Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
727 am EDT Friday Mar 14 2014
high pressure will remain over the area and moderate warmer
into Saturday. A moist low pressure system will affect the southeast
from late Saturday through Monday with dry high pressure briefly
returning on Tuesday. Another frontal system is expected to develop
and bring a cold front through the region by the middle of next week.
Near term /through tonight/...
as of 530 am...forecast is on track. I did tweak hourly T/dew point grids to
line up better with observation.
As of 130 am...dry high pressure will continue to slide east off the
southeast Atlantic coast today into tonight under quasi-zonal
middle-upper level flow. Increasing return flow behind the system will
allow temperatures to rebound into the 60s across the Piedmont and Lower Mountain
valleys under sunny skies. The combination of breezy SW winds and very
low humidity will result in another day with fire weather concerns (see
fire weather section below).
Tonight...an upper shortwave will quickly cross the Great Lakes/Ohio
Valley...pushing a weak/dry cold front/surface trough through the area toward
daybreak Saturday. Forecast soundings indicate no deep relative humidity with the passage
of the wave...so the only sensible weather will be an increase in
middle-high clouds and wind shift from SW to northwest in the mountains min temperatures
will be near normal.
Short term /Saturday through Monday/...
as of 230 am EDT Friday...a 130+ knots jetlet will bisect the forecast
area on Sat in zonal flow aloft. Westerly 850 mb flow should provide
some degree of downsloping east of the mountains to warm temperatures above
climatology...with greater sky cover over the western mountains in upslope
flow. Meanwhile...a surface frontal boundary will likely remain
stalled just north of the region into Sat night.
Heights will start to fall in earnest to the west Sat night through
sun...allowing jet right entrance region divergence to set up over
the forecast area and steadily enhance low level isentropic lift
ahead of the developing lower MS River Valley system. The leading
edge of the deeper moisture should surge into the forecast area from
the SW late Sat night...with the best combination of forcing and
moisture solidy in the Sunday period. In addition to raising Sunday
probability of precipitation...will feature a smaller diurnal temperature change in the Sat night
through Sun night period. Although some degree of cad is likely
Sunday given the abundant precipitation...northern tier high pressure will be
quite slow to get established...with the parent surface high remaining
over eastern Canada. This should allow the lead surface wave to wrap along
the boundary through the area sun/Sun night. Convection will be
possible in any uncovered warm sector during the Sunday PM
hours...and wind shear should be rather Stout...however there will
be a middle level capping inversion through much of this period to
An 500 mb cutoff low will likely develop over the lower MS River Valley
by Sunday night and then migrate eastward through Monday. The general
consensus between the slower GFS/ecm Camp and the faster NAM/CMC
Camp keeps the trough axis to the west of the forecast area through Monday
afternoon. Ahead of this feature...a secondary surge of moisture may fill
back in across the area later Sunday night into Monday as another
surface wave forms over the deep S. As this low migrates to the southeast
coast...cooler thicknesses should spill southward Monday afternoon...but not cool
enough for any mixed ptype mention. Although the middle level capping
inversion will weaken with the approach of the upper trough
Monday...shear profiles and surface instability will weaken as well. The
small diurnal temperature range will likely continue through Monday afternoon.
Long term /Monday night through Thursday/...
as of 215 am EDT Friday...a progressive pattern will be in store
over the ext range. There is decent agreement with the exiting short wave
to the south of the County warning forecast area Monday night into Tuesday...however much
uncertainty exists with another short wave approaching the region Wed/Thu.
Atl moisture flux should still be high enough to produce -shra Monday
night with isent flow over a short lived and fairly weak wedge
through 12z. Soundings and partial thick nomograms indicate the
potential for -fzra across the northern NC mountains and perhaps the northwest
Piedmont later Monday night...basically during the time of lowering quantitative precipitation forecast
and probability of precipitation. Utilized the energy method in the grids which yielded a
small area of frozen precipitation in these areas...however ice accums
should be very low.
The Wedge lifts and weakens Tuesday afternoon while moisture flux
wanes. A good amount of insolation will help offset the NE/ly...then
veering surface winds...yet maximum temperatures should still be held about 5-7
degrees below normal. The next system and pre/frontal isent lift
could be affecting the area early Wednesday...but there remains some
uncertainty with the dampening of the upper wave and it/S probable
northward progression. The European model (ecmwf) is a conspicuous dry outlier while
the GFS/CMC both develop shallow moist mech lift in good southeast/ly flow
by Wednesday afternoon. Slight chance probability of precipitation were aligned with the eastern
facing upslope regions to account for this possibility. The atmos
will remain rather stable and no strong forcing will be present
through the period...yet low level moisture will be available to some
degree...enough for isolate probability of precipitation through Thursday across most locales with
perhaps some -snsh developing across the NC mountains Wednesday night
associated with a relatively weak frontal passage. With good S/ly flow and
then a downsloping flow...maximum and min temperatures will warm Wednesday and Thursday
back to normal levels over much of the County warning forecast area.
Aviation /12z Friday through Tuesday/...
at kclt and elsewhere...VFR conditions expected through the
period...with dry high pressure in place. Winds pick up out of the
SW with some 15-20 knots gusts possible...primarily across the Piedmont
sites around midday. Then winds decrease slightly and lose gustiness
this evening. Skies will be clear through the morning...then gradual
increase in mainly cirrus...lowering to a high-based altocu/St deck
this evening with the approach of a fairly dry upper wave.
Outlook...a low pressure system will develop across the southern
states over the weekend...bringing deep moisture and precipitation across
the western Carolinas from late Saturday through Monday.
11-17z 17-23z 23-05z 05-11z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 100% high 100%
khky high 100% high 100% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% 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: (must be lower case)
fire weather conditions will remain somewhat critical again today.
Temperatures will rebound more dramatically than dewpoints on
southwesterly return flow. Relative humidity thus will be only slightly higher than
yesterday. SW winds will increase to 10-15 kts...with gusts in the
15-22 knots range. Fortunately...these winds are below red flag
criteria. So after collaboration with the neighboring offices...will
drop the watch...and issue an increased fire danger Special Weather Statement for NC.
Also...a fire danger Special Weather Statement will be issued for all our SC zones...given
similar conditions to yesterday are expected again today. For NE
Georgia...fuel moisture of 6-8% and at least four hours of relative humidity...will be
enough to warrant a Fire Danger Statement Special Weather Statement for our six Georgia counties.