Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1245 am EST Wednesday Nov 25 2015
cold and dry high pressure will linger over the region through
midweek. A moist cold front is expected to approach the area by the
end of the week increasing the chance for widespread precipitation
through the weekend and into the start of next week.
Near term /through today/...
as of 130 am...grids look good early this morning. Only minor tweaks
for extreme near term temperature/dewpoint trends. No significant changes.
As of 930 PM...patches of cirrus continue to move overhead...and
that will persist overnight. The forecast remains on track. No changes.
As of 155 PM...continued quiet through the near term. Upper ridge
builds into the area tonight and Wednesday. At the surface...high pressure
center over our area weakens...but ridging remains in place as
another high pressure center strengthens and moves east from the
Great Lakes into New England. Jet stream cirrus will continue to
spread over the area and will thicken with time. Low level flow will
turn southeasterly during the day Wednesday allowing moisture to move north toward
the area. However...do not expect any low clouds to move in until
after this period as the best moisture remains south of the area.
Should see warmer lows tonight with increasing thicknesses and cirrus.
Values will be around 5 degrees below normal. Highs Wednesday will be
similar to Tuesday...and could even be a little warmer...depending on
how thick the cirrus becomes.
Short term /tonight through Friday/...
at 230 am Tuesday...on Wednesday evening low amplitude upper
ridging will be over the Gulf states...while a weak upper trough
will be north of the Bahamas...and a strong closed low will be over
Nevada. By Thursday morning the Atlantic low drifts NE...the Gulf states
ridge weakens...and the western low progresses to Utah. The upper
ridge amplifies from the Gulf states to middle Atlantic coast...while
the upper low to the west remains nearly stationary...and the
Atlantic low drifts southeast to the east of the Bahamas. By Thursday
evening the eastern ridge flattens slightly as an upper trough
progresses across eastern Canada.
At the surface...high pressure will remain along the eastern
Seaboard from Wednesday night through Friday....with the European model (ecmwf)
showing a bit more Atlantic moisture spreading inland toward the
Appalachians than the NAM. This moisture should be quite shallow...
and isentropic upglide will generally be lacking...however some
moist upslope flow into the Blue Ridge may support a small chance of
A cold front will approach from the northwest on Friday...reaching the Ohio
and middle MS river valleys by days end. Moisture ahead of the this
front will extend nearly to the Appalachians. Temperatures will warm
from near normal to above normal under the amplifying upper ridge.
Long term /Friday night through Tuesday/...
as of 205 PM Tuesday...the medium range forecast picks up at 00z on
Saturday with flat upper ridging over the southeast Continental U.S. And a broad upper
trough digging down across the Great Lakes. At the same time...a long
lived and large cut-off low continues to spin over the western
Continental U.S.. over the weekend...the Great Lakes trough gradually moves
offshore with most of its energy remaining to our north. The upper
ridge is expected to maintain its presence to our south while the
closed 500 mb low eventually approaches the Ohio River valley by the
very end of the period. The models had been trying ot reabsorb the
low back into the northern stream...however they are keeping it
largely intact as it slowly drifts across the Continental U.S..
At the surface...the evolution of the synoptic pattern remains fairly
unclear for most of the period. At the start of the period late
Friday/early Sat...an elongated and moist cold front will be
approaching the County warning forecast area from the northwest. The latest model runs are
suggesting a slower progression of the frontal bndy with the deeper
moisture not penetrating as far south as previously depicted and the
front essentially laying down across our northern fringe. Both the
GFS and European model (ecmwf) now have a very brief reinforcing high moving into the
Carolinas by late Sat/early sun. The remainder of the medium range
is unclear. The GFS tries to keep some degree of wedging over the
County warning forecast area well into Tuesday with corresponding deep moisture in place. The
European model (ecmwf) develops a mesolow to our west on sun and moves it up towards
New England over the next 24 to 48hrs. This acts to push the surface
high away from the forecast area early next week. As for the sensible
forecast...no major changes were made with probability of precipitation lowered on Sat and early
sun and increased a bit for Monday. Temperatures start out above climatology
and cool on sun and Monday as The Wedge pattern persists.
Aviation /06z Wednesday through Sunday/...
at kclt and elsewhere...VFR through the period. The center of the
surface high pressure area will continue shift farther NE late
tonight. Winds will generally be light/vrb early in the period picking
up from the NE during the day as the ridging strengthens. High
clouds will continue to stream across the area through the
period. Southeasterly low level flow will pick up late in the
period and should begin bringing more middle- to possibly low VFR
clouds especially toward kclt at the end of the period but timing
and heights differ quite a bit with different guidance so will
wait for 12z tafs to reevaluate and introduce into the tafs.
Outlook...low level moisture will return from the Atlantic Wednesday
night and continue into the weekend...which could result in a low
cloud ceiling restriction at times.
05-11z 11-17z 17-23z 23-00z
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)