Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
357 am EDT Tuesday Jul 7 2015
warmer breezes today. Cold front approaches from Midwest tonight...
stalling near Ohio River Wednesday. Frontal oscillates north again
Wednesday night...then south again Thursday. Flash flood concerns.
Near term /through tonight/...
overnight showers exited our NE counties past few hours.
Every fog night is unique. Thick valley fog formed by 03z in the deeper
valleys of southern West Virginia...mostly S and southeast of crw. At first
glance...it looked ideal for fog developing/spreading elsewhere too.
However...boundary layer and 925 mb flow was increasing. 88d VAD here
at rlx was 15 knots when we began the graveyard shift...it increased to
20 knots by 06z. So backed off the fog for areas west-north of crw. The deeper
valleys east and S of crw should still have fog to greet the dawn.
Do not have a great feel on how today unfolds. Am concerned the warm air
advection in the 925 to 850 mb layer may form a renegade shower early this
morning in our western counties...will have some 20/30 probability of precipitation for that.
Still hard to time prefrontal convection into the Ohio Valley counties later
today into this evening. Did go a bit earlier...based on near term model trends.
However...both 00z NAM...GFS...ECMWF were not that quick. May have more cellular
convection at first...with larger clusters moving in 00z to 06z Wednesday...and
hope weakening in rain rates during the night. Did include some gusty winds
in late afternoon and evening convection in southeast Ohio and the Ohio River
counties. Have dew points around 70 in The Lowlands this evening.
We are still concerned about the flash flood hazard for tonight into Wednesday
evening. Will continue in the hazardous weather potential and will continue
to contemplate flash flood watches.
Short term /Wednesday through Thursday night/...
a meandering front will keep the short term active. Models all have
slightly different timing and placement of this front as it meanders
across the area in response to several waves moving along it. To
start the period the front should be just to the west of the Ohio
River. While convection will sink southeast through the County Warning Area on
Wednesday...the front looks to actually lift north as a weak surface
wave moves across IL/in. Have a lull in the probability of precipitation...although still
carrying slight chance...on Wednesday night as the front remains to
As the surface wave passes to our north Thursday...the front will
sink back in Thursday afternoon and likely wash out across the
forecast area Thursday night. Some uncertainty here as the NAM looks
to actually clear the front to the south as high pressure builds
over the southern Great Lakes. The lower resolution GFS and European model (ecmwf)
are fairly Muddy through this time...but do hint at the front
at least making it into southern County Warning Area.
Have probability of precipitation beginning to increase again toward early Friday morning as
the next surface wave organizes to our west. In response the front
will sharpen and drift begin drifting back north by the end of the
Precipitable water values hangout in the 2 inch range along the
front Wednesday. Precipitable waters dip into the 1.5 inch range Wednesday night
as the front lifts farther north...but then increase back to around
2 inches Thursday as the front sinks through. This spells rounds of
showers and storms with downpours likely in thunderstorms and
stronger showers. Also have upper ridge building through the period
which should slow down cell movement some. This spells potential
water issues...and debated an area wide Flash Flood Watch. However
with uncertainty in exact placement and heavy rain coming in waves
separated by dry periods...will opt to expand severe weather potential statement mention until
Long term /Friday through Monday/...
a upper high lingers across the southeastern Continental U.S. To start this
period. Models agree with upper shortwave sliding across the
northeast periphery of the ridge to start the weekend and across the
forecast area. This will keep the pattern unsettled through the
weekend with showers and thunderstorms. With the grounds already
saturated...will have to keep a continued eye on water concerns. A
stronger wave will slide across the western Great Lakes and begin to
break down the Southeast Ridge. This will only be replaced with a
trough across the eastern Continental U.S.. the stormy pattern looks to be
maintained into next week.
Aviation /07z Tuesday through Saturday/...
every fog night is unique. Thick valley fog already formed in the deeper valleys
of southern West Virginia...mostly S and southeast of crw. In earlier tonight...it looked
ideal for fog developing/spreading elsewhere too. However...boundary layer
and 925 mb flow is increasing. 88d VAD here at rlx has increased to 20 knots
at 925 mb. Will back off on the fog for the Ohio Valley and even crw.
The warm air advection may form a renegade shower 12z to 15z in the Ohio
Valley counties...but pop too low for taf insertion.
Still hard to time prefrontal convection into the Ohio Valley counties. Did
go a bit earlier...based on near term model trends. However...both 00z NAM and 00z
GFS were not that quick.
Will transition more to multiple layers clouds and showers 03z to 06z Wednesday...
with a few embedded thunderstorms. Despite being south of front...widespread
visibility 3 to 5 miles figured...lower in any heavier precipitation.
Forecast confidence and alternate scenarios through 06z Wednesday...
Forecast confidence: medium.
Alternate scenarios: coverage of fog 06z to 12z Tuesday could vary. Timing
of convective rounds arriving between 18z today and 00z tonight in the western
lowlands could vary.
After 06z Wednesday...
IFR possible in showers and thunderstorms near the frontal
boundary Wednesday into Thursday. Potential for low stratus and fog
at night in the muggy air.