211
FXUS61 KRNK 202334
AFDRNK
Area Forecast Discussion
National Weather Service Blacksburg VA
634 PM EST Wed Nov 20 2024
.SYNOPSIS...
A strong cold front pushes east tonight. Gusty winds will
persist through Saturday with a strong upper disturbance
bringing accumulating snow showers to the mountains.
&&
.NEAR TERM /THROUGH THURSDAY/...
As of 620 PM EST Wednesday...
Key Messages:
--Winter Storm Warning for western Greenbrier.
--Winter Weather Advisory SE WV to NW NC mountains.
--Wind Advisory Blue Ridge Roanoke to Boone
Front has almost tracked out of our forecast area this evening
and strong pressure rises with cold advection is leading to
winds gusting 20 to 45 mph in the mountains, with higher gusts
along the Blue Ridge where we have the advisory. Showers will be
exiting the piedmont this evening with dry weather overnight as
temperatures fall into the 30s for most. Winds will stay gusty
overnight but should weaken after midnight.
Previous discussion...
A cold front will be over the Ohio and Tennessee Valleys this
afternoon. This front will move over the mountains this evening
and clear the piedmont by midnight. With a later arrival of the
front, temperatures will warm into the 60s this afternoon. With
enough heating, convective non-severe showers will track across
the area this afternoon and evening. Quick pressure rises, 50
knot cross- barrier jet and modest cold air advection directly
behind the front will bring wind and gusty conditions for a few
hours. The strongest winds will be along the Blue Ridge from
Floyd County VA to Watauga County NC. A Wind Advisory is posted
for this area for tonight.
There will be a brief break in the precipitation overnight into
Thursday morning. Precipitation returns to the mountains in the
afternoon as an upper level low moves across the Ohio Valley.
Models are tracking this low further to the south, which will
expand snow showers into the south Appalachian mountains. Cool
air will follow the front, but cold enough for precipitation to
start and remain as snow through this event, especially along
western slopes and elevations above 4000 ft of southwest VA and
southeast WV. Snow should start around noon for western
Greenbrier with daytime totals of 1 to 3 inches. From Summers
County WV to Watauga County VA, snow should start to fall during
the mid to late afternoon, but may not start to accumulate on
the ground until after 4p-5p. Higher elevations, such as Burkes
Garden and Whitetop may see an inch or two before the sun goes
down. High temperatures Thursday will range from the mid 30 to
upper 30s across the mountains and mid 40s to lower 50s in the
foothills and piedmont.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 1230 PM EDT Wednesday...
Key Points:
1. Prolonged period of upslope snow/rain showers over the
mountains, especially for SE West Virginia. 2. Very gusty
northwest winds through Saturday. 3. Temperatures trending
colder through the period.
A look at the 20 Nov 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows a closed low centered over the region of
PA/MD/WV/VA for the start of Thursday evening. An associated
trough axis is washed out in the averaging, but there may be one
extending south into the Carolinas and a second extending
southwest into the Lower Ohio Valley. By Friday evening, the
center of the low makes minimal progress eastward to over NJ,
again potentially with one trough axis extending south into the
far western Atlantic over the coast of the Carolinas and one
southwest to near the spine of the Appalachians. By the start of
Saturday night, the low is expected to located farther north,
over the Canadian Maritimes. Northwest flow is expected to be
over our region with weak ridging over central CONUS.
At the surface, low pressure Thursday night is expected to be
over southern New England with a cold front extending southwest
across central VA/NC. A reinforcing cold front is expected to be
extending west of the low into the Upper Ohio Valley. The
1000:500mb thickness values are expected to be around or below
540 dam for much of our region with 528 dam over the
intersection of OH/WV/PA. By Friday night, little movement is
expected in the location of the surface low. However the
reinforcing cold front is expected to extend southwest over the
region, with the axis of the lowest 1000:500 thickness values
shifted just east of the area. By Saturday night, the center of
the low is expected to be near the Canadian Maritimes with axis
of the coldest air also shifted northeast of the region.
Additionally, the center of surface high pressure is expected to
be located over the Deep South.
Output from the 20 Nov 00Z Ensemble Situational Awareness Table
shows 850mb temperatures Thursday night around -6C to -4C
across the region. For much of the region, these values fall
within the 2.5 to 10 percentile range of the CFSR 30-year
climatology. For Friday, temperatures slowly moderate to values
around 0C for much of the area by the afternoon with these
values continuing through Friday night. On Saturday, values
trend slightly upward with ranges around 0C to +3C by the
afternoon. Temperatures continue to trend milder through
Saturday night, reaching a range of roughly +4C to +7C by
daybreak Sunday. Precipitable Water (PW) will average 0.25 to
0.35 inch across the area Thursday night, increase to around
0.50 inch on Friday through Saturday, and decrease slightly to
0.35 to 0.50 inch for Saturday night.
The above weather pattern offers a scenario with a prevailing,
robust west to northwest wind across the region through at least
Saturday. The strongest winds may occur Friday morning through
afternoon, concurrent, then just behind the passage of the
reinforcing cold front. This flow pattern, along with PW value
around the median for this time of year, sub 540dam 1000:500mb
thicknesses for at least Thursday night and Friday, point
towards a prolonged period of upslope showers, with snow showers
probable especially Thursday night and Friday. As we head into
the weekend with 850mb temperatures and 1000:500mb thickness
values rising, rain showers will be more probable with only
pockets of snow showers remaining at the highest elevations of
southeast WV by Saturday night. Additionally, as the surface low
progresses northeast and a ridge builds to our south, trend of
the 850mb winds will be to gradually decrease in speed, and back
in direction from northwest to west. This will result in an
overall trend of decreasing coverage of precipitation Friday
night into Saturday night. Temperatures will trend milder
through the period.
Confidence in the over synoptic pattern for the above forecast
is high. Specific timing, location, and amounts/speed of the
expected precipitation/winds is moderate.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 1230 PM EDT Wednesday...
Key Points:
1. Temperatures trending milder through Tuesday, then cooler.
2. Dry Sunday and Monday with showers returning for Tuesday and
Wednesday.
3. Snow showers possible Tuesday night at the higher
elevations.
A look at the 20 Nov 00Z NCEP Ensemble Mean 500 mb Geopotential
heights shows an upper level ridge situated Sunday evening from
the Great Lakes region to the Deep South. A closed low is
expected to be located just northeast of the Canadian Maritimes.
By Monday night, the ridge axis shifts northeast to over New
England with southwest flow over our region. There is a small
hint of a shortwave trough over the Upper Mississippi River
Valley. A slightly more robust trough will be developing over
the Pacific Northwest. By Tuesday night, the trough over the
Pacific Northwest is expected to be located over the Rockies and
be more amplified. Southwest flow will continue across our
region. By Wednesday, the trough in the west shifts a bit
farther east towards central CONUS.
At the surface, the center of high pressure shifts from the
Deep South to just off the GA coast. Also on Sunday, low
pressure starts to develop over KS/OK. The positioning of these
two features will yield an increasing southwest flow over our
region. On Monday, both the trough to our west and the high to
our southeast shift slightly east. For Tuesday, expect the same
trend with the trough and and ridge again shifting a bit more
east. This may yield the apex of the base of the trough to be
close to skirting portions of the Lower Ohio Valley. For
Wednesday, model averaging offers the placement of an inverted
trough over our region with the more dominate trough just east
of New England.
Output from the 20 Nov 00Z Ensemble Situational Awareness Table
shows 850mb temperatures rising through the day on Sunday,
reaching a range of +7C to +9C by sunset. For Monday, the trend
continues for milder temperatures with the range by the
afternoon of +8C to +10C. On Tuesday, values trend lower during
the day, reaching a range of +6C to +8C by the afternoon. For
Wednesday, values continue trending lower, reaching a range of
+1C to +5C by the afternoon. PW values will range from 0.35 to
0.50 inch Sunday and Sunday night, increase to 0.50 to 0.75 inch
for Monday, Tuesday, and Wednesday.
The above weather pattern offers mainly a dry weather pattern
until Tuesday/Wednesday when a trough and potential surface
front approach/cross our area. Temperatures through the period
are expected to trend milder through Tuesday, then cooler for
Wednesday. Currently, low level temperature profiles suggest the
precipitation Tuesday/Wednesday will be primarily rain showers.
Temperatures may be cold enough Tuesday night at the highest
elevations for a mix with, or change to snow showers.
Confidence in the above weather pattern is moderate.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 630 PM EST Wednesday...
Expect the wind to be more of an issue this evening with
northwest gusts in the 20-40kt range, with the higher gusts
around ROA/BCB. Cigs will become VFR and scatter out through the
night with showers exiting the LYH/DAN terminals by 01z.
Winds will be slowly subsiding overnight but pick up again by
18z Thursday but not quite as strong as this evening. An upper
disturbance will bring snow showers to the BLF/LWB area Thu
afternoon where cigs/vsbys drop to MVFR, possibly IFR.
Forecast confidence is above average, except on cigs/vsbys Thu
afternoon.
EXTENDED AVIATION OUTLOOK
Gusty northwest winds continue through the end of the week.
Prolonged period of upslope snow and sub-VFR cigs possible over
the mountains. Aviation conditions improve Sunday into Monday.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory until 7 AM EST Thursday for VAZ015>017-022.
Winter Weather Advisory from 1 PM Thursday to 7 AM EST
Saturday for VAZ015.
Winter Weather Advisory from 1 PM Thursday to 7 PM EST
Saturday for VAZ007-009.
NC...Wind Advisory until 7 AM EST Thursday for NCZ001-002-018.
Winter Weather Advisory from 1 PM Thursday to 7 AM EST
Saturday for NCZ001-018.
WV...Winter Weather Advisory from 1 PM Thursday to 7 PM EST
Saturday for WVZ042>044-507.
Winter Storm Warning from 1 PM Thursday to 7 PM EST Saturday
for WVZ508.
&&
$$
SYNOPSIS...RCS/WP
NEAR TERM...RCS/WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...RCS/WP
NWS RNK Office Area Forecast Discussion
