Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
1245 PM EST Friday Dec 13 2013
cold high pressure moves off the North Carolina coast today. A low
pressure system tracks northeastward through the middle Ohio Valley
late Saturday...and then reforms along the East Coast on Sunday.
Near term /through tonight/...
no changes to the package this morning.
high pressure will slide off to the east today...with a
southwesterly flow...and warm air advection ensuing. Temperatures will be much warmer
today than as of late...with many lowland counties topping out in
the upper 30s to lower 40s.
Flow will turn more southeasterly late tonight as low pressure
across the Southern Plains moves towards the region and the high
continues to push off to the east. This low will spread
precipitation back into the area...mainly after 03-06z Saturday.
Some timing issues concerning onset of precipitation...but general
agreement that most areas...particularly southeast Ohio...northern
WV...and northern mountains will be mainly snow. May see a very
brief period of a mix at onset...but wet bulbing effects will
quickly cool atmosphere enough for bulk of precipitation to be
snow. Parts of the WV lowlands...including Charleston...the
southern Coal fields...southwest Virginia...and eastern Kentucky...will be more
likely to see a mix Saturday morning...as temperatures will remain
With saturated soundings...and good dynamics/lift...will see some
light snowfall accumulations begin Friday night/Saturday morning.
Generally have around an inch coded up across southeast
Ohio...northern WV...and northern mountain zones...but will see
additional accumulations past the 12z/end of the near term forecast
time. So...thinking a good burst of snow in aforementioned areas at
end of near term period.
Short term /Saturday through Monday/...
main feature this period is a low pressure system already impacting
the area as the period begins...all the way from its position over
the middle Mississippi Valley. The low pressure center moves NE to the
middle Ohio Valley by 00z sun...and then western PA by 12z sun.
This track brings warmer air into the area first thing Sat morning.
Temperatures start out near and just below freezing far northern
lowlands and in the northern mountains...getting above freezing for
all but essentially Pocahontas County come 00z sun. Temperatures
aloft actually lag surface temperatures as far as getting above
freezing...with 850 mb values starting out near or below freezing over
much of the area Sat morning...and then rising above freezing all
but Pocahontas County but also much of southeast Ohio come 00z sun.
All of this minimizes the freezing rain threat...except perhaps the
Pocahontas County-ish area Sat afternoon. In Ohio...temperatures
holding below freezing suggest some form of mixed precipitation
throughout the day. The upper level; system is an open short wave that
does not phase with its more northern stream kicker at least until
it has passed beyond the County Warning Area...so total quantitative precipitation forecast amounts of a third to two
thirds of an inch seem reasonable...used a NAM/GFS blend there.
Snowfall amounts come out to 2-3 inches in 12 hours ending 18z Sat
for interior southeast Ohio son have severe weather potential statement mention for possible advisory
there. Similar amounts in the northern WV mountains are below the
higher criteria there...but may have to watch for a little ice there
at least in Pocahontas County Sat afternoon so highlighting that
area in severe weather potential statement as well.
Have upslope snow showers Sat nt into sun as the surface lows combines
with a coastal low near Long Island...New York by 12z sun...and then moves
up the New England coast on sun. Also have increased cloud cover as
low level moisture hangs on through the day under the weak middle
December sun Sunday. High pressure passes by to the S sun
nt...allowing warm advection cloudiness to spread into the area
Monday...making for a rather cloudy forecast overall this period.
Not much change to hourly temperatures Sat in light of the latest
NAM. Highs are similar to previous package and closest to the lower
NAM guidance. Highs sun were left largely unchanged...a bit lower
over the higher terrain with little diurnal recovery in the cold
advection there...closest to the lower mav. Little change to highs
Monday...closest to the all-blend which is lower than the mex.
For lows...blended in the higher met for Sat nt for little
change...and the bias corrected adjmex for slightly higher values on
the now cloudier sun nt. Overall small diurnal ranges in a cloudy
middle December forecast.
Long term /Monday night through Thursday/...
models are struggling with a series of northern stream disturbances
and their timing during this period. For now...will run a blend of
European model (ecmwf) ensemble mean and gefs ensemble mean. This actually damps out
the disturbances...so the forecast may show a bit of a dry bias.
Forecast confidence during this period remains low.
Aviation /18z Friday through Wednesday/...
ceilings gradually lower through 06z tonight with the approach of
another winter storm system. Forecast begins MVFR...then
deteriorates as precipitation overspreads the area. Precipitation
types are likely to change through the forecast at each
terminal...and this will result in the lowering of the confidence
of the forecast due to timing issues and uncertainty as well.
Most locations will see snow at the onset...with a transition to
ice pellets and eventually rain...with combinations of said types
in between. Freezing rain is not in the forecast at this
time...even in the mountain terminals of bkw and ekn...although
eastern slopes of Pocahontas County may end up with freezing rain
In the end...could see a quick change from VFR to IFR visibilities
in snow at first...with a possible improvement to MVFR as rain
mixes in. All the while...ceilings will continue to lower and
flirt with the IFR threshold as well. A stronger wind at bkw will
help keep the ceilings up just a bit.
Forecast confidence and alternate scenarios through 18z Saturday...
Forecast confidence: medium.
Alternate scenarios: timing of and precipitation type could
vary...resulting in fluctuating flight categories.
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 18 19 20 21 22 23 00 01 02 03 04 05
EST 1hrly 13 14 15 16 17 18 19 20 21 22 23 00
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 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 h h h h h h h h
ckb consistency h h h h h h h h h h h h
After 18z Saturday...
IFR may linger in snow showers into Sunday.