Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
127 am EST Sat Dec 27 2014
high pressure maintains control into Saturday. A cold front crosses
Saturday night and Sunday. A wave of low pressure moves along the
front Sunday. Drier...colder air slowly builds in to close out 2014.
Near term /through today/...
added sprinkles across the extreme southern WV per latest radar
images and surface observation detecting light precipitation.
Previous discussion below...
tweaked sky and temperature grids. Otherwise...no changes needed.
Previous discussion follows...
surface high pressure centered over the southeastern states will
shift east tonight and Saturday...allowing a continuing southerly
flow across the area. While the air remains relatively dry in the
lower levels until later on Saturday...middle to upper level moisture
will be increasing on broad southwest flow aloft as a progressive
upper trough well to our west shifts eastward. Models are in basic
agreement on the mass fields...but satellite imagery shows they are
likely too slow in advecting this middle to high level moisture into
our area. Main deviation to the models will be to increase clouds
faster later tonight and especially Saturday...and in turn go
slightly lower on maximum temperatures Saturday. Nevertheless...temperatures will
still be above normal Saturday despite the cloud increase. The
attending cold front remains well to the west...with only a small
chance for rain over far western and southwestern sections at the
end of the period.
Tonight will be tranquil with very light winds and increasing mainly
thin high clouds...allowing for radiational cooling to drop
temperatures below freezing again...but not as cold as last night.
Short term /tonight through Monday/...
pattern this period is characterized by fast upper level flow
through a central Continental U.S. L/west trough...and a tenacious Bahama high
that slowly flattens. Short wave trough minors out as it lifts east-northeastward out
of The Rockies...and crosses the Great Lakes on Sat. Second short wave
trough a little behind the first one and more in the southern
stream...also minors out as if lifts east-northeastward...reaching the Tennessee Valley
on sun and then crossing the Appalachians sun nt.
The short wave first drives a SW to NE oriented cold front into the area
Sat nt...and then the second short wave pushes it on through on sun even as
it generates a flat wave along it. Rain should increase from west to east
Sat nt as the front moves through. The NAM was the fast outlier
here...leaned more toward the 09z sref...which was considerably
Sunday figures to be a rainy day throughout the area with the
approaching short wave generating the flat wave along the front crossing
the area. The rain only gradually moves out of the area sun nt and
Monday...as the upper level flow does not veer much behind the exiting
short wave trough. Have total quantitative precipitation forecast with this prolonged event ranging from
almost an inch in the mountains to two dimes in Ohio...off rfc and
in generally agreement with the models...although the CMC and GFS
hint at a second maxima along the Ohio River.
The column may get just cold enough to support snow surface and aloft on
the back side of the precipitation shield over the middle Ohio
Valley Monday morning...and in the WV mountains very late Monday...as the
precipitation diminishes to a few showers and / or drizzle there.
There may be a brief opportunity for sleet or freezing rain in the
transition if sufficiently cold air arrives at the surface before we
lose the warm nose aloft. These precipitation types may eventually
need coded in explicitly depending upon how models resolve current
differences with timing and thermal structure.
Used mainly NAM based sources for temperatures...except late Monday
where the influence of colder models was allowed in. The NAM does
not support snow in the mountains through 84 hours. In the
meantime...temperatures will be steady or slowly falling sun over
the middle Ohio Valley...in the wake of the front.
Long term /Monday night through Friday/...
overall a fairly quiet long term period. Have probability of precipitation tapering off
Monday night as moisture departs. Bring back in some slight chance
probability of precipitation in the mountains for late Tuesday and Tuesday night with 850mb
temperature trough and weak 500mb shortwave trough sliding through.
High pressure noses in for Wednesday and Thursday. Both GFS and
European model (ecmwf) showing a system moving out of the lower Mississippi Valley at
the end of the week...so do start increasing probability of precipitation right at the end
of the period. Blended new wpc guidance into previous forecast for
temperatures...and then went just a touch cooler on lows.
Aviation /07z Saturday through Wednesday/...
high pressure remains in control with VFR conditions prevailing
through at least 00z Sunday. Plenty of high level clouds will move
across the area overnight. These clouds will be in the increase
Saturday as a cold front approaches from the west. Winds will
continue light from the south.
Cold front and associated precipitation will move into southeast
Ohio towards 00z Sunday...with isolated MVFR conditions forming
Forecast confidence and alternate scenarios through 06z Sunday...
Forecast confidence: high.
Alternate scenarios: none.
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.
Date Sat 12/27/14
UTC 1hrly 06 07 08 09 10 11 12 13 14 15 16 17
EST 1hrly 01 02 03 04 05 06 07 08 09 10 11 12
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 06z Sunday...
IFR possible in rain Sunday into Monday.