169
FXUS62 KCHS 230222
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
922 PM EST Fri Nov 22 2024

.SYNOPSIS...
Canadian high pressure will remain the primary feature through
early next week. A cold front could approach the area towards
the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
No major changes were made for the late evening update. 23/02z
observations show temperatures have already cooled into the
upper 30s/lower 40s across the interior with the coldest
temperatures located over Berkeley County away from the Santee-
Cooper lakes. Would not be surprised to see a few spots in the
normally colder areas make a run for the freezing mark by
daybreak, but any such conditions should be fairly localized.
There are signs that the boundary layer is trying to decouple
with a few sites already reporting calm winds. The current Frost
Advisory area looks on track, although there are signals that
an expansion could be needed into parts of Evans and Tattnall
Counties. Winds at KRVJ are calm suggesting at least some
localized decoupling has already occurred in this area. An
expansion may be considered with the midnight update.

Another chilly night will occur as high pressure featuring a
slightly modified cP airmass dominates the region. The 1022 hPa
high is currently centered over northern Missouri/southern Iowa
with an enhance pressure gradient in place across the Carolinas
and Georgia between it and low pressure emerging off the Mid-
Atlantic coast. Guidance is in pretty good agreement in showing
the pressure gradient relaxing quite a bit after midnight as the
high propagates into the lower Mississippi Valley and the low
pushes farther offshore. This should allow the boundary layer to
at least partially, if not completely, decouple away from the
coast early Saturday morning under clear skies. With lows
expected to drop into the mid 30s well inland, conditions look
to become increasingly favorable for the formation of scattered
(areas of) frost.

The latest HREF combination probs for surface temperatures
<=35F AND wind speeds <=5mph (conditions typically favorable
for advisory-level frost) are running about 50-80% from roughly
along and north of a Metter-Statesboro-Estill-Walterboro-
Summerville-Francis Marion National Forest line. Given much of
this area is lagging average first freeze dates by about 2-3
weeks due to an impressively warm November observed so far, a
combined criteria and impact-based Frost Advisory has been
issued for the far interior from 2 AM until 8 AM Saturday.

Elsewhere, patchier frost will be observed outside of the Frost
Advisory area and could reach as far east as the far interior
areas of the coastal counties of south coastal South Carolina
and coastal Georgia. Lows will range from the the mid 30s well
inland to the lower-mid 40s at the beaches, including Downtown
Charleston and areas right along Lake Moultrie and far eastern
portions of Lake Marion.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
An amplified trough/ridge/trough pattern will be in place
across the CONUS to start the period with anomalously deep
stacked low pressure migrating off the mid Atlantic/New England
coast and short-wave ridging building through the central and
into the eastern CONUS later Sunday into Monday. Meanwhile,
surface high pressure will continue to build across the central
and southeastern states through the weekend and eventually off
the coast by Monday. This will prolong our recent stretch of
rain-free conditions into early next week.

Saturday through Monday: After a cool start to Saturday, quick
temperature moderation takes shape with high temperatures
rebounding back into the lower 60s Saturday, middle to upper 60s
Sunday (near normal), and back into the 70s for Monday. Another
chilly night/early morning is anticipated Saturday night/Sunday
morning with inland lows in the middle to upper 30s, warmer
along the coast of course. But with a weaker pressure gradient
and lighter/calm winds, the greatest frost potential still
appears to be Saturday night. Forecast will advertise patchy to
areas of frost away from the coast and a Frost Advisory will
need to be considered. Sunday night/Monday morning low temps
should run a bit warmer and frost potential looks low.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Large scale pattern transitions to a more zonal arrangement
through the middle part of next week, fully erasing the cold
temperature anomalies across the eastern/southeastern U.S. There
may be a weak surface boundary pressing through the region
later Tuesday/Tuesday night with little fanfare other than a
wind shift and temperatures dipping back down into the 60s for
Wednesday. By later in the week, longer term guidance does hint
at the re-development of deeper troughiness across the eastern
CONUS late week along with an attending stronger storm system
that traverses the region during the Thursday into Friday
timeframe. That will be our next chance of appreciable rainfall.
Temps warm ahead of the boundary into the 70s for highs
Thursday but back into the 60s on Friday after FROPA...subject
to later revisions.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
23/00z TAF Discussion:
KCHS/KJZI/KSAV: VFR.

Extended Aviation Outlook: VFR.

&&

.MARINE...
The Small Craft Advisory for the Charleston Harbor will expire
at 7 PM.

Tonight: Northwest winds will average 15-20 kt with gusts to 25
kt over the all Atlantic legs tonight with seas 2-4 ft within 20
NM And 3-5 over the Georgia offshore leg out 20-60 NM. Small
Craft Advisories remain in effect for all areas except
Charleston Harbor.

Saturday through Wednesday: High pressure will build across the
coastal waters this weekend into early next week, with winds
diminishing to 10 to 15 knots for the Saturday through Monday
timeframe ans seas diminishing to 3 feet or less. Winds will
increase slightly for the Tuesday/Wednesday timeframe as a weak
boundary slips through the region. But winds/seas remain below
headline criteria.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Frost Advisory from 2 AM to 8 AM EST Saturday for GAZ087-088-
     099-100.
SC...Frost Advisory from 2 AM to 8 AM EST Saturday for SCZ040-
     042>045-052.
MARINE...Small Craft Advisory until 7 AM EST Saturday for AMZ350-352-
     354.
     Small Craft Advisory until 10 AM EST Saturday for AMZ374.

&&

$$