746
FXUS63 KABR 131921
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
221 PM CDT Sun Sep 13 2026

.KEY MESSAGES...

- Cooler than normal temperatures expected through Wednesday (highs
in the 60s to low 70s) with the exception of a brief warmup on
Monday (highs in the upper 60s to upper 70s over much of the
forecast area). A gradual warming trend will begin mid-week and
continue through the weekend.

- Confidence is high on widespread rain and perhaps weak
thunderstorms overnight tonight through Monday afternoon. Highest
probability of rainfall totals that may exceed one inch (55-60%
chance) is along a line from Clark to Watertown through Ortonville,
MN.

- Strong northwesterly winds will increase behind a cold front
Monday afternoon into evening. Wind gusts will range between 35 to
50 miles per hour with the highest gusts over north central SD. A
Wind Advisory has been issued for Corson and Dewey Counties late
Monday morning through Monday evening.

- Strong winds and the combination of low RH, 40% and below, will
lead to High to Very High fire danger Monday afternoon and evening
across central SD. An increase in humidity and slight decrease in
winds will limit fire weather concerns further east.

&&

.DISCUSSION...
Issued at 214 PM CDT Sun Sep 13 2026

Our attention turns to late tonight through Monday where confidence
is high on widespread rain across the CWA. Model ensembles are
pretty consistent on the large closed low aloft tracking eastward
across the Northern Plains/Canada through the day and deepening
before tracking northeastward into Manitoba/Ontario Monday
night/Tuesday. A jet streak (~50kts) on the PVA/southeastern side of
this low will provide lift across the region with speeds at 250mb at
70+kts aiding in divergence aloft. At the surface, the low/cold
front will be over the western Dakotas/MT/WY 12Z Monday with the
front tracking swiftly eastward, exiting our far eastern CWA by
early Monday evening. Ahead of the cold front within the warm
sector, ample amounts of warm air and low level moisture is forecast
per south to slight southeast winds with 850mb temps between 12 to
15C and dewpoints at this level as high as 15C. Dewpoints at the
surface will rise into the mid 50s to mid 60s (highest east of the
James River) per surface winds out of the south/southeast. The leads
to strong IVT transport from the gulf with PWAT values still
forecast between 1.5 to 1.75" which is well over the 90th percentile
for this time of year per with NAEFs still indicating these values
about 3 standard deviations above climo!

So with this setup, models are also consistent on this WAA rain
moving in from the west/southwest and over central SD around ~06Z
where it will track and become widespread across the CWA by 12Z.
Several CAMS indicate an additional line or cluster of heavier
rain/storms developing over southern to southeastern SD per better
forcing and moisture. This looks to clip and/or merge with the
ongoing widespread rain over east central SD/MN potentially
leading to higher QPF here. Behind the front/drier air, rain
will diminish west to east across the CWA with the rain exiting
central SD by the midday/early afternoon and exiting eastern
SD/western MN by late afternoon. If the low slows down, then
rain will move in and exit the area later. Confidence remains
high as NBM pops range from 80-100% over the CWA.

06Z run of EC/Canadian ensembles overall indicate 24 hr QPF totals
between 0.3 to 0.8" with the higher QPF over northeastern SD/MN per
Canadian and more east central SD per EC. GEFS is still running
lower on overall totals with mean around 0.3". Latest NBM
deterministic QPF matches up well with the Canadian and ENS with
highest amounts east of the James River. However, HREF and NBM
5.2 does run a bit higher in totals, with a potential for rain
in excess of an inch east of the James River. Therefore,
NBM(5.0) probability of a half inch is 50-90% widespread over
the CWA and 1" is 55-60% over east central SD through west
central MN. 2" or more is 15-20% over portions of Big Stone
County in MN. 90th percentile (10% chance) has values of 1-2".
EC EFI range from 0.5 to 0.7 and no shift of tails meaning most
EC members are near reforecast climatology therefore nothing
anomalous forecasted. However, as the previous shift mentioned,
the warmer air will lead to a large warm cloud layer (11-12K
feet) that is an ingredient for flash flooding along with this
excess moisture expected. WPC ERO does highlight a marginal
risk (15%) mainly Coteau and eastward per this better
moisture/QPF and deepening low. Storm motion is forecast to be
about 20kts so not overly fast but not too slow either which
should help keep flooding to a minimum along with soils being
able to handle the moisture. However, any training/backbuilding
(especially Coteau/eastward) may result in localized flooding.
Lastly, CAPE will be at most 500-800j/kg over portions of south
central to east central SD with shear of 50kts across the CWA.
With lack of strong vertical growth aloft, no severe weather
anticipated, however, weak thunderstorms will be possible with
the rain.

Lastly, winds will be on the increase across central SD per
steepening pressure gradient between the exiting high and incoming
low with gusts up to 30kts along and west of the Mo River. Adding in
the LLJ and these gusty winds will spread eastward with gusts of 25-
40 kts across the CWA by 12Z Monday. Behind the front per CAA and
weak pressure rises (CAA strongest over north central SD 18Z) winds
will turn westerly to northwesterly Monday afternoon through Monday
evening with gusts increasing between 30 to potentially 45kts across
the CWA, with highest gusts over Corson/Dewey. NBM is bit bullish on
winds compared to HREF with models indicating the better CAA right
behind the front not coinciding with the higher pressure rises,
which occur more Monday night. Also the CAA becomes weaker as
it tracks east. Anyways, winds will remain gusty (20-35kts) through
the night before diminishing through Tuesday as low exits the
region and high moves in. Therefore with collab, issued a Wind
Advisory for Corson and Dewey valid 17Z Monday to 03Z Tuesday.
Strong winds and the combination of low RH, 40% and below, will
lead to High to Very High fire danger Monday afternoon and
evening across central SD. An increase in humidity and slight
decrease in winds will limit fire weather concerns further east.

Due to clouds and precip, in collab we did lower the highs for
Monday overall ranging in the upper 60s to the upper 70s, lowest
temps James Valley and eastward. High pressure moves in behind the
exiting low Tuesday with dry weather expected and temps in the 60s
to low 70s. Zonal/southwest flow is forecast by the midweek as a
positive tilted trough/low will be over the western CONUS and ridge
building over the central/southeastern US and mid level high. This
pattern results in multiple shortwaves moving across the region
bringing pop chances here and there through the end of the week.
This building ridge will also lead to temps warming up a bit.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1221 PM CDT Sun Sep 13 2026

Terminals KABR,KATY,KPIR,KMBG

Per shortwave aloft, mid to high clouds continue over portions
of south central and north and northeastern SD. Brief clearing
of skies late this afternoon and evening before overcast lower
clouds move in late tonight and continue through Monday
afternoon associated with a low that will track across the
region bringing widespread rain/weak thunderstorms to all
terminals ahead of a cold front. This sets the stage for some
potential sub-VFR cigs, and perhaps even some pockets of IFR
fog, particularly over the KPIR/KMBG terminals. Precip will end
west to east across the region with the last of the precip
exiting eastern SD by late afternoon/early evening.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 11 AM to 9 PM MDT Monday for SDZ003-015.
MN...None.

&&

$$

DISCUSSION...MMM
AVIATION...MMM