Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
638 am EDT Sat Sep 20 2014
a weak ridge of high pressure will linger atop the region through
tonight. Temperatures will moderate over the weekend before a cold
front crosses the Carolinas Sunday night. Cool and dry high pressure
will spread across the region through middle week.
Near term /through tonight/...
1030 UTC update...sky cover has been updated from the latest
infrared satellite imagery. Probability of precipitation have been further reduced along the
Blue Ridge per radar trends.
At 230 am EDT Saturday...an upper trough will amplify over the upper
MS River Valley today...while an upper low persists off the Georgia
coast. The upper trough reaches the lower Great Lakes tonight...
while the upper low weakens and moves up the Carolina coast.
A ridge of high pressure associated with a high off the coast of
Nova Scotia will remain banked up against the southern Appalachians.
The models show drier air moving into our area from the NE today...
limiting the chance of precipiation....despite a light upslope flow
from the southeast. By tonight surface winds back from NE to north...
introducing a downslope component...as a surface wave moves up the
Carolina coast. Temperatures will run near normal.
Short term /Sunday through Monday night/...
as of 200 am EDT Saturday...the main feature of the short range
forecast will be the cold frontal passage Sunday night which will
have little fanfare. We start at 12z Sunday with plenty of dry air
and low level wind shifting from north to northwest in response to a
coastal low departing the NC Outer Banks moving NE. There will be a
500mb trough dropping southeast from the Great Lakes at 12z with associated
cold front crossing the Ohio Valley. Low level wind will back from
northwest at 12z to west at 18z Sunday then west-southwest at 00z Monday ahead of the
cold front. All models show good instability and convection ahead of
the front as it crosses middle Tennessee and Kentucky with 1700 cape on the GFS at
18z passing Nashville. All instability GOES away quickly when the
sun GOES down which is when the front arrives at the NC mountains
there is now enough cape in the GFS model to to have thunder in the
NC counties bordering Tennessee from 22z Sunday to 04z Monday. Only showers
after midnight which may last in the NC mountains until near daybreak
Monday. The front crosses NE Georgia...Carolina foothills and much of the
Piedmont without any shower activity late Sunday night and early
Monday. Maximum heating late Monday will result in some convection but
the front will be toward the coast at that time. Dry air will move
in from northwest over our area late Monday and Monday night with center of
dry and cooler high pressure over Indiana at 12z Tuesday.
Long term /Tuesday through Friday/...
as of 220 am Saturday...the medium range forecast picks up at 12z
Tuesday with the longwave upper trough already lifted NE of the region
on the GFS and the last frame of the NAM showing axis of the trough
aligned across the East Coast states. Heights will be rising from
the west. The center of the high will move from Indiana 12z Tuesday to
New England 12z Wednesday. This high will remain near New England creating
a cool wedge down the eastern Seaboard for our region Wednesday through
Friday. Another high will cross central Canada in middle week and merge
with this first high. 925mb wind will be from the NE Tuesday and become
more easterly Wednesday and Thursday with a good fetch off the Atlantic.
Cloudiness will slowly increase. The upper pattern in middle week will
be a broad ridge across the Continental 48 states. A trough enters
the western states at the end of the week. In the later half of the
week there will be deeper moisture to the south of our region and
the semi upslope with a general east wind at times depending on the
orientation of the high. Will continue to slight probability of precipitation for the south
and east zones late in the week. Temperatures will be a few degrees below
normal with perhaps the cooler of these days being on Thursday.
Aviation /12z Saturday through Wednesday/...
at kclt...VFR. Drier air moving in from the NE will limit sky cover
and precipitation chances. NE winds will persist today...backing to
the north tonight as low pressure moves up the coast. A guidance blend
does not favor fog this morning or Sunday morning.
Elsewhere...the arrival of drier air from the NE will limit sky
cover and probability of precipitation in the foothills. Morning restricitions even appear
unlikely at kavl as cloud heights have risen. Guidance does favor
restrictions at kavl Sunday morning. NE winds will persist in
the foothills today...backing to the north tonight as low pressure moves
up the coast...while kavl winds will back from southeast to northwest.
Outlook...conditions should remain generally VFR for the latter part
of the weekend...but with Mountain Valley fog near kavl in the early
morning hours. A cold front will bring a chance for restrictions
mainly over the mountains Sunday night and Monday morning. High pressure
builds back in early next week.
10-16z 16-22z 22-04z 04-10z
kclt high 100% high 100% high 100% high 100%
kgsp high 86% high 100% high 100% high 100%
kavl medium 77% high 100% high 100% high 100%
khky high 93% high 100% high 100% high 100%
kgmu high 86% high 100% high 100% high 100%
kand high 87% 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)