Scientific Forecaster Discussion
fxus62 kgsp 251045
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
645 am EDT Tue Apr 25 2017
an area of low pressure will gradually weaken and drift northeast
along the mid-Atlantic coast today through tonight. Warm and dry
high pressure will filter in behind the low through Wednesday. A
dissipating cold front crosses our region Thursday, then warm and
humid high pressure builds back in for Friday and Saturday.
Near term /through tonight/...
as of 645 am EDT, last round of showers rotate trough the area this
morning. Only light precip expected with the showers.
Showers quickly taper off from SW to northwest late this morning with
precip ending by early afternoon. Clouds will linger longer however
as the cold air damming wedge takes longer to dissipate. Low level
winds do become downslope during the afternoon bringing clearing
skies from SW to NE. With these trends, highs across the I-77
corridor will remain cool while warming develops to the west. This
means highs near or slightly below normal west and around 5 degrees
below normal east.
Ridging surface and aloft move in tonight. Light winds and clearing
skies will create good radiational conditions. This and lingering
low level moisture will lead to increased fog potential. Too early
to be sure, but areas of dense fog will be possible. Lows will be 5
to 10 degrees above normal.
Short term /Wednesday through Thursday night/...
as of 300 am EDT tuesday: Wednesday looks like a quiet, pleasant
day, as sfc high pressure builds in under an East Coast ridge. Any
fog or stratus should lift/scatter out by late morning, leaving
mostly sunny skies and a light southwest wind. Max temps are
expected to be 6 to 9 degrees above normal.
Wednesday night into Thursday, the upper ridge axis will shift, as a
negatively tilted short wave trough lifts up the eastern side of a
broad long wave trough covering 2/3rds of the Continental U.S.. the short wave
looks to brush the NC mountains midday Thursday, but should be
accompanied by decent instability with a plume of moisture advecting
in from the SW. So pops ramp up to high-end chance to likely in the
west, and low-end chance east. The operational models are in agreement
on decent overlap of 40-50+ kts of 0-6 km shear and 1000-2000 j/kg
of SBCAPE just to our SW. So it will interesting to see how
convection evolves along and ahead of the trough. Temps will remain
about 5-10 degrees above normal.
Convection may linger east of the mountains well after sunset, as
25-35 kt southwesterly low level jet continues advecting higher Theta-E air into the
County warning forecast area. Min temps will be about 8-12 deg above normal.
Long term /Friday through Monday/...
as of 300 am EDT tuesday: it is going to feel like Summer this
weekend, as an upper ridge amplifies over the eastern conus, setting
up a strong Bermuda high pattern over the southeast. Diurnally
driven convection is expected both Friday and Saturday with temps
well above normal. Saturday looks like the warmest day of the next
seven, where a few spots may hit 90 in the Piedmont.
Sunday and Monday, the broad long wave trough will begin to progress
across the central conus, with its axis entering the Ohio and
Tennessee Valley states by early Monday. An attendant cold front
looks to have plenty of moisture to work with, and may be strongly
forced as it approaches the southern Appalachians. The 00z European model (ecmwf) has
come into good agreement with the GFS on the timing of the fropa
being in the 12z Monday to 00z Tuesday. The front looks to lose a
lot of its better buoyancy, as the best mid and upper support
remains in the cold air region behind the sfc front. Depending on
the speed of the front, it could provide a solid soaking rain. At
this point, it doesn't look like quantitative precipitation forecast will be excessive. Temps will
be a category or two cooler than Saturday, but still above normal.
Aviation /12z Tuesday through Saturday/...
at kclt and elsewhere: light showers and associated visibility
restrictions will end this morning. However, IFR cigs will continue
at the NC sites and MVFR cigs at the SC sites this morning. NC
improves to mfr for the afternoon and low VFR early this evening. SC
improves to VFR by noon. West to northwest winds continue through the day at
the SC sites then go light this evening. North to northwest winds for the NC
sites before going light this evening. Expect at least MVFR fog to
develop overnight with the moist ground, light winds, and clear
skies. Kavl most likely to see IFR, so have included that there. May
see dense fog elsewhere by daybreak, but not certain enough for the
taf at this time.
Outlook: conditions should continue to improve through Wednesday as
dry air works in behind the departing low. Return flow moisture
ahead of the next system will develop late in the week.
10-16z 16-22z 22-04z 04-06z
kclt Med 66% Med 72% Med 77% low 57%
kgsp high 91% Med 66% high 100% high 100%
kavl high 89% high 94% high 100% high 100%
khky high 100% high 94% high 100% high 87%
kgmu high 80% Med 63% high 100% high 100%
kand Med 66% high 80% high 100% high 100%
The percentage reflects the number of guidance members agreeing
with the scheduled taf issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link: