441
FXUS62 KCHS 171423
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1023 AM EDT Sat May 17 2025

.SYNOPSIS...
Broad high pressure will persist through the weekend. A weak
cold front may push over the region early next week, remaining
generally stationary through Tuesday. A stronger cold front is
timed to sweep across the region Wednesday into Wednesday
night, followed by high pressure through late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
This afternoon: No significant changes were made with the late
morning update. The consensus of models continues to indicate
that convection currently upstream/well west of the area this
morning, will struggle to stay together as it moves eastward.
The main reason for the decay is the presence of a mid level
inversion. Although models indicate that this inversion will
decay through the day, it will likely remain strong enough to
hold off development of any strong convection. However, if there
are any boundary collisions, which may be possible closer to the
coast and over our SE GA region later this afternoon/evening,
some isolated to scattered storms could form. Some storms could
become strong to low end severe, with the main impact being
strong straight line wind, Given DCAPE values above 1000 J/Kg
this afternoon/evening.

For now, have kept slight chance to chance PoPs for this
afternoon, with the highest over the our GA zones. The high
temperature forecast continues to be tricky given the presence
of broken to overcast high clouds. Feel most areas will see
upper 80s to around 90. Slight more sun is possible over our
extreme southern region, where I have kept lower 90s. Maximum
Heat Indices could reach the upper 90s to near 100, especially
over the southern GA zones.

Climate note /more details below/: both CHS and CXM are on
target to either tie or break record High Minimum temperatures
for today 5/17. The record for CHS is 74, and so far, CHS has
only fallen to 74, which would tie the previous record. The
record for CXM is 75, and so far, CXM has only fallen to around
77, which would break the record. These records will hold of
temperatures don`t fall below 74 for CHS and 75 for CXM through
midnight.

Tonight: Any convection that formed along the left over outflow
boundary from the decaying MCS will also be weakening tonight.
Another warm night is forecast with lows in the upper 60s to lower
70s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
Sunday: Aloft, a substantial mid-lvl low will slowly traverse the
Northeast, with a primarily zonal flow anticipated between this
feature and a rather broad ridge extending across the Gulf and
western Atlantic. At the sfc, a weak front arrives from the west-
northwest, stalling over or near the area to start off the week. H5
shortwave energy quickly traversing across the region and the
stalled boundary should be a sufficient force for afternoon showers
and thunderstorms. Some guidance hints at a MCS developing well
upstream, potentially shifting across the local area during the
afternoon, encountering a somewhat modestly sheared and unstable
environment, sufficient for isolated to scattered showers and
thunderstorms, including some stronger/marginally severe thunderstorms
should the MCS arrive prior to mid-late evening hours. High
temps should peak in the upper 80s to lower 90s away from most
coastal areas, although mid 90s are possible along and just west
of the I-95 corridor across Southeast Georgia. Overnight, convection
shifts offshore during the evening with dry conditions to arrive
by midnight. Lows should remain mild, generally in the upper
60s inland to lower 70s across coastal areas.

Monday and Tuesday: Aloft, weak ridging takes place over the
Southeast while a lingering sfc boundary is positioned across or
near the local area. H5 shortwave energy rounding the northern
periphery of the ridge places highest precip potential across
northern zones, primarily across Southeast South Carolina, but with
a lessor chance of a strong and/or marginally severe thunderstorm
both days. Temps will be the warmest of the week, with afternoon
highs generally in the low-mid 90s away from the coast (warmest
across Southeast Georgia). Heat Index values in the upper 90s/around
100 will be common each afternoon. Low temps remain mild, generally
in the upper 60s to lower 70s, but slightly warmer along the
beaches.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Wednesday: The mid-week time frame appears to be the most active
part of the week, with a fairly strong mid-upper trough driving
a cold front into the local area late day and/or evening. SBCAPE
around 1500-2000 J/kg, 0-6 km Bulk Shear around 50 kt and strong mid-
lvl lapse rates suggests some organization to convection arriving
with the front within a southwest-west flow. Strong and severe
thunderstorms are possible during afternoon and/or evening hours.
High temps should range in the low-mid 90s. Low temps should range
in the upper 60s to lower 70s away from the beaches.

Thursday through Saturday: A mid-upper lvl low will shift off the
Northeast and Mid-Atlantic Coast during the second half of the week,
helping drive high pressure and a dry downslope wind across the
Southeast United States. Temps will be noticeably cooler post fropa,
generally in the low-mid 80s Thursday, then upper 70s/lower 80s
Friday, followed by slightly warmer conditions heading through the
weekend. Overnight lows will also be cooler, generally in the mid-
upper 50s inland to lower 60s near the coast.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
Today and Tonight: Convection has made it to the SC/ NC border
this morning but has quickly started to weaken. There are also
storms located over north/ central MS moving southeast. The
main concern continues to be how fast will the convection
weaken. The general thinking has not changed since the 06z TAF
issuance with storms forecast to continue to weaken as they
advect towards the mid-level ridge. Timing out the convection
has arrival of the southern stream convection between 16 and
17z. All TAF sites now have VCSH starting at 17z with no mention
of thunder given the rapid weakening state. This afternoon into
evening, there is a slight chance of some redevelopment of
showers and thunderstorms along the old outflow from the late
morning decaying storms. VFR conditions are forecast outside any
showers or thunderstorms that might form.

Extended Aviation Outlook: Brief MVFR cigs/vsbys are possible with
showers/thunderstorms associated with a weak front Sunday
afternoon/evening. VFR conditions should then prevail Monday and
Tuesday, followed by a more substantial risk for flight
restrictions with showers/thunderstorms associated with an
arriving cold front Wednesday/Wednesday night.

&&

.MARINE...
This afternoon: No significant changes were made with the late
morning update.

Surface high pressure will remain southeast of Bermuda with the
ridge axis elongated southwest to central Florida. Convection
currently over the Appalachian Mountains will move southeast
this morning and weaken. The pressure gradient is expected to
support 10-15 knots with some gusts up to 20 knots, but
winds/seas are expected to remain below SCA today.

Tonight: Southwest winds 10 to 15 kt with seas 2-4 ft. There is a
slight chance of showers and thunderstorms over the waters from the
left over outflow boundary.

Sunday through Thursday: A weak front could stall over or near
coastal waters with a risk for a stronger thunderstorm drifting off
the Southeast Georgia coast during late day and/or evening hours.
However, conditions are expected to remain below Small Craft
Advisory levels through Tuesday. On Wednesday, a stronger cold front
arrives from the northwest late day and/or night, producing an
enhanced pressure gradient across local waters with the potential of
marginal Small Craft Advisory level conditions across most waters by
late day, and perhaps with cold air advection post fropa Wednesday
night. Additionally, severe thunderstorms could accompany the front,
producing higher seas and wind gusts. Seas will generally build to 3-
4 ft during this time frame as well. The flow turns even more
directly offshore on Thursday, with conditions that should remain
below Small Craft Advisory levels entering the second half of the
week.

&&

.CLIMATE...
Record High Temperatures:

May 17:
KCHS: 96/1963
KCXM: 94/1899
KSAV: 97/1899

May 18:
KSAV: 97/1899

May 19:
KSAV: 97/1996

May 20:
KSAV: 96/2006

Record High Minimum Temperatures:

May 17:
KCHS: 74/1995
KCXM: 75/1998
KSAV: 74/1995

May 18:
KCHS: 75/1995
KCXM: 77/1991
KSAV: 74/1899

May 19:
KSAV: 74/1930

May 20:
KCHS: 72/2022
KCXM: 76/2022
KSAV: 73/1896

May 21:
KCHS: 74/2022
KSAV: 74/2017

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$

NEAR TERM...Haines/RFM
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...DPB/Haines
MARINE...DPB/Haines/RFM