boundary lowers ceilings and brings light
rain especially western TAFs. Potential for slick runways at LWB
due to initial freezing rain. As dewpoints begin to climb to
values above freezing over at least a light cold snowpack,
potential for MVFR fog to develop over the snow is possible and
feel the best chance at this would be at DAN. South winds 6-11 kts
should predominate with gusts to 25 kts at BLF through
Precipitation into early Wednesday may prove spotty at best.
However as southern end of frontal boundary sags southward but
still hangs around by late in the day Wednesday ceilings will
begin to lower to an eventual IFR/LIFR. South winds on Wednesday
4-8 kts eventually become light and variable by late Wednesday
Extended Aviation Discussion...
Moisture returns back north Wednesday night ahead of a stronger
frontal system and associated low pressure to the west. This
likely to maintain areas of sub-VFR within lower cigs and patchy
rain showers Wednesday evening into Wednesday night before
seeing improvement back to VFR on Thursday ahead of the next
This second frontal system will work its way into the region
Friday into Saturday, maintaining the threat for additional sub-
VFR in low cigs along with light rain and/or drizzle. Unsettled
weather will continue into early next week.
-- End Changed Discussion --
VA...Freezing Rain Advisory until 1 AM EST Wednesday for VAZ019-020-
WV...Freezing Rain Advisory until 1 AM EST Wednesday for WVZ507.