Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 210833

Area Forecast Discussion
National Weather Service Charleston SC
433 AM EDT Wed Mar 21 2018

High pressure will build in from the west today and prevail
through Saturday. A cold front will drop south through area on
Sunday. High pressure will return early next week.


Pre-dawn: Winds shifted west overnight in the wake of a cold
front. Skies cleared earlier but there are still areas of
stratocumulus moving into locations to the west of I-95 in
GA as deep cyclonic flow dominates aloft. Cold air advection
in the low levels were ongoing, temps continue to tail off;
likely dipping into the upper 40s inland by daybreak. We saw an
initial surge of winds post-front and elevated breezes should

Today: A deep upper low will pass through the Mid Atlantic
region, fueling another deep surface coastal low off of southern
New England. Our region will be on the dry side of this system
today as sinking and drying air in the low levels usher in much
lower dew points across the region. A powerful 125 kt 500 MB jet
if forecast to arc through south GA later today with 850 MB
flow occasionally in excess of 40 kt. The setup is primed for a
windy day across the area. The best chances for wind gusts
reaching 40 mph during peak heating this afternoon appear to be
across coastal southeast GA where gradients remain tighter. We
hoisted a wind advisory for this region for the afternoon.

Elsewhere this afternoon, it will could be close to advisory
criteria inland GA and far southern SC with the period of
deepest mixing from 3 pm to 6 pm. Clouds may increase over
our northwest and northern zones where moisture is a bit
better below the subsidence inversion between 700 and 800 MB.
There should be enough of a weak downslope factor along coastal
zones to touch mid 60 north and the mid 60s south, inland and
northern zones will struggle to reach 60.

Tonight: Models suggest a gradient wind will tend to persist
across the region but we think far inland areas may have a
chance to decouple late. Even if some cooler inland areas
dip to the mid 30s late, frost potential appears too poor at
this time to intro any frost mentions. The cool temps will feel
chillier early Friday with light breezes along the coastal

Lake Winds: We extended the advisory for Lake Moultrie a bit
longer into the early evening hours.


Expansive area of low pressure off the New England coast will lift
northeast, allowing high pressure to continue to build in from the
west Thursday and Friday. Aloft, broad troughing will persist over
the east coast. Deep dry air will keep skies mostly clear and rain-
free conditions. Despite little to no cloud cover, cool northwest
flow will limit heating. Temperatures are forecast to stay below
normal, with highs peaking in the 60s. Good radiational cooling
setup for Thursday night, with winds expected to drop off late. As
low temperatures drop to the mid 30s inland late, some patchy frost
could develop. Lows Friday night will be more mild in the 40s with
no frost concerns.

The surface high will drift overhead and then into the Atlantic on
Saturday as an area of low pressure drops out of the Midwest into
the Ohio River Valley. Some moisture return expected as flow turns
southerly, but nothing more than an increase in cloud cover
expected. Temperatures will moderate some with highs forecast to
range from the mid 60s across northern zones to mid 70s near the


Models are in good agreement on the synoptic pattern through the
long term period. A cold front is progged to drop south through the
forecast area on Sunday, as high pressure wedges in from the north.
Some rain will accompany the front, although models vary on coverage
so have capped PoPs in the 30-40% range. A wedge-like setup will
persist through Monday with clouds and cool northeast flow keeping
temperatures below normal. On Tuesday, the high will begin to expand
over the area and help temperatures moderate closer to normal.


VFR. Gusty WNW winds will impact the terminals into the late
afternoon Wednesday. Gusts will likely top 30 kt at times during
the mid/late afternoon hours.

Extended Aviation Outlook: VFR through Saturday. Sub-VFR ceilings
possible Sunday as a front drops into the area.


Today: We maintained current Gale Warnings for the coastal waters
along with a higher-end SCA in the Charleston Harbor. Strong
jetting offshore flow will tend to be a bit stronger to the
south of Charleston but hazardous conditions are expected in all
near shore waters today. Gusts should top 40 kt well offshore
over outer 20-60 NM GA waters where seas will be in the 6-9 ft
range. Down river locations such as Fort Pulaski GA should have
excellent exposure to surging and jetting conditions today and
gusts to 35 kt may be common there today.

Tonight: The Gale warnings should be lowered to SCA in our near
shore waters but frequently gusts to 35 kt are expected closer
to the Gulf Stream.

Thursday through Monday: High pressure will continue to build in
from the west Thursday into Friday. Elevated pressure gradient will
keep northwest winds around 15 knots on Thursday, before it slackens
on Friday. The high will shift overhead and then into the Atlantic
on Saturday allowing winds to become more southerly.  A cold front
will drop south through the waters on Sunday as high pressure wedges
in the from the north. Marine conditions will deteriorate, and Small
Craft Advisories will be possible beginning Sunday evening and
persisting through Monday.


GA...Wind Advisory from noon today to 7 PM EDT this evening for
SC...Lake Wind Advisory until 10 PM EDT this evening for SCZ045.
MARINE...Gale Warning until midnight EDT tonight for AMZ350-352-354.
     Gale Warning until 4 AM EDT Thursday for AMZ374.
     Small Craft Advisory until midnight EDT tonight for AMZ330.


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