Scientific Forecaster Discussion
fxus61 krlx 212040 cca
Area forecast discussion...corrected
National Weather Service Charleston WV
440 PM EDT Wed Aug 21 2019
late night storms possible tonight. Cold front nudges into area
Thursday afternoon. Reinforcing cold front Thursday night and
Near term /through Thursday/...
as of 439 PM Wednesday...
Re-did pops and quantitative precipitation forecast for the entire near term period. Very dry
air aloft has negated much in the way of convective development
this afternoon. Thus, I limited convective coverage to isolated
for the remainder of today (perhaps locally better coverage
between kpkb and kckb where a sliver of deeper moisture exists).
This evening, a convective complex is prog to develop in the
vicinity of the lower Ohio River valley and shift eastward
overnight...before gradually weakening. Some of this activity
may move into the western County Warning Area late in the night, before
weakening further as it tries to push into West Virginia. As
such, I have added a mention of precip for late tonight for
roughly the western third of the County Warning Area. An isolated strong storm
may occur late tonight, but chances of severe weather are
currently on the lower end of the scale.
Amount of late night convection will greatly impact the chances
of additional convection during the day on Thursday. If
coverage late tonight becomes greater than currently forecast,
then much of the day on Thursday could be rather quiet. However,
if the aforementioned convection fails to materialize across
the area tonight, then coverage during the day Thursday good be
quite significant. For now, limited pops for Thursday afternoon
to only 50 percent, with higher pops then expected early
As of 225 PM Wednesday...
Surface high pressure continues in control with mostly clear
skies. Afternoon temperatures could reach around 90 degrees over
The Lowlands. With surface dewpoints in the upper 60s and
diurnal cu developing, differential heating boundaries could
initiate showers or storms this afternoon and evening. Shower
and storm activity, if any, will decrease before midnight.
A cold front is expected to reach portions of southeast Ohio and
northern WV by 12z Thursday. Although showers or storms can not
be ruled out, convective activity should stay relatively quite
Synoptic models slowdown the front, weakening or becoming
diffuse while drifting south on Thursday. Surface dewpoints in the
lower 70s and pwats around 1.6 inches should remain in place
Thursday afternoon. Models suggest sfc-based cape exceeding
2,500 j/kg and deep layered shear values from 25 to 30 knots.
These ingredients together with h500 vorticity maxima passing
through, pose a threat for strong storm to produce gusty winds
and periods of heavy rain.
Models bring a secondary cold front with a surge of dry and
cool air from the northwest that should push lingering moisture,
showers and storms south and east of the area later on Friday.
Short term /Thursday night through Saturday night/...
as of 250 PM Wednesday...
Surface front will sag into the area Thursday evening
with convection ongoing to start the period. Models are
consistent in slowing the boundary down considerably overnight.
While there may be a lull at some point Thursday night,
convection should increase in coverage again late with favorable
jet dynamics overspreading the area as a surface wave develops
along the surface front. Where the boundary becomes nearly
stationary will ultimately determine the axis of heavy rainfall
heading into Friday morning with latest runs of models
indicating along and in the vicinity of the i64 corridor
extending into the northern lowlands. We will have to watch
portions of the northern lowlands for flood potential given the
antecedent conditions. Further south toward the i64 corridor,
despite the abnormally dry conditions and high ffg across this
area, I cannot rule out isolated high water given high pwats and
the potential for training. This would most likely be limited
to urban and poor drainage areas.
The upper trof axis sharpens as the day progresses Friday as it
pivots into the area. This will drive the cold front south of
the area late Friday, which is now supported by most of the
model solutions. I suspect there will be some dense River Valley
fog to contend with by Saturday morning. After the fog
dissipates, a nice it will be a nice afternoon with lower
humidity and temperatures.
Long term /Sunday through Wednesday/...
as of 250 PM Wednesday...
Upper level low across New England will keep the influence of
the trof across the area with another comfortable day for
Sunday. Thereafter, the trof moves out and is replaced by brief
S/W ridging Sunday night and Monday. Southwesterly flow will
develop Tuesday and Wednesday with deep moisture advection aimed
at the region ahead of another upper trof. This will allow for
scattered, mainly diurnal, convection each day.
Aviation /21z Wednesday through Monday/...
as of 130 PM Wednesday...
Widespread VFR conditions will continue as a surface high
pressure remains in control through tonight. Afternoon
differential heating will likely produce sfc boundaries where
convective initiation could take place. However, poor forcing
from above will keep most showers or storms disorganized. Therefore,
isolated thunderstorms could be possible, but uncertainty runs
low for a direct hit to any of our terminals.
A cold front will approach from the northwest overnight,
reaching portions of southeast Ohio by 12z Thursday. Showers or
storms ahead of the cold front should stay disorganized per the
lack of heating during the morning under weak deep layered
shear of 20 knots. The cold front should become nearly
stationary while weakening through Friday. Models bring sfc-
based cape values exceeding 2,000 j/kg south of the frontal
boundary. Pwats should stay around 1.7 to 2 inches into Thursday
evening. Thunderstorms could produce periods of IFR and strong
gusty winds along their path Thursday and early Friday.
Synoptic models suggest a reinforcing shot of dry and cool air
from the northwest should push moisture, clouds and any
convection south of the area by Friday evening.
Forecast confidence and alternate scenarios through 18z Thursday...
Forecast confidence: high.
Alternate scenarios: afternoon storm coverage may vary. Valley
fog or stratus possible Thursday morning where afternoon storms
produce precipitation prior to arrival of slow moving cold
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 18 19 20 21 22 23 00 01 02 03 04 05
EDT 1hrly 14 15 16 17 18 19 20 21 22 23 00 01
crw consistency h h h h h h h h h h h M
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 M M
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 18z Thursday...
IFR/LIFR conditions along strong thunderstorms possible.
Increasing shower/thunderstorm potential along a sagging cold
front through the day Thursday and Friday with widespread
MVFR/IFR ceilings. Cold front slowly sags south through Friday
evening with cooler and drier conditions expected Saturday.