Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 240138

Area Forecast Discussion
National Weather Service Charleston SC
938 PM EDT Fri Mar 23 2018

High pressure will remain across the region through Saturday. A
backdoor cold front will push southwest across the area late
Sunday night into early Monday morning. Atlantic high pressure
will dominate the region during the mid and late work week.
Another cold front should arrive by Friday evening.


The current forecast is in good shape. Did nudge overnight lows
down 1-2 degrees for the coastal corridor into the Francis
Marion National Forest.

High pressure will extend south across the region tonight.
Cirrus associated with a jet streak embedded in the polar jet
will approach from the northwest this evening and overspread the
region early Saturday. There may be just enough isentropic
assent along the nose of increasing 850 hPa warm air advection
to produce some light sprinkles across the interior after
midnight, but measurable rainfall is not expected at this time.
The boundary layer should decouple after sunset yielding
calm/light winds. However, increasing warm air advection and
thickening cirrus aloft should yield a warmer night with lows
ranging from the lower 40s across interior Southeast South
Carolina to the mid-upper 40s elsewhere.


On Saturday, cold air damming is forecast to develop across the
western Carolinas during the daylight hours. Sfc low pressure is
timed to approach the southern Appalachians through the evening
hours. The wedge boundary will likely remain north of the forecast
area as the sfc low is positioned west of the I-20 corridor.
Conditions across the CWA are forecast to remain dry with light SE
winds. High temperatures are forecast to range from the mid 60s
across the CHS Tri-County to the mid 70s across the SE GA counties.

Short term guidance indicates that the sfc low will shift off the
Carolina coast between 9Z-12Z Sunday. Circulation around the low
should drive the wedge front southward, likely exiting the southern
CWA by late Sunday afternoon. NAM12 indicates that a thin band of
instability will develop along and ahead of the backdoor front
across SE GA. Enough instability should exist to support a mention
of thunderstorms along with the likely showers. Temperatures across
the SC Lowcountry should remain nearly steady in the mid to upper
50s as temps may spike near 70 across SE GA, then cooling.

On Monday, strong sfc ridging will remain across the Carolinas and
GA, sourced from a 1045 mb high centered over New England. GFS
indicates that deep isentropic lift, centered between 295K-305K,
will develop over GA during the morning and then lift north during
the day. The combination of the deep moisture and decent llvl lift
should yield likely coverage south and chc PoPs north of the
Savannah River. High temperatures are forecast to range in the upper
50s across the CWA.


Models generally agree that a wedge of high pressure will slowly
weaken and shift offshore Tuesday into Wednesday, allowing a
northeast sfc flow to become southeast mid week. The change in the
pattern will likely result in a noticeable warmup during the period
with highs in the mid/upper 60s on Tuesday, then mid/upper 70s on
Wednesday. A persistent southerly wind under ridging aloft will
continue to drive warmer air over the region on Thursday ahead of
low pressure developing to the west. In general, temps should peak
in the lower 80s over most areas away from the immediate coast
Thursday afternoon. The next chance of precip should come on Friday
with a cold front that sweeps through the Southeast.



Extended Aviation Outlook: A backdoor cold front will push across
the terminals on Sunday. A wedged air mass should remain across the
region through Monday night. This pattern should yield widespread
restrictive ceilings with periods of restrictive visibility during
showers and drizzle. Conditions should improve on Tuesday and remain
into Friday.


Tonight: Quiet marine conditions will prevail with winds <10 kt
and seas <3 ft.

Saturday: A cold front will remain north of the region on
Saturday. Conditions across the marine zones should feature
steady south winds and wave heights of 1-2 ft.

Saturday Night and Sunday: Short term guidance indicates that a
sfc low will shift off the Carolina coast between 9Z-12Z
Sunday. Circulation around the low should drive a wedge front
southward, likely exiting the southern CWA by late Sunday
afternoon. Winds are forecast to veer from SW during the morning
to NE during the afternoon. By the afternoon, gusts could
frequently gusts into the mid 20 kts, wave heights building to
3-5 ft to around 6 ft across northern AMZ350. Small Craft
Advisories will likely be issued.

Sunday Night and Monday: Tight pressure gradient will peak
across the near and offshore waters. NE winds should increase
Sunday night and remain through Monday, with gusts around 30
kts. Wave heights should range from 4 feet along the beaches to
10 across eastern AMZ374.

Tuesday and Wednesday: High pressure will shift over the
western Atlantic Tuesday and Wednesday. Winds should gradually
shift from the SE and weaken, resulting in decreasing wave




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