textproduct: Aberdeen

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.

UPDATE

Issued at 1031 AM CDT Sun May 17 2026

Made some updates to PoPs and Sky grid earlier this morning to bring them in line with the satellite/radar obs. Most of the forecast area remains sort of in a holding pattern now through about midday before convection is expected to start inching closer into our south/west zones. The mid to late afternoon hours looks to be the window of opportunity for our area to see strong to severe convection, mainly from south central SD to northeast SD and points east and south of that line. Morning showers and storms across parts of central SD have exited out of our area to the north with this next wave of showers and thunderstorms already on radar across the NE panhandle and southwest SD. That activity is part of this next wave that will bring this convection north and east into parts of our forecast area this afternoon.

UPDATE Issued at 629 AM CDT Sun May 17 2026

UPDATE for 12Z Aviation discussion.

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 /12Z TAFS THROUGH 12Z MONDAY/

Issued at 632 AM CDT Sun May 17 2026

Terminals KABR,KATY,KPIR,KMBG

We're staring off with showers and isolated thunderstorms mainly west of the MO River. The precipitation near ATY has been limited and east of the airport. Expect mainly dry conditions through the morning at ABR and ATY, with precipitation remaining steady at PIR/MBG. ATY will see the highest probability of thunderstorms 20-24Z today. Other locations will be more temporarily and we will need to keep an eye on the latest radar/model trends for additional thunderstorm mentions at the rest of the airports (particularly PIR/ABR).

ABR WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None.