Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
853 am EST Sat Dec 20 2014
a weak disturbance clips the area today. Dry Sunday. System may
clip mountains Monday. Strong occlusion crosses Christmas evening.
Near term /through tonight/...
845 am update...
lowered temperatures today especially through midday based on
hrrr/lav beneath the cloud cover. Middle level baroclinic Leaf moves
northeastward through the area through this evening...so the gist of the pop
forecast looked good.
models show an upper level disturbance moving over the region today
while a surface low stays well south of the region. Radar shows lots
of returns to the west...but most of this is struggling to get
through a lower level dry layer. Some precipitation in southern Illinois
and western Kentucky is making it to the ground where the mesoscale NAM shows
that the lower levels have mostly saturated. Based on this...think
some light precipitation could make it to the ground as the
disturbance moves across our region...as the mesoscale NAM shows that
moisture making it into the lower levels here. Therefore will add
some small probability of precipitation in the western counties today and this evening.
The system moves off to the east tonight...but mesoscale NAM shows the
stratus deck that retreats northwestward today...pushing back
southeastward tonight. Will go on the warmer side of MOS low
temperature guidance in southeast Ohio due to this deck persisting
through the night.
Short term /Sunday through Tuesday night/...
short wave ridging works in on Sunday as warm air advection slowly begins to spread
across the area. The low level flow to veer around to southeast in the
afternoon. This should help in eradicating any lingering stratus
although flow is rather weak. Will also have some warm air advection from the S
to help. Unfortunately...quite a bit of cirrus will be streaking
in from the west in the afternoon...to filter what sunshine we manage
to get. Inherited temperatures close to new guidance with little
Cirrus Sunday night along with stratus developing on east slopes
may keep temperatures from bottoming out. Trend in models is for a weaker
surface low along southeast coast early Monday. As such...probably
looking just light precipitation across the mountains Monday
morning...with thermal profiles supporting mainly -fzra with a
brief shot of snow on the front end. Most of this concern would like
in Pocahontas Colorado. Elsewhere...outside of the mountains...just have
some schc probability of precipitation for a passing -shra in the morning. There may be some
lingering -ra or dz in the northern mountains Monday
afternoon...otherwise looking at a dry but cloudy end to the day.
Tried to code up some warmer temperatures east of i79 corridor to west slopes
aided by some downsloping...where some middle 50s possible in the
afternoon. Have generally upper 40s to lower 50s elsewhere. Cad
locations will struggle to get out of the 30s however.
Attention quickly turns to well advertised strong synoptic system
for midweek. Upper trough will undergo significant amplification
across the plains and upper Midwest Monday night and Tuesday.
Energy rotating around the base of the trough will close of an upper
low midweek amid strong upper jet dynamics. As this occurs surface
cyclogenesis across the deep south will occur and track into Great
Lakes by Wednesday. While the models vary on eventual lowest
pressure with this...they all seem to agree on the magnitude of
pressure falls with bombogenesis likely to occur before becoming
This all means chaotic sensible weather heading into Christmas. With
strong and deep southeast flow developing Tuesday and Tuesday
night...felt a drier forecast was the way to go except along the east
slopes where light rain or dz is possible. Did leave some schc probability of precipitation
in though but thinking mainly dry for daylight hours Tuesday. It
will be rather warm despite middle and hi clouds overhead. Warm GFS
looks to be the way to hedge with low 60s a good possibility
across The Lowlands and especially downslope region just east i79
where middle 60s is not out of the question. Quite a bit cooler on
east slopes. Rain showers chances begin to increase Tuesday night...first
across southeast Ohio and NE Kentucky...increasing across remainder of County Warning Area toward
Wednesday morning as the surface low strengthens and resulting
baroclinic zone approaches. Lows Tuesday night were held up
significantly given the amount of downsloping bl winds. Temperatures
will fall quickly behind the front with shsn expected. Highs
Wednesday tricky as ckb to ekn may be able to sneak up to near 60
before the front crosses. As the cold front pushes through suspect
some of those strong winds aloft will mix down...especially in the
Post frontal regime. Flow nearly perpendicular across isentropic
surfaces along with a tight surface gradient and cold air advection will ensure
strong gusty winds...Christmas evening night and early Christmas day
itself. 30 to 35 knots gusts looks to be in the cards...higher across
the mountain ridges.
Long term /Wednesday through Friday/...
active weather pattern continues in the long term period. Still a
chance for some light precipitation Monday night/ Tuesday as low
pressure moves northeast along the coast. Expecting precipitation to
mostly be in the form of rain...except across the mountains there
-sn or a -rasn will be observed. At this point...impacts for this
event look minimal.
Focus then shifts to an upper low across the Midwest...with surface
low pressure and associated cold front Tuesday night into Wednesday.
Out ahead of the front...moisture and temperatures will be on the
increase...with precipitable water values prognosticated to rise over an inch...and
temperatures expected to be warm enough everywhere for precipitation
to initially fall as rain. This will change however on
Wednesday...as a cold front moves through the area Tuesday
night/early Wednesday...with temperatures falling behind the front
on Wednesday...gradually changing any lingering precipitation to
snow County Warning Area wide. In addition to the snow...winds will pick up along
and Post frontal passage. Also...a rumble of thunder cant be ruled
out during this period with the frontal passage.
This remains a tricky system to forecast in terms of overall
impacts...as ground temperatures may at least initially remain warm
enough...particularly across lowlands...to limit snowfall
accumulations. Have however decided to go ahead and highlight the
storm in the severe weather potential statement...since it will affect the area Christmas evening into
Christmas. Speaking of Christmas day...area will be under the
influence of the upper low for at least the first part of the
day...with periods of -shsn.
Aviation /14z Saturday through Wednesday/...
stratus deck should gradually lift northwestward early this
morning...but may remain in Ohio today. A low pressure system
moving well south of the region will provide some clouds today and
possibly some precipitation...mainly in Virginia and southeastern WV. Some
MVFR cloud restrictions are also possible in Virginia and southeastern WV.
As the system moves away...the stratus deck is expected to build
back southeastward over much of the area tonight.
Forecast confidence and alternate scenarios through 12z Sunday...
Forecast confidence: low on the timing and placement of the stratus
Alternate scenarios: timing of the stratus deck moving northwestward
could change considerably. Timing of the stratus deck returning
Saturday night could vary.
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 14 15 16 17 18 19 20 21 22 23 00 01
EST 1hrly 09 10 11 12 13 14 15 16 17 18 19 20
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 M h h h h h h h h h h h
ekn consistency h h h h h h h h h h h h
pkb consistency h h h h M M M M M M M M
ckb consistency h h h h h h h h h h h h
After 12z Sunday...
IFR possible in mountains Sunday night Monday with a wintry mix.
IFR possible in rain changing to snow Tuesday night into Wednesday.