Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1000 PM EST Sat Nov 22 2014
high pressure will slide east into the Atlantic tonight into Sunday.
Then...a storm system moving northward through the Mississippi
Valley will push a warm front into the Appalachians and central middle
Atlantic region...bringing wet and windy conditions to the area by
Sunday afternoon. Unseasonably warm conditions are expected Monday
in the wake of this system...before a cold front moves through
Tuesday...returning temperatures to below normal for the rest of
Near term /through Sunday/...
as of 930 PM EST Saturday...
Very dry airmass...lack of clouds and lighter winds have allowed
temperatures to fall faster this evening than forecast...and have allowed
for colder lows...with 20s in the east and deeper valleys in the
west. Shield of thicker high clouds starting to edge northeastward from the
Gulf Coast states...but models show them dissipating some as they
head into this drier airmass. Backed off the timing on probability of precipitation in the
NC mountains until dawn or thereafter Sunday. Will have to watch for
potential for sleet...but as temperatures warm late with clouds will see
mainly light rain Sunday morning.
Previous valid discussion...
High pressure will slide east tonight into Sunday.
A strong southern stream shortwave will move across the region from
southwest to northeast Sunday afternoon into Sunday night. In
advance of a broad trough will curves out in the central U.S. Sunday
into Monday...leading shortwave will take on a strong negative tilt
and rotate out of the arklatex region toward the Ohio Valley Sunday
evening into Sunday night.
A warm front will approach the region from the south Sunday
afternoon with widespread overrunning rain. Shaped timing and probability of precipitation
for rain towards a blend of GFS...NAM and hiresw-arw with moisture
spreading quickly up the southern Blue Ridge with the isentropic
Winds are another concern with a 70-80kt low level jet traverses the area in
association with the warm front/upper trough Sunday afternoon into
Sunday evening. High winds near advisory levels are possible
across the higher terrain in the northwest North Carolina and
Smyth/Tazewell/Mercer region with the strong low level jet. Some moderate
rain may also be possible Sunday afternoon into Sunday night
especially along the eastern slopes of Blue Ridge mountains with
upslope component. High temperatures Sunday will range from the
upper 40s in the mountains to the middle 50s in the Piedmont.
Short term /Sunday night through Tuesday night/...
as of 335 PM EST Saturday...
Broad southwest 500 mb flow on Sunday night with well defined
vorticity maximum track from the Tennessee Valley into the eastern
Great Lakes by Monday morning.
Strong warm air advection and impressive upslope winds Sunday
evening will focus the highest precipitation amounts on the east
slopes and foothills of the Blue Ridge. Plus the southeast wind will
be advecting precipitable water values close to 1.5 inches up the
ridges. Axis of convergence crosses the forecast area by 06z/1am
Sunday night with a sharp dry slot immediately following.
In-situ wedge erodes once the precipitation ends with strong warm
air advection late Sunday night and Monday. Behind the rain on
Monday 850 mb temperatures continue to rise into the +10 to +12
range. But by the end of the day the surface cold front has crossed
east through the area. Models bring the 850 mb front through during
the evening. Expecting a non diurnal rise in temperatures Sunday
night then above normal maximum temperatures on Monday...especially
east of the Blue Ridge.
The big push of colder air comes in Tuesday night. Surface high
pressure will be over the County Warning Area Tuesday and Tuesday
night. Winds diminish late Tuesday. Low pressure developing off the
southeast coast will result in east winds over the forecast area.
This will bring deeper moisture back into the area as well as a
chance of precipitation. How far west the precipitation will reach
was still questionable. If precipitation extends all the way to the
Blue Ridge...temperatures may be cold enough on the western edge to
have snow or a rain snow mix. Too soon to tell if there will be any
precipitation actually falling...much less any amounts.
Long term /Wednesday through Saturday/...
as of 130 PM EST Saturday...
Two distinct systems have the potential for bring some precipitation
to parts of the area during this segment of the forecast. The first
item of interest is a low pressure wave moving northward along a
baroclinic zone that will be positioned along the coast during the
Wednesday and Wednesday night time period. The various models are
still inconsistent with each other...and with their own previous
model runs regarding the timing...track and associated precipitation
with this feature. Yesterday...the ecwmf was the only operational
model run that hinted at precipitation skirting the eastern extent
of the forecast area. Today...its solutions is more robust on this
scenario with precipitation now the whole way west to eastern
Kentucky. Today...the GFS solution is only slightly more robust as
compared to the ecwmf from yesterday...but still...has all but our
southeast West Virginia counties with at least 0.01 precipitation. The
Canadian solution keeps the system farther off the coast with not a
drop of precipitation reaching the forecast area. Our forecast from
yesterday reflected a model blend consensus that was more in line
with the wetter ecwmf solution. Given both the GFS and ecwmf are
wetter for the region...and the model blend consensus is also wetter
across the region...have followed suit in the forecast.
Precipitation chances for Wednesday have been increased to reflect 50
percent in the east...with 20 to 25 percent in the west. Surface and
low level thermal profiles suggest mainly a snow or rain/snow
forecast across the mountains on Tuesday...with primarily rain
across the Piedmont. Wednesday night...colder air arriving on the
backside of the departing system will allow for more light
snow...but with the system exiting...much less coverage.
Out next potential weather maker will be associated with a shortwave
trough that zips through the Ohio Valley and middle-Atlantic region
during the Thursday and Thursday night time period. Both the GFS and
ecwmf solutions have changed compared to their -24 hour
counterparts. Prior...model solutions were hinting at a more
prolonged closed low strengthening over the central Appalachians
with a more profound shot of colder air in its wake. The latest
solutions offer a more glancing blow of energy across the
area...with the colder air not having as much chance to make the
turn south prior to zonal flow developing in the wake of the passage
of the shortwave trough. While the forecast will still offer some
isolated to scattered rain/snow showers across parts of southeast
West Virginia and neighboring counties of southwest Virginia through
Thursday night...the temperature forecast from Thursday through
Saturday will be a bit milder than what as offered in the previous
Aviation /03z Sunday through Thursday/...
as of 635 PM EST Saturday...
Going to see VFR conditions through Sunday morning before airmass
moistens up ahead of a storm system moving across the middle miss
valley bring a warm front across by Sunday night.
Expect MVFR ceilings to arrive by midday/early afternoon at most sites
with light rain following close behind. Moderate and at times
heavy rain is possible in the roa/bcb late in the taf period.
NAM/local WRF model also show potential low level wind shear
concerns toward late afternoon as the strong low level jet moves
into the mountains/foothills. Left it out of tafs for now given
rain and potential embedded convective elements.
Light winds this evening will become southwest to southeast and
more gusty on Sunday. Winds at blf may stay up a bit tonight as
the influence of approaching low pressure and warm front start to
Medium to high confidence in ceilings...visibilities and winds
during the taf period.
Rain and wind continue with MVFR to IFR conditions Sunday night.
A brief return to VFR during Monday outside of the mountains as a
dry slot develops between the exiting front from Sunday and the
next upstream cold front. Monday into Tuesday look to feature
quite a bit of wind. Northwest flow into may keep sub VFR ceilings into blf
and possible lwb...with VFR to the east. Another storm system is
expected to move up the southeast coast by Wednesday into Thursday
which may bring wintry precipitation to the area along with sub VFR at
as of 215 PM EST Friday...
The visibility sensor at klyh...Lynchburg Airport...will be out
of service until parts arrive to replace the sensor. Until then
the visibility will only be reported when the control tower is
short term...air mass