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000
FXUS62 KCHS 202350
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
650 PM EST Thu Feb 20 2020

.SYNOPSIS...
Developing low pressure offshore will move northeast tonight.
High pressure will then move into the area on Friday, bringing
cold, drier air through the weekend. Another warm front will
move into the area early next week, bringing more rain to the
area.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
The much anticipated cyclogenesis off the Southeast U.S. coast
is well underway with 20/23z surface objective analysis placing
the low about 170 miles east of Tybee Island, GA. Widespread
light moderate rains associated with the low with support from
a shortwave digging across the Ohio Valley and a powerful polar
jet across the Deep South will persist across southern South
Carolina into Southeast Georgia through at least midnight before
slowly winding down from west-east through the overnight as the
surface low pulls propagates farther offshore. The heaviest of
the rains will fall over the next 3-4 hours before tapering
off.

High resolution guidance has trended slightly lower with
the ending of the precipitation across the Charleston Tri-County
area late tonight. With this slower movement, there is some
concern with p-type as temperatures fall into the lower-mid 30s
north of the I-26 corridor. High resolution soundings with
support from both the 20/18z NAM3km and GFS show there should be
just barely enough moisture left over in the dendritic growth
zone (DGZ) to support some ice nucleation. Soundings at KCHS,
KMKS and Jamestown in the 09-13z time frame show a sub-freezing
layer above the boundary layer so expect hydrometers to remain
frozen before melting just before reaching the ground. This
scenario will support either a rain-snow mix or possibly a
brief burst of very light snow before as the precipitation moves
offshore, mainly along/north of the I-26 corridor. Sleet
appears unlikely given the depth of the cold air. No impacts are
expected given the warm ground temperatures and this should be
more of a novelty event this far to the south.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
High pressure will continue to build into the area through Friday. A
strong pressure gradient will support gusty winds up to 25 kts
through Friday night into Saturday morning over Lake Moultrie.
Temperatures will continue to be below normal, with lows in the
upper 20`s and low 30`s through the weekend. High pressure will then
prevail through the weekend, bringing quiet weather. Sunday will see
temperatures in the upper 50s/low 60s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A warm front is forecast to lift north through the forecast area on
Monday as low pressure lifts into the Ohio River Valley. Some rain
could accompany the front, but the best rain chances will come late
Monday night and Tuesday as a cold front passes through. Another
stronger front could approach on Wednesday as a deep upper trough
moves into the eastern U.S. Temperatures through the period are
expected to be near to above normal.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
High-end IFR to low-end MVFR cigs will linger through the
evening before lifting to more solid MVFR after midnight as rain
begins to diminish. VSbys of 2-4 miles will persist before
returning to P6SM as the rain wanes. There is a slight chance
rain could mix with or briefly change to snow at KCHS just
before daybreak as the precipitation ends, but there will be no
impacts. VFR will return by mid-morning as skies begin to clear.
Gusty winds will persist through the 00z TAF period with gusts
20-25 kt at both KSAV and KCHS.

Extended Aviation Outlook: VFR will prevail through the weekend with
gusty winds through Friday night. Some restrictions likely
starting Monday.

&&

.MARINE...
Tonight: Solid Small Craft Advisory conditions will give way to
Gale Warning conditions outside Charleston Harbor as the
pressure gradient intensifies due to low pressure strengthening
just east of the waters. We do not have a Gale Warning in
Charleston Harbor at this point but certainly can`t rule out a
few gale force gusts near the mouth of the harbor. Waves will
build substantially with 6-9 foot seas beyond the pilot buoys
and 10-12 ft out closer to the warm Gulf Stream waters.

Friday through Tuesday: Winds will remain quite gusty through
Saturday evening. Gale warnings will be in effect through Friday
evening for all Charleston waters except the Charleston Harbor,
which has a small craft advisory. As the pressure gradient
relaxes, small craft advisories will be needed to replace the
gale warnings which should remain in effect until Saturday
afternoon/evening for all waters.

No concerns expected Sunday into Monday, however an uptick in winds
and seas is possible on Tuesday ahead of the next low pressure
system.

&&

.TIDES/COASTAL FLOODING...
Strong northeast winds are likely to cause minor coastal
flooding with the Friday morning high tide along the SC coast,
possibly Saturday morning as well.

&&

.EQUIPMENT...
There will be a 03Z special sounding released in support of the
NASA IMPACTS winter storm project.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Lake Wind Advisory until 7 PM EST Friday for SCZ045.
MARINE...Gale Warning until 5 PM EST Friday for AMZ350-352-354.
     Gale Warning until 10 PM EST Friday for AMZ374.
     Small Craft Advisory until 7 PM EST Friday for AMZ330.

&&

$$