Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS62 KGSP 170732

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
332 AM EDT Mon Jul 17 2017

A weak frontal boundary will approach the area today, increasing
the chances for widespread showers and thunderstorms. A strong
upper ridge will then gradually build into the region during the
mid-to-late week, bringing hot temperatures and reducing the coverage
of diurnal showers and thunderstorms.


The axis of the long wave trough will retrograde a bit today, as a
short wave trough digs from the Ohio Valley toward the southern
Appalachians. Weak boundary/surface trough should become positioned
near the Appalachians this afternoon, which along with the usual
differential heating/ridge top convergence will allow scattered to
numerous showers and storms to fire across the high terrain by
mid-afternoon. Very weak shear combined with moderate-to-high
downdraft CAPE should ensure that outflow boundaries associated with
any developing convection once again run amok, providing a focus for
additional convection across the foothills and Piedmont during the
late afternoon and evening. Moderate to strong buoyancy, supported
in part by unseasonably steep mid-level lapse rates (6.5-7 C/km)
within the mid-level thermal trough will support a higher risk for
isolated pulse severe storms than what was seen yesterday.
Microbursts will be the main threat, but large hail cannot be ruled
out in light of the slightly lower freezing levels. Max temps are
expected to be 2-3 degrees below climo thanks to the anomalously low
heights. Convection will diminish through the evening, giving way to
a seasonably mild night.


As of 255 AM EDT Monday: the short-term fcst picks up at 12z on
Tuesday with weak upper trofing over the East Coast and persistent
and very broad upper ridging in place over the rest of the CONUS.
The upper trof is expected to linger over the region thru most
of the period before finally moving offshore early Thurs. As it
does, the upper ridge will spread farther into the region from
the west. At the sfc, broad high pressure will be centered well
to our north with the Bermuda High in place offshore. The overall
synoptic-scale pattern is not expected to change significantly
thru the short-term period with weak high pressure persisting
to our north and relatively steep low-lvl lapse rates remaining
over the fcst area each day. Tues will likely see more widespread
convection compared to Wed, as the upper trof axis is expected to
have shifted east of the CWFA by early Wed. Temps should remain
near normal thru the period.


As of 240 AM EDT Monday: the extended fcst picks up at 12z on
Thursday with very broad upper ridging covering most of the CONUS
and a lingering upper trof slowly moving off the Atlantic Coast.
Over the next couple of days the ridge will flatten as upper trofing
amplifies over Eastern Canada. By the end of the period early next
week, heights will start to lower again as the Canadian upper trof
digs farther southward. At the sfc, broad high pressure will be in
place over the southeast with the Bermuda High in place offshore.
The models keep some degree of weak lee trofing over the fcst area
for most of Thurs and Fri and then dissipate it as low-lvl sly flow
strengthens over the weekend. Other than that, no other significant
pattern changes are evident. As for the sensible fcst Thurs should
be the least active/driest day of the period, with the rest of the
period seeing a return to diurnally-driven climo PoPs each day.
Temps will be a good 4 to 6 degrees above climatology thru the
period with heat index values approaching advisory criteria over
the weekend.


At KCLT and elsewhere: A light/moist SE flow, along with wet ground
resulting from heavy rain/convection Sunday evening is expected to
result in development of low stratus and fog across much of Upstate
SC and in the mtn valleys toward daybreak. In fact, some IFR clouds
are already showing themselves in these areas, and expect cigs to
gradually expand and lower to LIFR over the next 3-4 hours. At least
IFR visby is also expected, but periods of LIFR certainly cannot be
ruled out. At KCLT/KHKY, restrictions are a little more uncertain,
owing in particular to the lack of rainfall on Sunday. However,
there`s enough of a signal in guidance to tempo a brief period of
LIFR cigs at KCLT around sunrise. Otherwise, surface winds will
remain light, generally favoring a S/SE direction. Another round of
scattered convection is expected this afternoon/evening, and all
sites receive a prob30 for TSRA by late afternoon.

Outlook: Scattered to afternoon and evening thunderstorms are
expected again Tuesday across the area, with better coverage over
the mountains. Morning fog development can be expected in the
mountain valleys and in areas that receive rainfall the previous
afternoon/evening. Drier air will likely limit convective coverage
for Wednesday and Thursday, with typical mid-summer conditions
returning by Friday.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       Med   69%     High  96%     High 100%     High 100%
KGSP       Med   64%     High  85%     High 100%     High 100%
KAVL       Med   77%     High  93%     High 100%     High  96%
KHKY       High  93%     High  96%     High 100%     High 100%
KGMU       Med   70%     High  83%     High 100%     High 100%
KAND       Low   58%     Med   76%     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:




AVIATION...JDL is the U.S. government's official web portal to all federal, state and local government web resources and services.