Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 282343
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
743 PM EDT THU JUL 28 2016
Broad surface high pressure will linger over the Southeast, while a
surface low tracks along a stationary front across the Mid-Atlantic.
This front will sag south into our area this weekend and early next
week. Another front will approach by the end of next week, keeping
afternoon thunderstorm chances elevated.
.NEAR TERM /THROUGH FRIDAY/...
2315 UTC Update: Winds were updated with a blend of the latest NAM
and ADJMAV guidance. Sky cover was updated from satellite imagery.
Pops and QPF were adjusted based on radar trends, allowing for
convection crossing the upper Savannah River Valley.
As of 2:30pm: Another hot day is underway with only subtle changes to
the forecast at the moment. Heat indices near 105 are still
forecast in far eastern zones, supporting the HEAT ADVISORY for that
area. Scattered afternoon thunderstorms are also expected, mostly
over the mountains, though some CAMs have some very isolated cells
over piedmont areas. Summertime tropical conditions continue with
high BL moisture and warm overnight low temperatures. Field of
cumulus is increasing from the west with denser coverage over areas
that the CAMs have scattered TRW. Some of these cumulus clouds may
develop into showers later this afternoon, though current radar is
Models have midlevel shortwave west of the Appalachians becoming
more diffuse tonight and Friday, with another piece of mid-level
energy replacing it from the West by late Friday. Relatively strong
surface trough along and in the lee of the Appalachians weakens on
Friday in concert with the upper wave. Result will be fewer diurnal
wind gusts as 850mb winds of 20kts today weaken to below 10kts on
Friday. Temperatures on Friday will also be generally a few degrees
cooler as due to reduction in strength of upper ridge over the area
east of the diffusing trough. Heat indices in the warmest areas
today will approach 105, areas which are currently covered by a HEAT
ADVISORY. Warmest heat indices should be at or just below 100
degrees on Friday with the lower max temps.
Afternoon CAPE is analyzed at about 1000 j/kg, with a little CIN and
not much forcing. CAMs have some scattered TRW over the mountains
this afternoon (where CAP should be broken more easily) and isolated
convective activity in Piedmont areas. Slightly better low-level
shear with the 850mb flow may support some storm outflows
approaching severe limits, though upper winds are extremely weak.
Some similar convective activity is possible Friday afternoon, but
with reduced CAPE and shear factors.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 230 PM Thursday...it looks like we will see a gradual shift of
the upper pattern through the weekend, as the broad weakness in the
subtropical ridge drifts east on Saturday and Sunday. This subtle
change should promote a bit greater coverage of deep convection east
of the mountains both days, although it might still take awhile for
convection to really get going. Thus, precip chances are slow to
ramp up and then expand east of the Blue Ridge on Saturday, meaning
that most places outside the mtns have a better chance in the early
evening. On Sunday, with a small increase in moisture, convection
may ramp up a bit earlier and coverage should be a bit better still,
so a chance will be included across the whole fcst area. Cannot rule
out a few strong/severe storms, but lapse rates look poor because of
some mid-level warm air, so that will be a limiting factor. Temps
will remain warm...on the order of a category or so above normal...
through the period. The combination of high temps and dewpoints
should not be enough to require any heat advisories.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 200 PM Thursday...the medium range begins 00Z Monday with a
modest upper level trough over the eastern CONUS. At the surface, a
weak quasi-stationary boundary will move over the southern
Appalachians and remain draped over our area through the early part
of next week. This surface boundary plus the moistening influence of
the subtropical "Bermuda" high will provide a focus for showers and
thunderstorms over the Carolinas and Georgia, so it appears
convection will be slightly enhanced over the normal diurnal
summertime trend. The boundary washes out by Wednesday as the upper
trough tilts and shifts over the east coast of the U.S. Upper
heights will rise briefly on Thursday, but lee troughing at the
surface and some upslope flow will prevent any lull in our enhanced
convective chances later next week. Another surface front and upper
trough will approach by the end of next week.
Though temperatures will decrease from current levels, maximum and
minimum temperatures will remain about a category above average
through the extended period.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
At KCLT: VFR. Southwest winds will diminish overnight, then increase
and veer northwest on Friday as a weak surface low and an
associated boundary move up the eastern seaboard. Model guidance does
not support daybreak vsby restrictions. Cigs, if any, will be brief
and at low VFR to high VFR. Convective chances are sufficient Friday
afternoon to warrant a mention in the TAF.
Elsewhere: Convective chances will be greatest in the mountains
this evening, although some activity was noted approaching the upper
Savannah river valley, and may reach SC sites this evening. Daybreak
cig and vsby restrictions are most favored in the mountains valleys
as well, including KAVL. Cigs thereafter should be brief and low VFR
to high VFR. Winds will favor the SW overnight in the foothills, and
NW at KAVL, with KHKY veering NW after dawn as weak surface wave and
associated boundary move by. Convective chances look better on
Friday, especially in the afternoon.
Outlook: Falling heights aloft and the arrival of gulf moisture will
support increasing chances of precipitation and perhaps associated
restrictions going into early next week.
23-05Z 05-11Z 11-17Z 17-18Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% High 100% Med 78% 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:
NC...Heat Advisory until 8 PM EDT this evening for NCZ037-057-072-