Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1023 am EDT Tuesday Jul 28 2015
high pressure will persist over the region through Wednesday...with
continued warm temperatures. A weak cold front will approach the
area from the northwest on Thursday and settle just south of the
region on Friday. The front will likely remain stalled just south of
the area through the weekend...with cooler temperatures expected.
Moisture should increasingly return northward over the front the
latter half of the weekend into early next week.
Near term /through tonight/...
as of 1000 am...fog and low stratocu is pretty much dissipated across
most of the area. Conditions are currently muggy...with dewpoints still
in the low-middle 70s across the Piedmont...and middle-upper 60s in the mountains
this should result in convective cumulus developing/filling in across the
region fairly quickly late this morning. The latest cams in decent
agreement on early convective initiation starting around
midday...with shotgun chance coverage expected during the afternoon hours.
Shear is weak...and instability will be modest. The biggest threat looks
to be heavy rain with thunderstorms this afternoon.
Near term models show the center of the 500 mb high over the Central
Plains...with northwest to southeast heights across the western Carolinas. Recent
west/v images indicated that well develop vorticity maximum was moving over the
western Ohio River valley. 0z runs of the near term models did
resolve this feature very well...but the NAM appears the best
initialized with the feature. The vorticity should track southeast through the
day...reaching the southern Appalachians by early this evening.
Forecast soundings show greater instability and lower level of free convection this
afternoon compared to the past several days. Given the approach of
the middle level feature and more supportive thermal profiles...I will
forecast 40 probability of precipitation across the mountains and 30 probability of precipitation east. The center of the
vorticity is expected to pass to the SW...however...convection across the
forecast area may remain well into the evening. I will keep scattered probability of precipitation in the
forecast until midnight. High temperatures this afternoon will
remain comparable to the past two days...slightly cooler than
Tonight...convection after midnight is forecast to remain
sparse...but enough to support schc probability of precipitation. Periods of debris
clouds...mild thicknesses...and light south low level winds should keep
min temperatures mild. Using a blend of preferred guidance...I will
forecast lows in the upper 60s within the mountain valleys to low 70s
Short term /Wednesday through Thursday night/...
as of 245 am EDT Tuesday...a broad upper ridge will stretch across
the southern tier of the United States on Wednesday. Weak lobes of
vorticity may drop southward through the western Carolinas Wednesday
afternoon along the eastern periphery of the ridge. Mountain triggering
of convection is likely early Wednesday afternoon...especially along the
eastern slopes where low level convergence will be best. Any early to
middle afternoon mountain activity may develop eastward off the higher
terrain into the Piedmont through the evening and early overnight
Gradual height falls are then expected through Thursday...but with
the best shortwave energy associated with a vigorous northern stream wave
passing north of the area from the Ohio Valley to the middle Atlantic through
Thursday night. The developing trough will allow a cold front to arrive
in the southern Appalachians from the northwest Thursday afternoon...but
it will likely stall over the lower Piedmont through early Friday
morning. Above climatology temperatures will persist through the period.
Long term /Friday through Monday/...
as of 245 am EDT Tuesday...more prominent height falls are expected
on Friday...with an eastern Continental U.S. Trough developing and lingering
over the region through the weekend into early next week. The
stalled boundary along the southern periphery of the area will allow
deeper moisture to remain close by...but with some measure of drying
arriving from the north Friday into Saturday. A decent north to S
gradient of slight chance to solid chance probability of precipitation will be warranted
both afternoons. Maximum temperatures will fall to or below climatology values.
There is some potential for a weak disturbance in the NE Gulf of
Mexico to get entrained into the trough and feed even better
moisture northward through the Piedmont of the Carolinas Sunday through
Monday. Will keep associated probability of precipitation fairly conservative in the chance
category given the uncertainty...but continued cooler maximum temperatures
looks more likely with no 90s expected anywhere in the County Warning Area Sunday to
Aviation /15z Tuesday through Saturday/...
at kclt...recent satellite images and observations indicated
widespread low clouds and patchy fog across the I-77 corridor.
Forecast soundings and several MOS guidance indicates that MVFR
ceilings may thicken one to two hours after sunrise...remaining
through most of the morning. I will use a tempo during the 12z to
15z period...followed by a from group for bkn035 at 16z. Cams and
persistence support a tempo between 19z to 23z for thunderstorms and rain. Winds
should remain between 160-180 degrees around 5 kts through the
Elsewhere...kavl and khky may see vlifr to LIFR conditions through
middle morning. Elsewhere...MVFR ceilings may linger at kgsp and
develop at kgmu during the early daylight hours. The afternoon
approach of a weak middle level disturbance should yield a round of
rain showers/thunderstorms and rain late this afternoon and evening. I will include a prob30
or tempo in each taf...generally between 20z to 24z. Mountain MVFR
ceilings may redevelop late tonight...especially over areas that see
rain this afternoon and evening.
Outlook...a middle level ridge will remain across the western Carolinas
through middle week. A longwave trough will amplify across the Atlantic
state late in the week...with the likely passage of a cold front on
Friday. The potential for convection will increase each day this
14-20z 20-02z 02-08z 08-12z
kclt medium 67% high 100% high 100% high 91%
kgsp medium 60% high 100% high 100% high 95%
kavl high 100% high 100% high 100% medium 72%
khky medium 67% high 100% high 100% medium 66%
kgmu medium 60% high 100% high 100% high 100%
kand high 100% high 100% high 100% high 95%
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)