Area Forecast Discussion
Issued by NWS Charleston, SC

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418
FXUS62 KCHS 281128
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
728 AM EDT Tue Mar 28 2017

.SYNOPSIS...
A weak cold front will stall over or near the area on
Wednesday before moving back north Thursday night into Friday as a
warm front. Another cold front will move through Friday night into
Saturday followed by drier high pressure Sunday. Unsettled weather
could return as soon as next Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 720 AM: Isolate showers were located offshore, expected to
continue to track to the ENE. A few weak showers could move over
the inland counties this morning. The headline for today will be
the record to near record high temperatures. Conditions should
warm quickly through the morning hours, then temps will level
off in the low to mid 80s. I will update the forecast to tweak
sky, PoPs, and temps.

As of 4 AM: Water vapor satellite channel indicated that a weak
mid level vort max sliding across the lower Savannah River
Valley. KCLX radar detected isolated showers from over the radar
site south to the GA coast. These showers will tracking north
across the coast plain. I will anticipate that the showers will
continue move north across CWA through early this morning,
likely linking to the southern end of the band of convection
pushing across the Piedmont of the Carolinas. Shower coverage
should decrease within and hour or two following sunrise,
reducing PoPs below SCHC.

This afternoon, the mid level S/W will ripple over the mid Atlantic
states, keeping the passage of the synoptic scale forcing well north
of the forecast area. By early this afternoon, a cold front is
forecast to slide off the east facing slopes of the southern
Appalachians, but moving very slowly ESE. As the front approaches
the forecast area, sfc winds will shift from the SW. The combination
of partly sunny conditions, off shore winds, and slight
compressional heating ahead of the front should result in
temperatures 3 to 5 degrees warmer than observed yesterday. In fact,
I will forecast 86 degrees at KCHS, which exceeds today`s record
high by a degree. During the mid to late afternoon, isolated to
scattered showers and thunderstorms should pass over the inland
counties.

Tonight, debris clouds should dissipate across the CWA
during the evening hours. The cold front is forecast to slowly
backdoor across the forecast area. The approach and passage of the
front will likely keep winds steady from the west. Using a blend of
guidance, min temperatures are forecast to range from the upper 50s
inland to the low 60s across SE GA.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Atlantic high pressure will give way to a cold front Wednesday which
should make it into southeast GA as high pressure builds from the
north. Drier air and minimal synoptic forcing will yield dry
conditions Wednesday, although cannot rule out a few showers and/or
storms near the Altamaha River which will be closer to the stalled
front. It should remain rain-free until later Thursday when deeper
moisture returns and isentropic ascent increases across the area
north of the stalled front which will be starting to move back north
as a warm front. Thus, showers and possibly a few thunderstorms
(mainly across GA) are expected. Rain chances will increase further
Thursday night into Friday as the warm front lifts north through the
area and moisture/forcing increase. Although wind fields will be
strengthening, instability appears minimal Friday and thus the
threat for severe weather is low at this time. Either way it should
be a breezy day with gusts up to around 25 mph.

Temperatures should push into the lower to mid 80s most inland
locales Wednesday, with some upper 80s possible given the offshore
flow and frontal compression. On Thursday, high pressure building
from the north will keep it a bit cooler, especially across SC where
it should stay below 80 degrees except close to the Savannah River.
Once again wouldn`t be surprised if upper 80s occurred Thursday
toward inland portions of the Altamaha River closer to the stalled
front. Temperatures Friday will be moderated by the clouds/rain,
likely only reaching close to 80 inland. Prevailing onshore winds
will keep coastal locations much cooler during the daytime through
the period.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A cold front will push through Friday night into Saturday followed
by drier high pressure Sunday. Unsettled weather could return early
next week as a storm system moves across the Deep South, although
there remains significant uncertainty regarding the timing of best
rain chances. Highest confidence in rain will be the first part of
Friday night when showers, and possibly some thunderstorms, are
expected. Temperatures should remain above normal through the
period.

&&

.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
VFR. At 1110Z, a few showers were drifting just offshore. Based
on the timing and placement of a H5 S/W, showers should push
north out of the forecast area by sunrise. Latest CAMs generally
agree that convection upstream over GA will weaken as it pushes
east of the fall line. By 18z, a cold front is expected to
slowly pushes east of the southern Appalachians. The forecast
area will remain between the cold front to the northwest and sfc
high pressure off the Atlantic coast of FL. The sfc pattern
will yield steady SW winds across the region. During this
afternoon, forecast soundings from the NAM12 indicate that the
mixed layer will rise above 5 kft, resulting in gusts into the
20kts. Winds should weaken after sunset, steady SW winds will
remain through this evening and overnight. The cold front is
forecast to slowly backdoor across the terminals late tonight.
The approach and passage of the front will veer winds from the
NW during the pre dawn hours Wed.

Extended Aviation Outlook: Restrictions possible Wed night/Thu
morning due to low clouds and/or fog, then likely due to
showers/thunderstorms/low clouds, mainly Thu night into early Fri
night.

&&

.MARINE...
The region will remain between a cold front across the Carolina
Piedmont and high pressure off the FL Atlantic coast. This pattern
should result in a 2-3 mb pressure gradient across the forecast
area. South winds should gradually strengthen across the marine
zones, becoming gusty this afternoon. The highest wind gusts are
forecast to occur across AMZ350 in the low 20 kts. Swells should
remain between 3-4 feet today, portions of AMZ 350 and all of 374
will see 5 feet. Tonight, winds will shift from the west and weaken
as a backdoor cold front slides over the Lowcountry. Wave heights
may decrease around 1 foot with the weaker offshore winds.

Wednesday through Sunday: A weak cold front will move into the area
Wednesday and Wednesday night as high pressure builds to the north.
The front will return back north through the area as a warm front
Thursday night/Friday. A cold front will then move through Friday
night/early Saturday. At some point prior to the cold frontal
passage Saturday sea fog could develop across the cooler near shore
waters and lead to low visibilities.

Expect a high chance for Advisories Thursday night across the outer
waters, expanding northward into the SC waters through Friday night
as strengthening winds build seas to 6-8 feet, highest beyond
20 nm.

Rip Currents: High risk for rip currents along the SC coast and
Moderate for GA today. Gusty winds and long period 3 foot swells
will likely produce rip currents. The combination of higher than
normal tides, onshore winds and swells in the surf zone will
support an enhanced risk for rip currents through mid week,
possibly lasting into Friday.

&&

.TIDES/COASTAL FLOODING...
High tides could reach Advisory levels,
mainly late Wednesday/Thursday, due to strengthening onshore winds
and swells impacting the coast. This could cause shallow to moderate
saltwater inundation in vulnerable coastal areas, possibly even
reaching major levels Thursday night. Thus, Coastal Flood Advisories
are expected with a potential for Watches/Warnings as well.

&&

.CLIMATE...
RECORDS FOR 03-28

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KCHS      85 2007     47 2011     65 1987     32 1969
   KSAV      89 1907     46 1955     67 1921     33 1955
   KCXM      91 1907     48 1955     68 1921     37 1982

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...High Risk for Rip Currents through this evening for SCZ048>051.
MARINE...None.

&&

$$
NEAR TERM...NED
SHORT TERM...RJB
LONG TERM...RJB
AVIATION...NED/RJB
MARINE...NED/RJB
TIDES/COASTAL FLOODING...RJB
CLIMATE...NED



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