Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 112352

Area Forecast Discussion
National Weather Service Charleston SC
752 PM EDT Tue May 11 2021

A cold front will advance into the area tonight then will
gradually settle south of the area and stall Wednesday. A
series of low pressure areas will track along the stationary
front until late week. High pressure will expand into the
region this weekend into early next week.


This Evening: Latest radar trends indicate isolated thunderstorms
developing upstream and moving into western most areas as well as a
few thunderstorms developing along an inland moving seabreeze. A few
thunderstorms could become strong and/or briefly severe across
inland portions of southeast South Carolina and southeast Georgia
this evening given sufficient shear (around 35-40 kt 0-6km bulk
shear) and instability (MLCAPE around 1000 J/kg) persisting across
the area. DCAPE around 800-1000 J/kg and -10C to -30C CAPE between
300-500 J/kg suggest the main concerns to be strong/damaging wind
gusts and moderate size hail for the next few hours, particularly
along and west of an inland moving seabreeze where the highest
parameter values overlap ahead of a h5 shortwave approaching from
the west.

Later tonight: A slow-moving cold front will stall over the area.
Moisture will steadily increase and PWats are progged to peak over
1.6 inches, which is well above early May climatology. With the
front in the vicinity, passing shortwave energy and isentropic
ascent, coverage of showers should increase, especially after
midnight. There is some instability available ahead of the front, so
the forecast maintains mention of thunder. Average rainfall totals
through tonight will be between a quarter and half of an inch,
highest across the interior. Temperatures will be a bit tricky. The
current forecast features lows ranging from the upper 50 across the
far northwestern tier to the upper 60s near the Georgia coast.


Wednesday: A cold front across far northern areas at the start
of the day will surge south and move south of southern zones by
evening. Precipitable water values from 1.7 to 1.8 inches in the
morning will trend a bit downward Wednesday afternoon and
Wednesday night. The combination of the front surging south and
decent isentropic lifting developing over top of the shallow air
mass, specifically along the 295K and 300K surfaces as depicted
very well by the NAM and ECMWF and to a slightly less extent
the GFS support likely to categorical POPs across most areas.
Pushed POPs up a bit in most areas but further upward trends are
quite possible. Highest rain chances are in the morning in the
north and during the afternoon in the south. There could be some
thunder along and south of the front, especially across
southeast Georgia during the late morning and into the
afternoon. Temperatures will trend downward during the day
across most areas with the highs for the day likely occurring
early in the north. As lift subsides and moisture drops off a
bit, rain chances will lower Wednesday Night, but still in the
high chance category, especially during the evening.

Thursday: Models have trended toward keeping more moisture around
and the potential for more lift to develop, so have raised rain
chances a bit for Thursday, with rain chances quickly dropping off
Thursday evening. With extensive cloud cover it will be cool for May
with highs in the lower to mid 60s.

Friday: Drying will commence and this will allow for some sunshine
especially by afternoon. Highs should be in the lower 70s.

Lake winds: Strengthening low-level winds and unusually cool air
flowing over the warmer waters of Lake Moultrie should promote
vigorous mixing/occasional wind gusts as high as 20-25 knots
Wednesday through Thursday. Hence have issues a Lake Wind Advisory
from 11 AM Wednesday through 11 AM Thursday.


High pressure and a much drier air mass will build into the
region and prevail through early next week. A gradual warming
trend will continue through the weekend and by Monday, high
temperatures will be back in the mid 70s to mid 80s. Friday
night will see low temperatures in the low to mid 50s inland and
upper 50s to low 60s just along the coast. Thereafter, each
night will see temperatures a few degrees warmer than the
previous night.


VFR conditions should prevail at both CHS and SAV terminals
during the evening, but flight restrictions are expected at both
terminals later overnight, initially at the CHS terminal starting
around 05Z tonight, then around 09Z at the SAV terminal. Tempo
IFR cigs have been introduced at both sites, 09Z-13Z at CHS and
10Z-13Z at SAV, but could need to become prevailing groups and
extended at both sites through late morning hours Wednesday. At
least MVFR conditions should persist at both sites during
Wednesday afternoon hours and into the evening. Gusty
north/northeast winds will develop tomorrow morning, especially
at KCHS with gusts upwards to around 18-20 kt.

Extended Aviation Outlook:
Flight restrictions possible through Friday morning during
periods of low clouds and showers.


Tonight: A slow moving cold front will remain in the vicinity
tonight. Outside thunderstorms that could drift offshore
this evening tonight, the pressure gradient doesn`t really
tighten until right after daybreak, so speeds will average
around 10 knots through the night. Seas will average 1 to 2 feet.

Wednesday through Sunday: As high pressure moves south into the
region and a cold front pushes south of the area, a tightened
pressure gradient will enhance NE winds and seas. Then, over the
weekend, high pressure will build into the area.

A Small Craft Advisory will be in effect for the South Carolina
nearshore waters starting Wednesday morning, with Small Craft
Advisory for both the nearshore and offshore Georgia waters starting
Wednesday afternoon. All of these advisories will be through Friday
evening as even if winds drop off a bit seas will remain at least in
the 5 to 6 foot range. A Small Craft Advisory for the Charleston
Harbor will also begin Wednesday morning and last through Thursday
for winds gusting over 25 knots. By Sunday, more ideal marine
conditions should return.

Rip currents: An elevated risk of rip currents is possible through
late week due to gusty northeast winds.


An unseasonably cool air mass, accompanied by clouds and showers,
could challenge the following record low maximum temperatures
Wednesday 5/12 and Thursday 5/13.

5/12 69 (1963)
5/13 68 (1996)

5/12 65 (1907)
5/13 68 (1996)

5/12 69 (1885)
5/13 69 (1928)


SC...Lake Wind Advisory from 11 AM Wednesday to 11 AM EDT Thursday
     for SCZ045.
MARINE...Small Craft Advisory from 11 AM Wednesday to 10 PM EDT Friday
     for AMZ350-352.
     Small Craft Advisory from 4 PM Wednesday to 10 PM EDT Friday
     for AMZ354-374.
     Small Craft Advisory from 11 AM Wednesday to 5 PM EDT Thursday
     for AMZ330.



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