Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 010017
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
817 PM EDT TUE MAY 31 2016

.SYNOPSIS...
The remnants of tropical system Bonnie will slowly lift northeast
along the Carolina Coast over the next couple of days. Moisture will
increase ahead of a weak cold front approaching from the northwest
on Friday. The front will stall out over the area over the weekend,
with a stronger cold front moving through the region early Monday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 8 PM: Regional radar composite indicated clusters of
thunderstorms along I-77 and across the Smokies. Mesoscale analysis
indicates that the storms are running out of untapped instability
across the forecast area. I would anticipate that convection will
ashe out over the next 2 to 3 hours. Otherwise, showers will linger
around the mtns and foothills overnight.

As of 530 pm: TCLT and KGSP radar continued to indicate sct to
numerous storms across the CWA. This activity should continue well
into the evening hours, developing over areas that have not been
worked over so far today. Pulse storms may produce brief severe hail
through the remainder of the daylight hours...then svr threat should
decrease. I will update the forecast to increase PoPs across the
forecast area. The sky grids will be populated with satellite data.

As of 220 PM: Deep convection has broken out over portions of
the NC mountains, with an appreciable Cu field covering much of
the Piedmont. An area of congested cumulus just north and NE of
Spartanburg has now also produced some heavy showers. Taking the
CWFA as a whole, our various convection allowing models are not
handling the coverage very well, mostly because they have been
overdone with coverage all day. Based on the development so far,
and what happened yesterday under similar circumstances, the
current activity is likely to expand mainly southward. Isolated
cells however are expected over the eastern Piedmont zones and
Savannah River Valley before the end of the day. The storms so far
have produced just heavy rain, and while profiles don`t support
a particularly great damaging wind threat, the weak shear implies
storms will remain in pulse mode and an isolated large hail event
or downburst is plausible.

Lapse rates are expected to remain unchanged tonight, with a
similarly weakly forced environment as we experienced Mon night
into early Tue. The low level flow is expected to veer, which could
provide some slight upslope forcing and showers to linger into the
early morning. I have handled this trending PoPs down more slowly
than they would on a typical diurnal curve. Despite the easterly
flow, low stratus looks unlikely (particularly given that it was
overforecast by guidance for today). Min temps will be a few degrees
above climo on account of partial cloudiness from convective debris,
and humid conditions. Overall the pattern will have changed little
by Wed aftn. Another round of diurnal thunderstorms is expected,
mainly forming over the mountains and moving into the foothills,
but with isolated to scattered cells developing over the Piedmont as
well. Weak wind profiles still point to pulse storms and associated
threats. Max temps will be a degree or two above climo.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 145 PM Tuesday: Flat ridging builds over the Southeastern US
through the period. Weak low level easterly flow remains in place
across the area Thursday as the remnants of Bonnie slowly move north
along the NC coast. With warm temps and copious low level moisture
in place, moderate instability will develop once again. Expect
numerous convective coverage to develop across the mountains with
high end scattered coverage elsewhere. Low level flow becomes
southwesterly on Friday as a weak cold front moves into the area
from the NW. Low level moisture remains quite high which keeps
moderate instability across the area. Expect convective coverage to
be similar if not slightly greater than Thursday. Shear remains weak
even with the approach of the frontal system. However, expect a few
severe storms to develop each day given the instability and
convective coverage. Isolated flooding is also possible with slow
moving storms both days. Highs rise from a couple of degrees above
normal on Thursday to around 5 degrees above normal Friday. Lows
will be up to 10 degrees above normal.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 210 PM EDT Tuesday: the medium range fcst picks up at 00z on
Saturday with relatively flat upper ridging over the southeast and a
nearly stationary southern stream upper low over Texas. Over the
next 24 to 48 hours, steep upper ridging amplifies over the Western
CONUS and broad upper troffing digs down over the Great Lakes. The
upper trof axis is expected to be east of the fcst area by the end
of the medium range on Tuesday as the upper ridge spreads farther
east.

At the sfc, the long range models are coming into better agreement
wrt the evolution of the sfc pattern. The pattern remains fairly
stagnate and weakly forced on Sat and most of Sun as a stalled cold
front lingers over the region keeping deep lyr moisture and healthy
amounts of instability in place. A stronger cold front approaches
the CWFA on Sunday and is expected to move thru the fcst area
sometime late Sunday into early Monday with drier and cooler air
overspreading the region in the front`s wake. As for the sensible
fcst, I kept solid chance to low end likely chances for numerous
showers and ts on Saturday and Sunday. Drying is expected during the
latter half of Monday with dry conditions for Tuesday. Temps will
start out just above climatology and cool on Sunday and Monday.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: regional radar composite indicated clusters
of thunderstorms along I-77 and across the Smokies. Mesoscale
analysis indicates that the storms are running out of untapped
instability across the forecast area. I would anticipate that
convection will ashe out over the next 2 to 3 hours. Otherwise,
showers will linger around the mtns and foothills overnight. I will
highlight the near term convection in the initial line, ending
mention around 1z to 2z. Winds will weaken overnight with bkn to ovc
mid and high clouds. On Wednesday, afternoon convection should
redevelop over the mtns and shift over the foothills by 19z. Between
20z to 22z, SHRA and TSRA should develop across western Carolinas,
highlighted with a Prob30.

Outlook...Remnant low from former tropical cyclone Bonnie is
expected to move very slowly up the coastal Carolinas over the next
several days. Scattered afternoon/evening SHRA/TSRA increasing in
coverage throughout during the week.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High 100%     High  99%     High  82%     High 100%
KGSP       High 100%     High  80%     High  94%     High  85%
KAVL       High 100%     Med   62%     Med   73%     High 100%
KHKY       High  89%     Med   71%     High  91%     High 100%
KGMU       High 100%     High  83%     High  94%     High  92%
KAND       High 100%     Med   77%     High  94%     High 100%

The percentage reflects the number of guidance members agreeing
with the schedule 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...JPT
NEAR TERM...NED/Wimberley
SHORT TERM...RWH
LONG TERM...JPT
AVIATION...NED/Wimberley



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