636
FXUS62 KCHS 100911
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
411 AM EST Fri Jan 10 2025

.SYNOPSIS...
A low pressure system will approach the region today, tracking
towards the northeast across the region tonight into tomorrow
morning. High pressure will then build into the region and
prevail into the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: A deep, elongated, and positively tilted long wave
trough extending from the Central Plains into western Mexico
will generate a surface low over the northern coast of the Gulf
of Mexico. The upper ridge axis will shift toward the eastern
seaboard, as the surface low tracks from the Gulf coast across
the southeast states into tonight. This would be a Miller Type-A
Classification, named after J.E. Miller (I had to look up the
year it was coined as such: 1946). Strong UVVs resulting from
DCVA ahead of the upper trough, the right entrance to a 185 kt
jet streak embedded within the polar jet, and strong isentropic
ascent from pre-frontal warm air advection, will spread into the
area through Friday night.

With the arctic high still over the area early on, the day
begins with temperatures in the mid 20s to lower 30s. A west to
east oriented arc of isentropically forced precipitation along
the nose of the warm air advection/850 mb warm front, will
begin to move into interior southeast Georgia shortly after
sunrise, then spread north-northeast across southern South
Carolina during the morning hours. Precipitation rates during
this time still look to remain fairly light, with so much dry
air beneath the cloud layer, which is still up near 5-6K feet.
With wet-bulb temperatures far below 0C from there to the
surface, this will result in enough evaporative cooling to near
or at the surface to generate some p-type concerns. This is most
concerning across Allendale, Screven and Jenkins County, where
there could be a little freezing rain between about 12Z and 17Z,
with temperatures hovering around or just below 32F. Much of
the guidance shows anywhere from a trace to maybe 0.01 or 0.02
inches of icing in these counties. After collaboration with WPC
and WFO CAE, we have raised a short duration Winter Weather
Advisory for those three counties this morning. Further east
and northeast, any light precipitation would be mainly snow or
rain. Although some parts of Hampton, Colleton, Dorchester, and
Berkeley County might have a little freezing rain. Outside of
the advisory area, no snow accumulation will occur. And any
freezing rain would only be over a limited area. So no advisory
is planned at this time anywhere else. Any freezing or frozen
precipitation should quickly transition to all rain by mid-
morning, as a pronounced warm advection spreads across the
entire area, and all surface temperatures are above freezing.

Temperatures are certainly a challenge with this forecast, but
guidance has trended lower than previously for many places. This
is heavily influenced by diabatic cooling, and where the warm
front sets up. With wedging inland and the precipitation ongoing,
this will keep the warm front further south than previously
anticipated. Highs will range from the upper 30s northwest tier,
to the lower and middle 50s south of the Savannah area where
the low level flow veers to the east-southeast. Adjustments to
the hourly temperatures will likely be necessary as we go
through the day.

Tonight: The upper trough will become even more elongated, as
it becomes in phase with the northern stream that draws closer
to the Appalachians. This allows for the surface low to pass
over or near the local counties early on, before it deepens near
or just east of the North Carolina Outer Banks late. Everywhere
will get rainfall, with storm total QPF of 1/3 to 2/3 inches.
There is still some concern for something other than liquid
precipitation, depending upon where the warm front is located,
and before the cold front moves through. Should this occur, then
parts of the northwest tier would be the most favored early on,
especially northern Berkeley County. This is when some of the
coldest temperatures in the middle 30s will occur. But at this
time it looks too warm for anything other than rain. Actual lows
will range from the mid 30s far inland to the lower and middle
40s at the beaches. But temperatures will likely rise overnight,
especially south and east.

Lake Winds: Conditions will be close to Lake Advisory
thresholds across Lake Moultrie late tonight into Saturday
morning. This will depend on the amount of mixing of winds in
the lower levels that occurs. For now we have winds shifting
around to the SW and W at 15-20 kt late tonight, or just shy of
the advisory level.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
High pressure at the surface will build into the region from the
west on Saturday. The center of high pressure will shift eastward
through the weekend, becoming centered over the southeastern states
on Sunday and shifting offshore on Monday. On Monday a cold front
will approach the region. Aloft generally SW flow will prevail
through the weekend and into early next week. Quiet weather will
dominate the weekend, with rainfree conditions and below normal
temperatures. Both Saturday and Sunday feature highs around 50 and
overnight lows in the 20s inland with 30s along the coastal
corridor. Isolated to scattered showers will be possible Monday
ahead of the approaching cold front. Temperatures Monday will be a
few degrees warmer than the weekend, likely reaching into the mid
50s.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Zonal flow will prevail aloft through midweek when the pattern aloft
shifts to broad troughing as a mid level trough swings eastward. The
aforementioned trough will push off the east coast late week with
broad NW flow in its wake. At the surface high pressure will prevail
through mid week, with a cold front pushing through the forecast are
on Wednesday. At this juncture FROPA is forecast to be dry, with too
much dry air in place to spur any showers. Temperatures through the
period will be below normal. Temperatures on Wednesday night will
likely be the coldest of the period, after FROPA with below freezing
temps at all locations and low 20s inland.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
VFR conditions will prevail at KCHS, KJZI, and KSAV into Friday
evening, with the risk for MVFR or IFR late in the valid TAF
cycle as low pressure and its associated frontal system impacts
the area with rain.

It is worth mentioning is that there is a very low chance for a
little liquid or non-liquid precipitation between 13Z and 17Z
today. A band of very light precipitation will move in during
that time while temperatures at the surface are expected to be
hovering close to 32F degrees. However, the lower and mid levels
of the atmosphere are very dry, and any precipitation that
falls should mostly evaporate and dissipate. Still, it is not
out of the question for a few snowflakes, sleet pellets, or
freezing rain, and/or rain at the terminals. No accumulations
will occur and no impacts are expected.

With the passage of a 40-50 kt low level jet tonight, LLWS (Low
Level Wind Shear) will occur at all sites starting around 02Z,
for S winds at least near 40 kt and E or ESE surface winds
around 10 kt.

Extended Aviation Outlook: Brief restrictions will be possible
around daybreak on Saturday as showers push through the
region. Prevailing VFR thereafter.

&&

.MARINE...
Today: High pressure gives way to a strong frontal system along
the the northern coast of the Gulf of Mexico. Winds that are
initially NE this morning will clock around to the E and SE this
afternoon. On average winds are 15 kt or less, with seas no more
than 3 or 4 feet.

Tonight: Dangerous marine conditions will develop as a 40-50 kt
southerly low level jet moves through in advance of the surface
low, before it passes off to the northeast late. Warm advection
will limit the mixing to some degree, but given modest pressure
falls later followed by modest pressure climbs, there is enough
of a chance to hoist Gale Warnings for the Charleston County
Atlantic waters, and the outer Georgia waters. S and SW winds
will reach 25-30 kt, with frequent gusts of 35 or 40 kt. For
the other waters, Small Craft Advisories are more likely, with
winds of 20-25 kt and gusty. Seas will build as high as 5-8 feet
within 20 nm, and 6-10 feet further out, with waves up to
around 2 feet in Charleston Harbor. Winds veer more westerly by
morning as the cold front clears the area, and as such winds and
seas remain elevated.

Saturday through Wednesday: In the wake of a low pressure system
pushing northeastward through the region, elevated winds and seas
will be present across all marine waters on Saturday. Headlines will
likely be in place to start Saturday across all waters, with
conditions improving through the day. High pressure will build into
the region through the weekend and into early next week. A cold
front will approach the region on Monday, with another surge in
winds forecast. Wind gusts Monday night into Tuesday could approach
Small Craft Advisory criteria across all waters, especially the 20
to 60 nm offshore GA waters. High pressure will return on Wednesday
with quiet marine conditions.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Winter Weather Advisory from 7 AM this morning to noon EST
     today for GAZ087-088.
SC...Winter Weather Advisory from 7 AM this morning to noon EST
     today for SCZ040.
MARINE...Small Craft Advisory from 1 AM to noon EST Saturday for AMZ330.
     Small Craft Advisory from 9 PM this evening to 1 AM EST
     Saturday for AMZ350.
     Gale Warning from 1 AM to 7 AM EST Saturday for AMZ350.
     Small Craft Advisory from 9 PM this evening to noon EST
     Saturday for AMZ352-354.
     Gale Warning from 9 PM this evening to 10 AM EST Saturday for
     AMZ374.

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...