Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 201918

Area Forecast Discussion
National Weather Service Columbia SC
218 PM EST Fri Jan 20 2017

A very active weather pattern expected to bring several rounds
of showers and storms to the region over the weekend with severe
weather possible. A deep upper low pressure system will move
over the area Sunday night and Monday followed by a couple of
days of high pressure and dry weather early next week. Above
normal temperatures early in the period then cooler late week.


Temperatures once again have risen above guidance with warm
advection over the forecast area in the wake of a passing warm
front earlier. Skies have been improving allow for more
sunshine and warmer temps. Adjusted max temperatures to the
mid/upper 70s this afternoon and cannot rule out a new record
high at Columbia with the old record at 76 last set in 1890.

Shallow low level moisture in place may still support an
isolated shower or two this afternoon but no widespread rain is
expected through evening but will hold on to a slight chance
pop. Southwesterly flow aloft later tonight associated with
upper trough over the middle of the country will allow another
shortwave lifting northeastward from the gulf coast to approach
the area by dawn Saturday. Precipitable water values will surge
again as values rise over 1.25 inches after 06z and support an
increase in pops through the early morning hours from southwest
to northeast, especially in the CSRA. Will reflect a gradient in
pops from southwest to northeast.

Abundant low level moisture overnight will support stratus
development with most guidance suggesting low clouds developing
during the 06-09z time frame which will limit radiational
cooling and keep overnight lows mild in the 50s.


There is a risk of severe thunderstorms over the weekend with
several rounds of convection moving through the area.

A warm front should be in area Saturday and Saturday night as
strong moisture flux and isentropic lift develops with deep
southwest flow aloft. Higher theta-e air will advect north into
the region during the day Saturday and air mass will become
increasingly unstable. Strong upward vertical motion early
afternoon across the Southeastern States associated with strong
upper level divergence ahead of deepening low pressure system
in the Plains. Deep layer shear increasing with helicity
possibly maximizing in the west Midlands and Piedmont during the
afternoon as suggested by NSSL WRF model. High resolution
models point to organized convective system moving through the
region during the late morning through early afternoon.
Convection in southeast Georgia and Florida may cut off moisture
advection into SC/East central Georgia. But continued categorical
pops and mild temperatures. There may be a lull in the
thunderstorms during Saturday evening period. Another round
during the late overnight and early Sunday period possible as
deepening low pressure approaches from the west.

The main event may develop Sunday afternoon as anomalously deep
upper low moves into the lower Mississippi valley. although dry
slot may develop early in the day...this may result in strong
heating and increasing instability. Global models...EC/GFS show
deep surface low moving through the Upstate region. Strong
instability/deep moisture and strong deep layer shear supports
threat for severe thunderstorms across the area. Tight surface
pressure gradient supports gusty winds especially in the
afternoon and evening.

The main severe weather threats will be damaging winds with bow
echoes and isolated tornadoes along quasi-linear convective

Followed the WPC rainfall forecast although trended slightly
higher given strong south moisture flux into the area. Heaviest
amounts Saturday night and Sunday. Forecasted weekend totals of
2 to 3 inches. Elevated threat for localized flooding although
convection should be moving rapidly through the area in waves.


The GFS and ECMWF display the upper low beginning to lift
northeast of the region Monday. Wrap-around moisture and
instability associated with the low supports a continued chance
of showers. Dry ridging should dominate Tuesday with an
approaching cold front Wednesday. The models show the front in
the area Thursday. Moisture appears limited with front mid to
late week. Model differences late in the period but trending


High confidence in VFR conditions through the evening hours
followed by deteriorating conditions during the predawn hours

Lower clouds have dissipated in the wake of a warm front that
crossed the area earlier. Southwesterly to westerly winds
around 10 knots will continue through the afternoon then become
light and variable with a predominant southwesterly direction
overnight. Abundant low level moisture will support
redevelopment of stratus and fog during the predawn hours
Saturday and supported by most of the guidance. Bring MVFR cigs
after 07z with a further reduction to LIFR cigs by 09z-11z all
terminals with possible IFR or lower vsbys. More uncertainty on
when or if conditions improve after 12z Saturday as an upper
disturbance moves into the region from the southwest with rain
overspreading the terminals after 15z. Thunder may be possible
towards the end of the forecast but not included at this time.

EXTENDED AVIATION OUTLOOK...Showers...and associated restrictions...
are likely Saturday through Monday as several waves of low
pressure cross the region.




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