Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 290147

Area Forecast Discussion
National Weather Service Columbia SC
947 PM EDT Mon Sep 28 2020

A cold front and upper low will cross the region Tuesday and
Wednesday bringing inclement weather. Dry weather and cooler
temperatures will return Thursday into the weekend.


Evening analysis shows the forecast area is in between systems
with a shortwave lifting northeast away from the area over
northeast SC and southeast NC and a much more potent upper
trough over the middle of the country. Water vapor imagery shows
significant mid level dry air across much of SC which will
remain in place overnight. PWAT values are less than 1.25 inches
over the forecast area, and will slowly rise late tonight but
remain below 1.5 inches through 12z.

The loss of heating and lack of deeper moisture has resulted in
no precipitation on radar in our area and expect generally dry
conditions overnight with no appreciable rainfall through
morning. There is a line of convection associated with a cold
front extending from eastern TN through eastern AL but expect
this to diminish before reaching our area around 12z, but did
bring some chance pops in from the west after 09z.

Widespread stratus is expected to expand over the entire
forecast area by midnight and will act as an insulation blanket
keeping temperatures from dropping much overnight. Diurnal range
is expected to be quite low with min temperatures expected in
the upper 60s to around 70 degrees.


The upper trough continues to deepen with a closed low developing
over the lower MS Valley on Tuesday. The cold front crosses our area
Tuesday through Tuesday night as the upper level cutoff low
approaches. The mid level flow is forecast to increase ahead of
cutoff low. Along and ahead of the cold front, abundant moisture
advects into the region with moderate instability and precipitable
water values increasing to 2+ inches across the eastern half of SC.
Still expect showers and thunderstorms with locally heavy rainfall
possible. Cannot rule out isolated severe thunderstorms Tuesday
afternoon into the evening.

Models indicate a surface wave developing along the front as it
moves through the area. Have indicated likely to categorical pops
Tuesday into Tuesday night. The cold front pushes east of the area
Tuesday night. High temperatures are expected to range from the mid
70s west to lower 80s east on Tuesday with lows Tuesday night in the
mid 50s to lower 60s.

The closed upper level low moves overhead on Wednesday which should
lead to scattered instability showers due to 500 mb temperatures of -
15 to -20C. Isolated thunderstorms with small hail also possible.
Have indicated temperatures in the low side of guidance...around 70
degrees. However, temperatures may struggle to get out the 60s with
cold air aloft and persistent cloud cover. As the upper low lift
northeast Wednesday night, should see clearing skies with lows in
the low to mid 50s.


Dry weather is foreseen Thursday through the weekend. We remain
along the southern edge of a deep upper trough over The Great Lakes
and New England. A moisture limited front will cross the area
Thursday night and reinforce the cooler airmass as surface high
pressure builds in through Sunday. Below normal temperatures can be
expected with highs mid to upper 70s on Thursday, cooling to the
upper 60s and lower 70s for the weekend. Overnight lows will be in
the upper 40s and 50s.


Two main issues. One will be stratus/low CIG and fog tonight,
and then the focus will shift to shower and thunderstorm
potential for Tuesday afternoon.

Latest obs indicate lowering CIGs. Some dry air aloft, noted on
satellite water vapor imagery, over our forecast area (FA)
tonight. This in combination with abundant low level moisture in
a SE low level flow is expected to provide strong stratus and
fog potential. Latest GFS indicating a 25 knot low level jet
overnight at CAE which would favor stratus over dense fog,
although some other models are indicating a weaker low level
jet. Guidance unanimous in favor of low CIGs, with most guidance
indicating low VSBYs in fog as well. Due to possibility of some
boundary layer wind staying up, will hit the stratus a little
harder than the VSBYs and keep VSBYs above dense criteria for
now. Nonetheless, the result is high likelihood of LIFR
restrictions for a considerable period of time tonight into
Tuesday morning.

Expect a deepening upper trough to our west tonight and
Tuesday. Some upper energy will shift NE through our region in a
SW upper flow Tuesday afternoon. At the surface, a cold front
will approach our FA from the west late tonight and Tuesday
morning. An area of low pressure is expected to form along the
front near our FA, which then shifts to the NE, allowing the
front to move through our FA Tuesday afternoon. The latest high
resolution models indicate a band of scattered showers and
thunderstorms developing along the front during the afternoon,
mainly over the central and eastern FA. This would favor OGB
with the best TSRA potential, with some TS potential at CAE/CUB
as well. It appears less TS potential for AGS/DNL as the front
and best diurnal heating and instability may be east of those
terminals during the afternoon.

Drier air will enter the FA behind the front Tuesday night.

EXTENDED AVIATION OUTLOOK...No significant impacts to aviation
expected Wednesday through Saturday.




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