textproduct: Sioux Falls

KEY MESSAGES

- Strong to severe thunderstorms are the primary concern tonight. Initial storms pose a risk for hail up to 2", eventually growing into clusters capable of 50 to 70+ mph winds as they track southeast into the early morning hours.

- Another round of strong to severe storms could develop late Tuesday afternoon and evening. These storms could also form into another storm cluster that moves southeast into Wednesday.

- Expect a cooler, unsettled pattern from Thursday through the weekend with high temperatures dropping into the mid-70s. Daily rain chances return, but the severe weather risks are expected to remain low.

DISCUSSION

Issued at 110 PM CDT Mon Aug 10 2026

THIS AFTERNOON: Quite a bit of strato-cu out there this afternoon, delineating the area where more abundant low-lvl moisture has pooled. Further west an area of ACCAS tied to modest mid-lvl theta- e advection continues to drift eastward. We'll have to watch this area, but would not anticipate any more than sprinkles as it slides east later today. A light southeasterly wind is expected to continue a push of upper 60 to lower 70 dewpoints northwest into portions of northwestern SD, where a focused risk for severe storms will develop later this evening. With the increased cloud cover and abundant wildfire smoke aloft, high temperatures may struggle to reach much past the middle 80s.

TONIGHT: Convection risks remain the highest concern into the evening and overnight hours. Water vapor imagery this morning showed a subtle shortwave trough moving through eastern MT, with this waved modeled to dip southeast this evening. A deep instability pool has pushed into western SD this afternoon, with upwards of 3000 J/KG MLCAPE. The issue may be some inhibition, impact of wildfire smoke, and lack of a focused trigger which could delay widespread development. CAMS however continue to hint at deeper convection waiting a few hours into the evening, and then triggering due to an increase of 850:700 mb warm advection in the West River areas as stronger vorticity moves into the Dakotas. This northward LLJ should also help push deeper instability further northeast over the eastern portions of SD. Where storms develop, signals will be strong for at least 2" hail, as elevated parcels will be within a corridor of 50 knots effective shear and should rotate. An increase of mid-lvl dry air will increase the potential for cold pool development in supercells, eventually suggesting one or more larger clusters of storms will form and try to track southeast after 10pm. Initial SCCRAM+HRRR guidance suggest rapidly increasing severe weather probabilities as early as 0-2 UTC in central South Dakota. After this, HREF 2-5 km UH paintball plots all indicate a tendency for this activity to track southeast along the instability axis reaching I- 29 around 12-1am and reaching the edge of the CWA around 4am. As stated earlier, initial updrafts may have potential for 2" hail, with greater risks for 50 to 70 mph winds in progressive clusters. This entire setup remains a bit uncertain, so it's imperative to continue monitoring the forecast.

TUESDAY-TUESDAY NIGHT: Behind any departing MCS we'll have a fair degree of stability and subsidence that could leave stratus in place in the morning. Warming in the afternoon and another potential shortwave crossing the Rockies could promote strong to severe storms over western and central SD/ND by the evening with another MCS or two moving southeast overnight. Guidance remains all over the place as it continues to struggle with resolving these embedded waves. Nevertheless, SPC slight risks could end up extending further southeast in subsequent updates.

WEDNESDAY-SUNDAY: Feel that most of Wednesday will again remain dry as shortwave ridging moves in and surface winds remain easterly. High temperatures will rise into the lower to mid 80s. The ridge centered over the Four Corners and responsible for multiple days of NW flow will shift eastward by the second half of the work week. This pattern shift will cause the ridge to flatten slightly in the Northern Plains, inducing slight westerly to southwesterly flow aloft into the weekend. We'll be subject to smaller embedded lobes of vorticity tracking northeast from the southwestern CONUS and Central Rockies. Medium range guidance is not handling this transition well, but seems to continue to bring nearly daily chances for rain into the weekend. At this point I highly doubt every day will feature rain, but there will be some increased potential for more showery activity at times Thursday and again late Friday into Saturday. Instability looks low, so severe weather risks should also remain low. Temperatures with more cloud cover and cooler influences of Canadian high pressure should trend into the middle 70s into the weekend.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1159 AM CDT Mon Aug 10 2026

MVFR to low VFR stratus trying to develop early this afternoon. These ceilings will rise slightly this afternoon but should remain quite prominent into the evening.

A separate area of ACCAS will drift eastward toward the MO River valley this afternoon, potentially producing a few sprinkles as it moves through.

Greater risks for convection develop late this evening and continue overnight as storms form over western and central South Dakota. This activity may merge into one or more clusters and impact the forecast area through 4am. Initially hail will be the main risk, but storms may turn into linear lines of wind. Confidence on impacts to the terminals remains low, so will continue with a Prob30 to indicate potential. These risks may increase quickly this evening.

Post convection, lower stratus may develop and continue into mid-morning.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...None. NE...None.