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fxus62 kgsp 190718 

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
318 am EDT Fri Jul 19 2019

summertime heat and humidity will continue into the upcoming
weekend. There is a good chance of afternoon and evening showers and
thunderstorms through the period as well. A cold front will provide
relief from the heat and humidity early next week. However, chances
for showers and storms will continue.


Near term /through tonight/...
as of 246 am friday: all quiet across the western Carolinas
and northeast Georgia...and expect it to stay that way through
daybreak. Some valley fog was noted out in the little Tennessee River
valley, but the Fr. Broad was covered by mid/high cloud debris,
which may limit the extent to which fog might develop in that part
of the mtns.

Otherwise...a weakness of sorts will remain across the fcst area
this afternoon, in-between the upper anticyclone building over
the Midwest and lower Ohio Valley region and the western extent of
the Atlantic subtropical ridge. Some subtle forcing may exist
in this weakness that could help to trigger showers and storms
again this afternoon, but the signal is not clear. Some of the
convection-allowing models show very little development, while
other flavors have better than scattered coverage. Am inclined
to believe the ones that show relatively less development given
the lack of forcing, weak lapse rates, and less sfc-based cape
than yesterday. Precip chances were scaled back just a bit as a
result. Severe storms look like less of a threat today. Temps will
be seasonally warm again today, with isolated locations reaching
upwards of 105 deg on the heat index over the wrn Piedmont of NC. As
it stands, the coverage does not warrant a heat advisory, but this
could become necessary later today with only small upward changes
in T or relative humidity. After convection dies off in the evening, the rest of
Friday night should be quiet with seasonally mild overnight temps.


Short term /Saturday through Sunday night/...
as of 300 am Fri: oppressive heat and humidity will continue
over the weekend beneath a broad 593 dm upper ridge enveloping
the south. Most guidance depicts highs in the mid-90s across
the Piedmont on Saturday, along with readings of almost 90 in
the mountain valleys. Rich moisture will be exemplified by precipitable water
values of 1.75 to 2 inches across most of the area. Dewpoints are
expected to start out in the lower to mid 70s Saturday morning,
though afternoon obs from recent days as well as the most trusted
guidance suggest these will mix out several degrees by peak
heating. That said, heat index values will easily surpass 100,
nearing the advisory threshold of 105 in the hottest spots mainly in
the southern lakelands and south of Charlotte. The dewpoints/pwats
are depicted as taking a slight hit Sunday seemingly due to more
downsloping low-level flow, and temps are also expected to be a
tad cooler, so if we avoid heat advisory conditions Saturday, it
looks likely we will Sunday as well. Nevertheless with folks heading
out for weekend activities extra caution is certainly advisable.

Otherwise, seasonably unstable profiles develop diurnally both
days with SBCAPE likely to top 2000 j/kg. Unsurprisingly given the
monster ridge, shear is almost nil on Saturday, and only a weak
southerly low-level flow develops Sunday in advance of a trough
that will approach early next week. Sfc-midlevel Delta-Theta-E is
20-25 k both days. This should result in a severe downburst threat
in addition to the possibility of marginally severe hail.


Long term /Monday through Thursday/...
as of 100 am Fri: pattern change is expected to begin Monday as
a sharp upper trough advances into the southeast, followed by
an unseasonably strong cold front. Abundant moisture pooling
preceding these features on Monday will allow temps to fall
back to around normal as a result of cloud cover and widespread
showers/storms. Truly cooler and drier air will settle in for
Tuesday and Wednesday--the contrast is easily seen with naefs
standardized moisture anomalies of +2 South Dakota in parts of the region
Sunday and Monday, falling to -1 South Dakota in some of those same areas by
late Tuesday. However, with the trough/front stalling out on our
southern fringe, convective initiation will be enhanced Tuesday
even if instability does end up being atypically low for this time
of year. Upper heights rise again after Wednesday, suggesting a
slight warming trend toward the end of next week.


Aviation /07z Friday through Tuesday/...
at kclt and elsewhere: VFR through the overnight hours with light
wind and only high cloudiness. The latest guidance has backed
off on the fog/low stratus development at kavl, and this trend
looks possible as a mid/upper cloud deck has moved over the French
Broad River valley at this late hour. Will keep a tempo for a fog
restriction around daybreak as a nod to the previous fcst. After
daybreak, convective low clouds should develop along with a
S to SW wind. The latest meso models are still in relatively
poor agreement with the storm coverage on Friday afternoon,
so confidence is relatively low. Kept the prob30 at most sites,
but eliminated it at kclt because of the confidence issue.

Outlook: scattered diurnal convection is expected through the
weekend, especially over the mountains. Patchy Mountain Valley
fog and low cigs remain possible during the overnight and early
morning hours. A transition to a more active pattern may occur
beginning Monday.

Confidence table...

07-13z 13-19z 19-01z 01-06z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 99% high 100% high 96%
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:



Gsp watches/warnings/advisories...



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