textproduct: Sioux Falls

KEY MESSAGES

- Critical fire weather continues into early evening as wind gusts over 40 mph produce pockets of blowing dust and lower air quality.

- 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!

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 /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 623 PM CDT Thu May 14 2026

East of I-29 light showers to thunderstorms are continuing to move east. Storms should be clear of the region late this evening. Ceilings around 7500 ft AGL will improve as clouds flow east with the showers. Skies clear rapidly after midnight and remain mostly clear for the duration.

A cold front roughly draped from Avon to Spencer to Arlington in South Dakota will continue to gradually drift east this evening. Winds have already dropped below 20 kts over south central South Dakota. Winds will continue to drop off rapidly behind the front through the evening, becoming light and variable overnight. Friday morning winds become northwest at 5-10 kts. For areas along and north of I-90 wind gusts will increase to 15-20 kts in the afternoon.

FIRE WEATHER

Issued at 158 PM CDT Thu May 14 2026

Widespread wind gusts 35 to 50 mph continue to be reported along and ahead of an approaching frontal boundary. Relative humidity values have been slower to fall given the increase in cloud cover, however will drop towards 25 to 35 percent in most areas into early evening. Will extend the Red Flag Warning for a couple additional hours into the evening.

Winds will drop on Friday, but along Highway 14 will increase once again towards the 20 to 30 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. Will issue a smaller targeted red flag warning for areas along Highway 14.

Widespread rain will be expected Saturday night through Monday.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning until 9 PM CDT this evening for SDZ039-040- 054>056-060>062-065>071. Red Flag Warning from 9 AM to 6 PM CDT Friday for SDZ038>040. MN...Red Flag Warning until 9 PM CDT this evening for MNZ071-072- 080-081-089-090-097-098. Red Flag Warning from 9 AM to 6 PM CDT Friday for MNZ071-072. IA...Red Flag Warning until 9 PM CDT this evening for IAZ001>003- 012>014-020>022-031-032. NE...Red Flag Warning until 9 PM CDT this evening for NEZ013-014.