Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
635 PM EST Thursday Dec 12 2013
cold high pressure moving off North Carolina coast on Friday. Middle
level shortwave crosses from the southwest...bringing mixed
precipitation late Friday night...becoming mostly rain on Saturday.
Near term /through Friday/...
decent dewpoint depression in place reducing the chances for fair
weather cumulus today as high pressure noses in from the west
southwest. Upper level northwest flow will bring some middle to high
level clouds this evening and overnight before the flow turns more
zonal Friday. On the whole...the forecast is fair and dry...if not
Overnight temperatures could bottom out in the deeper valleys and
hollows...while the hilltops and ridgetops stay up just a bit.
Examination of the forecast soundings indicate complete decoupling
may not occur tonight with a light wind at the surface. This wind
may not make it into the aforementioned valleys and hollows allowing
the decoupling to occur. Off the surface...see signs of warm air
advection in southwesterly flow at the 925mb level.
In the end...still cannot get away from another cold overnight. With
the warm air advection...should see a marked improvement in the high
temperatures Friday...but still a good 8 to 14 degrees off the pace
of normal values for this time of year.
Short term /Friday night through Sunday/...
new 12z run of models came in a touch slower/colder with the warm
nose for the Friday night/Saturday system. Will trend this way...but
still expect precipitation to transition from initial snow to mix to rain
through the day Saturday. With the warm nose a bit slower to
warm...there should be less of a threat of freezing rain across and
west of the WV lowlands as surface temperatures will be climbing above
freezing before full transition to rain takes place. Granted timing
will need to be monitored for changes. With southeast flow at the
surface...expect eastern slopes to remain cooler...and freezing rain
remains a threat. Models then show the dry slot moving in late
Saturday...into Saturday night. This causes some uncertainty on quantitative precipitation forecast
and thus ice accumulations along the eastern slopes...so will
continue mention in severe weather potential statement...anticipating that winter weather headlines
of some sort may be needed this weekend. Will also continue severe weather potential statement
mention of wintry mix for lower elevations for Saturday morning.
850mb temperature trough and wrap-around moisture move in with snow showers
Sunday....with the highest probability of precipitation in typical upslope regions. We
transition from a northern jet dominate to southern jet dominate
pattern this weekend...with kind of messy flow aloft Friday into
Saturday. By Sunday...the southern jet ramps up east of the
Appalachians. A 500mb low crosses the northern Great Lakes
Sunday...which keeps 500mb flow more west than northwest and may limit some of
the typical upslope snow accumulations.
Used European model (ecmwf) MOS guidance for highs Saturday and Sunday. Blended in
bias-corrected consensus guidance into previous forecast. Have a
non-diurnal trend late Friday night into Saturday based on blend of
raw NAM and consensus guidance. And then transitioned back to a
diurnal trend late Saturday.
Long term /Sunday 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 /00z Friday through Tuesday/...
VFR through the period. Areas of high and middle clouds at or above 10 thousand feet
scattered to broken.
Winds will continue to stir on hilltops overnight...but some valleys
near towns may see some smoke build up due to wood burning for home
Forecast confidence and alternate scenarios through 00z Saturday...
Forecast confidence: high.
Alternate scenarios: some stratocumulus may form over WV mountains vicinity
ekn overnight at 3 to 5 thousand feet above ground level.
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 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 00z Saturday...
IFR possible in snow...sleet...freezing rain and rain developing 06z
to 12z Saturday...transitioning to mostly rain by 18z Saturday. IFR
may lingering in snow showers on Sunday.