Area Forecast Discussion
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FXUS61 KRNK 160922
Area Forecast Discussion
National Weather Service Blacksburg VA
422 AM EST Mon Jan 16 2017
A warm front across the Carolinas slowly lifts northeast today
stalling across southwest Virginia. A cold front enters the area
by Tuesday afternoon shifting off to our south Wednesday. This
front edges northward again Thursday into Friday.
.NEAR TERM /THROUGH TONIGHT/...
AS OF 321 AM EST Monday...
Confluent flow over the northeast at 500 mb will keep high pressure
situated over this area, staying wedged southward over us this
morning. Weak lift over wedge front over the Carolinas providing
light rain/drizzle across the northern forecast area south toward
the VA/NC border, with fog along the ridges.
Models are differing some on northward push of front today, and
given the upper pattern and time of year, think will be hard pressed
to clear the low clouds out of the north and eastern forecast area,
roughly from Bath County to Halifax and northeast. Will be a tale of
two weather regimes today with our far southwest CWA starting to
push more into the warmer air with flow turning more south to
southwest. Highs from Bluefield WV to Chilhowie VA to Zionville, NC
should reach the upper 50s to lower 60s, while from Hot Springs, VA
to Danville and north look for highs in the mid 40s. But think about
this, Danville should be in the mid 40s for highs this time of year,
so overall the forecast area is an warmer regime. Any light
rain/drizzle this morning erodes away by midday with lingering
showers isolated in WV.
Tonight, a decent shortwave pushes across the midwest. At the same
time, surface high over the mid-Atlantic shifts offshore and well
east of the NC coast. Will still see some cold air damming in the
east tonight. Expect temperatures to drop a few degrees in the east
with upper 30s to mid 40s, while the west drops a little more,
though still mild for mid-January with mid 40s to lower 50s from
Southern WV to the NC mountains. Upstream cold front stays far
enough west that pops are expected to be less than previous forecast
with limited forcing. With some low level convergence near the Blue
Ridge, will see some low chance pops here overnight, with slight
over little chance in the piedmont. Rain showers should get pretty
close to southeast WV by dawn so have pops close to 50.
.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
As of 415 AM EST Monday...
While not overly significant, it continues to project to be a
relatively active short-term forecast period with at least two and
potentially three upper-level disturbances focusing rain chances
with above-normal temperatures continuing through most of the period
as we remain on the northern periphery of dominant, if rather flat
southeast CONUS mid-level ridging.
For Tuesday: 500 mb closed low roughly positioned over the mid-
Mississippi Valley deamplifies as it moves northeast. It streams an
weak warm front northeastward across the mid-Atlantic and
Appalachian region during the day, the warm front associated with
warming 850 mb temps and chances for rain. Given the best upper-
level support for large-scale lift is confined to our northern
counties (and frankly is better into northern WV and PA), I`ve
showed something of a gradient in PoPs/QPF associated with the warm
front with the highest respective values furthest north and lowest
in the southside Virginia and the foothills and Piedmont region in
North Carolina. PoPs then begin to decrease slightly into the
Chance/low Likely range into the afternoon, in a narrow warm sector
characterized by overcast conditions and weak to nil surface
convergence in deep southwest flow, ahead of a cold front likely to
be positioned over the Ohio/West Virginia border area. Rainfall
amounts range from a few hundreths south to up to one-quarter inch
furthest north. Tough forecast as it pertains to highs given the
likelihood of overcast and early-day rain offsetting southwest flow
and 850 mb temps warming to near +8 to +10C. I`ve sided toward some
of the more pessimistic/cooler raw guidance into the mid and upper
50s. Should greater clearing be realized, these may be 2-4 degrees
For Tuesday Night: Quasi-zonal confluent mid-level flow is replaced
by 500 mb height falls as a positively tilted shortwave trough
interacts with a southeastward-sagging cold front Tuesday night.
Expect any break in afternoon showers to blossom back up along the
boundary, with the highest PoPs across far southwestern Virginia,
southeast West Virginia and building into northwestern North
Carolina. Westerly boundary-parallel flow would argue for a slower
southeastward advance of the front and potentially higher QPF values
across the NC mountains into the Grayson Highlands/Mountain Empire
region (forecast near 0.25") to a tenth of an inch or less elsewhere
of additional rain. Cold advection should allow for low to dip into
the mid/upper 40s, but areas east of the Blue Ridge into the
Piedmont stand to only fall into the low 50s, a couple degrees
cooler than daytime highs.
For Wednesday: Baroclinic zone gradually builds southward into
central North Carolina with any early-morning showers dissipating in
southern sections. More variable cloud cover is anticipated with
greatest coverage along and west of the Continental Divide into
southeast West Virginia in weak ridging. 850 mb temperatures fall in
cold advection to values a couple degrees either side of 0C, and
Wednesday may be the only time our low-level thermal structure is
this cool for the foreseeable future. While post-frontal downslope
flow should push temperatures east of the Blue Ridge into the mid
60s, highs in the lower/mid 50s are more likely west of the Blue
Ridge into the Alleghany Highlands.
For Wednesday Night: Mid-level heights then begin to rise Wednesday
night in response to digging upstream trough over the central
Plains. Surface high pressure the rule in an otherwise uneventful
forecast, with some high clouds advancing in toward early Thursday
morning. Temps look to fall back into the upper 30s under better
radiational cooling conditions than the past couple nights.
For Thursday/Thursday Night: Ridging should generally prevail
through most of Thursday, but is gradually replaced by neutral to
negative height falls in mid-levels by Thursday night as highly-
amplified mid-level closed low over the central Plains moves into
the Mississippi Valley. Deep southerly flow across most of the South
yields a large shield of precipitation, some potentially convective
well to our southwest over the Tennessee Valley. It`s not likely we
see rain into our western zones until overnight Thursday/early
Friday morning. Think in reality the QPF shield may look similar to
that depicted in the 00z ECMWF, so I`ve weighted PoPs more heavily
in that direction. Highs Thursday in the 50s to near 60 in northwest
NC, with lows in the upper 30s/low 40s.
.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 330 PM EST Sunday...
The upper pattern will become highly amplified as we head into the
weekend with a sharp ridge along the east coast and a southern
stream closed low moving across the deep south. This pattern will
eventually bring abundant moisture to the region as we head into the
start of next week.
Focus for steadiest widespread rain remains on Friday. High pressure
over New England will then form a wedge down the east side of the
Appalachians for the weekend. Isentropic lift will be steadily
increasing as low pressure develops over the lower Mississippi
valley and low level southerly winds ride up over the wedge. This
will steadily increase our chances for precipitation, especially for
Sunday into Sunday night.
.AVIATION /09Z MONDAY THROUGH FRIDAY/...
As of 1155 PM EST Sunday...
A shallow wedge boundary continues to drift across the piedmont
this evening. Warm moist air overrunning this wedge will bring
IFR-VLIFR ceilings and visibilities to the forecast area with
mountain ridges remaining obscured, possibly into late Monday
afternoon. Light rain and drizzle will likely persist into
Monday morning. A warm front will gradually lift north of the
area by Monday evening with cigs/vsbys trending back to MVFR.
Extended Aviation Discussion...
A baroclinic zone will remain anchored across the region
sandwiched between a strong upper ridge over the southeast
states and an active jet stream from the southwest U.S. into the
northeast U.S. Thus, an unsettled, wet weather pattern is
expected to remain in place Monday into Tuesday. The frontal
boundary may lift north enough by Monday night for a brief
period of mainly VFR, but a stronger front will arrive By
Tuesday with more showers including widespread sub-VFR.
Generally looking at MVFR much of the period, although periods
of VFR as well as IFR-LIFR can be expected at times. Models
remain uncertain with timing of another wave along a passing
cold front during midweek. Some guidance showing another round
of showers with sub-VFR on Wednesday with improving conditions
Thursday. This while others slower with a break on Wednesday
before moisture returns from the southwest Thursday afternoon
into Thursday night.