464
FXUS63 KABR 170650
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
150 AM CDT Sun May 17 2026

.KEY MESSAGES...

- Slight Risk (2 of 5) mostly focused across far northeast South
Dakota and west central Minnesota Sunday afternoon/evening. Marginal
Risk for severe weather (1 of 5) includes parts of the northeast and
central South Dakota. Main threats are large hail and a tornado or
two.

- Colder air returns Monday through Wednesday, with high
temperatures around 15 to 20 degrees below normal. Temperatures
Wednesday morning may drop to near or below freezing, bringing the
potential for frost.

&&

.DISCUSSION...
Issued at 120 AM CDT Sun May 17 2026

Light shower activity associated with the first of several southwest
flow waves moving in from western South Dakota. This activity is
expected to slowly spread across the region through the morning
hours, though its facing some very dry air in the low levels
with a 20 degree dewpoint depression. Current radar returns are
a few hours behind model onset timing. Most of this will come
up through the Missouri valley, with lesser rainfall potential
across the eastern CWA through mid-day. Profiles indicate
skinny CAPE and weak mid level flow and that pesky dry subcloud
layer. HREF precipitation with this initial round of moisture
is around 1/3-1/2" west of Mobridge and a tenth of an inch or
less for the rest of the CWA.

In regards to instability later this afternoon, CAMS show a
decent gradient that runs up through Huron towards Sisseton.
Each has a slight variation in regards to this, but are
generally consistent with a peak instability around 4pm after
which is a rapid shift east. About that time 0-6km shear is
about 50kts, which is in line with previous discussions and is
dominated by the strong mid level unidirectional flow. For
Watertown, NAM/GFS BUFKIT profiles are still consistent in
indicating a stable boundary layer and possible stratus. The
RRFS RAP and HRRR are a little more unstable with the boundary
layer. This is thanks to southeasterly low level flow in the
lowest 1-2km. So the main question is whether we get surface
based convection or elevated convection. Either way, storm mode
continues to be fast moving/northeast moving supercells, maybe
splitting storms thanks to the unidirectional shear above the BL.
Surface based convection would favor right moving and increase
the tornado threat for the southeast Sisseton hills
(Deuel/Hamlin/Codington/Grant) and points south IF IF IF we can
get low level destabilization. In that regards most of the CAMS
bring in stratus with the gradient into our western Minnesota
counties. An yet more evidence for a warm advection/elevated
convection is the HRRR paintball >40dbz very much highlights the
northeast but on the north end of the instability gradient. The
one wrinkle to the convective mode is that the RRFS is a little
more on a wind threat kick, and several of its members present
with a blowing type system. Still not certain this should be the
outcome given the lack of dry mid level air in a southwest flow
regime.

Next round of moisture comes up from the southwest late in the day
Monday. Profiles are more indicative of strato-form rain, maybe
some weak instability. NBM mean QPF is only a tenth or two which is
a drop from the previous run, in line with the GFS, however the
Canadian and NAM both have a little higher QPF with a deformation
band lining up across central South Dakota and its possible the NBM
ensembles are smoothing this feature out.

NBM is still latching onto the frost potential for Wednesday
morning. Deterministic lows are still in the low-mid 30s. 75th
percentile for Aberdeen is only 33F, and 34F at Pierre/Mobridge.
Will maintain frost messaging.

Low moisture chances and seasonal temperatures as the upper flow
shifts back to zonal for late in the week/next weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1217 AM CDT Sun May 17 2026

Terminals KABR,KATY,KPIR,KMBG

VFR conditions start out the period, with MVFR ceilings over
most locations by around 13Z Sunday as a 60%+ chance of showers
moves in. Winds will continue to gust out of the east through
13Z, before diminishing and shifting out of the north (PIR/MBG),
and ABR by 21Z, and by 00Z at ATY as the surface low shifts
north and resides over southern MN. Thunderstorms remain
possible, especially Sunday afternoon over eastern SD.

&&

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

&&

$$

DISCUSSION...07
AVIATION...06