Scientific Forecaster Discussion
fxus62 kgsp 211131
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
631 am EST Thu Nov 21 2019
an area of high pressure will linger over the region today. A cold
front with rain showers will approach the area from the west on
Friday and move through the region on Saturday. Cool high pressure
returns on Sunday through early next week.
Near term /through tonight/...
as of 630 am: an upper ridge builds over the area today as the
center of surface high pressure slides east across the area.
Although thicknesses rise and a light southerly flow develops,
periods of thick cirrus will keep highs in check slightly. Still,
this should put highs up to 5 degrees above normal. The flow becomes
more zonal tonight as an upper low moves across the Great Lakes
pushing a cold front into the Ohio Valley. The flow turns more
southwesterly bringing some deeper moisture and forcing into the
mountains after midnight. Breezy conditions may develop across the
higher elevations. Have a small area of chance pop moving into the
Tennessee border counties toward daybreak. Clouds will thicken and lower
across the entire area overnight. Lows will be 5 to 10 degrees above
normal, keeping any precip that does develop all liquid.
Short term /Friday through Saturday night/...
as of 315 am thursday: an upper trough will swing thru the Great
Lakes and northeast Friday, while a closed low crosses the Central
Plains. A low pressure system associated with the upper trough will
push a cold front thru the Ohio Valley and central Appalachians,
possibly reaching the Virginia/NC border by Friday evening. The forecast
area should remain mild, with increasing clouds on Friday. Some
showers may develop within increasing swly flow across the
mountains, but chances will be lower to the east. Highs will be a
couple categories above normal.
The model trends seem to be for the aforementioned front to sag
further south and backdoor into the NC Piedmont Friday night then
stall. This will result in a tighter temp gradient across the
forecast area from north to south. The front will also be a focus
for increased shower chances in addition to the overall upglide. The
southern stream low pick up speed and open up into a deep trough as
it crosses the eastern states on Saturday. The associated sfc low
will track from the lower MS valley to the northern mid-Atlantic
states. The low will push a cold front thru the forecast area during
the day on Saturday. The front will be strongly forced, and have
1.5" pwat air with it. So could see a band of some moderate to heavy
rain showers cross the area. Dry antecedent conditions and a fairly
progressive fropa should limit the excessive rain threat. With that
said, some southwesterly upslope areas will likely get 1-3" of quantitative precipitation forecast in a 6-12
hour period. So a marginal day 3 excessive rain threat has been
posted by wpc. The 00z GFS and NAM both show a band of 100-300 j/kg
of SBCAPE with the front. Confidence is still low, but will
introduce a slight chc of thunder Saturday aftn in the western and
southern zones. Given the strong shear and forcing, this could
result in a non-zero severe threat. Will continue to monitor trends.
Temps will tricky due to the fropa, but should start out above
normal in the south, and cool to near normal Saturday night.
It's still looking like only a few hours of northwest flow shower activity
may linger late Saturday night, with the higher peaks seeing a few
flakes of snow before the moisture dissipates around daybreak Sunday.
Long term /Sunday through Wednesday/...
as of 330 am thursday: quiet weather returns to the area on Sunday
(with some lingering clouds and gusty winds in the NC mountains).
Temps will top out at or slightly below normal under mostly sunny
skies. The pattern remains progressive with high pressure crossing
the area Monday, followed by the next cold front approaching the
area on Tuesday. There is still some disagreement on the details on
this next storm system, but the 00z ec and GFS agree on a cold front
and associated band of precip crossing the forecast area late
Tuesday thru early Wednesday. Temps moderate back to slightly above
normal, and precip is expected to be all rain.
Aviation /12z Thursday through Monday/...
for kclt and elsewhere: VFR conditions will continue at the
terminals as cirrus slowly thickens through the period. Mid clouds
move in overnight. Any fog this morning, at the non-taf sites, will
quickly burn off after daybreak. Light and variable winds this
morning become S to south-southwest for the afternoon with light S to SW wind
Outlook: increasing precipitation chances and flight restrictions
are expected with a low pressure system and associated cold front on
Friday and especially on Saturday. VFR returns Sunday into Monday.
11-17z 17-23z 23-05z 05-06z
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: