Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 312138

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

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.


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.


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.


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

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.


At KCLT: There is potential for a TSRA to impact the field this
afternoon and early evening. Some meso model runs depict clustered
storms moving thru the KCLT area, though based on these models`
poor performance so far today, this appears too unlikely to warrant
a mention. A TEMPO may be needed in subsequent amendments, but most
likely all impactful convection will remain west of the field. Low
VFR Cu will persist into early evening, with some stratocu or altocu
seen overnight. Guidance that suggested restrictive stratus would
move overhead this (Tue) morning was incorrect, and under nearly
the same pattern the same guidance is making the same prediction for
Wed. I will maintain VFR fcst. Winds remaining in NE quad and light.

Elsewhere: SCT +SHRA/TSRA are expected to grow in coverage thru
mid-aftn, gradually moving S-SE off the Blue Ridge. TEMPOs are
included accordingly at KAVL/KGSP/KGMU. A chance does exist at
KHKY/KAND though not great enough to warrant a TEMPO. Some showers
will linger into tonight though likely not having much impact. Some
patchy fog is expected to develop over the mtns early Wed AM,
particularly where +RA falls today, and perhaps at KAND. Winds will
be mainly SW at KAVL and NE elsewhere, going light/VRB overnight.

Outlook...Remnant low from former tropical cyclone Bonnie is
expected to move very slowly up the coastal Carolinas over the
next several days, maintaining increased precip and morning
stratus chances at KCLT. Otherwise, patchy fog chances continue
at KAVL each morning, with scattered afternoon/evening SHRA/TSRA
increasing in coverage throughout during the week.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High  83%     High 100%
KAVL       High 100%     High 100%     High  90%     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:




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