Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
136 am EDT Sat Aug 30 2014
warm front crosses tonight into Saturday. Turning hot and more
humid Saturday in deep southwest flow. Moisture increases in that
flow...with an upper level disturbance from the Gulf Crossing Sunday.
Near term /through today/...
isolated convection is less than impressive...but really cannot
take it out of the forecast through 12z given the warm front...as
weak as it is...moving northeast.
Previous discussion below...
clear to start beneath upper level ridge...as surface high moves
offshore. Cumulus was starting to pop across SW Virginia and southwestern WV...along
and S of a warm front there. Have schc / isolated convection there late
this afternoon into this evening.
Any early evening convection will likely die with the sunset...but
then refire overnight over central portions of the area as elevated
convection ahead of the advancing warm front...along axis of 345k
850 mb Theta-E and negative showalter. Have 20 kts of feed...30 kts west
of the Ohio River but no real focused low level jet spatially and forcing is
weak...so expect area coverage overnight into Sat to be scattered at
best. Latest near term models have actually backed off on
convection late overnight into Sat morning.
Afternoon convection may fire along and SW of the warm front over
the northern WV mountains Sat. Convection may also start firing over the
western fringes of the forecast area late Sat...as the first of a series of
waves coming out of the Gulf of Mexico...ahead of an upper level short wave
trough approaching from the west...approaches.
Liked higher met values for lows tonight...blended in bias corrected
version. Little change on highs Sat...which are between the met and
Short term /tonight through Monday/...
Saturday night - Sunday... area remains under SW flow aloft as a
short wave trough progresses eastward across the Great Lakes. Deep layer
moisture will arrive overnight Saturday night and...along with an
approaching short wave trough from the SW...will increase probability of precipitation to
categorical by 12z sun for most lowland locations. It appears that
there will be two waves of precipitation Sunday...with the first wave
crossing west/SW to NE during the morning hours and a second wave
towards the late afternoon and early evening hours. Without being more
deterministic than the science can offer...did make an attempt to
depict the two waves of precipitation with categorical probability of precipitation with
each...surrounded by likely and high chance probability of precipitation. Did in fact
lower probability of precipitation to high chance for locations to the northwest of the
mountains around the 18z-21z time frame...when and where cross
section analysis indicates decent downward motion almost up to
500mb in the S/southeast downsloping flow. In reality...precise timing of
convective precipitation is a bit tough and may certainly vary...but in
the end do believe that by the time Sunday comes to an end many
locations will see some precipitation Sunday. Generally expecting around
a half inch...with the usual higher amounts in stronger storms.
Will leave the potential for flash flooding in the severe weather potential statement as there is
some potential for training cells. Previous forecast had a good handle on
maximum temperatures...still expecting general low 80s in The Lowlands.
Sunday evening - Monday... prognosticated second batch of precipitation will be
exiting to the northeast middle/late evening. Lingered slight/low
chance probability of precipitation through the entire overnight period for most locations
with a decent amount of low level moisture remaining yet suspect that
most lowlands will be dry after midnight-2am heading into Monday
morning. However...another short wave with lesser moisture will be arriving
for Labor Day and have middle/high chance probability of precipitation with this feature by Monday
afternoon...which previous forecast had a good handle on. Maximum temperatures Monday
will be similar to Sunday/S...perhaps a degree or two warmer.
Long term /Monday night through Friday/...
long term period can generally be characterized by zonal flow aloft.
Leaned wpc for the most part with a few tweaks here and there. Warm
and muggy conditions will continue for the most part with periodic
disturbances and subsequent mainly diurnally-driven precipitation chances.
Aviation /05z Saturday through Wednesday/...
crw trying to go into fog at this time...but have some developing
cloud cover off to the southwest and likely moving in. Big
question is will it prevent the fog from fully developing over the
next half hour...or will it sneak down briefly. Also...the nature
of the cloud cover does not lend much confidence to it remaining
established through the night. Yet another wrinkle to deal with in
the fog forecasting tonight.
All in all...believe that the clouds will win out...and do not
carry many restrictions tonight. Ekn and ckb look to stay clear
the longest...but have clouds moving in after 09z or so. Neither
site shows signs of fogging just yet with a 3-4 degree dewpoint
depression. Would really Love another ob before issuing
these...but that is not going to happen.
Forecast confidence and alternate scenarios through 06z Sunday...
Forecast confidence: medium.
Alternate scenarios: timing...extent and dissipation of fog
overnight depending upon timing of clouds associated with the
approaching warm front.
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 08/30/14
UTC 1hrly 06 07 08 09 10 11 12 13 14 15 16 17
EDT 1hrly 02 03 04 05 06 07 08 09 10 11 12 13
crw consistency M M M h h h h h h h h h
heights consistency h h M M h h h h h h h h
bkw consistency h h h h h h h h h h h h
ekn consistency l l l l M M M h h h h h
pkb consistency h h M M h h h h h h h h
ckb consistency h h M M h h h h h h h h
After 06z Sunday...
IFR possible in showers/storms Sunday...and then in dense early
morning valley fog early next week.