Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 270746
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
346 AM EDT WED JUL 27 2016
Broad surface high pressure will linger over the Southeast, before
sliding offshore as a surface low develops and moves northeast
across the Midwest and Great Lakes regions. A surface front will
remain off to our north and linger within a region between the Ohio
Valley, lower Great Lakes, and Mid-Atlantic regions. This front may
finally move into our area over the weekend.
.NEAR TERM /THROUGH TONIGHT/...
As of 315 AM: Short range guidance indicates that a sfc front will
remain stationary across the Virginias and mid Appalachians today.
The forecast area should remain of the western edge of a H5 ridge
centered off the GA coast. By this afternoon, a weak mid level
shortwave is expected to ripple east of the mtns, resulting in a
frontal wave to develop across eastern VA and a lee trof across
Carolina Piedmont. Convection should develop very similar to
Tuesday. I expect that storms will initially develop over the ridges
around 18z, then development occurring east of the mtns by 20z. I
will indicate 40 to 50 PoPs across the mtns, 30s across the NC
Piedmont, decreasing to schc over the Lakelands. One or two storms
may spawn a damaging wet microburst late this afternoon and evening.
Wind are forecast to remain out of the SW, speeds between 5 to 9 kts.
Hot temperatures are forecast across the foothills and Piedmont this
afternoon. High temperatures may generally range a degree less than
observed on Tuesday. However, mid to late afternoon dewpoints are
forecast to remain near 70, with 71 to 72 possible east of I-77. The
combination of the hot temperatures and RH values between 45 to 50
percent should support Heat Advisory criteria across the eastern CLT
metro plus Rowan. I will highlight the Heat Index values of 105
degrees with an Advisory. Elsewhere east of the mtns, Heat Index
values are forecast to range from 101 to 104, plan to mention in the
Tonight, deep convection is expected to ash out one to two hours
after sunset. Light patchy fog may develop around dawn over wet
soil. Otherwise, conditions should feature light SW winds with
periods of calm. Decreasing cloud cover, primarily associated with
linger debris clouds. Low temperatures are forecast to range from
the 60s across the mtns to mid 70s east.
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
of 310 AM Wednesday, an area of height falls emanating from the
Midwest will allow a weak tropical disturbance, currently located
over the NW Gulf of Mexico to be absorbed into the westerlies across
the TN and OH Valleys early in the short term period. As this upper
trough approaches the East Coast, relative upper level high pressure
will become increasingly suppressed into the western Atlantic. This
will also finally instigate some SE movement to the quasi-stationary
front currently draped from the ctrl Appalachians/OH Valley into the
Miss Valley. Pops will increase to likely across the far western NC
mtns by the end of Thursday, as the front, or the numerous to
widespread showers and storms that are expected to develop within
the tropical moisture enhanced frontal zone approach from the area
from the TN Valley. Farther SE, model guidance continues to suggest
that the strengthening W/SW flow developing in response to height
falls to our west will only act to advect very poor mid-level, less
than 5 C/km into the Piedmont Thu afternoon. Model instability and
QPF response therefore remains weak to non-existent, and pops no
better than slight chance still appear to be a good bet south of the
I-40 corridor in the foothills and Piedmont.
Across the NC mtns, increasing shear combined with better buoyancy
could result in somewhat organized clusters of convection developing
across the TN Valley, pushing into the area and posing a threat for
locally damaging wind gusts. Temps will remain above normal on
Thursday, especially across the Piedmont, where mid/upper 90s once
again look to be a good bet.
Thursday night into Friday, guidance suggests that the mid-level
vorticity max apparently representing the remnant of the weak
tropical disturbance will lift west and north of the area, while a
mean/low amplitude long wave trough will remain over the TN/OH
Valleys. The front and moist plume is therefore expected to make
limited progress into the forecast area during this time. In fact, a
decent W/NW low level flow is expected to develop across the area
Friday, as the vort max lifts north of the area. While mid-level
lapse rates look to remain poor, the westerly flow may also result
in dewpoints mixing out at the surface, leaving little in the way of
buoyancy outside the mtns. Nevertheless, with short term guidance
hinting at some weak ripples in the SW flow aloft, and in light of
the fact that at least scattered showers and storms should develop
near the front upstream, essentially climo pops will be advertised
for Fri afternoon into the evening.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 335 AM Wednesday, the next short wave energy overspreading the
East from the northern Plains/upper Midwest may finally allow
heights to fall sufficiently to push the front into the forecast
area over the weekend. Forecast sounding profiles look quite warm,
but also relatively moist, and we will allow chances for diurnal
convection to increase above climatology in all areas by the end of
the weekend. In fact, this trend will be carried through Day 7, as
mean troughing remains west of the area through much of the period,
providing a favorable setup for rising motion and supporting the
presence of a weak surface boundary somewhere in our vicinity.
Daytime temps are expected to remain above climo, yet moderated from
this weeks`s values in light of lower thicknesses and the
expectation of more clouds and convection.
.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and Elsewhere: Early morning MVFR fog is possible at KAVL
and KHKY, highlighted with a TEMPO. Short range guidance indicates
that a sfc front will remain stationary across the Virginias and mid
Appalachians today. The forecast area should remain of the western
edge of a H5 ridge centered off the GA coast. By this afternoon, a
weak mid level shortwave is expected to ripple east of the mtns,
resulting in a frontal wave to develop across eastern VA and a lee
trof across Carolina Piedmont. Convection should develop very
similar to Tuesday. I expect that storms will initially develop
over the ridges around 18z, then development occurring east of the
mtns by 20z. I will highlight the period of favor TSRA with a
PROB30, KAND is expected to remain dry. Deep convection is expected
to ash out one to two hours after sunset. Wind are forecast to
remain out of the SW, speeds between 5 to 9 kts.
Outlook: A plume of deep moisture will gradually build across the
western Carolinas and NE GA through the late week. SCT SHRA and
TSRA will be possible each afternoon and evening, coverage the
greatest across the mtns. Pre dawn fog and low clouds will be
possible over areas of recent rainfall.
07-13Z 13-19Z 19-01Z 01-06Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 93% High 100% High 100% High 100%
KAVL High 86% High 100% High 100% High 100%
KHKY High 93% 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 from noon today to 8 PM EDT this evening for