185
FXUS63 KABR 171849
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
149 PM CDT Thu Sep 17 2026

.KEY MESSAGES...

-Heavy rain is expected beginning this evening over and continuing
through Friday evening. The highest accumulations are expected over
south central and eastern South Dakota. The probability to see two
inches of rain or more reaches 40-60% over east central and south
central South Dakota (decreasing elsewhere as you move north and
west).

-There is a Slight Risk (level 2 of 4) for excessive rainfall
leading to flooding across across the forecast area tonight into Friday. The
heaviest rainfall is expected overnight tonight through early Friday
morning.

- Near-normal temperatures continue today, with highs in the low to
mid 70s across much of the forecast area. Friday and through the
weekend will have slightly cooler temperatures, with highs generally
in the low 60s to low 70s.

&&

.DISCUSSION...
Issued at 148 PM CDT Thu Sep 17 2026

A weak and fairly small upper-level ridge will be sitting over SD
this afternoon through the weekend. This ridge, as well as winds
from the east and southeast aloft and at the surface will help to
move warm and moist air in over SD. This will create a saturated
atmospheric environment over central and northeastern SD through the
remainder of today and into Friday. PWAT values across central and
northeastern SD will be around 1.75 inches, which is above the 90th
percentile and the maximum value for this time of the year. This
shows how much moisture there is over central and northeastern SD. A
low pressure system is moving out of Colorado today and will move
over southern SD tonight, into this moist environment. Precipitation
along the northern and western side of the low will move into
central SD this evening and then over northeastern SD and west
central MN tonight. There is a little bit of instability over
southern SD moving in with this system this evening and overnight.
This could help a few storms to develop and dump a lot of rain in
portions of south central SD and a heavier band of precipitation to
develop over east central SD late tonight into Friday morning.

Models have been fairly consistent with the location of a heavy band
of precipitation, with the heaviest rainfall occurring over south
central SD, in a line from around Vivian to Miller and Redfield,
late this evening and overnight. Additionally, this band of heavy
rainfall will move over east central SD between Watertown and Sioux
Falls tonight into Friday morning. There is currently a 40-60%
chance of areas along this line to receive 2 inches of rainfall or
more. There is a bit more uncertainty about the northern edge of
this line of precipitation and how far north the chances for 1 inch
or more of rainfall will be. Models show a 40-60% chance for an inch
or more of rain in a line from Eagle Butte to Leola and in areas to
the southeast until it runs into the line of heaviest precipitation
mentions before, as this line has 70-90% chance. The saturated
atmosphere will help to get these rainfall totals but the strength
and timing of the band of precipitation will also contribute. With
the instability over south central SD and the ability for convection
to develop, the rain will likely be heavier for a shorter period of
time over this area. East central SD on the other hand will have the
precipitation around for a much longer time, leading to higher
rainfall amounts. There is a slight risk for excessive rainfall from
this system over most of central and northeastern SD tonight into
Friday. While the ground should be able to take in a lot of the
water, depending on how fast it comes down and in areas that get an
abundant amount of rain, there could be some impacts in low lying
and poor drainage areas as well as some localized areas of flooding.
Additionally, there will be minor impacts to rivers and streams from
the potential runoff of the rainfall.

After Friday, there will be a couple of shortwaves that move over
central and northeastern SD this weekend. This will lead to some more
scattered rain showers moving through occasionally during the
weekend. There will be some cooler temperatures moving in with the
low pressure system starting Friday into the weekend. Temperatures
at the surface will be around to slightly below normal, with highs
getting into the low 60s to low 70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1231 PM CDT Thu Sep 17 2026

Terminals KABR,KATY,KPIR,KMBG

There are currently some scattered low clouds lingering around from
this morning over a KATY and KABR. While these clouds will stay
around for a little while longer, the ceilings should be MVFR/VFR
through the afternoon. A low pressure system will be moving in
this evening over KPIR and KMBG before moving east to also be
over KABR and KATY overnight. The rain chances will be moving
out of KMBG and KPIR during the morning on Friday and will stick
around over KATY and KABR into the afternoon. Heavy rainfall
from the system could cause ceilings to decrease to IFR/MVFR.
The easterly winds will be strengthening as the low moves in
tonight and into tomorrow, with gusts of 25-30 mph possible at
the terminals after midnight into Friday afternoon.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.

&&

$$

DISCUSSION...12
AVIATION...12