809
FXUS63 KABR 011931
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
231 PM CDT Mon Jun 1 2026

.KEY MESSAGES...

- There is a Slight Risk (Level 2 of 5) for severe weather Tuesday
evening, mainly along and west of a line from Eureka to Murdo. There
is a Marginal Risk (Level 1 out of 5) for severe storms east of this
line. Large hail of 1-2" in diameter and wind gusts of 60 to 70 mph
are the main threats. Tornadoes cannot be ruled out within the
Slight Risk along with heavy rain that could lead to flash flooding.

- Another Slight Risk (Level 2 of 5) for severe weather is in place
for Wednesday for parts of north central and northeastern South
Dakota. Large hail of 1-2" in diameter and wind gusts of 60 to 70
mph are the main threats. Once again, heavy rain is possible that
could lead to flash flooding. Areas west of the Missouri River and
east of Interstate 29 are under a Marginal Risk (Level 1 of 5).

- Chances for showers and thunderstorms will continue for the end of
the work week.

&&

.DISCUSSION...
Issued at 231 PM CDT Mon Jun 1 2026

Not much change with the pattern aloft with a large closed low
continuing to spin over MT/PacNW into southern Canada with winds
aloft remaining out of the southwest. At the surface, high pressure
will remain over the region this evening and track northward late
tonight before diminishing. Lee side trough along with embedded
shortwaves moving out of CO and WY this afternoon and evening,
tracking northeast, looks to bring showers/tstorms mainly west and
south of the CWA late this evening. RAP is the most aggressive in
showing precip entering our western CWA, however, other CAMs show
any storms diminishing (or very weak) before reaching our western
CWA. A few of the CAMs also indicate a forming line over southern
SD/NE/KS with the northern extent of this possibility clipping south
central SD (or breaking off and tracking into south central SD per
NAMNest). NBM is a bit bullish on precip chances for both areas so
added in ECAM to diminish the pops a bit. With model discrepancy,
low confidence exists at this time on potential outcome.

Upper level low remains in place before it starts to drift a bit
northward Tuesday evening with ongoing southwesterly flow aloft.
Southwest to northeast oriented mid level jet (30-50kts)/shortwave
will circle cyclonically around the low setting up from eastern
MT/WY through the western Dakotas by the afternoon into the evening.
Winds at 850mb (20-35kts) will be stronger over western/central SD
in the morning, decrease, then strengthening between the Mo and
James River Tuesday evening (00Z onward) between 30-40kts. This will
help support a linear setup/MCS potential. By 00Z, a secondary
surface low will develop along a cold front (from the Canadian low)
over western SD with a surface trough extending southward through
western NE/KS. This will set the stage for convection firing up
along and ahead the front Tuesday evening as dewpoints will range in
the upper 50s to lower 60s and mid level lapse rates around 7C/km
mainly west of the James River.

CAMs/REFS indicate discrete cells/clusters developing along the cold
front over the western Dakotas late Tuesday afternoon then growing
upscale and possibly forming into a clustery line of storms as it
moves in over central SD into ND around ~00-03Z where it will become
better organized into more of a linear system. There is some
indication by HRRR/NAM Nest of part of this line bowing out over
north central SD and/or into ND. REFS has the line bowing out over
central/south central SD. As this enters the James Valley we see
storms diminish in severity as convection becomes more messy as it
tracks into ND or diminishes with both HRRR/REFS indicating
additional clusters forming behind it over north central SD and
tracking into ND as well. NAMNest doesnt show much convection behind
the line with an additional line of storms tracking over western ND
and possibly clipping our northern north central SD counties. So
still some discrepancies between models on exact track and location.
HREF/REFS indicates CAPE of 1000-2500 j/kg over central SD and
decreasing eastward across the CWA with values really diminishing
after sunset. Potential max amounts of 2000-3000 j/kg are possible,
highest west of the James River. Bulk shear vectors will be out of
the west/southwest between 30-40kts with most of this higher shear
over north central SD with the higher amounts of 40-50+kts over
western SD/ND and mid level lapse rates of 6-7C/km. UH>150m2s2
highlights the threat of supercells but this mostly looks to stay
north and west of the CWA for now (possibly clipping Corson County)
and closer to the boundary per HREF/REFS. 0-3km shear is forecast
between 20-30kts with 0-1km shear fairly weak.

Due to this, the SPC has a slight risk (level 2/5) for the threat of
scattered severe storms Tuesday late afternoon/evening into Tuesday
night along and west of a line from Eureka to Murdo with the main
threats being large hail, quarter to 1.50" inch in diameter. If
supercells do form over north central SD then 2+" in diameter is
possible. As of now this mostly looks to stay north and west of the
CWA. Wind gusts of 60-70mph is also possible with an increased
threat of 70 mph (or locally higher) if we get a bowing line. The
tornado threat would be from any supercells that do develop in
central SD or if we end up getting mesovortices that spin up if we
can achieve a balanced/shear dominant line, RIJ, and line normal
shear. Lower confidence on the tor threat. A Marginal Risk (level
1/5) for locations mainly east of the Missouri River to the James
River as there is less instability to work with and storms look to
decrease in strength past the Mo River, however, quarter hail and 60-
70 mph gusts still possible. Heavy rain is also possible which may
cause flash flooding with any slower moving storms or locations
receiving training thunderstorms.

By Wednesday, mid level low will center itself over Saskatchewan and
ongoing troughing pattern south of this low over the Northern Plains
in southwest flow. East of the Mo River remains ahead of the cold
front at 12Z as a high moves in behind it. By the afternoon/evening
the cold front will track a bit east with James Valley ahead of the
front. Upper energy aloft along with surface convergence, return
flow aiding in moisture, CAPE of 1-2K J/kg, bulk shear of 20-35ks
perpendicular to the cold front, and lapse rates of at least 7C/km,
discrete to clusters look possible as indicated by the NAMNest ahead
and along the front Wednesday afternoon and evening. So SPC has a
Slight Risk for severe storms (level 2/5) east of a line from
Mobridge to Pierre to Sisseton to I29. If supercells can from, then
up to 2" hail is possible and wind gusts of 60 to potentially 70 mph
with any organized clusters. A Marginal Risk (level 1/5) extends
along and west of the Mo River and east of I29 with threat of
quarter hail and 60 mph wind gusts.

Otherwise we will continue to chances of showers and thunderstorms
through the end of the week as this cold front lifts north Thursday
and becomes a stationary front with weak troughing aloft per overall
zonal flow. Best widespread chances of rain look to be Thursday
evening into Thursday night (NBM pops of 50-60%) with pops of 30-50%
north of northeast of south central SD Friday. Temps will continue
to run in the 70s and 80s though the week with temps forecast to be
in teh mid 80s and even 90s by the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1236 PM CDT Mon Jun 1 2026

Terminals KABR,KATY,KPIR,KMBG

Some clouds over KATY and northeastern South Dakota are
forecast to start clearing out over the next few hours and
increasing ceilings. At the same time, some higher clouds will
be moving in over KPIR. Rain and storm chances mainly stay out
of central and northeastern South Dakota through the rest of the
day and into the night. Rain and storm chances start to
increase through Tuesday afternoon over KPIR and KMBG. Winds
will be shifting through the afternoon to be from the east
southeast through the evening and overnight, with gust up to 15
to 20 mph. Winds then turn to be from the south Tuesday morning
and start to pick up, with gusts of 25 to 30 mph.

&&

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

&&

$$

DISCUSSION...MMM
AVIATION...12