827
FXUS63 KABR 110250
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
950 PM CDT Mon Aug 10 2026

.KEY MESSAGES...

- There is an Enhanced Risk (level 3 of 5) for scattered to
  numerous severe storms over portions of central and
  northeastern SD. Storms are expected to form over central SD
  this evening and track east and southeast through the
  overnight hours. The main threats are 2" or greater diameter
  hail and wind gusts in excess of 70 mph. A tornado or two will
  also be possible.

- There is a Slight Risk (level 2 of 5) for scattered severe
  storms Tuesday evening through Tuesday night for all of
  central and portions of northeastern SD. There is Marginal
  Risk (level 1 of 5) for portions of northeastern SD through
  west central MN. Main threats include 1 to 2 inch diameter
  hail and wind gusts of 60 to 70 mph.

&&

.UPDATE...
Issued at 946 PM CDT Mon Aug 10 2026

Will just start off by saying that CAMS are all extremely aggressive
with convection developing in the next hour or two and persistent in
their depiction of a large wind complex moving across the CWA from
northwest to southeast. Granted its still too early for the 8/11 00Z
run of the HREF, but the 12Z was still generating local areas of 60-
70kt wind speed max in central South Dakota with this convection.

I have a deep suspicion that temperatures were a little suppressed
by the smoke, so maybe not quite so much surface based instability as
SPC mesoanalysis still has about 25-50 j/kg CIN outside of the
supercell moving just west of the CWA. Low level instability isn`t
the only limiting factor for tornadoes, but low level shear, and a
lack of a developing low level jet are also noted.

Thus the focus remains on large hail (for now) with the supercell in
Perkins county and headed south southeast moving through an area
that has 3-4k j/kg CAPE to work with however. Shear is still about
50kts with 200-300 m2/s2 storm relative helicity. MESH has been as
high as 5" so the storm has a history of at least dual pol large
hail.

Without much of a low level jet, the question then is what will be
our motivating factor for storm development that fits the CAMS and
thus warrants the severe weather threat overnight? There is warm
advection and a weak wave aloft, and we remain in a favorable
west/northwest unidirectional shear environment. Suspect the storm
out west will/is whats depicted in CAMS with too far east a
placement in the models. Will continue to monitor for additional
storm developments.

&&

.DISCUSSION...
Issued at 139 PM CDT Mon Aug 10 2026

West to northwest flow continues aloft over the region per a weak
broad ridge over the western CONUS. Another weak embedded shortwave
(500mb winds 35-45kts) will track east/southeast across SD this
evening into IA/MN through early Tuesday morning with the bulk of
the vorticity over central through southeastern SD. At the surface,
a weak low will be over southwestern SD this evening with an
inverted trough extending northeastward from it through SD/MN
through the overnight hours with not much movement with the low and
a slight track southeast with the trough. 700mb temps are not overly
strong, ranging from +8 to +14C this evening, warmest over south
central SD. With 850mb to sfc winds out of the south and southeast,
this continues to usher in warm moist air with dewpoints rising into
the upper 60s to potentially lower 70s, before winds switch more
east/northeast overnight. There is no lack of instability with HREF
mean CAPE between 2000-3500j/kg (RAP=3000-4000j/kg) this evening to
around 1500-2500j/kg by 06Z with the highest amounts over
central through southeastern SD. Bulk shear will range between
40-50kts through the overnight with 0-3km SRH 200-400m2s2,
highest over south central through east central SD, and steep
low to mid level lapse rates. Only thing really lacking is a
strengthening LLJ overnight.

This sets the stage for showers and thunderstorms to fire up
starting this evening as the cap erodes, however, it remains tricky
with several potential outcomes. Overall consensus per CAMS has
discrete cells/clusters developing over north central SD/ND and
potentially one over south central/southern SD. This earlier stage
of development and storms tracking over central SD is when the
largest hail (potentially over 2") and the threat of tornadoes
would be with any supercells given surface based storms
interacting with surface trough (and moderate Cape/shear) with
0-1km SRH between 100-200m2s2 and stp of 1. As mergers and
additional development occurs, storms will grow quickly upscale
as they track east/southeast into an organized cluster (MCS)
with possible bowing segments if an RIJ develops. However,
HRRR/REFS has nothing developing until around midnight with
storm mode being more clustery over east central through
southeastern SD. Between the individual CAMS, there are
differences in where these storms initially develop, whether 1
or 2 areas of convection will merge or track separately,
timing/location of upscale growth to a MCS, if bowing segments
do form, and and exact track of it. Due to this, confidence is
very low on which scenario will play out at this time. So
continued with sticking with the NBM for pops given this
uncertainty which does a good job, keeping pops broad due with
highest pops (50-75%) over central through east central SD where
the majority of the CAMS show this area being impacted the
greatest and where our best instability lies and energy aloft.
Another caveat is the ongoing thick smoke from the PacNW
blanketing the region. If thick enough, this could damper
instability and convection and we get little in the way of
storms.

With this, there is a Slight Risk (level 2/5) per SPC for much of
the CWA (with the exception of far NESD/MN which is in a marginal
risk) for the potential of scattered severe storms. There is a cig 1
hail threat (potential 2"+ in diameter) given supercell potential,
mainly along and west of a line from Aberdeen to Huron. SPC has
added in a 2% tornado threat along and south of a line from Mobridge
to Redfield where tornadoes are possible mentioned above. Wind gusts
of 60-70 mph are possible with the potential for winds in excess of
75mph if an MCS develops especially for locations where the
potential bowing system could track. Therefore a Cig 1 is
outlooked for wind mainly along and east and southeast of a line
from Gettysburg to Pierre where some of the CAMs indicate this
greatest potential.

Not much change aloft Tuesday and Wednesday in ongoing west to
northwest flow aloft and potentially weak embedded shortwaves tracking
across the region and a front tracking southward out of Canada
Wednesday evening/night. Adding in daytime heating/instability and
ongoing low level moisture and shear, we will continue with the
threat of showers and thunderstorms each afternoon/evening into
the overnight hours. A Sight Risk (level 2/5) is in place
mainly west of the James River and a Marginal Risk ( level 1/5)
east of James River Tuesday. A Marginal Risk extends along and
south of a line from Eagle Butte to Brookings Wednesday. Broad
ridge that has been over the western CONUS will shift eastward
and over the central CONUS for the end of the week. Add in
surface features and additional instability and chances for
showers and thunderstorms continue through the end of the week
with low confidence this far out on any severe weather
potential. As of now ML guidance keeps the threat low. Behind
fropa and cooler air aloft per deepening low over Canada, highs
will be cooler only in the 70s for the end of the week and into
the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 630 PM CDT Mon Aug 10 2026

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast at the start of the TAF period.
There is a threat of TSRA/+TSRA across the region later tonight,
but confidence is low on areal coverage and overall placement of
storms. Using PROB30 to handle this for the time being. Any
stronger TSRA/+TSRA that move over a TAF site could bring
MVFR/IFR VSBY. There are also suggestions for MVFR/IFR CIGs and
FG/BR in the KATY region early Tuesday morning and have
inserted mention of this into the TAF.

&&

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

&&

$$

UPDATE...07
DISCUSSION...MMM
AVIATION...TMT