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Area Forecast Discussion

062
FXUS62 KGSP 291101
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
701 AM EDT SUN MAY 29 2016

.SYNOPSIS...
Moisture will spread across the region today as tropical system
Bonnie stalls near the South Carolina coast. Bonnie will then drift
northeast along the coast of the Carolinas through the week. A weak
cold front will push into the southern Appalachians from the west
and stall late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 650 AM EDT: Higher PoPs have been pushed more quickly farther
west with the leading edge of light showers reaching the ground.
Otherwise, the forecast remains on track with the center of Tropical
Storm Bonnie just off the southeast South Carolina coast. Bands of
mostly light rainfall continue to work westward into the eastern
escarpment of the mountains. It is quite possible that the best
convection and deeper moisture with the system could continue wrap
to the northwest side of the circulation as it meanders into coastal
SC. Although this setup has the potential to produce heavy rainfall
across parts of our forecast area, particularly the piedmont, the
axis of any heaviest rainfall remains difficult to pin down and QPF
could be more evenly spread about the region. The more eastern
solution of the NAM and SREF members appears reasonable given the
expected coastal track of Bonnie, but the more western GFS and its
members have verified better thus far this morning. Will lean
heavily on WPC QPF guidance mixed with a model blend to put the
heaviest 1 to 1.5 inch stripe through tonight mainly from Chester to
Monroe. In addition, the better instability will generally remain
east of our area. No flood watches appear needed at this point, but
the piedmont gradient in QPF could be quite sharp and it bears
watching.

In addition to the tropical system rainfall, upper level divergence
over the mountains today should produce some scattered convection
over the high terrain this afternoon. Otherwise, Bonnie should
meander slowly NE along coastal SC through tonight with PoPs slowly
diminishing from the southwest. Anticipate a small diurnal range on
temperatures with mostly 70s this afternoon and 60s tonight except
50s in the mountains.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...Bonnie...which is expected to weaken back to a
tropical depression by Monday morning...should begin to drift
east/northeast over NE SC. The deeper moisture and mid LVL
circulation will also shift east...so Monday will feature a little
less cloud cover...esp west of I-77 with typical slight CHC to
low-end CHC Pop for AFTN convection. The heavy rain threat directly
associated with Bonnie should pretty much end by Monday
AFTN...unless the system ends up further inland and doesn/t make the
eastward drift right away.

Models agree on weak steering flow to continue on Tuesday...with
Bonnie or its remnants still INVOF Wilmington NC by Tuesday evening.
There should be ENUF INSTBY for ISOLD to SCT convection again
ACRS the area...but not really ENUF for a pulse severe threat. Temps
both days will be slightly above normal.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 315 PM Sunday...Upper ridge builds along the East Coast
Wed-Thu...while a northern stream short wave trough tracks into the
Great Lakes and Ohio Valley. The medium range guidance generally
agrees the the remnants of Bonnie will linger near eastern NC or
just off the Outer Banks. This results in continued weak deep-layer
flow atop the CWFA. Generally little change in air mass is
expected...except for slightly warmer temps which should result in a
little better INSTBY each day. PoPs trend above climo by
Thursday...and continue the usual diurnal cycle. Temps will be a
category or two above normal both days.

Friday and Saturday...A cold front associated with the approaching
upper trough will slow down and eventually stall roughly along the
appalachians. The air mass should be fairly moist with good INSTBY
ACRS the CWFA both days. Above climo PoPs (high-end CHC to likely)
is forecast for both days. Temps will trend slightly cooler for highs
and warmer for lows due to the increased clouds and precip.

&&

.AVIATION /11Z SUNDAY THROUGH THURSDAY/...
At KCLT: Light tropical shower bands continue to work northwest
across the piedmont around daybreak this morning. MVFR clouds do not
appear too far upstream and should invade the airfield by 14Z. Slow
recovery from MVFR to lower end VFR is possible through the
afternoon hours. Northerly winds will increase through the day with
low end gusts likely as T.S. Bonnie moves into the SC coastline.
Scattered showers from additional weak tropical bands are expected
through tonight.

Elsewhere: Moisture from T.S. Bonnie remains a bit more uncertain
across the mountain and foothill TAF sites, but occasional light
showers are already in place and should continue through mid
afternoon before drier air starts to work back in from the
southwest. MVFR restrictions look most likely later this morning at
KHKY. Expect occasional northerly gusts across the foothills through
the day as the Bonnie circulation reaches the SC coastline.

Outlook: Bonnie is expected to move very slowly up the coastal
Carolinas over the next several days. Lingering shower chances into
the early part of the week would be greatest at KCLT. Otherwise,
patchy fog chances continue at KAVL each morning, with scattered
afternoon/evening SHRA/TSRA increasing throughout during the week.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High 100%     High 100%     High 100%     Med   78%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     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 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...ARK/HG
NEAR TERM...HG
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...HG



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