292
FXUS63 KABR 170707
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
207 AM CDT Mon Aug 17 2026

.KEY MESSAGES...

- There is a Slight Risk, level 2 of 5, for isolated to scattered
severe storms this afternoon and evening along and east of a line
from Sisseton to Murdo. Main threats are large hail, 1 to 2" in
diameter, and wind gusts of 60 to 70 mph. A tornado or two is
possible south of a line from Murdo to Watertown. Brief heavy
rainfall is also possible.

- There is a Marginal Risk, level 1 out 5, for isolated severe
storms along and south of a line from Pierre to Brookings Tuesday
afternoon through Tuesday evening. Main threats include 1 inch
diameter hail and wind gusts of 60 mph. Brief heavy rainfall is also
possible.

&&

.DISCUSSION...
Issued at 206 AM CDT Mon Aug 17 2026

As of 2am, a decaying storm is exiting far south central SD with
additional convection moving in over north central SD. Current temps
range in the upper 50s to the upper 60s and winds light. By 12Z
models have a good handle on a positive tilted trough over ND
extending northeastward to a stronger surface low, and its upper
low, over the Hudson Bay area. On the southern extent of this
trough, the weaker surface low is forecast to be over Canada/ND
border with its weak warm front extending through central SD as the
high pressure system that was overhead continues to shift off
towards the southeast. By this afternoon and into early this
evening, the center of the low will track southeast and over
ND/SD/MN border (00Z) with the warm front turned surface trough
extending southwestward through northeastern SD into western NE (to
a weak surface low here) and its cold front draped across ND/SD
border. Late afternoon through this evening is when we start to
really see an increase in shortwave activity and an increase in the
500mb winds, between 40-55kts, with the CWA on the southern extent
of this UL system in Canada.

Latest run of the HREF ensemble mean indicates the potential for
spotty convection over portions of north central through
northeastern SD/MN into ND this morning through the early afternoon,
however, there are differences in timing and exact location of this
with some of the CAMs not showing much at all due to a slight cap
till about 15Z. So low confidence on outcome and therefore stuck
mainly with the NBM. We will see the potential in increased activity
around ~20Z where scattered showers and thunderstorms are forecast
to fire up (northeast to southwest over the CWA) with the convection
increasing in coverage (and potential strength) along and near the
surface trough from south central through northeastern SD/MN through
the early evening. Both HREF/NBM locks into the bulk of the precip
and pops over northeastern SD/MN during this time. Beyond ~02Z, the
trough will be more to our southeast with the bulk of the storms
over southern to southeastern SD into MN. Individual CAMs do differ
on storm mode whether its more of cells merging into clusters
(FV3/HRRR/NAMNEST) or more of a line of clusters (HRW NSSL). HRRR
and NAMNest also have cells developing or moving in over south
central SD from the Black Hills. So overall low confidence in exact
storm type and location and which scenario will play out so again
went with the NBM for now but added in 20% pops over central SD
where NBM had none. Closer to time, HREF or Conshort can be added to
the pop grids.

Surface dewpoints will range in the 60s to potentially lower 70s
over the eastern CWA with highs overall in the 80s creating warm and
moist conditions at the lower levels. The greatest instability of
1000-2000j/kg of CAPE will be over the eastern half of SD into MN
with the highest values over southeastern SD into NE by the evening
time with potential max values above 3000 j/kg per HREF. RAP is a
bit higher on the instability between 2000-3000j/kg of ML/MUCAPE
with CAPE decreasing with sunset. Wind shear will range between 30-
40kts with an increase in shear to 50kts+ after 00Z. Mid level lapse
rates will also range between 6-7C/km. Therefore, any storm has the
potential to become severe especially over the eastern half of SD
where the higher shear and instability lies, especially along the
northeast to southwest oriented trough. With the bulk shear and
steep lapse rates supercells will be able to form along with the
clusters as mentioned. If they do form, splitting supercells are
possible given the long and straight hodographs (especially over
NESD/MN where the better overlap of Cape/Shear). SPC did add a 2%
tornado risk south of a line from Murdo to Watertown, however, as
mentioned hodographs seem to lack low level curvature with 0-1KM SRH
around 100m2s2 or lower, 0-1km shear below 15kts, and STP below
1.The greatest potential looks to be more south of the CWA.
However, you cannot rule it out especially when the atmosphere
has the potential to produce supercells along the boundary and
lower LCLs. So due to the severe threat, the SPC expanded the
Slight Risk (level 2/5) and now is along and east of a line from
Murdo to Sisseton where the potential for larger hail (1-2") is
possible and wind gusts of 60-70 mph. There is a Marginal Risk
(level 1/5) along and west of a line from Sisseton to Murdo to a
line from Eagle Butte to Eureka with the potential of quarter
size hail and wind gusts of 60mph. Brief heavy downpours are
also possible in both the marginal and slight risk areas.

The cold front will track a bit southward overnight and extend
horizontally across central through east central SD by 12Z before
stalling out. Additional chances of showers and thunderstorms are
possible tonight/overnight as CAMs suggest more isolated or clustery
storms passing over the CWA during this time. A lack of a LLJ will
keep any storms long lived, but as mentioned, storms will have 50kts
of bulk shear to work with so an isolated severe threat may
continue. Additional spotty convection is possible again with
daytime heating and instability Tuesday afternoon and evening.
Isolated severe storms are possible near/ahead the front, as SPC
highlights a Marginal Risk (level 1/5) along and south of a line
from Pierre to Brookings. Main threats include quarter size hail and
wind gusts of 60 mph. Another shortwave moves in from the northwest
interacting with a surface boundaries bringing additional chances of
showers and storms Wednesday.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1223 AM CDT Mon Aug 17 2026

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are expected to prevail at all terminals through
this TAF forecast cycle. KABR could see a passing shower later
this morning after sunrise. Light and variable winds through the
early morning will eventually be followed by southwest to
northwest winds during the daytime hours today.

&&

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

&&

$$

DISCUSSION...MMM
AVIATION...Vipond