Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 052109
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
409 PM EST Mon Dec 5 2016

.SYNOPSIS...A storm system will affect the area through Tuesday
evening. A strong cold front will sweep through Thursday night
followed by cold high pressure through early next week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Surface high pressure moving into the northeastern U.S. states
late tonight will initially generate NE winds across our area.
The best cold air damming will be to our north. Inland
temperatures will initially start in the mid 50s this evening.
Low pressure moving up the TN Valley will allow deep moisture
to move in from the southwest, overspreading the area from the
southwest to the northeast. PWATs approaching 2 inches are well
above normal for this time of year and this along with the
combination of the right entrance region of the 130-150 kt 300
mb jet over our area and a warm front approaching from the
south will lead to good rainfall across our area late this
evening and overnight. Likewise, temperatures are expected to
rise late this evening and overnight, so lows could be reached
in the evening. As for QPF, overnight amounts should be in the
1 to 2.5 inch range. Also of note, models still show some
elevated instability working it`s way in from the south , so we
kept thunder in the forecast, beginning late this evening
across the south and then spreading to the north after midnight.
Given the overnight timing, the risk of severe weather is low.
But plenty of shear is in place and worth watching for a wind or
maybe isolated tornado threat.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday: A surface warm front should be located along the South
Carolina coast then extending westward into interior portions of
Georgia shortly after day break. The warm front is then expected to
slowly develop northward and should be north of the area by the
afternoon as an area of surface low pressure moves from the Midlands
into the Pee Dee region of South Carolina. Widespread rain with some
embedded thunderstorms is expected to be ongoing early Tuesday
morning, but as the upper level short wave lifts northeast of the
area by the afternoon, isentropic assent greatly diminishes, and the
deep level moisture gets shunted northeast away from the area, the
widespread rain should end from southwest to northeast. The warm
sector should overspread most if not all of the area in the wake of
the warm front and ahead of the cold front. With some CAPE values up
to 600 J/KG in the warm sector, cannot rule out a couple of
thunderstorms. However, limiting factors for thunderstorm
development are the dry air in the mid levels of the atmosphere and
only modest convergence along the front. Have lowered rain chances
in the afternoon, but it is quite possible that nothing develops
behind the departing area of rain. For any thunderstorms that
develop in the warm sector, there is a small threat that a storm or
two could become severe with strong damaging winds the most likely
threat. Very small chance for a brief tornado, but with decreasing
low level helicity values during the day it appears quite unlikely
that the best instability will coincide with the best helicity,
thereby making the threat very low. Assuming everyone gets into the
warm sector, highs will range from the lower 70s in the northwest to
the upper 70s in the south.

Tuesday night: Any lingering showers during the evening will quickly
come to an end. Skies should become partly cloudy with lows by
Wednesday morning mainly in the lower to mid 50s. There could be
some areas of fog around by daybreak Wednesday.

Wednesday through Thursday: Weak high pressure builds in Wednesday
through Thursday with cooler temperatures and dry weather. A strong
cold front is expected to move through the area by late Thursday
afternoon. At the present time, limited moisture should result in
nothing more than some cloudiness associated with the cold
front.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A mainly dry cold front will sweep through the area Thursday
night followed by cold and dry high pressure through early next
week.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
KCHS and KSAV are forecasted to become IFR by this evening as
moderate rainfall overspreads the area. There is a chance of
thunder at both sites after midnight, but confidence was too low
to include in the TAFs. Conditions will improve Tuesday
afternoon as rainfall diminishes across the area.

Extended Aviation Outlook: Sub VFR conditions are possible Tuesday
afternoon in and near any showers or thunderstorms and then again
late Tuesday night into early Wednesday associated with fog and/or
low ceilings. VFR conditions return Wednesday and then likely
persist into the weekend.

&&

.MARINE...
Tonight: Northeast winds will prevail for the first part of the
night as widespread precipitation spreads across the local
waters. Then, a warm front will begin move northward late
tonight, causing winds to become southerly by sunrise. Wind
speeds will increase during this time, reaching the 15-20 kt
range, especially beyond 20 nm. Seas, after falling to the 2-3
foot range early in the evening, will build to 2-4 feet by
sunrise.

Sea Fog: The combination of southerly winds and increasing moisture,
could generate sea fog/low stratus across the waters. However, water
temperatures are still in the low to mid 60s and the overall
residence time of the southerly flow won`t be long. Confidence
for sea fog is low, so we opted to leave it out of the forecast.

Gusty southwest winds and seas rising above 6 ft will yield Small
Craft Advisory conditions for the GA offshore waters Tuesday into
Tuesday evening. A small craft advisory is in effect for this area.
Conditions will be close to Small Craft Advisory levels in the outer
portions of the South Carolina near shore waters Tuesday, especially
for the waters off the Charleston County coast. However, given the
cool waters in a warm advection pattern, feel that limited mixing
should preclude winds and seas from reaching the Small Craft
Advisory criteria levels.

Tranquil conditions will develop across the waters by Wednesday
morning and then persist well into Thursday as weak high pressures
develops across the area.

Thursday night through Friday night will feature strong winds in the
wake of a strong cold front that moves through. Strong offshore flow
with cold advection will likely result in advisory conditions across
most if not all of the waters.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 7 AM to 11 PM EST Tuesday for AMZ374.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...JRL
AVIATION...
MARINE...


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