Scientific Forecaster Discussion
fxus61 krlx 240229
Area forecast discussion
National Weather Service Charleston WV
929 PM EST Tue Jan 23 2018
low pressure system exits northeast, but remains unsettled
through Wednesday. Warmer to end the week. Cold front next
Near term /until 6 am Wednesday morning/...
as of 620 PM Tuesday...
updating the forecast to raise sky cover overnight. Will also
adjust temperatures a bit warmer for the next several hours
based on current trends.
As of 620 PM Tuesday...
updated the pops to better handle when the atmosphere will go
auto convective with the cold air advection and hence start the
snow in earnest.
As of 205 PM Tuesday...
Lull in the precipitation this afternoon, however, low clouds
are gradually sneaking their way back into the cwa, with cold air advection and
upper trough influence across the area. Gusty
west/northwesterly wind continuing across the area this
afternoon, will decrease somewhat overnight, but overall remain
gusty for much of the period. With increase in moisture depth
overnight, and a couple of shortwaves during the period, one
late tonight/early Wednesday, and another one on Wednesday,
expecting periods of light snow showers. Little to no
accumulation expected across The Lowlands, with light
accumulations across the higher terrain. Although quantitative precipitation forecast will be
light, high snow to liquid water ratios will allow for a few
inches across the higher terrain counties. Possible that on
Wednesday, area of -shsn activity may need to be increased in
coverage and duration, but will allow future shifts to
reevaluate this based on trends.
Short term /6 am Wednesday morning through Friday/...
as of 230 PM Tuesday...
Any brief lull in showers during the day on Wednesday will fill
in Wednesday night with the passage of another shortwave evident
on all long-range models. Renewed cold air advection and some low-level flow
off the Great Lakes will again generate snow showers, primarily
across the WV mountains and perhaps into the northern WV
lowlands immediately adjacent to the mountains. Many models are
indicating more widespread snow shower activity, however cold air advection
won't be as strong as our normal Post- frontal scenarios so have
opted to dial back pops some, similar to previous forecasts,
and defer to future forecasts when hi- res moisture data becomes
available as it is more of a limiting factor. Accumulations
through Thursday morning will be on the order of 2-3" in the
High pressure builds to the southwest and slides from west to
east, turning surface and low-level flow westerly, effectively
cutting off any snow showers. Drying and warming will prevail
through the end of the short term. Clouds from the southwest
will start to stream in early Saturday morning ahead of the next
Long term /Friday night through Tuesday/...
as of 250 PM Tuesday...
Long-range models continue to struggle to grapple with the next
system, with differences existing from the top-down. This model
run, the GFS (still) tends toward a faster solution, the
Canadian toward a slightly slower/deeper solution, and the European model (ecmwf)
toward somewhere in the middle. Either way, there is
consistency in widespread, overriding precipitation setting up
over the lower Mississippi through the Ohio River valley Friday
night into Saturday, shifting westward through the weekend with
the passage of a long-wave trough in the upper levels.
Widespread rain showers are most likely late Saturday into Sunday...
model differences return for the exit of precipitation. Again,
the GFS is quite progressive with a digging trough making for a
hasty exit of rain by mid-day Sunday and enough northwesterly
flow behind to generate decent cold air advection/upslope showers. Meanwhile
the European model (ecmwf) is slightly slower with less favorable low-level flow
for showers on the backside of the system until the mid-level
trough swings past Monday evening. A stronger, digging
troughing would equate to a greater likelihood of widespread
snow showers with the arrival of stronger cold air advection on the backside of
the trough and cooler temperatures to start the work week.
Opted to stick close to a blend of operational models Sunday
through the end of the period given large model differences.
Aviation /03z Wednesday through Sunday/...
as of 625 PM Tuesday...
Colder air will gradually filter into the area overnight,
allowing for ceilings to gradually lower into the MVFR category.
The atmosphere will become auto convective later tonight,
allowing for some light snow, IFR at times. The best
restrictions should be in the WV mountains, with some
restrictions west of the mountains as well. Snow showers should
tapper off Wednesday morning, but ceilings should remain MVFR
for much of the area.
Forecast confidence and alternate scenarios through 00z Thursday...
Forecast confidence: high.
Alternate scenarios: timing and location of restrictions in
snow 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 00 01 02 03 04 05 06 07 08 09 10 11
EST 1hrly 19 20 21 22 23 00 01 02 03 04 05 06
crw consistency h h h M l h h h h M M M
heights consistency h h M l M M M h h M l M
bkw consistency h h M M h M l l l l l l
ekn consistency h M l l l M l l l l l l
pkb consistency l h h h l M h h h M h l
ckb consistency h h M l l l l l h l h l
After 00z Thursday...
IFR snow possible in mountain terminals Wednesday night.