Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 191416

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1016 AM EDT Mon Jun 19 2017

A cold front will approach the area from the west today, bringing an
increased chance for storms today. The front should then slowly push
into the Carolinas tonight through Tuesday, before stalling across
the Midlands.


As of 1015am EDT:  Currently only some light showers along the
Tennessee border with more showers anticipated this afternoon.
Latest CAM guidance suggests increasing convection after 1pm over
Western North Carolina and Northeast Georgia and spreading eastward
through the evening. NAM has convection exiting southeast out of
piedmont areas Tuesday morning as front makes some progress in that

The next 24 hours should be relatively busy as a cold front drops
slowly into the region from the WNW, nudged eastward by short waves
rotating around an upper trof whose axis remains to the west through
tonight. The best mid/upper forcing will move past to the N, but
some upper divergence could come into play late tonight across the
Piedmont. Convective instability is modest at best, though deep
layer shear improves over the recent past.  SPC outlines some slight
risk area for severe thunderstorms over northeast parts of the CWA,
though morning CAMs do not impress. There is some potential for a
flash flood threat late tonight over the Piedmont and Upstate as
storms might develop and move repeatedly along the boundary in the
presence of high PW/deep moisture/deep warm cloud depth.


As of 300 AM EDT Monday: an upper trough axis will remain nearly
stationary across the Great Lakes to the Tennessee Valley, but
should deamplify slightly on Tuesday. Then the trough will begin to
shift east. The result is that guidance is now converging a little
on the track of a tropical disturbance that will move into the Gulf
of Mexico. The consensus track is to take the low NNW toward the LA
coast or even toward eastern TX. Meanwhile, a sfc front will stall
out across central GA thru the Midlands and eastern NC. As the
tropical low drifts north across the Gulf, the front front may start
to activate and lift back north into the area late Tuesday thru
Wednesday. The 00z ECMWF continues to be the weakest and driest with
the boundary over the area. It also happens to be the furthest south
and west with the tropical track. With the front just to our south,
the southern tier will feature likely PoPs Tuesday, with CHC pops
for the rest of the area, except slight CHC near the TN border.
Wednesday may end up being relatively quiet, but the GFS and
Canadian bring moisture and instability back into the area from the
south. Will go with mainly slight CHC to low-end CHC on wednesday.
Temps are also tricky, as the bullish GFS has max temps as much as
10 deg below normal, which is pretty hard to do in mid June. Will go
with max temps a category or two below normal and min temps near to
slightly above normal under mostly cloudy skies. Heavy QPF
associated with tropical moisture looks to remain south and west of
the CWFA at least thru Wednesday night.


As of 330 AM EDT Monday: the 00z models are generally sticking to
their guns. The GFS is still the easternmost with the tropical low
track, while the ECMWF is the furthest south and west. So the GFS
lifts the low into the lower MS Valley on Thursday bringing a
potential for heavy rain with the tropical moisture then. While the
ECMWF takes the low into south TX, then gradually picks it up into
the westerlies and has the moisture spread into area Friday thru
Sunday. Either way, unsettled weather with above climatology PoPs
will remain in the medium range forecast. The exact time frame for
the biggest heavy rain and flood threat is still too uncertain to
pin down yet. Max temps will remain at or slightly below normal
Thursday and possibly thru the weekend, as the area remains very
moist with plenty of cloud cover. Min temps will be slightly above
normal thru the medium range.


KCLT and elsewhere: The main concern at daybreak was the presence
of a low cloud ceiling restriction around the CLT metro area,
hovering at the threshold between IFR and MVFR. Expect to have to
deal with this for the first hour or two until the lowest cloud deck
mixes out/lifts with some morning heating. Conditions should be VFR
but with a low cloud ceiling possible in the 040-060 range. Wind
should be S and gradually veering to SW, with some occasional gusts
in the afternoon. Wind direction may vary around thunderstorm
outflows. We will look to the development of deep convection as all
the ingredients should be in place ahead of an approaching cold
front. We really could see development at any time after about 15Z
or so, but an attempt was made to shoot for a four hour window when
convection was most likely, during the afternoon hours. This was a
difficult target to hit as the convection-allowing model guidance
had quite a bit of difference in the timing. Decided to follow it up
with a PROB30 into the evening hours after that. The actual cold
front will drift in from the NW during the early morning hours. As
this boundary lays down, it may keep precip near KCLT for the rest
of the TAF period, but the remainder of the TAFs should start to
improve. Expect some fine tuning.

Outlook: Cold front will stall over the area on Tuesday, maintaining
scattered convection and associated periodic restrictions. Morning
fog/stratus is likely to return Tue-Wed mornings. Drier conditions
may finally return during the latter part of the week if the cold
front can push south of the area. A possible tropical system could
throw all this into disarray late in the week.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High  88%     Med   68%
KGSP       High  88%     High 100%     High 100%     High 100%
KAVL       High 100%     Low   58%     Med   72%     Med   70%
KHKY       High  97%     Med   66%     High 100%     Med   66%
KGMU       Med   78%     High 100%     High 100%     High 100%
KAND       High  90%     High 100%     High 100%     High  87%

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:




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