Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
328 am EDT Friday Aug 22 2014
a broad upper level ridge of high pressure will continue to provide
very warm temperatures across the region into Saturday. A back door
cold front will then push into the area from northeast ushering in
cooler temperatures starting Sunday. Temperatures will gradually
return to normal through next week.
Near term /through tonight/...
should be quiet for the remainder of the pre-dawn hours with only
some high level convective debris clouds. Meanwhile...an mesoscale convective system should
break up to the north as it moves over the central Appalachians.
For the next 24 hours...the upper pattern will undergo some
amplification...especially with a ridge axis off to our west that
will also sharpen. At the same time...an upper trough will dig off the
East Coast. This will gradually veer the upper flow around to north-northwest by
Saturday morning...that should point the train of vorticity centers
topping the ridge in a sort of ring-of-fire in our direction.
Whether or not any of these remnants brings anything other than more
debris clouds is the big question. There is a general consensus
among the models that most of the deep convection will move down
across Virginia and then the eastern half of NC today. However...am not
willing to rule out some convective development on the SW flank that
would move down over the mountains and northern foothills late in the day or
this evening...similar to what is seen in the Storm Prediction Center 4km WRF. So...the
forecast will feature a chance pop mainly over the mountains and along/north of
I-40 through the afternoon and into the late evening. Additional storms
could also arrive on our northern border through early Saturday morning.
That leaves most of the upstate and NE Georgia with at best isolated
coverage. Temperatures will be hot this afternoon...but probably not hot
enough for a heat advisory.
Short term /Saturday through Sunday/...
as of 245 am Friday...short range guidance indicates that a h592
ridge will remain centered across the lower Mississippi River valley
as a trough ripples across the Atlantic coast. The middle level pattern
may place the County Warning Area within the path of northwest to southeast tracking mesoscale convective system Sat PM.
Forecast soundings indicate that a weak inversion will exist around
700 mb...with convective available potential energy ranging from 1500 j/kg across the mountains to sub 500
j/kg east. The pattern and guidance would favor the mountains for
shra/tsra...with weakening expected east of the mountains as storm
encounter limited instability and down slope flow. I will indicate a
40 probability of precipitation across the mountains with 30 pop east Sat afternoon and evening.
High temperature are forecast to range around 5 degrees above normal.
Saturday night...NAM and GFS indicate that a backdoor cold front
will slide NE to SW...reaching the NC Piedmont and foothills around
midnight. Scattered rain showers and possibly thunderstorms and rain will develop along and ahead of
the backdoor cold front. I will maintain chance probability of precipitation across the County Warning Area
Saturday night. The NAM is aggressive with advecting drier air from
the NE during the daylight hours on Sunday. However...the GFS and
European model (ecmwf) are slower with the arrival of drier air...resulting in
lingering weak convection...I will linger chance probability of precipitation. Temperatures
under cloud cover and NE low level winds will likely range around 5
degrees below normal.
Long term /Sunday night through Thursday/...
as of 3 am Friday...Monday through Wednesday...medium range guidance
indicates that middle level ridging and surface high pressure will build
across the County Warning Area. GFS forecast sounding through the period shows a
persistent layer of dry air...yielding little to no instability. I
will forecast a dry period across the County Warning Area...with isolated convection
limited to the mountains high temperatures on Monday will range around 5
degrees below normal...recovering to nearly normal by Wednesday. On
Thursday...models time a cold front across the southern Appalachians
during the daylight hours. Return flow should result in build
moisture and low level dewpoints. I will forecast chance probability of precipitation for rain showers/thunderstorms and rain
with near normal temperatures.
Aviation /08z Friday through Tuesday/...
at kclt...VFR through the period. Middle/high level convective debris
expected through most of Friday morning...with a light west-northwest wind.
Expect wind to come around to something even more northwest Friday
afternoon with a few high based cumulus developing. There should be a few
thunderstorms and rain around...but the better chances will be over the higher
Elsewhere...the guidance once again hits the fog hard over the NC
mountains. Prefer to take more of a wait and see approach because
this looks like another overforecast at this time. Will keep an MVFR
at kavl for fog...but that is not certain. Wind should be west or northwest
through the period. The mountains and foothills have the best chance for
precipitation...so the prob30 will be kept at kand/khky.
Outlook...a similar pattern is expected Friday night...with mainly far
northern tier scattered convection possible. A backdoor cold front will sag
into the region through the weekend...with chances of restrictions
increasing at khky and kavl. A more diurnal pattern of early morning
low clouds/fog and scattered afternoon thunderstorms may return early next week.
07-13z 13-19z 19-01z 01-07z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 94% high 95% high 100% high 100%
khky high 91% high 95% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 91% high 95% 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)