Scientific Forecaster Discussion
fxus62 kgsp 171504
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1104 am EDT Tue Sep 17 2019
a cold front will drop southward through the area today and tonight,
with cool, surface high pressure building in behind this feature,
and remaining in place through the end of the week.
Near term /through tonight/...
as of 1050 am: deep northerly flow acting on mid-level moisture is
resulting in a decent amount of terrain-induced mid-level cloud
cover across the forecast area this morning. These should gradually
dissipate as drying occurs in the mid-levels and the flow begins to
veer in the low levels. This will give way to another unseasonably
warm and humid day across the forecast area, with moderate
instability expected to develop this afternoon, especially across
the mtns. Differential heating should result in isolated to widely
scattered convection developing across the usual high terrain
locations by mid-afternoon. Pops will then increase across the
northern Piedmont/foothills zones by the end of the day, as
low-level convergence increases along back door cold front that is
forecast to approach the I-40 corridor this evening.
Into tonight behind the front, as showers/tstorms gradually taper
off, cool sfc high pressure will begin to build in from the NE - the
beginning stages of The Wedge scenario on tap for rest of the week.
Short term /Wednesday through Thursday night/...
as of 300 am EDT tuesday: the short term begins Wednesday morning
with upper ridging stretching from the Texas Gulf Coast to the Great
Lakes, Humberto off the East Coast moving toward Bermuda and slowly
phasing with a deep trough off eastern Canada, and another trough
pushing into the Pacific northwest. Surface high pressure in place
over eastern Canada under the confluent flow aloft will dam down the
eastern slopes of the Appalachians, with a marked change in
temperatures in store...10 to in some areas almost 15 degrees cooler
for highs on Wednesday than what we'll see today. Orographic lift
combined with a little wave moving down the northerly flow aloft
will lead to some precip chances especially across the mountains,
though certainly not a wash-out. Much cooler temperatures for
Wednesday night as well.
The upper ridge will elongate to the northeast as we move into
Thursday, but the damming will remain even as the parent high slides
south toward Long Island. Another really beautiful day in store for
Thursday with skies clearing and highs again 3-5 degrees below
Long term /Friday through Monday/...
as of 310 am EDT tuesday: damming high will be in place as we move
into the extended, but with the upper ridge continuing to shift
east, the high will slide toward the Carolinas and continue to
moderate as it does so. Northeasterly winds will shift around to
southeasterly as the high works toward the region. As we move into
the weekend, the western trough will push east along the northern
tier, forcing the upper ridge to stretch east-west across the south and
Gulf Coast, and the surface high will push just offshore. Expect a
slow warming trend through the period, such that by early next week
we'll be back 5-7 degrees above normal. At the end of the period, a
weakening cold front will be approaching the area and may bring some
showers to the mountains, but otherwise no rain expected through the
Aviation /15z Tuesday through Saturday/...
at kclt and elsewhere: aside from patchy Mountain Valley fog this
morning, expect VFR to prevail at all taf sites through the morning
hours. This afternoon, expect increasing coverage of VFR cloud cover
with isolated to scattered showers and thunderstorms as a weak back
door cold front drops southward through the area. Rain showers/thunderstorms and rain activity
could linger into the overnight hours, but given lower confidence,
have not highlighted this in going fcst. Cigs will gradually lower
per latest guidance, to MVFR late overnight into, with patchy areas
of fog possible. Winds overall will NE at or below 5 kts, increasing to at or below
10 kts tonight.
Outlook: anticipate the return of VFR by Wednesday afternoon. Dry
high pressure builds in for the end of the week, with just some
Mountain Valley fog each morning for restrictions.
15-21z 21-03z 03-09z 09-12z
kclt high 100% high 100% high 98% high 87%
kgsp high 100% high 100% high 100% high 96%
kavl high 100% high 100% high 80% high 90%
khky high 100% high 100% high 85% Med 68%
kgmu high 100% high 100% high 100% high 82%
kand high 100% high 100% high 100% Med 78%
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: