Area Forecast Discussion
Issued by NWS Greer, SC

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519
FXUS62 KGSP 240227
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1027 PM EDT Wed May 23 2018

.SYNOPSIS...
Unsettled weather will persist over the next week, with chances for
showers each day, along with a few thunderstorms. As low pressure
develops over the Gulf of Mexico, deep tropical moisture will
overspread the area over the weekend and persist into early next
week, making precipitation especially likely for Memorial Day.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 1025 PM EDT Wednesday: Line of showers and thunderstorms
dropping into the Southern Foothills and Piedmont of NC have been
weakening. However, brief heavy rainfall and gusty winds will
continue until midnight. The line should weaken further as it drops
into the Eastern Upstate and eventually dissipates shortly after
midnight. May even see some ponding of water on roads and flooding
of low lying or poor drainage areas as the line slowly moves south.
Elsewhere, only isolated showers are expected. That said, coverage
of showers may increase toward morning as the boundary stalls and
weak low level southeasterly flow develops. Lows still look on
track.

In the big picture, very little is expected to change over the
next 24 hours. The relatively high amplitude upper pattern remains
intact with a ridge over the center of the country and a trof
well off the east coast, and a weakness/upper low trapped over
the Deep South. The guidance drops the surface front down into
the fcst area late tonight. This could provide a focus for some
shower activity after midnight and so the precip prob actually
goes up in the pre-dawn hours across much of the region. Overnight
temps will remain seasonally mild. The boundary will not make it
through on Thursday morning and should lift back nwd or wash out
by the afternoon. Any brief northeasterly flow will be replaced by
a veering southeasterly flow at low levels on Thursday afternoon,
which should favor the development of shower activity with daytime
heating across the southern third of the fcst area and near the
Blue Ridge. Severe weather chances look remote again on Thursday
with only modest sbCAPE topping out around 1500 J/kg in a fairly
thin profile, generally weak lapse rates, and weak shear. The
dry air aloft remains as well, which should cut down on potential
precip amounts. High temps look about a category cooler on Thursday
afternoon as compared to today.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 200 PM Wed: Thursday night through Friday, an upper ridge
axis will extend from the southern Appalachians to the Great
Lakes. Offshore high pressure will have diminishing influence over
the Carolinas as it moves further offshore. Low-level flow will
veer to southerly, leading to better moisture flux which more or
less persists through the weekend. Accordingly, PWATs are shown
to return to anomalously high values by Friday afternoon and
remain there through Saturday. Lapse rates will be mediocre and
forcing fairly weak, with the most likely initiation mechanism
being upslope lift; PoPs generally follow a diurnal trend,
albeit still at least slight-chance nocturnally. NAM and GFS
both depict the mesolow currently over GA as drifting north into
our area early Friday, possibly bringing with it some convection
at that time. Given the abundant moisture and short hodographs,
impacts from any showers/storms will continue to be heavy rain
from slow-moving cells. Other than any areas of flash flooding,
severe weather appears unlikely. Max temps will be near normal,
with mins at least a couple categories above normal on account of
very high dewpoints.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 2pm EDT Wednesday:  Long term continues wet with good chances
for precipitation each day Sunday through Wednesday with fairly
monotonous humid and warm temperatures continuing with generally
cloudy skies. Most days will have a diurnal pattern to showers and
thunderstorms, with thunderstorm chances highest in the afternoons.

Latest GFS model run takes the tropical low developing over the Gulf
of Mexico further west than previous runs and more in-line with the
upper low and closer to, but still East of, the EC solution. Current
GFS path for the low is into central Georgia, while the EC has the
low into Mississippi/Louisiana; with both modeled lows into the US
South by Tuesday or Wednesday. Depending on the ultimate path of the
tropical low, the GSP area could see enhanced winds and rain for the
Monday through Wednesday period.  Impacts do not look profound at
this point, with the worse case GFS having 850mb winds of 25kts or
so early next week, and precipitation amounts only a little above
the non-tropical wave solution, with 2+inches total for the Sunday
through Wednesday period. It appears it will be fairly wet
regardless of the destiny of the Gulf low.

Wet forecast is due to persistent general southerly flow with
quiescent synoptic conditions that have no moisture scouring fronts
of any kind.  Northward moisture transport will be enhanced by
development of Gulf low, regardless of its path, and  support mid-
60s dewpoints through Wednesday.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Prevailing VFR outside of isolated showers
and thunderstorms through the early overnight hours. Line of showers
and thunderstorms will move across KCLT late this evening then
dissipate as it moves south of the airfield. Winds turn NE overnight
as the boundary drops through the area, light N at KAVL. Guidance
can`t agree on the amount of fog overnight, but most likely to be
KAND, KAVL, and KHKY. However, this could dissipate early with the
increasing NE wind overnight leading to increased mixing. That said,
MVFR cigs look likely for KAND and possible elsewhere, but again
guidance is not in agreement. Do expect low VFR cigs to develop near
or just after daybreak as heating works on the moist atmosphere. NE
winds could become gusty with mixing then diminish slightly and turn
ENE. KAVL will see S to SE wind during the day. Scattered showers
and thunderstorms expected again Thursday, with the best coverage at
KAND and possibly KGSP/KGMU. PROB30s in place.

Outlook: The unsettled pattern will continue through early in the
weekend, with flight restrictions possible each day under diurnal
showers and thunderstorms. Tropical moisture may increase by the
late weekend. Morning stratus/fog are possible each day - especially
following heavy rain the previous day.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High  97%     High  89%     High 100%
KGSP       High 100%     High  89%     Med   78%     High 100%
KAVL       High 100%     Med   73%     High  84%     High  92%
KHKY       High  91%     Med   73%     High  87%     High 100%
KGMU       High 100%     High  91%     High  83%     High 100%
KAND       High  98%     High  83%     High  85%     High  92%

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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...Wimberley
NEAR TERM...PM/RWH
SHORT TERM...Wimberley
LONG TERM...WJM
AVIATION...RWH



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