textproduct: Sioux Falls

KEY MESSAGES

- Winds weaken slightly Friday, but relative humidity and lingering afternoon gusts along Highway 14 lead to critical fire danger.

- Risk for convection grow over the upcoming days, but remain conditional through Saturday afternoon.

- Significantly higher thunderstorm risks develop Saturday night through Monday. Potential for widespread severe storms is focused on Sunday afternoon and early evening. Monitor the forecast!

UPDATE

Issued at 857 PM CDT Thu May 14 2026

Light showers and thunderstorms have moved east of the region. A cold front currently located roughly along I-29 will also continue to move east. Behind it winds will become northwesterly and clouds will clear. Overnight winds will become light and variable.

Friday morning winds will become north to northwest around 5-10 mph. Winds have continued to trend down slightly, however CAMs and soundings indicate a localized enhancement in areas at elevation along the Buffalo Ridge. For areas south of Highway 14, gusts will be around 15-20 mph. Along and north afternoon winds look to gust around 20-25 mph. Highs will be hot, in the 80s to low 90s over northwest Iowa. In addition, Friday will be another dry day with afternoon relative humidity falling to 17-20% for most of the region. Since winds continue to look marginal the current, more focused Red Flag Warning looks to be in good shape.

A period of more active weather looks to begin Friday night and continue into the early portion of next week. See the Discussion below for further details.

DISCUSSION

Issued at 158 PM CDT Thu May 14 2026

THIS AFTERNOON: Synoptically driven strong southwesterly wind gusts of 30 to 45 mph continue to develop ahead of a surface front moving eastward gradually. We've had quite a few reports of elevated dust as well as blowing dust impacting west to east roadways this afternoon. While widespread visibility remains above 5 miles, very highly localized visibility may drop below 1 mile in higher gusts. While temperatures are slower to respond today with the cloud cover, we're still headed towards critical fire danger. See separate discussion for more details. Otherwise, a few lingering high based showers will remain over NW Iowa into the late afternoon, with isolated shower/tsra possible along the aforementioned front moving east through sunset.

TONIGHT: The frontal boundary will slide into the eastern CWA after dark tonight with some persistence of mid-lvl clouds along it. Elsewhere, winds do turn light and variable as temperatures cool into the upper 40s and 50s.

FRIDAY-FRIDAY NIGHT: We'll begin to see gradual shifts in the mid- lvl pattern on Friday as zonal flow develops. Two concerns on Friday, one being marginal RFW conditions along the Highway 14 corridor in the afternoon, and the second being potential convection forming along surface convergence zone over eastern Nebraska and western/northwestern Iowa late in the afternoon. Soundings along the Highway 20 corridor show some inhibition lingering at mid- afternoon, but dissipating as convective temps in the low 90s are met. With mid-lvl flow increasing late in the day, just enough forcing on the boundary could force isolated to scattered storms along and south of Highway 20 in the evening. MLCAPE around 1000- 1500 J/KG could support marginally severe hail for a few hours as storms will track southeast with the mean flow away from the CWA. Further north, weaker low-lvl flow should prevent widespread convection from forming into Saturday morning, but it's also a non-zero chance.

SATURDAY: The vast majority of the daytime hours of Saturday is anticipated to be dry as brief mid-lvl ridging slides through the area. The surface front that passes through the area today will settle near or north of I-80 but may make a slow retreat northward in the afternoon. By early evening deeper synoptic lift associated with an upper trough ejecting out of the Central Rockies will focus low-lvl convergence and strong theta-e advection south of I-90 or towards Highway 20. This is where some uncertainty begins to grow in the forecast. Models have some variability on the northward extent of surface based activity but strongly support elevated storm development across northern Nebraska eastward into north central Iowa. There may be some potential given 40 knots effective shear, for a few supercells with very large hail to form initially. Later in the evening a potential MCS may try to form over northern Nebraska and lift northeast through the nearly 1500 J/KG MUCAPE bringing both a risk for very large hail but some modest strong wind risks into the Tri-State area into daybreak. Pockets of heavy rain will be possible in this thunderstorm activity.

SUNDAY: While some considerable uncertainties remain on Sunday, there continues to be increased potential for impactful and potentially widespread severe weather in the area. As alluded to in Wednesday's discussion, the greatest uncertainty continues to revolve around the extend of the northward advection of the warm sector into the Plains during the day. Overnight and morning convection may play a large role in this process, but ensemble data has trended towards instability shifting further north over the past 24 hours, even showing MLCAPE exceeding 3000 J/KG over portions of NW Iowa by late afternoon. The other limitation we'll need to monitor is the EML that remains in place for much of the daytime hours once morning convection passes. A stubborn warm layer continues to present itself in soundings near 700 mb deep into the afternoon, but thoughts are the amplitude of the slightly negatively tilted trough may be enough to overcome this limitation. Given the magnitude of bulk shear, supportive mid- lvl lapse rates, low-lvl helicity and buoyancy there is certainly potential for a higher end severe weather day well into the evening/overnight hours which includes all modes. This thought is backed up by AI-learning outlook products and CIPS analogs that support a significant severe weather potential. Still quite a few issues to work though and plenty of time for things to change, but it's time to really start monitoring the forecast if plans exist on Sunday or Sunday night.

MONDAY: Uncertainty grows further on Monday as models diverge on the positioning of a cold front and how far east it may track. Ensembles of these models are also split with the GFS shoving the effective boundary east. The ECMWF/CMC both stall the front over the eastern CWA and allow it to retreat westward as a secondary trough lift out of the Central Plains. These drastically different scenarios mean a big difference in severe weather risks especially east of I-29 Monday afternoon and evening.

QPF TOTALS: A wide array of potential QPF totals remain with this system with NBM continuing to spread low probabilities of higher QPF totals, but expressing a wide array of 10/90th percentile potential between 0.25-2". Convection will ultimately drive the highest totals, and would not be surprised to see pockets of 2"+ by Monday evening.

TUESDAY-THURSDAY: Behind this trough, cooler weather will arrive through the middle of the week with minimal hazards expected.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1208 AM CDT Fri May 15 2026

VFR conditions are expected to prevail with mostly clear skies for the duration of the period. Winds are light and variable through Friday morning before becoming westerly for I-90 and north. Areas to the south will be more southerly. A surface boundary passes through after 00Z Saturday, turning winds to the north. Winds become breezy in the afternoon with 15-25 kt gusts, highest near and north of Highway 14.

Chances for thunderstorms increase after OOZ Saturday. Some storms could be strong to severe producing 2 inch hail and 60 mph wind gusts. Area most likely to see strong storms is northwest Iowa, especially along and south of Highway 20. Areas to the north are not likely to see any precipitation. Storms should be southeast of the area shortly after 06Z.

FIRE WEATHER

Issued at 158 PM CDT Thu May 14 2026

Winds will drop on Friday, but along Highway 14 will increase once again towards the 15-25 mph gust range early in the afternoon. Widespread low relative humidity is expected throughout the Tri- State area with values as low as 15 percent. A smaller, targeted red flag warning is in effect for areas along Highway 14.

Widespread rain will be expected Saturday night through Monday.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from 9 AM this morning to 6 PM CDT this evening for SDZ038>040. MN...Red Flag Warning from 9 AM this morning to 6 PM CDT this evening for MNZ071-072. IA...None. NE...None.