913
FXUS63 KABR 011908
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
208 PM CDT Tue Sep 1 2026

.KEY MESSAGES...

- There is a Slight Risk, level 2 of 5, for isolated to
  scattered severe storms along and east of a line from Murdo to
  Miller late this afternoon through late this evening. Main
  threats include hail, one to two inches in diameter, and wind
  gusts of 60 to 75 mph. A tornado or two cannot be ruled out
  over portions of south central SD this evening. Heavy
  rainfall is also possible.

- There is a Marginal Risk, level 1 of 5, for isolated severe
  storms along and near a line from Pierre through Redfield to Gary.
  Main threat includes large hail, 1" in diameter, and wind
  gusts of 60 mph. Heavy rainfall is possible.

- Above normal temperatures (+5 to +10 degrees) continue through
  the week, peaking at 10 to 20 degrees above normal
  Friday/Saturday.

&&

.DISCUSSION...
Issued at 203 PM CDT Tue Sep 1 2026

A negative tilted shortwave (originating from the southwestern
US/monsoonal moisture) will continue to track northeast over the
region with additional shortwave energy developing on the southern
tail of this wave over the eastern half of SD/NE into MN through
late tonight. At the surface, a stationary boundary lies south of
the CWA extending through central/northern NE into IA as a high
pressure system lies just to the north of the CWA over ND. With this
mid level moisture, current radar indicates scattered rain (and a
few embedded weak thunderstorms) with HREF paintballs/NBM indicating
a gradual northeast track across the CWA with additional development
of showers and thunderstorms (forcing from this secondary energy
aloft) this afternoon/evening through late tonight. Did a blend of
HREF/NBM for pops through 12Z Wednesday. As the shortwave exits the
region, the last of the convection is forecast to exit eastern SD/MN
by 12Z Wednesday.

Instability wise, HREF mean MUCAPE runs from 500 to about 1000j/kg
south of highway 12 with the highest values over far south central
SD. Bulk shear ranges from 30-50kts over the CWA, highest over south
central through east central SD with the overall better forcing and
instability lying south/southeast of the CWA. Dewpoints will rise
into the lower to mid 60s over this area with ample amounts of low
and mid level moisture as PWATs run between 1.3 to 1.6" over the
southern half of the CWA (gradient increasing further south you go)
which runs between 92 to 97th percentile per climo for this time of
year. Latest HREF mean 2-5km UH>75ms2s indicates the bulk of this
potential organized convection developing over SD/NE border between
~22-00Z along the SD/NE border and tracking northeastward through
southeastern SD into MN with portions of south central to east
central possibly being clipped being on the northern side of the
convection. 2-5km UH>150m2s2 indicates supercell potential with most
of the HREF models keeping this threat again south of the CWA.
Looking at the HRRR/REFS specifically, it does indicate discrete
cells developing over south central/southern SD (potentially
supercells), as 0-3km SRH is up to around 400m2s2 around 00Z, with
additional development/storm mergers with storms potentially growing
upscale into a condensed bowing segment over southeastern SD into
MN. Otherwise north of this, isolated cells or clusters (potentially
strong to severe) will track across central through northeastern
SD/MN late tonight early AM mainly east of the Mo River. There is a
bit of a difference in CAMs on exact storm mode and track at this
time so low confidence exists on exact outcome.

With this threat, the SPC has shifted the Slight Risk (level 2/5) a
bit more southward due to the latest HREF run with the slight risk
along and east of a line from Murdo to Miller with a Marginal Risk
(level 1/5) north and northwest of the slight risk mainly from
Pierre to Gettysburg and eastward. The main threats will be large
hail, quarter to golfball sized, with the potential for 2"+ in
diameter within the cig 1 hatched area over southeast Jones, Lyman,
Buffalo, and the southern half of Hyde/Hand counties per the
supercell threat. With this threat of supercells, this hatched area
is also highlighted in a 2% tornado risk being closer to the frontal
boundary as hodographs are curved over far south central, southern,
and southeastern SD this afternoon and evening. STP is under 1 with
0-1km shear running between 15-20kts and 0-1km SRH between 100-
200m2s3. Wind gusts of 60-75 mph with a hatched area over southern
Lyman County and eastward through southeastern SD. Due to higher
PWATs, any slow moving and stronger storms could lead to heavy
rainfall.

With high pressure and winds mainly out of the east and recent rains
leads to the possibility of upslope fog along the eastern slopes of
the Coteau early Wednesday morning. Otherwise, continuing in
southwest flow aloft, another shortwave will move in over the region
Wednesday night/Thursday morning. With lack of instability and weak
forcing, there is really only spotty chances of moisture over
portions of south central SD for now per NBM. Additional threat of
showers and thunderstorms are possible over far northeastern SD/MN
Thursday afternoon and evening, associated with a surface low, with
the higher pops and instability to our northeast closer to the low.
Otherwise a trough deepens over the western CONUS by the end of the
week and weekend which will amplify the ridge overhead with really
only sight chance of pops here and there for the weekend. Highs will
overall warm into the upper 80s to the lower 90s Thursday-Saturday,
with Friday and Saturday temps around 10-20 degrees above average!
Temps will gradually cool Sunday into early next week as the ridge
breaks down and cold front moves through.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1210 PM CDT Tue Sep 1 2026

Terminals KABR,KATY,KPIR,KMBG

Scattered showers and thunderstorms will mainly affect KPIR and
potentially KMBG through this evening with the showers and
thunderstorms, and additional development, spreading northeastward
across the region through early Wednesday morning that could affect
all terminals. There is the potential that some storms could be
severe over KPIR and KATY this evening with the main threat being
large hail, quarter to golfball size, and wind gusts of 60-70 mph.
Heavy rainfall will also be a threat. Once the moisture clears out,
some fog for KATY is possible around 12Z to end of the TAF period.
VFR cigs are forecast through the TAF period, however, any stronger
storms/heavy rain could lead to sub VFR cigs temporarily or if
thicker fog develops over KATY Wednesday morning.

&&

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

&&

$$

DISCUSSION...MMM
AVIATION...MMM