Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
441 PM EDT Monday Jul 28 2014
Canadian high pressure will move in behind a cold front tonight and
will dominate the surface pattern through midweek...leading to well
below normal temperatures more typical of late Summer or early
autumn. The surface high will weaken and moisture will return for
the weekend...but temperatures will remain below normal.
Near term /through Tuesday/...
430 PM EDT update...very nice dry airmass continues working in from
the north with fairly deep vertical mixing producing moderate gusts
mountains and low end gusts non/mtns. No sigfnt change needed to the forecast
with only minor tweaks made to the T/dew point grids.
As of 2 PM Monday...an anomolously strong upper trough will continue
to establish itself over the eastern U.S. Through Tuesday an upper low
spins over the northern Great Lakes. The surface cold front has
cleared the area early this afternoon and will reach the coast by
evening. Behind the front...gusty northwest winds are bringing much dryer
and cooler air into the region. The airmass that is overspreading
the region is similar to what you would expect in middle to late
September. Outside of the mountains...sky conditions will be mostly
clear through Tuesday with winds diminishing early tonight. In the
mountains...a few northwest flow showers are expected as deeper moisture
noted in satellite pics over the Ohio Valley pivots southeast and reaches
the NC border counties tonight. Will carry low end probability of precipitation in the NC
border counties to account for that. The northwest flow showers should end
early Tuesday as dryer air arrives. Minimum temperatures tonight are
forecast to be in the low to middle 50s over the mountains with even
some 40s possible at elevations above 5000 feet. Outside the
mountains...low to middle 60s are expected. On Tuesday...maximum temperatures will
be 8-10 degrees below climatology.
Short term /Tuesday night through Thursday/...
as of 145 PM...the main story for middle-to-late week will be the
abnormally deep upper trough over the east. The upper trough bottoms out
with 500 mb height values more than 3 Standard deviations below
normal on Wednesday morning centered over NC. The Continental
surface high moving in behind the trough is not especially strong...
but thickness values will be such that temperatures will be on the order of
ten degrees below normal. The temperatures are expected to be similar to
what is normal for the last day of Summer...and with the dryness of
the air mass...it will feel more like early autumn both Wednesday
and Thursday. There should be some return of moisture at low levels
with a light southeast or east flow...so isolated showers were included mainly
over the balsams on Wednesday afternoon...and then across most of
the mountains on Thursday afternoon. Forecast soundings show warmer air at
middle levels which will cut down on buoyancy to a great degree...so
thunderstorms are not likely.
Long term /Thursday night through Monday/...
as of 230 PM Monday...the latest guidance shows an upper trough
remaining over eastern North America through the weekend...although
the axis of the trough migrates to the west on Friday. This should
allow for continued weak moisture return at low levels through the
period...making the atmosphere a bit less inhospitable to deep
convection. That should permit the development of mainly diurnal
showers and thunderstorms each day...with the better chances over
the mountains as is typical. The upper trough will pull out a bit on
Monday as an Atlantic subtropical ridge strengthens and consolidates
over Bermuda. That should allow for an even better chance for
showers and storms on Monday afternoon. Temperatures will start to slowly
warm for Monday Onward.
Aviation /21z Monday through Saturday/...
at kclt and elsewhere...VFR conditions will prevail through the taf
period at all sites as cold front moves away from the area and
breezy donwslope winds prevail. Winds will be northwest and gusty through
the afternoon hours...but diminish after sunset. Winds will
gradually neer to the north-NE late tonight.
Outlook...dry high pressure will prevail through midweek. The only
possible restrictions will be early morning fog in the mountain
valleys. Moisture will increase by late week as easterly flow
returns leading to increasing precipitation/fog/stratus chances.
20-02z 02-08z 08-14z 14-20z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 97% medium 62% 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)