textproduct: Sioux Falls

KEY MESSAGES

- Showers and isolated thunderstorms continue this morning into the afternoon hours. Brief moderate rain may be possible.

- Continued conditional and very low chance for isolated strong storms through this morning. Quarter size hail is the main threat through the southern Missouri Valley and east of Iowa/Minnesota State Highway 60 through mid morning.

- After rain ends this afternoon and evening, an extended period of cooler than normal temperatures continues through the work week with only minor rain chances late Wednesday.

- Warmer temperatures return by the weekend with highs around 10 degrees above normal, climbing into the 70s.

UPDATE

Issued at 329 AM CDT Mon Apr 27 2026

Some patchy and locally dense fog has been observed so far this morning. Overall, fog has been limited to the MO River Valley where we've seen a longer break in the precipitation and some breaks in the clouds earlier in the overnight. Based on obs to the south, visibility seems to improve as showers and storms move through, increasing winds and mixing out some of the fog. Will continue to monitor, but not anticipating the need for a Dense Fog Advisory at this time. Temperatures remain in the mid 40s to mid/upper 50s, with scattered showers and isolated storms.

Still a very conditional threat of an isolated stronger storm through this morning, mainly for the MO River Valley through daybreak and east of IA/MN Hwy 60 through late morning. However, current mesoanalysis shows MUCAPE around or less than 500 J/kg, with the better instability off to the south and east of our area. Think that the on-going convection across KS/MO continues to hamper our severe potential. Thus far this morning, storms have struggled north of the NE/KS border. Better LLJ dynamics are to the east with the WAA. Mid level wave, steepening mid level lapse rates, and shear around 35-45 knots may be enough to overcome the lack of instability to produce hail to the size of quarters in the eastern MO Valley and into the IA/MN Hwy 60 corridor toward daybreak into mid morning, but confidence in this potential continues to wane.

Wind guidance for this afternoon and evening has been tapering down over the last 24 hours, including decreasing probability of gusts at or above 45 mph. Will hold off on a Wind Advisory at this time, but gusts around 40 mph are possible this afternoon and evening as the surface pressure gradient compresses and CAA increases. Highest gusts are expected across south central SD and also across the higher elevations of the Buffalo Ridge.

DISCUSSION

Issued at 1242 PM CDT Sun Apr 26 2026

THIS AFTERNOON: Scattered showers and embedded thunderstorms continue to develop and lift northward this afternoon. Driven by a combination of moderate dPVA and broad warm advection. Elevated instability is slowly crawling northward, but doesn't seem to extend much past I-90. This may limit overall precipitation rates as this activity moves northeast, but with PWAT values near the 90th percentile, pockets of moderate rainfall will still be possible. Portions of NW Iowa have seen a bit more clearing today, but with clouds increasing, that warm-up and low-lvl lapse rate increase may diminish.

THIS EVENING AND OVERNIGHT: Questions still remain on the degree of elevated instability that can advect northward both this evening and then after midnight. Initial wave of vorticity is expected to track into SW Minnesota very early this evening, leaving a bit of a lull in forcing for a few hours. Trailing instability along with some sharpening mid-lvl lapse rates could still lead to the development of a stronger marginal hailer or two south of I-90 through sunset (focused in a sector from Vermillion to Spencer southward), but focus for development remains uncertain. A few CAMs do also suggest the edge of the warm sector approaches Highway 20, which could support a wind gust transporting downward in any stronger storm.

As multiple MCS develop over the Central and Southern Plains as even stronger upper troughing enters the region, we may begin to see a weak sfc low try to develop over northeastern Nebraska with a northward extended inverted trough. Short term guidance (mainly NAM/RAP) show some persistent northward advection of elevated instability (800-1200 J/KG) ahead of this feature along and east of I-29. Other models (GFS/EC) suggest weaker lapse rates with only 300- 600 J/KG MUCAPE. Thoughts are that while the LLJ begins to veer off to the NW, there may be enough convergence combined with dPVA to induce scattered thunderstorms after 2am. An isolated hailer could be possible, but severe weather risks remain on the lower side.

MONDAY: The aforementioned inverted trough will turn towards a cold front early in the day and surge east. Latest CAMs have sped up the boundary just enough to keep any renewed sfc based convection along or just east of the CWA by late morning. Further west, as the upper trough opens up and passes through the Central Plains and toward the Upper MS River Valley, we'll begin to see a deformation area of rain develop in central SD. This precipitation will drag it's foot eastward during the day, potentially dissipating by time it reaches I-29 by mid-afternoon. Additionally, deepening surface low pressure induced a stronger SPG through the Dakotas, and when combined with strong low-lvl cold advection we should see wind gusts approach the 30 to 40 mph range through the day before settling in the evening. Daytime highs may take place early in the day with falling temperatures in the afternoon. Have adjusted the NBM diurnal temperatures trend to account for afternoon clouds and cold advection.

PRECIPITATION TOTALS: Amounts have tapered off slightly over the past 24 hours, potentially indicating less instability further north, but also some redirection of moisture after dark from convection in the Southern Plains. Nevertheless the probability of an additional 1" of rain breaks the 75% mark in areas along and north of I-90. There are also some stripes of 50% probability of 2"+ of rain towards the Madison, Brookings, and Marshall areas in HREF guidance. Average totals based on the 25/75th percentile likely run between 0.50" and 1.5" with pockets of higher numbers.

TUESDAY-THURSDAY: We'll remain in a dominant troughing pattern for much of the remainder of the work week. Long wave troughing centered over Hudson Bay will keep northwesterly flow aloft in the Tri-state area. The result will be temperatures near to slightly below normal at times, along with a low chance (30%) of showers by Wednesday night into Thursday.

FRIDAY-SUNDAY: The good news is that it appears the mid-lvl pattern may break slightly by the end of the week as long wave ridging moves out of the West Coast and towards the Plains by the weekend. Medium range deterministic and ensemble guidance still remains a bit split in this potential, with quite a bit of spread in ensemble guidance. NBM 25/75th spread approaches 10-15 degrees by Sunday, suggesting a range from the mid 60s (should ridge be slower to advect east), to the upper 70s and 80s by Sunday (if ridge move east faster). At this point the NBM mean in the lower 70s seems appropriate.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 625 AM CDT Mon Apr 27 2026

MVFR and lower stratus and visibility continue through much of the day and into this evening. Reduced visibility this morning is due to fog in addition to the scattered showers and thunderstorms. Added mention in a TEMPO group this morning for KFSD and storms approach the terminal through 12z and just after. Omitted any TS mention from KSUX, as activity is already out of the vicinity. Showers and storms taper off through the day, although KHON and areas west of the James may see some wrap around showers during the day. Conditions will be slow to improve, but do expect a return to VFR late this evening into tonight across the area.

Other aviation concern through Tuesday morning is the increasing northwesterly winds this afternoon, with gusts 30 to 35 knots, with higher gusts in south central SD and along the higher elevations of the Buffalo Ridge. Winds slowly taper down through the overnight hours.

FSD WATCHES/WARNINGS/ADVISORIES

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