Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 240217
Area Forecast Discussion
National Weather Service Charleston SC
917 PM EST Mon Jan 23 2017
An area of low pressure will lift northeast away from the area
tonight. High pressure will then prevail through Wednesday
before a cold front pushes through early Thursday. Cooler high
pressure will then return into the weekend.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
As of 915 PM: Latest scans from KCLX indicated a thin band of
light rain or sprinkles centered over Colleton County. The small
shower has developed on the western wall of the wrap around
moisture associated with the closed low over the NC Outer Banks.
The moisture should slide north of the forecast area over the
next two hours, resulting in the shower to dissipate. I will
update the forecast to add a mention of isolated showers across
and near Colleton County. Otherwise, the current forecast
appears on track.
As of 645 PM: The center of low pressure is forecast to track
from the Outer Banks of NC this evening to the New England coast
by Tuesday evening. As the low departs, the pressure gradient
will tighten to 4 to 5 mbs during the late night hours,
supporting WNW winds gusts into the teens to low 20s. The sfc
pressure gradient is expected to decrease during the early
daylight hours on Tuesday. I will update the forecast to adjust
winds and decrease sky and PoPs.
Previous Discussion... Tonight: Water
vapor imagery clearly shows the deep upper low centered over
North Carolina and this feature will continue to move eastward
through the overnight. At the surface, the 990 mb low to the
north will continue to pull away from the region, leaving behind
elevated west to northwest flow. Visible satellite imagery
shows the wrap around moisture and clouds steadily thinning with
time as drying downslope flow begins to take hold. As such,
skies will gradually clear out this evening and should be
totally clear for most of the overnight. Lows are expected to
fall into the mid to upper 40s in most areas, and winds will
remain elevated. Occasional wind gusts to 20-25 mph will be
possible, especially along the coast.
Lake winds: Winds are expected to increase this evening and
tonight across Lake Moultrie. Gusts to 25 knots can be expected
and the Lake Wind Advisory remains in effect.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
High pressure to build in behind departing low pressure Tuesday
leading to diminishing winds. The high is expected to slide off to
the south and east Wednesday ahead of an approaching cold front,
which should push through southeast SC/GA Thursday morning with some
showers. Clearing, but cooler and breezy conditions will then settle
in for Thursday afternoon. Temperatures will be on a warming trend
through Wednesday night before cooling down on Thursday.
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The long term period will be fairly quiet with high pressure to
persist late week through much of the weekend. A dry backdoor cold
front could then drop south into the area early Monday. No
mentionable PoPs are in the forecast at this time. Perhaps the most
notable feature of interest will be the return of cooler, more
seasonable temperatures after an extended warm period. Highs will
generally be in the 50s, with lows in the 30s.
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
VFR conditions expected through the 0Z TAF period. The center of
low pressure is forecast to track from the Outer Banks of NC
this evening to the New England coast by Tuesday evening. As the
low departs, the pressure gradient will tighten to 4 to 5 mbs
during the late night hours, supporting WNW winds gusts into the
teens to low 20s. The sfc pressure gradient is expected to
decrease during the early daylight hours on Tuesday. I will
indicate winds remaining between 10 to 15 kts, but models
soundings do not support a mention of gusts. Sky should become
SKC late tonight.
Extended Aviation Outlook: VFR through Saturday, although
breezy/gusty conditions likely Thursday through Saturday, mainly
during the afternoon.
Tonight: Improving cold advection and an expected tightening of
the pressure gradient in the wake of departing low pressure will
result in a period of increasing winds tonight across the local
waters. In fact, we expect there to be a period of gale force
gusts across the nearshore Georgia waters, so the Gale Warning
has been expanded to include all of the Georgia zones.
Elsewhere, solid Small Craft Advisory conditions will continue
through the night. Winds will begin to take on a slightly more
northerly component overnight, and a west-northwest direction
Tuesday through Saturday: High pressure will build in behind
departing low pressure Tuesday leading to lessening winds and thus
seas as well. The risk for gale force gusts, mainly across the GA
waters, will end Tuesday morning, although Advisory conditions will
likely hang on into early afternoon. Across the near shore waters
Advisory conditions should end by the afternoon. Conditions will
then go downhill again Wednesday as a cold front approaches and then
finally passes through early Thursday. Advisory conditions will be
likely beyond 20 nm and across the Charleston County near shore
waters Wednesday night and Thursday. Winds will remain elevated
through the end of the week, possibly again reaching Advisory levels
mainly across the Charleston near shore and Georgia offshore waters.
SC...Lake Wind Advisory until 4 AM EST Tuesday for SCZ045.
MARINE...Small Craft Advisory until 10 AM EST Tuesday for AMZ350-352.
Gale Warning until 7 AM EST Tuesday for AMZ354-374.
Small Craft Advisory until 7 AM EST Tuesday for AMZ330.