Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
1058 am EST Friday Feb 12 2016
Arctic front crosses this evening...accompanied by snow showers
into Saturday...and bitterly cold weather for the weekend. A
complex system could bring mixed precipitation early next week.
Near term /through tonight/...
1030 update. Changed wind chill watch over northern mountains to
Wind Chill Advisory. No other change to headlines. Otherwise...no
significant change to forecast. Most accumulations of snow this
afternoon will be over southwest Virginia.
Previous discussion below...
A fast moving upper level impulse will round the base of the mean
trough over the east Continental U.S. Today. This will bring a swath of mainly light
snow to S Kentucky/SW Virginia/and portions of southeast WV. Quantitative precipitation forecast amounts look
light...ranging a few hundredths to around a tenth. After
incorporating the latest rap/hrrr runs for quantitative precipitation forecast and converting to
snow using NAM snow ratios resulted in mainly one inch amounts over
those locations with up to 2 inches on the East Ridge of Dickenson
County. Since headlines are already out surrounding SW Virginia and the
forecast amounts of 1 to 2 inches...elected to hoist a winter weather advection
until this afternoon for those counties. Elsewhere...thinking it
will be hard for measurable precipitation to make it north aside from the
mountains. Thus anticipate a partly to mostly cloudy day elsewhere
with temperatures recovering into the upper 20s to lower 30s.
Attention then turns to an Arctic front which will usher in the
coldest temperatures of the season for the weekend. Some snow
showers may break out ahead of the front late this afternoon but
overall will wait for frontal passage which will bring with it a healthy dose
of squalls with plummeting temperatures and gusty winds. These
looks to put down a skiff with some lollipop amounts to an inch in
The Lowlands. Have the front crossing in the 00z to 06z time
frame from northwest to southeast across the region. With plummeting 850 mb temperatures
and cross flow...think efficient momentum Transfer will be
realized to create very gusty winds. Have coded up some 20 to 30
knots gusts overnight...with gusts to 40 kts over the higher
elevations of the WV mountains. Surface temperatures will bottom
out in the single digits to lower teens outside of the mountains
by 12z Saturday...with below zero readings in the higher elevations.
Wind chill conundrums will be realized over the high terrain and
adjacent counties. After coordination with surrounding offices we
elected to raise a wind chill watch for Randolph/Pocahontas and a
Wind Chill Advisory from Raleigh to Taylor counties in WV.
Mentioned the high winds in the headline. Snow showers will
continue behind the front...most numerous in the mountains where a
general 2 to 4 inches are forecasted which falls short of advisory
level amounts. Snow showers will diminish outside of the mountains
late tonight...becoming confined to moisture streams from Lake
Short term /Saturday through Monday/...
Sat morning finds the forecast area in the deep freeze and deep layer
northwest upslope flow. High pressure representing the center of the
Arctic air mass builds over the area late dat nt...before moving
on to the east on Sunday. The approaching high will cut off the northwest
flow...killing any lake plumes Sat morning...and then the upslope
snow showers Sat nt. Fluffy but minor additional accumulations are
possible until then with temperatures aloft favoring dendritic
growth if not almost too low...-22c at 850 mb.
As the deep l/west trough starts to lift out...and a short wave trough
approaches from the northwest...the area gets into a warm advection
pattern that will bring on increasing cloudiness Sunday...followed
by snow late in the day and at nt. The warm advection could take
temperatures high enough for a change over to rain over The
Lowlands Monday afternoon.
Introduced an severe weather potential statement mention for possible mixed wintry precipitation
Monday and Tuesday although temperatures on the cold side of the system
are prognosticated to be marginal for snow vs rain.
Blended in mostly raw model data for temperatures Sat in the
Arctic air and the bias corrected mav for lows Sat nt...the
higher ridges leveling off and even rising a tad toward dawn
Sunday. Highs Sunday were mainly between MOS and raw model output
and were accepted. After falling initially Sunday
nt...temperatures rise overnight...and guidance suggested higher
temperatures for Monday.
In the Arctic air...temperatures do not rise much on Sat...so the
wind chill advisories and watches continue through the day Sat and
Sat nt into Sunday morning in and near the mountains. The winds
do die down there Sat nt but not until very late...and lastly on
the ridges where wind chill values will be closest to warning
Long term /Monday night through Thursday/...
still lots of uncertainty in the extended period...although
models are gradually trying to come together. Series of potent waves
to affect the area early next week. First Sunday night into
Monday...as wave moves into Great Lakes region...spreading mainly
light snowfall into the region. The second more powerful wave and
associated low will move northeast out of the southern U.S. Towards
the region by Monday night into Tuesday. Depending on the track of
the low...will determine whether area is looking at an all snow
event...or a wintry mix at times. At this point...looks like a
wintry mix can be expected at times...particularly across The
Lowlands...which of course will limit snowfall potential. With the
overall uncertainty in the models at this time...will keep a mention
out of the severe weather potential statement for one more day...and allow focus to remain on
systems and impacts expected this weekend.
Aviation /16z Friday through Tuesday/...
weak upper disturbance crosses southern portions of area this
afternoon with some snow. An Arctic front drops southeast across
the area this evening...with IFR squalls possible along with gusty
winds 20 to 35 kts...followed by mainly mountain snow showers.
MVFR or lower conditions in snow this afternoon mostly confined
to far southern areas of West Virginia and southwest
Virginia...affecting bkw...then mainly into mountains later this
afternoon and tonight as upslope snow showers kick in.
Forecast confidence and alternate scenarios through 18z
Alternate scenarios: snow looks to be more scattered this afternoon
outside of southwest Virginia and southern mountains.
Experimental table of flight category objectively shows consistency
of weather forecast office forecast to available model information:
h = high: taf consistent with all models or all but one model.
M = medium: taf has varying level of consistency with models.
L = low: taf inconsistent with all models or all but one model.
UTC 1hrly 15 16 17 18 19 20 21 22 23 00 01 02
EST 1hrly 10 11 12 13 14 15 16 17 18 19 20 21
crw consistency h h h h h h h h h h h h
heights consistency h h h h h h h h h h h h
bkw consistency h h M l M M h h h h h M
ekn consistency h h M h h h h h h h h M
pkb consistency h h h h h h h h h h h M
ckb consistency h h h h h h h h h h h M
After 18z Saturday...
IFR conditions in snow...rain...or mixed precipitation Monday and Tuesday
WV...Wind Chill Advisory from midnight tonight to 9 am EST Sunday
Virginia...Winter Weather Advisory until 4 PM EST this afternoon for