Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
1220 PM EDT Wednesday Jul 23 2014
cold front slowly sinks south...increasing showers and storms
through tonight. Shortwave passes over front early Thursday.
Drier air arrives on Thursday. Brief high pressure Friday.
Near term /through tonight/...
1030 am update...
adjustments made to probability of precipitation and sky to reflect current conditions and
trends. Increased probability of precipitation/sky just a bit mainly southeast of the i79
corridor as a couple of thin prefrontal bands of showers and
embedded thunder move slowly east/southeast. Lowered probability of precipitation through
the morning hours over the northwest half of the area with current
visible showing a good amount of sunshine over that area. Still expect
a quick ramp-up of clouds and precipitation by the early/middle afternoon hours.
certainly was a warm and muggy overnight and early morning...with
dew points on either side of 70 degrees.
Have low confidence on exactly how the areas of convection will
evolve today into tonight. Yet...tried to keep the higher probability of precipitation...in
the likely range...out ahead of the front for today...then lingered
those higher probability of precipitation a bit longer in our southern counties late
tonight...as the middle level 500 mb trough axis acts on the baroclinic
Even as dawn approaches...could not rule out showers forming this
morning...patches of clouds have been forming past few hours.
Probably related to the increase low level flow...could not
locate/find any disturbances. So we still kept the fog at a minimum
for dawn. Mostly in the deeper mountain valleys.
Some thunderstorms could form during the daytime instability further
south...away from the approaching front...over southern counties.
Equilibrium levels try to reach 35 to 40 thousand...especially across
southern lowlands this afternoon. Middle level winds rather weak.
Yet...could not rule out a pulse storm reaching severe limits...but
overall the threat for a lot of damaging wind gusts or large still
appears to be rather low. Of course the usual lightning and
downpours still deserves respect.
Have the front itself reaching into the middle Ohio Valley near
Marietta and Parkersburg around 00z this evening...then reaching out
southern mountains around bkw about 09z Thursday. Yet...winds at
most levels begin to veer before the surface front passes.
Have thunder chances decreasing north/S overnight...even though probability of precipitation
remain relatively high in the south during the late night hours.
Lowered maximum temperatures...especially in the north where clouds
and higher probability of precipitation expected sooner.
Have the north wind driving south in southeast Ohio tonight...with
some clearing there late tonight...and lowered minimum temperatures
a bit especially from Hocking Valley North.
Short term /Thursday through Friday night/...
while cold front will be through forecast area to start the short
term...Post frontal precipitation will still be lingering as upper level
trough approaches. Will be drying out for Friday as surface high
pressure crosses. All models show a fairly weak 500mb shortwave
trough sliding across in northwest flow Friday night into Saturday.
Increased probability of precipitation Friday night anticipating decaying convective complex
approaching from the west on a strong warm air advection at 850mb. Also increased
probability of precipitation on Saturday with the actual upper level ripple.
Behind the cold front...and with lingering clouds...expect high
temperatures on Thursday to stay below 80. Added a couple degrees to that
for Friday with more sunshine...and then another couple degrees
Saturday as the winds turn more southerly. Expecting a cooler night
Thursday night with lots of readings in the 50s. Clouds should keep
Friday night just a touch warmer.
Long term /Saturday through Wednesday/...
two distinctive short wave evident in 500 mb charts will cross the area
Saturday and Sunday...keeping chances for showers and storms at
least parts of up coming weekend. The first comes along the back
side of an upper trough and the second one in a zonal flow aloft.
Models quantitative precipitation forecast fields keep Saturday relatively dry...and target more the
system on Sunday with a vorticity maximum in the northern stream passing
over an old frontal boundary over our County Warning Area. The a cold front
approaches the area from the northwest early Monday
morning...keeping the possibility for more precipitation.
Therefore...increased chance probability of precipitation Saturday night into likelies for
Sunday...as expected convection moves east Sunday night.
High pressure behind the cold front takes control later Monday
through the middle of next week with near normal temperatures.
Used a blend of different guidance...warmer Saturday night into
Sunday per deep southwest flow and associated warm advection...with
a cooler trend after the weekends front.
Aviation /16z Wednesday through Sunday/...
near term models continue to form spotty showers and a few
thunderstorms this morning. Cells did form pkb to ckb vicinity around
10z. May be related to the increasing low level flow...after 2
days of dead flow.
Outflow fromm older convection sinking south through Ohio. Increased
probability of precipitation sooner in southeast Ohio this morning.
Still timing the front to reach the middle Ohio Valley around pkb about
00z...then ekn to crw around 04z...and the southern mountains around
bkw before dawn...around 08z.
Timing the various rounds of convection today into tonight...has
confidence level lowered to low. There could even be some separate
convection forming over the southern counties...away from the
front...due to the daytime instability. Have the likely
probability of precipitation...most coverage...ahead of the front itself. Those likely probability of precipitation
reaching into southeast Ohio after 15z...and into central West
Virginia toward 18z...then heights to crw corridor 20/21z...and bkw
after 00z. Again that is for the most coverage.
Ceilings 2 to 3 thousand feet and visibility at or below 3 miles in any prefrontal
In the wake of the front...have showers lingering across southern
and mountain counties at 06z Thursday...with wave action along the
front. So holding likely probability of precipitation through the night...but transitioning
to mostly showers...rather than thunderstorms.
Ceilings lowering 1 to 2 thousand feet and visibility around 3 miles in Post
frontal showers. Ceilings over high mountains likely to drop below
1 thousand feet and visibility below 3 miles.
Meanwhile...drier air moving south into southeast Ohio and toward
pkb. So have ceilings starting to improve/lift from the north toward
06z Thursday...then continuing to improve in the middle Ohio Valley 06z
Forecast confidence and alternate scenarios through 18z Thursday...
Forecast confidence: low.
Alternate scenarios: timing the various clusters of showers and
thunderstorms today and tonight will likely 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
EDT 1hrly 10 11 12 13 14 15 16 17 18 19 20 21
crw consistency h h h h h h h h M M M M
heights consistency h h h h h h h M M M M M
bkw consistency h h h h M h h h h h h M
ekn consistency M h h h h h M h M M M h
pkb consistency h h h h h M M h h h h h
ckb consistency h h h h h h M M M M M h
After 18z Thursday...
IFR conditions in lingering wave along the front over southern West
Virginia and southwest Virginia into Thursday morning.
IFR possible Saturday and Sunday in rounds of convection.
pkb ASOS is not sending a complete observation. National Weather Service techs are
working on the problem.