Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 151742
Area Forecast Discussion
National Weather Service Blacksburg VA
1242 PM EST Wed Feb 15 2017
Low pressure over the Tennessee valley will cross the southern
Appalachians this morning, then move east to along the North
Carolina Coast this afternoon. Meanwhile, a cold front over the
Great Lakes and Ohio Valley will move east, also crossing the
Appalachians this morning, then to along the Mid-Atlantic coast
this afternoon. The area of low pressure is then forecast to
move northeast along the front tonight, strengthening into a
winter storm as it passes near the New England coast.
.NEAR TERM /THROUGH THURSDAY/...
As of 1013 AM EST Tuesday...Update to remove the Winter Weather
Advisory for Tazewell County as snowfall has shifted well
eastward and accumulating snowfall from earlier this morning
having shifted well to the east.
Generally nowcasted PoPs/Wx across the eastern part of our
forecast area through 17z. Higher-resolution guidance is
running about 2 hrs slower than the band of ongoing light rain
across Caswell NC and Halifax/Charlotte counties in VA is moving;
but used a blend of it into the updated forecast to reduce PoPs
in these areas.
Cold front aloft - essentially manifesting itself as a fine line
of reflectivity extending from central PA southwestward into
north-central WV - gradually working its way southeastward. HRRR
and WRF ARW/NMM depict at least some potential enhancement into
southeastern WV again into the early afternoon. So I`ve
generally maintained isolated snow/rain showers into the
afternoon for these areas.
Otherwise, made no other changes to the forecast at this point.
Expect some breaks in overcast through the early afternoon with
temps only slowly climbing west of the Blue Ridge, with a bit
more of a diurnal trend out east.
Previous near-term discussion issued at 500 AM follows...
Vigorous short wave trough over the eastern TN valley will move
east this morning crossing the southern Appalachians. Area of
precipitation cover the central and southern Appalachians with
primarily rain in the lower elevations, and some snow in the
higher elevations. Within our CWA, the snow has been confined
mainly to the western New River Valley and into the high country
of NC and the mountains of far southwestern VA, including
Mercer County WV. Do not have a lot of ground truth to offer,
but there has been a mesoscale band of moderate snow aligned
from west to east across Tazewell County Virginia since
midnight, so would anticipate upwards of 2 to 4 inches of snow
between Bluefield and Marion...especially across the higher
terrain... such as East River Mountain, Rich and Brushy
mountains, and along Big Walker mountain near Bland.
Models indicate moisture associated with the area of low
pressure will peak early this morning between now and 9AM, then
taper from west to east across the CWA between 9AM-Noon...exiting
the CWA for this afternoon. The eastern part of the New River
Valley, and higher terrain near the Blue Ridge may see a mix or
change over to snow before the precipitation comes to an end.
Ground temperatures are warm, so not expecting any road
issues, other than just being wet.
For this afternoon, the short wave and associated surface low
will pass off the NC coast, and will begin to phase with an
upper level long wave trough which is moving east across the
Great Lakes. This phasing will result in a rapid strengthening
of the surface low (initially at 1000 mb), the pressure
dropping to near 975 mb as the storm moves northeast along the
New England Coast tonight. End result will be a winter storm
with heavy snow for parts of New England, and strong Northwest
winds across the Mid-Atlantic with near advisory level gusts
across the mountain ridges. In addition to the wind, wrap
around moisture from the storm will combine with low level
moisture from the Ohio Valley side of the mountains to produce
snow showers and flurries across the VA/WV highlands with some
accumulating snow north and west of Lewisburg.
Temperatures today will warm very little until we begin to clear
this afternoon. Introduction of a little sun, will allow
temperatures to sneak above freezing in the mountains and into
the 40s to near 50 for the foothills and piedmont. 85H
temperatures take a respectable plunge tonight (M8 to M10 deg C
by 12Z/7AM Thursday), so all areas expected to drop below
freezing tonight, with readings in the teens for elevations
above 3500 feet MSL and wind chill readings in the single digits
for Thursday morning for areas west of the Blue Ridge.
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 400 AM EST Wednesday...
Northern stream and southern stream systems will be phased
together along the eastern seaboard at the beginning of this
period resulting in a deep upper trough anchored just east of
the Appalachian Divide and centered over New England. Lingering
upslope snow showers will be possible through the first half of
the day with low-level cold advection in place. Expect a fairly
decent surge of cold air to be in place as 850mb temps plunge
back toward the -12C level. The ECMWF has trended a tad colder
with this air mass while the GFS has trended a tad warmer, but
both are in the -10C to -12C range across the northern parts of
the CWA. This will yield lows in the upper teens across the
higher elevations of the western mountains to the mid and upper
20s across the Piedmont. Gusty northwest winds will be the main
concern for Thursday until the upper trough begins to lift out
during the afternoon. Winds may well approach wind advisory
criteria across northwest NC into southwest VA, especially along
the higher terrain of the Blue Ridge. For now, will just
highlight the mention of such in the HWO and allow the day shift
to take a closer look at this before issuing an advisory.
The upper trough will begin to lift out fairly quickly during
the afternoon and evening allowing low-level warm advection to
ensue sooner than with previous similar such cold fronts/air
masses. This will allow afternoon maximum temperatures to
recover to the 30s west to the 50s east, roughly just a bit
Weak northwest flow aloft will prevail for Friday as the upper
trough lifts further northeast away from the region. The
northern stream will gradually lift north Friday through
Saturday with the southern stream remaining quite active along
the southern border of the U.S. A powerful storm system will
shift eastward into the southwestern U.S. with pieces of energy
ejecting eastward from this system along the Gulf Coast states.
Meanwhile, a mean ridge will dominate the east central U.S.
during this period. 850mb temps will rise dramatically toward
+10C by the end of the day resulting in a rapid warmup from the
cold weather of Thursday. Maximum temps Friday will be a good
10-15 degrees warmer than Thursday, namely 50s west to 60s east.
The first southern stream system of concern for our area will
lift northeast from the southeast states in a greatly weakened
fashion. Despite the weakness of this system and generally
lifting into an area of confluent flow, the models have
gradually been increasing the impacts of this system on our
region resulting in a period of light rain likely spreading into
the area Saturday night into Sunday morning. With temperatures
well above freezing, there are no concerns for any winter
precipitation with this event. Increased cloud cover Saturday
will hold max temperatures into the 50s west and 60s again east,
but this is still well above normal for mid-February.
.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 445 AM EST Wednesday...
The deep upper low along the west coast will slowly shift
eastward through the far southwestern U.S. into Texas and the
western Gulf Coast states during the first half of next week.
Meanwhile, an upper ridge in advance of this upper low will
drift slowly east into the eastern U.S. Beyond Monday,
significant timing and track differences are noted between the
various long range models, with the ECMWF faster and further
south with the upper low, while the Canadian and GFS remain
further north and much deeper/more intense. The ECMWF solution
would take the track of the upper low so far to the south that
the Mid-Atlantic region/central Appalachians would only be left
with some light showers in a lingering confluent zone. The GFS,
on the other hand, would bring a substantial amount of rainfall
and possibly even some stronger convection into our area late in
the week. At any rate, it will be mid week or later before any
model brings sensible weather from this system into our region.
Thus, mostly dry and unseasonably warm weather will prevail
until that time. With 850mb temps hovering in the +10C to +12C
range throughout this period, look for surface lows in the 40s
and 50s and highs in the 60s and 70s. These temperatures are a
good 15-20 degrees above normal.
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --As of 1241 PM EST Wednesday...
Generally SCT-OVC VFR stratocu through 00z as a dry cold front
advances southeastward, with a wind shift to northwest 10-12 kts
gusts to 25 kts accompanying the frontal passage. While skies
clear early this evening for most of the TAFs, expect a lowering
to MVFR around/after 02z as moisture from the Great Lakes is
forced upslope, predominantly affecting BLF and LWB. These
ceiling trends generally continue until around mid-day Thursday.
Gusty northwest winds will continue through the remainder of the
TAF period, gusting the strongest at BLF and ROA (30-32 kts).
Given the strong wind field, some potential for turbulence
in/around the ridgetops due to mountain waves Thursday.
Extended Aviation Discussion...
Ceilings begin to improve to VFR all terminals late Thursday
afternoon. While winds will continue to be rather gusty,
anticipate a diminishing trend to northwesterly sustained wind
and gusts during the overnight hours on Thursday.
Generally VFR overnight into early Friday, perhaps briefly
falling to an MVFR ceiling at BLF and LWB as a shortwave trough
rotates southeastward. Next potential for sub-VFR conditions
is not until later Saturday as a disturbance moves in from the
Deep South producing showers. Lower ceilings may linger into
Sunday across BLF and LWB, but becomes VFR Sunday night through
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