National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCAE 290808
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
308 AM EST Sun Nov 29 2020

.SYNOPSIS...
An approaching warm front will provide increasing chances of
rain late this afternoon and evening. The warm front will move
north through our forecast area (FA) tonight, followed by a cold
front moving through Monday morning. Expect showers and some
thunderstorms with this system. Drier air and increased winds
expected Monday behind the cold front. Significantly cooler air
will then filter into our region through Wednesday. The air mass
will begin to modify Thursday and Friday, as moisture begins to
move back into our region Thursday night through Friday night.
Another cold front will bring a return to cooler and drier
conditions by Saturday or Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Widespread fog continues to blanket most of the forecast area
and therefore have issued a dense fog advisory through 14z.
Thought the thicker high/mid clouds arriving may help improve
visibilities but that has not been the case. Surface high
pressure centered over West Virginia continues to ridge down
across the southeastern states with a stalled front extending
across central Florida westward to a weak surface low off the
southeast TX coast. 500mb analysis reveals a deep closed upper
low along the TX/OK border with moist southwesterly flow across
the Gulf Coast states.

Current precipitable water values are relatively low around a
half inch across the forecast area. However, the southwesterly
flow ahead of the approaching upper trough will combine with
increasing southeasterly low level flow off the Atlantic through
the day resulting in PWATs rising to between 1.25-1.5 inches by
00z Monday which is 200-225 percent of normal. As high pressure
shifts eastward off the coast and the surface low over the
western Gulf of Mexico lifts northeastward through the day,
isentropic lift will increase over the forecast area from midday
through the early evening hours as a weak inverted trough along
the coast lifts northward. This will provide likely to
categorical pops during the afternoon and evening hours
especially across the eastern and central Midlands, shifting
northward into the Pee Dee and northern Midlands this evening.

Temperatures today will be slow to rise due to abundant cloud
cover and the development of rain this afternoon. Expect highs
today to generally be in the lower to mid 60s.

Tonight: The upper trough will lift northeastward into the
southern Appalachians tonight with the surface low also lifting
northeastward to near the TN/NC/SC border area by 06z. The warm
front to our south will lift northward and isentropic lift north
of the front producing moderate rainfall will then shift north
of the forecast area overnight into North Carolina which may
bring a brief break in the rain, especially across the eastern
Midlands as forecast by the hi- res CAMs.

A surge in moisture advection ahead of the surface low and
associated cold front will push PWAT`s to near 1.5 inches and
250 percent of normal during the 03z-09z time frame. There is
expected to be a broken line of convection along and just ahead
of the cold front lifting northeastward into the forecast area
during the 06z- 12z time frame. This is a very dynamic system
with strong jet dynamics present and an 850mb jet around 50-60
knots which will provide the potential for damaging wind gusts
with stronger storms that may occur.

The limiting factor regarding severe weather potential is
instability. The NAM is more aggressive in showing surface based
CAPE trying to work into the area just ahead of the cold front
compared to the GFS but both are not showing very much so think
the severe threat is limited. However, given the strong wind
fields, any storms that develop will have potential to produce
damaging wind gusts and isolated tornadoes cannot be ruled out
in a brief 2-3 hr window just ahead of the front where whatever
instability is present will be best. QPF has been trending
downward on the past several model runs, but it should be noted
that the models struggled with the past 2 precipitation events
under forecasting them and the moisture associated with each
system. Expecting generally less than an inch of rain with this
event but cannot rule out some locally higher amounts. Lows
tonight will be driven by the location of the front and cold
advection behind it but have overnight lows ranging from the
lower 50s west to upper 50s east.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The cold front, and associated band of showers and some
thunderstorms, will move east through our FA early to mid
Monday morning. Weak instability but strong wind fields will
provide a continued possibility of severe weather Monday
morning.

Upper low expected to cut off over the Midwest Monday while
surface low will intensify and move rapidly to our NE. Pressure
gradient between the low to our NE and surface high to our west
expected to result in breezy west winds Monday. A lake wind
advisory may be required Mon/Mon nt. Best cold advection
appears will be behind a secondary front late Monday and Monday
night.

Upper trough to move through our region Tue/Tue nt. Models
indicate any associated moisture/lift to remain to our north.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Surface high pressure will build in for Wednesday and Thursday.
Some airmass modification expected Thursday as a weak shortwave
ridge moves overhead. SW flow aloft expected late Thursday and
Friday as upper low cuts off over the Plains and moves east
into the Miss valley. Some timing differences with the next
system, with GFS indicating moisture return and isentropic lift
as early as Thursday night, while EC holds it off towards
Friday or Friday night. Cold frontal passage expected over the
weekend to bring in drier and cooler air again under possibly
breezy conditions.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
High confidence in LIFR/IFR restrictions through 09z or so with
some brief improvement expected after that into the early
afternoon but then restrictions return for tonight.

Widespread LIFR fog impacting all terminals except OGB to start
the forecast period. Some thicker high and mid level clouds will
move over the area by 08z-10z which may improve vsbys due to
warming surface temps but confidence is limited in that scenario
so will show that improvement in a tempo group. A deep upper
trough and associated front will approach from the west this
afternoon. Ahead of this system, southeasterly flow will
increase today allowing Atlantic moisture to stream over the
region and expect MVFR cigs to spread northwestward over the
terminals during the late morning into afternoon. An inverted
trough along the coast will lift northward and bring scattered
showers to parts of the central and eastern Midlands so will
include VCSH at OGB after 16z and CAE/CUB after 19z.

More significant rain is expected to develop by 00z across the
region as a warm front sets up to our south and increasing
isentropic lift will result in lowering cigs and development of
widespread rain with MVFR/IFR vsbys expected. Winds will
generally be light and variable through 15z then increase to
around 5 to 7 knots from the east through the afternoon before
diminishing again around 00z.

EXTENDED AVIATION OUTLOOK...Restrictions likely to continue
into Monday morning as a low pressure system moves through the
region.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...Dense Fog Advisory until 9 AM EST this morning for GAZ040-
     063>065-077.
SC...Dense Fog Advisory until 9 AM EST this morning for SCZ016-018-
     020>022-025>031-035>038-041-115-116.

&&

$$