Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 291457

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1057 AM EDT SUN MAY 29 2016

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.


As of 1045 AM EDT Sunday: Have increased pops again through the day
for most of the area, expanding the categorical farther west and
north to line up where this persistent band has remained through the
morning. Also tightened up the gradient across extreme western zones
due to clearing skies over the SW NC mountains. We are watching
rainfall closely, as some areas down in Greenwood/Abbeville Counties
are already over 1" over the last 6 hours. Certainly nothing to be
concerned about but this is higher than QPF values were, plus if
CAMs are to be believed they could easily see another 2-3" if the
rain continues across those areas. Made some minor adjustments to
T/Td/MaxT to account for trends and still thinking that highs will
be kept in the mid 70s at best across most of the area due to the
widespread cloud cover and rain.

Otherwise, the forecast remains on track with the center of Tropical
Storm Bonnie just off the southeast South Carolina coast. 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.


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 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.


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.


At KCLT: 15z AMD will include improvement in cigs since MVFR
cigs are spotty at best, so will convert to TEMPO. Otherwise not
much change to the forecast. Light tropical shower bands continue
to work northwest across the piedmont. Northerly winds will
increase through the day with low end gusts likely as T.D. 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...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       Med   74%     High 100%     Med   69%     High 100%
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  87%     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:




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