466
FXUS63 KABR 311908
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
208 PM CDT Sun May 31 2026

.KEY MESSAGES...

- Active pattern continues, and chances for showers and
  thunderstorms are in place through at least mid-week.

- There is a Marginal Risk (Level 1 of 5) for all of central and
  portions of northeastern South Dakota this afternoon through
  tonight. Main threats include wind gusts of 60 mph and hail
  up to an inch in diameter. Brief heavy downpours with any
  stronger storms are possible.

- There is a Slight Risk (Level 2 of 5) for severe weather
  Tuesday for locations along and west of the Missouri River.
  There is a Marginal Risk Level 1 out of 5) for severe storms
  for locations between the Missouri and James River. Large hail
  (1"+ in diameter) and wind gusts of 60+ mph are the main
  threats.

&&

.DISCUSSION...
Issued at 159 PM CDT Sun May 31 2026

The nearly stacked 500-850mb large closed low continues to spin over
MT with several vort lobes/weak circulations spinning cyclonically
around the low over WY, western SD, and MT. This pulse over WY will
continue to move into western SD later on this evening with
additional vort max`s developing over WY and moving into western SD
early Monday morning, all tracking northward. South to southeasterly
WAA flow continues at 850mb to the surface. This continues to usher
in moist air with dewpoints at the surface ranging in the upper 50s
to the mid/upper 60s and 850mb dewpoints 11-13C. At the surface, low
pressure is over northwestern SD with its occluded front tracking
southeast from the low through central SD. Dry slotting is occurring
as satellite indicates overall clear skies along and west of the Mo
River, south of the low. Satellite also indicate cumulus clouds
developing west of the James River. Through this evening, the
center of the low will track over south central SD with more of
an occluded surface boundary setting up north to south along the
Mo River by 00Z, north of this low. Through tonight, this low
and surface boundary will all track eastward with the occluded
front mainly along and east of the James River by 06Z and center
of low over southeastern SD. Not much movement by 12Z Monday
where this system will finally tracking eastward and out of the
CWA by the midday/afternoon.

Cloud cover over northeastern SD/western MN will keep the atmosphere
from reaching its full potential to destabilize and prevent any
widespread convection. However lack of cloud cover over north
central may help with additional instability. HREF/REFS
surface/MuCape will be on the order of 1000-2000 j/kg east of the Mo
River with potential max values of 2000-2300 j/kg as RAP is a bit
more aggressive in higher cape values. The highest instability will
stay south of our CWA in FSD WFO and onward. Once again we will be
lacking strong bulk shear which will be at 30kts or less. It will be
increasing overnight but after the convection and mainly west of the
James River. Low level lapse rates will be steep with mid level
lapse rates not overly impressive running around 6 to just under
7C/km. CAMs/REFS indicate spotty showers and thunderstorms here and
there firing up along and east of this occluded boundary, around
00Z, with additional spotty elevated convection moving in over north
central SD, per embedded shortwaves/mid level low as mentioned.
These cells will track northeast with much of this activity moving
out by late tonight(Cam depending). A few cells/clusters could grow
vertical enough into the cooler air aloft to produce up to quarter
size hail. Secondary threats are wind gusts of 60 mph and brief
heavy downpours as PWATs still run 2 to 3 standard deviation above
normal over northern and northeastern SD/western MN. So a Marginal
Risk,(level 1/5) of severe weather continues for much of the CWA
with the exception of far northeastern SD/west central MN which has
a general threat of thunder and sub severe hail/winds.

With this occluded front (and with triple point near center of low
over our east central CWA) and UL low just to the west this
sometimes sets up the threat of tornadoes. 0-1km SRH increases to
about 100-150m2s2 a few hours after 00Z mainly James Valley and
eastward but 0-1km shear is only up to 20kts or so. STP runs between
0.5 to potentially 1, highest over Hand/Hyde and southeastward. RAP
indicates curved hodographs in this area but small due to the weak
shear. So why tornadoes are not a main threat, they cannot be ruled
out for a few hours if discrete cells can fall within this area of
tor parameters. Confidence is very low on formation but wanted to
talk about the potential threat.

Monday, this closed upper low will continue to spin over the
MT/Canada border with a little bit of ridging over the CWA and
southwest flow aloft. High pressure will be over the region through
Monday evening keeping conditions dry and winds out of the
northwest. While SPC has pulled back the risk of marginal severe
threat to now over far east central SD, CAMs are less than excited
on the formation of storms (even with shear and marginal
instability)in this area so this will be something to watch for. Our
attention turns to Tuesday as winds turn southerly 850mb to the
surface, east of a lee side boundary with a jet streak/shortwave
energy over central SD on the eastern and southeastern side of this
closed ongoing stacked low (now in Canada). This along with daytime
heating and destabilization, and the low tracking east,
thunderstorms are forecast to fire up head of a cold front within
the warm sector over western to central SD. NAM indicates drier air
aloft then what we have been dealing which will lead to more of a
wind threat, however, steep lapse rates, moderate instability, and
stronger bulk shear could help produce strong to severe storms. NAM
Nest is the only CAM to go out this far but does show discrete cells
transitioning to a line over central SD by the afternoon and
tracking eastward. It is still a bit early for specifics which will
be better nailed down as additional hi-res guidance comes in over
the next day or so. SPC has issued a Slight risk (level 2/5) for
severe storms along and west of the Mo River Tuesday (where the
stronger winds aloft and better instability lies) with a Marginal
Risk (level 1/5) for locations between the Mo and James River.

Middle to end of next week, Clusters indicate this persistent mid
level low will finally weaken as it tracks over Canada with more
zonal flow/weak ridging pattern Wed/Thurs. Models hint at another
closed low moving in off the Pacific and becoming an open wave with
ridging over the central to eastern CONUS by the weekend. Still some
discrepancies in the intensity of and position of features but do
agree on this -PNA pattern continuing.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1230 PM CDT Sun May 31 2026

Terminals KABR,KATY,KPIR,KMBG

Scattered to overcast skies continue over KABR/KATY with clear
skies at KPIR and a few high clouds at KMBG. VFR/MVFR cigs are
forecast through the TAF period at KABR/KATY with VFR cigs
forecast at KMBG/KPIR. Isolated to scattered showers and
thunderstorms will continue to fire up mainly east of the
Missouri River this evening and over portions of north central
SD a few hours later. KPIR should stay south of much of this
convection. Due to the spotty nature, kept prob30 in the TAFs
for thunderstorms and will amend if storms go near or over the
terminals. Some storms may become strong to severe with hail up
to an inch and thunderstorm wind gusts up to 55 knots possible.
Any stronger storm could also cause brief drops in visibility to
IFR.

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

&&

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

&&

$$

DISCUSSION...MMM
AVIATION...MMM