487
FXUS63 KABR 030548 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1248 AM CDT Wed Jun 3 2026

.KEY MESSAGES...

- There is a Slight Risk (Level 2 of 5) for severe weather this
  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 through the James River Valley. Large
  hail of 1-2" in diameter and wind gusts of 60 to 70 mph are
  the main threats. Tornadoes cannot be ruled out over north
  central SD for a few hours this evening. Heavy rain is also
  possible that could lead to flash flooding.

- Another Slight Risk (Level 2 of 5) for severe weather is in
  place for storms Wednesday afternoon and evening mainly along
  and east of the Missouri River. Large hail of 1-2" in
  diameter and wind gusts of 60 to 70 mph are the main threats.
  Tornadoes will also be a threat in the evening over the James
  Valley and eastward. Areas west of the Missouri River are
  under a Marginal Risk.

- Thursday, yet another Slight Risk for severe weather is in
  effect along and south of US Highway 12. Areas to the north
  of US Highway 12 are under a Marginal Risk. Large hail of 1-2"
  in diameter will be the main threat, with wind gusts of 60
  mph and tornadoes possible as secondary threats.

&&

.UPDATE...
Issued at 1242 AM CDT Wed Jun 3 2026

Updated for 06Z Aviation Discussion below.

UPDATE Issued at 851 PM CDT Tue Jun 2 2026

Most of the activity this evening is across central/south
central SD, with a void in precipitation over north central SD.
Earlier this evening, convection developed over north central SD
but has since moved into ND. Have been adjusting PoPs to keep up
with radar trends and expectations. Another cluster of showers
and storms across southwest SD may affect central/south central
SD later tonight. Thunderstorm cores have been marginally severe
at times this evening, but have seen gusts recently around 50
mph. Overall, the severe storm threat looks to continue over the
next few hours across south central SD.

&&

.DISCUSSION...
Issued at 141 PM CDT Tue Jun 2 2026

An active weather pattern continues over the next few days
with the threat for strong to severe storms and heavy rain at times,
that could lead to flash flooding, especially locations that have
recieved lots of rain over the past few days. Synoptic setup
consists of an upper low continuing to spin over MT/Canadian border
with southwest flow aloft. An embedded jet streak (40-60kts) lies
along the eastern side of the low over eastern WY/MT and western
Dakotas with a negative embedded shortwave that will move in over
western SD this evening, tracking east/northeast over central SD
through 06Z. 700-500mb lapse rates range between of 6-7.5C/km
tapping into the cooler air aloft with the highest values along
and west of the Mo River into western SD (up to 8C/KM there!).
At the surface, a cold front is stalled out vertically over the
western Dakotas (with a low on the front over eastern WY)
attached to the main low over southern Saskatchewan. By 00Z,
everything shifts just slightly east with the fropa draping
through north central SD and southwestward and actually
retrogrades back west by 06Z. Along and ahead of this front,
warm moist low levels continue with winds at the surface from
850 out of the south/southeast as dewpoints continue in the
upper 50s to the lower 60s with temps in the 80s and overall
sunny skies helping to destabilize the atmosphere, as the cap is
eroding, as cumulus cloud streets are developing along and west
of the James River.

CAPE has increased between 1000-2000j/kg (RAP indicates
2000-3500j/kg possible this evening!) over the CWA (highest
values over central SD) with bulk shear/EBWD out of the
south/southwest over central SD and west James Vally and
eastward between 20-40kts with the higher speeds over north
central SD. As storms track across the CWA this evening, values
do increase behind it to 30-40kts west of the James River.
Current radar has isolated to scattered storms over the western
Dakotas ahead of this front. Consensus of CAMs show these storms
moving in, and additional formation, tracking from ND through
north central SD and southwestward through western SD late this
afternoon to evening time frame per HRRR/REFS. Storms at this
point will either be evolved into a clustery line of storms or
in the process as this line will continue to track
east/northeast across central SD this evening as shear is/
becomes parallel to the boundary over central SD. HRRR indicates
the line breaking up over the James Valley (and more of a messy
cluster of storms) as shear and instability are weaker here.

The SPC continues with a Slight Risk (level 2/5) for severe storms
along and west of a line from Eureka to Murdo where we have this
better instability. Main threat will be large hail of 1-2" in
diameter with a Cig 1 intensity (2" diameter hail threat) for
locations west of the Missouri River. UH>150m2s2 does indicates the
potential for right moving supercells within this area of higher
CAPE/Shear (mainly Corson/Dewey) as 0-3 SRH is about
100-200m2s2. There is a 5% tornado risk over western
Corson/Dewey and westward and 2% tor threat east of here to the
Mo River (intensity Cig 1 meaning max expected EF2+). So any
supercells that do form have 0-1 SRH of 100-200m2s2 and 0-1km
shear of 20-30kts with STP between 0-1. RAP soundings out here
indicate a curved (smaller) hodographs for a few hours this
evening (~0Z-4Z) before diminishing as we transition into a
line of storms with more of a wind threat taking over. Lastly
wind gusts of 60 to potentially 70 mph with the higher wind gust
threat if we can get more of an organized line (help of LLJ) as
DCAPE is around 1000-1200 j/kg but dropping off the more east
you go in the CWA. There is a marginal risk (level 1/5) between
the Missouri and James River, as mentioned, storms will continue
to weaken as they track east/northeast east of the Mo River,
however, locations in this area could see quarter size hail and
60 mph wind gusts with any stronger storms. Lastly, PWAT values
are still running 1-1.50" with storm motion out of the southwest
between 20-30kts with upwind propagation of about 5-10kts. So
any stronger storms will produce heavy downpours that could lead
to flash flooding, especially for areas that have recieved
quite a bit of rain over the last few days. There is a slight
risk (15%) for flash flooding per WPC over north central SD.

For Wednesday, it is rinse and repeat as the cold front will be
draped from east central ND and southwestward through central SD at
12Z. HRRR indicates the possibility of additional clustery cells
moving in or developing over north central SD and convection that
could be ongoing leftover from the line breaking up east of the
James River through the late morning. By the afternoon through the
evening there is a slight shift eastward of the front as locations
along and behind Mo river will be behind the fropa and northwest
flow with locations mainly James Valley and eastward well within the
warm sector. Ahead of the front, meso parameters will be similar to
today with bulk shear a bit higher of 30-40kts. CAMs show convection
really firing up late afternoon east of the Mo River as
discrete/clusters form into a line James Valley and eastward into
the evening, tracking eastward with HRRR indicating the line exiting
our far eastern CWA around midnight for now. Due to this there is a
Slight Risk (Level 2/5) mainly for locations along and east of the
James River with a 2% tornado threat over the James Valley where
UH>150m2s2 highlights this supercell potential lining up with the
better low level shear/helicity coinciding with the bulk shear/cape
with the threat of hail up to 2". Wind gusts of 60-70 mph are
possible and once again heavy rain with the potential for flash
flooding. Another Slight Risk of severe weather is in place for
Thursday afternoon and evening with all severe modes possible. Still
a couple days out for exact setup but supercells and clusters of
storms are possibly Thursday afternoon and evening. Rainfall amounts
this evening through THursday evening have about a 40-60% chance of
amounts of an inch or more. As mentioned, any stronger storms may
lead to heavier rainfall amounts for any one location.

We will continue with rain and thunderstorms Friday before this low
and front move out and dry weather is forecast Saturday through most
of Sunday as a ridge builds aloft. This will also bring in warmer
air as temps are forecast in the upper 80s to lower 90s for the
weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1242 AM CDT Wed Jun 3 2026

Terminals KABR,KATY,KPIR,KMBG

Convection timing and intensity will be the primary concerns
for the forecast period. Ongoing convection over south central
SD will shift to the east through the night. Thinking that the
thunder threat will diminish with time, so showed PROB30s for
the showers potentially making it far enough east/northeast to
reach KABR/KATY. Meanwhile, expect KPIR to stay primarily rain
showers as the existing thunder threat departs to the east and
the upstream convection likely stays south of the site.

Convection is expected again this afternoon as a cold front
moves east through the area. Expect initial development in
central and especially north central SD around 20-21Z, then
spreads to the east-southeast with time through the evening.
Tried to time out the best rain/thunderstorm threat in the
FM/PROB30 groups, with future TAF issuances likely being able to
bump the thunder into the FM groups. Finally, behind the front,
could see some MVFR ceilings in north central SD (KMBG) in the
evening.

&&

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

&&

$$

UPDATE...SRF
DISCUSSION...MMM
AVIATION...SRF