Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 240809

Area Forecast Discussion
National Weather Service Columbia SC
409 AM EDT Mon Apr 24 2017

An approaching low pressure system will slowly cross the region
today and tonight resulting in persistent showers and
thunderstorms. Dry weather and above normal temperatures will
return by Wednesday as high pressure takes control.


Analyzed closed upper low is currently over northern Alabama
with diffluent 500mb flow over the forecast area with a strong
45kt southerly low level jet extending from the southern coast
northward into the Pee Dee region. This is resulting in the
widespread convection across the eastern half of the forecast
area this morning. Widespread amounts of 1 to 2.5 inches of rain
have already fallen resulting in some urban flooding around
Columbia. The surface front extends across southern SC from near
Georgetown to south of Barnwell to a surface low near Statesboro

The closed upper low will continue to dive southeastward today
over southern Georgia then shift offshore tonight. The surface
low over southeast Georgia will slowly lift northeast through
the day into southern SC then also shift offshore tonight. This
will result in the axis of higher precipitable water air (values
around 1.6 inches) to be over the Pee Dee region and eastern
Midlands through the day before shifting northeast into NC
tonight. Hi-res models indicate best upper dynamics and low
level convergence across the northeastern half of the forecast
area and will continue to carry the highest pops there. Another
band of convection is expected to develop this morning along the
Savannah River and shift northward through the day along a low
level convergence boundary. Training cells will again be a
possibility and could result in additional localized flooding
threat so will continue the flash flood watch already in effect
across the area.

Confidence is low in potential severe convection given the
current position of the surface low and frontal boundary
generally south of the forecast area with the exception of the
far eastern Midlands but SPC does have a marginal risk outlook
generally along and south of the I-20 corridor. There will be
much colder mid level air moving over the region today with
500mb temperatures around -17C which could support a hail threat
within stronger updrafts. As the upper low shifts by and
offshore tonight the bulk of the heavy rain should be shifting
north and east of the forecast area and will decrease pops from
southwest to northeast through the night. Temperatures today
will likely remain quite cool across the northern and western
Midlands well into the cooler stable air wedge with a gradient
to warmer temperatures in southeastern Midlands near the front
and surface low. Trended cooler with highs in the lower 60s
northern and western Midlands with mid 70s in the far
southeastern Midlands.


The upper low will lift northeastward away from the region on
Tuesday with an upper ridge to the west shifting eastward over
the area. There could be some scattered showers across the
northern half of the forecast area through midday Tuesday but
any precipitation should be ending by the afternoon shifting
north of the forecast area. Temperatures will be warmer but
still expect to see a gradient in highs ranging from the upper
60s to lower 70s in the northern Midlands to the upper 70s in
the CSRA. Skies should clear out Tuesday night with good
radiational cooling which will allow overnight lows to fall into
the mid to upper 50s.


Fair and drier weather with a warming trend expected during
much of the extended period.

An upper ridge will move over the forecast area Wed/Thur
providing dry weather and moderating temperatures. A
deamplifying upper trough will approach late Thursday into
Thursday night breaking down the upper ridge and bringing a
slight chance of rain to the western part of the forecast area.
Deep troughing over the western part of the country Fri/Sat will
result in the upper ridge rebuilding over the southeastern
states. At the surface high pressure over the western Atlantic
will provide southerly low level flow and increasing moisture
into the region resulting in warm and more humid conditions for
the end of the extended period. Temperatures will be nearly 10
to 15 degrees above normal through the period with highs in the
upper 80s to around 90 and lows in the 60s.


Upper and surface lows will slowly traverse the region through
today/tonight. Will monitor radar trends and latest high
resolution guidance and concentrate on the near term for the
TAFs. In then near term, it appears heaviest band of
thunderstorms will push to the east of CAE/CUB/AGS, though
periods of shower activity expected for a few hours, with a few
embedded thunderstorms possible. Band of showers and
thunderstorms expected to develop west of DNL/AGS and shift east
into that area later tonight. Additional shower and
thunderstorm activity expected to develop Monday afternoon,
mainly affecting the CAE/CUB/OGB sites. Widespread CIG
restrictions expected to continue with VSBY restrictions at
times due to precipitation.

EXTENDED AVIATION OUTLOOK...Bulk of heaviest thunderstorm
activity expected to push east of our TAF sites Monday night,
but lingering showers and CIG restrictions expected to continue
through at least Tuesday morning.


GA...Flash Flood Watch through this evening for GAZ040-063>065-077.
SC...Flash Flood Watch through this evening for SCZ015-016-018-


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