Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
1035 am EST Friday Dec 20 2013
high pressure hangs off Atlantic coast as a front approaches from
the west. That front will get held up by a wave before crossing late
Sunday and Sunday night.
Near term /through tonight/...
1030 am update...
Forecast generally on track. Started out on the warm side this morning
but thickening clouds have tempered a further rise for now. Band
of rain showers this morning across southeast Ohio/NE Kentucky to continue into afternoon
with more of the scattered variety. Some of these will try to sneak
into lowlands today. With dry layer in the low levels...would
initially be more sprinkles than anything else.
Previou discussion below...
First wave in the series riding up the boundary to our west
currently in western Oklahoma...with boundary stretching from there
up to around Detroit. Models in good agreement with not a whole lot
of eastern push expected on this boundary through the near term...as
the surface wave slides NE into the eastern Great Lakes by early
Saturday morning. With this wave...have likely entering northwest County Warning Area by
around 18z...and making it as far east as the Ohio River before
lifting north along with the wave. Next surface wave approaching by
late in the forecast period...so having probability of precipitation increasing again over
southeast Ohio toward 12z Saturday. Aloft...several ripples move through
the 500mb flow with plenty of moisture advection...so do have slight
chance to chance probability of precipitation across the rest of the County Warning Area tonight.
For highs today...the mav and met are fairly close...and blending
them into previous forecast resulting in only minor changes. Used a
consensus/met blend tonight...going a bit warmer in the west and
just a touch cooler in the east. Have a near steady to gradually
rising trend after midnight. Regardless...very mild night for middle to
late December with lows only dropping into the lower 50s across The
Lowlands...and 40s in the mountain valleys.
Short term /Saturday through Sunday night/...
primary forecast concerns in the short term continue to revolve
mainly around flooding potential from prolonged rain event...with a
secondary concern for severe wind gust potential late Saturday and
Overall not much change from previous forecast thinking. Deep layer
moisture will be over the area by 12z Sat with quasi-stationary
front waffles to the northwest from Lake Erie southwestward towards
the lower Ohio River. First surface low pressure wave already passing by
the north will attempt to push the front southeast initially but
quickly return northwestward and away from the northwest zones between 18z Sat
- 00z sun as the next stronger low moves towards the lower Ohio
River by 00z sun. Much of the stronger lift...and thus heavier and
more persistent precipitation...remains north of the warm front during this
time and should serve to keep the highest amounts of precipitation over
central and SW Ohio much of Saturday. Still however...plenty of
moisture over the northwest zones to continue categorical probability of precipitation through much
of Saturday...although in reality there should be some breaks.
Further southeast over central lowlands of WV...expecting very
little in the way of precipitation by the afternoon and a few breaks in the
clouds may actually be realized. MOS guidance giving generally low
70s for locations such as crw. 925mb temperatures of ~17c would actually
suggest around the 75f-77f range. Won't go that high with a good
deal of clouds around...but with good warm advection ongoing during
the day Saturday and precipitation not appearing to be much of a factor for
the central WV lowlands...have continued trend of nudging maximum temperatures
upward just a bit. Cooler of course across the southeast Ohio zones closer
to frontal zone along with periodic precipitation. Still expecting upwards
of 1.50in to perhaps 2.00 inches across the far northwest
zones...which is about on par with previous forecast. Elected not to
issue any flood highlights with this package.
Saturday night the surface low continues northeast along the front and
is prognosticated to be located around the Southeast Michigan/Northwest Ohio region by
12z sun. Surface cold front will be entering the western zones by this
time with the occlusion process driving the front east despite
continued SW flow aloft. A convective line of showers should be
located along or perhaps out ahead of the front which will also
propagate east across the forecast area...with the front and deep
layer moisture east of the i79 corridor by 18z sun. This will be yet
another high momentum Transfer event with 925mb winds around 50kts
and 850mb winds around 70-80kts. Also looks like some accompanying
weak instability...which may or may not result in any thunder...yet
might aid in dragging some strong wind to the surface. The southeast Ohio
zones will be most prone to this possibility as the 925mb low moves
northeast across central Ohio...with the strongest winds associated with
it remaining over that part of the forecast area and mainly between 06z
and 12z sun. All in all certainly not expecting a widespread wind
event but from an operational standpoint cannot with complete
certainty rule out a severe wind gust or two across the west. Storm Prediction Center
still has the extreme western counties of Ohio/Kentucky in a slight risk
for winds...and with those things in mind went ahead and mentioned
the small possibility of strong wind gusts in the severe weather potential statement. Outside of
the expected main line of convective showers...will be generally a
very breezy night...especially over the eastern high terrain.
Should see a break in the precipitation for most...if not all...by late in
the day on Sunday with slightly cooler temperatures. However...another surface
low on the front now to our southeast along with the approaching
upper trough still to the northwest...will bring another slight
chance/low chance of probability of precipitation mainly by and after 06z Monday.
Long term /Monday through Thursday/...
the long term begins with an exiting cold front to the east Monday
and a return to more seasonal temperatures with surface high pressure
building in from the west...upper level trough remains in our
vicinity Monday and Tuesday with mostly slight chance rain Monday
and slight chance snow showers Tuesday as cold air builds in...by
midweek upper level ridging reinforces surface high while a
deepening trough over the northern plains begins to move southeast
toward the Great Lakes and Ohio Valley...introduced slight chance
probability of precipitation in southeast Ohio early Thursday afternoon with a mix of
snow/rain...slight chance precipitation spread into WV overnight Thursday
and early Friday before slowly drying out through Friday...before
another clipper system moves quickly across the Ohio Valley Saturday.
Aviation /15z Friday through Tuesday/...
expect gradually lowering VFR ceilings from west to east through the
taf period. Will be dropping into MVFR ceilings along and west of the
Ohio River this afternoon into tonight. Will also start to see some
rain showers along and west of Ohio River with MVFR visibilities.
Surface winds have picked up at heights and pkb...so removed low level wind shear
mention there. Still calm at crw...however low level VAD winds off
the krlx radar were under 35kts and expect surface winds to pick up
soon so did not include low level wind shear at crw either with 12z tafs. Surface
flow remains out of the SW through the period with gusts of 15-20kts
this afternoon into tonight.
Forecast confidence and alternate scenarios through 12z Saturday...
Forecast confidence: high.
Alternate scenarios: timing of MVFR across west may 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 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 12z Saturday...
IFR in rain at times this weekend...more middle Ohio Valley than