Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston WV
502 PM EDT Wednesday Apr 1 2015
high pressure heads east tonight. Warm front Thursday. Wave along
strong frontal zone Friday. In its wake...cold front sweeps through
Friday evening. Cooler Saturday...with high pressure building in.
Near term /through Thursday/...
lots of sunshine today...with nary a cloud on visible satellite
across the County Warning Area. This is thanks to a high pressure system currently
over northern West Virginia. This high will pass to the east
tonight...with southerly winds beginning to increase on the back
side by morning. With the high overhead this afternoon...light
and variable winds are in place. Very dry air in the lower
atmosphere is yielding relative humidity values in the 20s and low 30s east of
the Ohio River...and in the low to middle 30s in southeast
Ohio...creating some fire weather concerns.
Surface low will move into the western Great Lakes tonight...and
drive a warm front across the forecast area on Thursday. Best
chance of precipitation with this will be in southeast Ohio...but have isolated
to scattered showers/storms across most of the County Warning Area at some point
Thursday afternoon. The chance of thicker clouds does create the
potential for a bust on Thursday high temperatures. Previous forecast is
higher than all new guidance...in fact the mav went from low 80s
for crw a couple runs ago to upper 60s with the recent 12z run.
Bias corrected guidance is running quite a bit higher than the raw
output. With all that said...opted to blend in some of the warm
bias corrected numbers...ending up 2 or 3 degrees cooler than the
previous forecast...and quite a bit warmer than MOS.
Short term /Thursday night through Saturday/...
two distinct areas of strong divergence aloft at 250 mbs...one
overnight Thursday night moving through southern Indiana into Ohio by 06z
Friday. Another was associated with the surface wave along the
frontal boundary during the day on Friday. 12z GFS further south on
that support Friday...compared to the 12z NAM.
Precipitable water increases to around 1.3 inches by 06z Friday and
remains until frontal passage. Basing forecast on front passing
pkb-heights around 00z Saturday...then quickly reaching ekn-bkw by
With support aloft...have one heavier batch of showers/embedded
thunderstorms figured for overnight Thursday night in our Ohio
Valley counties including southeast Ohio and NE Kentucky. I lot of leftovers
should linger Friday morning. Second batch of heavier showers and
embedded thunderstorms Friday afternoon into early evening.
Currently have its heaviest rain axis from north central WV SW to
With low level flow at 40 to 50 knots on Friday....despite minimum
instability and the leftover convection Friday morning...still
concerned some of that wind may mix down in the showers Friday
afternoon or early evening. Would not need T. The gusty wind threat
may be a bit further south than the maximum rainfall axis.
Will add the 2 concerns to our hazardous weather potential in .
Still thinking about 2 inches of rain storm total would be needed
for high water concerns. If The Rounds Friday afternoon affect the
same areas as overnight Thursday night...we could not completely
rule that out. Also...some damaging wind gusts may develop Friday
afternoon in the showers as the wave organizes.
In the wake of the front...held onto higher probability of precipitation a bit longer in the
western lowlands during Friday night. We still have on either side
of an inch of snow accumulate at or below 3500 feet in the WV mountains for 06z
to 12z Saturday. Clearing develops Saturday...with high pressure
No big changes to our maximum and minimum temperatures. Of course...
temperatures will remain mild Thursday night in the warm sector.
Friday maximum temperature highly dependent on the timing of
specific rounds of showers.
Long term /Saturday night through Wednesday/...
high pressure provides a dry close to this upcoming Easter weekend.
A front approaches from the north and gets close to the northern edge of the
County Warning Area sun nt...before retreating north on Monday. This continues the dry
Models concur on a low pressure system and cold front approaching
from the west Monday nt and Tuesday. After that...though...model timing
differences show up. The European model (ecmwf) continues to present the slower
solution...with the low center degenerating into several weaker flat
waves passing just north of the County Warning Area through the balance of the period.
It has a new low pressure center just reaching the lower Ohio Valley
at the end of the period...12z Thursday day 8...which then crosses the
County Warning Area day 9.
The faster GFS has the original low center plugging right
along...passing north of the area Tuesday nt...and dragging its cold front
across the area overnight into Wednesday morning. The wpc maps follow the
European model (ecmwf) but their probability of precipitation and other elements reflect more of a blend...as
does this forecast.
This all hinges on how much energy from western Continental U.S. Troughiness scoots
east. The GFS quickly scoots a piece of it east...allowing ridging and
surface high pressure to build in its wake day 7. The European model (ecmwf) tries to
bring the bulk of the trough eastward...but much more slowly...keeping
the weather unsettled pretty much the balance of the period...if not
the balance of the work week.
Blended in wpc and bias corrected MOS guidance for lows through the
period and for highs Monday. Have lows a little lower than previous
under high pressure Sat nt...and highs a bit higher for Easter
Sunday. Little temperature changes made beyond Monday with previous
forecast accepted for highs Tue-Wed.
Aviation /21z Wednesday through Monday/...
VFR expected through the period...although am expecting some
showers/storms Thursday. Best chance will be across southeast Ohio...and
could get MVFR in any stronger showers or storms. Did mention thunderstorms in the vicinity
at heights and pkb. Variable winds today will become more southerly
tonight into tomorrow...with some gusts around 20 kts during the
Forecast confidence and alternate scenarios through 18z Thursday...
Forecast confidence: high.
Alternate scenarios: may get brief flight category restrictions in
showers/storms Thursday afternoon.
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 20 21 22 23 00 01 02 03 04 05 06 07
EDT 1hrly 16 17 18 19 20 21 22 23 00 01 02 03
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 18z Thursday...
IFR possible in showers and/or storms Thursday night through
fuel moisture generally running under 10 percent according to RAWS
across the forecast area. This combined with relative humidity values dropping
into the 20s this afternoon will continue to provide enhanced
risk of fire spread. Fortunately...winds are fairly
light...generally under 10 miles per hour.
Winds will pick up late tonight out of the south as a high
pressure passes to our east. Expecting southerly winds of 5-15 miles per hour
gusting to 20-25 miles per hour. Dewpoints will increase as a warm front
passes...but a very warm afternoon will still yield relative
humidity levels dropping into the 30s to low 40s. Isolated to
scattered showers or storms are possible with the warm front.
A cold front will bring wetting rain Friday into Friday night.