Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 271858

Area Forecast Discussion
National Weather Service Columbia SC
258 PM EDT Sun May 27 2018

Tropical moisture will stream north into our region from the
south tonight. Heavy rain possible. Expect a moist pattern to
remain through late week.


Deep tropical moisture will continue to advect northward into
the region between Subtropical Storm Alberto and a strong ridge
over the western Atlantic. Precipitable water values will surge
to 2.0 to 2.4 inches tonight, or about 175% of normal, highest
across the eastern Midlands. This will result in a threat for
heavy rainfall capable of producing flash flooding later
tonight, and a Flash Flood Watch is in effect for the entire
area beginning at midnight.

Despite extensive cloud cover, the majority of the forecast
area has been rain-free through early afternoon. However, a
batch of light to moderate rain will shift in from the coastal
plain and advance northwest to about the I-20 corridor through
the remainder of the afternoon. Models show that while scattered
to numerous showers could persist through the evening across
most of the area, a band of showers and isolated thunderstorms
capable of producing very high rainfall rates should move in
from the south well after midnight...maybe even closer to
daybreak and lift north across the area. Models are also in
agreement showing a general 1-2 inch rainfall event tonight, but
some locations that experience the heaviest rainfall could see
isolated amounts up around 3-4 inches. The greatest concern
appears to be across the eastern Midlands where precipitable
water values are highest. Given the later timing, we have
delayed the start of the Flash Flood Watch until midnight. Due
to recent heavy rains and already saturated soils, flooding of
low-lying, poor drainage and urban areas is possible with any
heavy rainfall.

The other concern late tonight is the small potential for an
isolated/brief tornado. There appears to be a weak low-level
mesoscale low that forms, and an area of enhanced 0-1 km
helicityspreads northward across the eastern Midlands from 09Z
and persisting beyond daybreak. Weak instability would be a
limiting factor, but still potentially supportive of the
isolated tornado threat.


Alberto is still forecast to be located over the far northern
Gulf of Mexico, just off the Florida panhandle coast early
Monday morning. Official forecast keeps the storm well west of
the area. However, plenty of moisture will be moving inland off
the Atlantic on the eastern fringes of the storm early in the
day. Models show a good batch of heavy rainfall possible across
the central Midlands early Monday, then moving northward into NC
by late morning. Heavy rainfall potential will exist with that
area of rain. Also with moderate shear and instability through
the day, the possibility will exist for a brief/isolated
tornado in any stronger activity. Later in the day Monday and
even into Monday night, activity remains scattered showers and
storms as some dry slotting moves into the area. SPC does place
much of the cwa under a marginal risk during the day and night
hours Monday. Heavy rain will continue to be the primary threat
Monday with precipitable water values remaining at or above 2
inches, although coverage may be more scattered at times. WPC
continues to advertise a slight risk of excessive rainfall over
the forecast area Monday and Monday night.

By Tuesday, models still consistent with moving the remnants of
Alberto northward and into the Tennessee Valley. Region remains
in the right quadrant of the circulation on much of Tuesday,
so still can not rule out the possibility of an isolated brief
tornado. Western portions of the area are under a marginal risk
on Tuesday.

Temperatures will be near normal for highs in the mid to upper 80s
and well above normal for lows in the lower 70s.


Albertos remnants will lift towards the Great Lakes region
through the end of the week. Models then bring those remnants
back towards the southeast by the weekend and into early next

Chances of rain should become more diurnally driven each
afternoon. Driest days may be Friday and Saturday ahead of the
upper low due to drier air aloft pushing into the area. Still
should see some sort of afternoon activity across the region
though even into the weekend, with coverage more limited. Near
normal high temperatures expected early in the extended forecast
period, but as the atmosphere dries out a bit later in the
period, temperatures are expected to rise above normal with
highs pushing into the 90s Fri/Sat. Overnight lows expected to
be well above normal the entire period in the lower 70s.


Light to moderate rain showers will continue to shift northwest
into the terminals later this afternoon into this evening, but
generally expect VFR conditions to prevail. Widespread heavy
rain will shift north over the terminals late tonight into
Monday morning, resulting in flight restrictions at all
terminals. There is a potential for isolated thunderstorms, but
have kept mention out of the forecast given limited coverage.

EXTENDED AVIATION OUTLOOK... A moist atmosphere is expected to
remain in place, providing of late night and morning IFR to MVFR
ceilings and possibly visibilities, along with mainly diurnal
showers and thunderstorms through the period.


GA...Flash Flood Watch from midnight EDT tonight through Monday
     evening for GAZ040-063>065-077.
SC...Flash Flood Watch from midnight EDT tonight through Monday
     evening for SCZ015-016-018-020>022-025>031-035>038-041.


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