Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 202349
AFDCAE

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TONIGHT/...
SW flow aloft associated with upper trough over the middle of
the country will allow a 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.

&&

.SHORT TERM /SATURDAY MORNING THROUGH SUNDAY NIGHT/...
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
lines.

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.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
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
cooler.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
High confidence in VFR conditions this evening followed by
deteriorating conditions after 06Z.

Mainly high level clouds and light southerly wind this evening.
Could see mid level clouds over central GA at 00Z move into
AGS/DNL this evening.

Abundant low level moisture will support development of stratus
and fog during the predawn hours...this is supported by most of
the guidance. Have continued MVFR cigs after 07Z with conditions
deteriorating to LIFR 09Z-11Z all terminals. More uncertainty
on when or if conditions improve after 12Z as an upper
disturbance moves into the region from the southwest with rain
overspreading the terminals after 15Z. Thunder may be possible
during the afternoon...but not included at this time given
uncertainty due to lingering stratus.

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

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

$$



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