textproduct: Aberdeen

KEY MESSAGES

- A Marginal Risk (level 1 out of 5) for severe weather has been posted for along and south of the I-90 corridor late this afternoon, evening and into the overnight hours. The main threats will be hail around 1" diameter and winds up around 60 mph.

- A Marginal Risk (level 1 out of 5) for severe weather has been issued for between the Missouri and James valley regions Wednesday late afternoon and through the evening hours. Hail around 1" diameter and damaging winds are the main threats.

UPDATE

Issued at 823 PM CDT Tue Aug 18 2026

Convection that has developed/moved into western South Dakota has upper support (mid-level low pressure circulation and 90-100kt speed max aloft), including 40-50kts of deep layer shear and adequate low level thermodynamics/instability enough to probably keep things going well into the overnight hours. At least, that's what the HRRR's been forecasting to happen now for several runs in a row. There's not much for a low level jet tonight, though, so will have to see what storms can muster without a LLJ. PoPs are already in the forecast for overnight convection potential. No changes planned to the tonight period forecast.

UPDATE Issued at 640 PM CDT Tue Aug 18 2026

See below for an aviation forecast discussion for the 00Z TAFs.

DISCUSSION

Issued at 132 PM CDT Tue Aug 18 2026

We are tracking a weak wave moving through southeast North Dakota headed into far northeast South Dakota and western Minnesota. Just some ACCAS and light radar returns. The rest of the area is marginally unstable in NAM/HRRR BUFKIT profiles for the afternoon. There is a broad trough overhead, and an upstream wave that is expected to move south of the area this afternoon. Generally, cant rule out a storm or two in the heat of the afternoon so broadly added some low POPs. Profiles are mainly dominated by skinny CAPE and unidirectional shear. A wave that moves down across central South Dakota later this evening and overnight provides a better impetus for convection, hence the marginal risk outlined by SPC.

Activity diminishes/moves out of the CWA during the morning Wednesday, with another wave coming down from the northwest late. Again we're still under this broad upper trough centered to the northeast, and as such marginally unstable through the day as well. Yet again, profiles are defined by skinny CAPE and unidirectional shear.

The upper ridge out west gradually increases in amplitude and strength, with increasing heights across South Dakota Thursday/Friday we we'll begin to say with more consistency and confidence in dry conditions most of the area Thursday and across the Dakotas Friday. Thursday will see another trough passage not too dissimilar to yesterday's but with warmer air aloft and lower dewpoints to limit instability. Fridays temperatures will be slightly cooler in comparison to Thursday on the backside of the front/south end of high pressure.

The upper ridge crests over the region during the weekend. 700mb temperatures increase to about a standard deviation above climo. This warm air collapses with the passage of an upper wave late Sunday. NBM POPs early Sunday align with the GFS brining in some ACCAS/mid level convection. The wave that passes through doesn't break down the ridge permanently, with a rebound of the upstream ridge for the first half of next week. This is trending temperatures back above normal though right now about 5-10 degrees for next week.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 640 PM CDT Tue Aug 18 2026

Terminals KABR,KATY,KPIR,KMBG

Other than a few hours of light night sub-VFR stratus potential down around KPIR, VFR conditions are in the forecast for all terminals. Cant rule out a short-lived storm this evening at/near KMBG and KABR. Then, later tonight near the KPIR terminal, more storms are possible, rumbling in from western South Dakota after dark. KABR/KMBG/KATY should maintain a dry forecast beyond any early evening showers/storms that may develop or move over terminal airspace.

ABR WATCHES/WARNINGS/ADVISORIES

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