Sioux City, IA 51108 Weather

Key Messages

- Elevated Fire Danger Friday: Warm temperatures in the 70s and 80s combined with wind gusts up to 45 mph will create near- critical fire danger Friday. Avoid outdoor burning or activities that create sparks such as fall harvest activity may want to consider postponing.

- Breezy with Isolated Showers Tonight: There is a small chance for a stray rain shower or thunderstorm after 3 AM into mid- morning Friday, but most locations will remain completely dry.

- Cooling Down This Weekend: A cold front will move into the area on Saturday, bringing light, spotty rain and dropping afternoon highs into the 60s for the western half of the region.

- Soaking Rain and Chilly Air Next Week: Expect a major weather shift Sunday night through Tuesday. Widespread, persistent rain will arrive with many areas receiving between a half- inch and nearly one and a half inches, alongside a sharp cool- down into the 40s and 50s.

Discussion

Issued at 124 PM CDT Thu Oct 22 2026

THIS AFTERNOON: Another beautiful afternoon across the Tri- State area as temperatures continue to rise into the 70s. As the SPG continues to increase surface winds are beginning to gust over 20 to 25 mph at times, highest along and west of the James River valley. Mid- lvl clouds associated with a broad increase in 600:500 mb RH will continue to spread northeast, through have been thinning. Fire danger remains high in most areas west of I-29 so caution should be used in farm fields into the evening.

TONIGHT: Winds will remain breezy through the overnight hours, keeping overnight lows much warmer than normal. After midnight, we'll begin to see the breakout of mid-lvl clouds as warm advection within the 700:600 mb range increases. Short term CAMs are coming into more consensus in the development of scattered high based showers after 3am, which may increase further by 12-15Z as lift maximizes on the increased LLJ moving into SW Minnesota. While a very low chance, MUCAPE in the effective layer rises up to 200-300 J/KG indicating at least isolated lightning potential. Will increase POTThunder to account for the risks.

FRIDAY: Any morning shower and isolated storm activity will lift into west central and central Minnesota by mid-day. Troughing entering the Central Rockies will further intensify the SPG through the day, with sustained winds of 15 to 20 mph developing by mid-day. Despite the SE surface flow, we're likely to see gusts increase towards the 35 to 45 mph range by mid-day with these gusts continuing into the very early evening hours. Temperatures may be a bit more uncertain Friday afternoon, somewhat dependent on lingering mid- lvl cloud cover. The warmest reading are still expected along and west of the James River where upper 70s to lower 80s may be possible. Greater temperature spreads remain over SW Minnesota where highs could range anywhere from the lower 70s with clouds to the upper 70s. Warm temperatures and strong winds will lead to elevated to near critical fire danger. Please see separate discussion on fire weather risks.

SATURDAY: A frontal boundary that remained over western South Dakota Friday will begin to advance eastward overnight reaching into the western half of the CWA by daybreak Saturday. Mid-lvl vorticity streaming NE along this frontal zone may lead to scattered high bases showers to sprinkles through the day on Saturday. Soundings show ceiling bases only as low as 8K ft AGL by Saturday afternoon, with a fair amount of dry air still infiltrating the sub-cloud layer in the afternoon. This should help keep any QPF on the low side and rain more sporadic. The front and clouds could have a profound impact on afternoon temperatures, with some guidance suggesting highs near 60 well behind the front, with highs closer to 75 in areas near Sioux City to Storm Lake and Spencer more displaced from the boundary. This light rain opportunity will continue through Saturday night into Sunday morning as the surface and low-lvl boundary remains stalled overhead.

SUNDAY-WEDNESDAY: A bit more uncertainty develops on Sunday, focused around the positioning of the surface front. Models like the NAM, that tend to be overly strong on cold air surges southeast, push the front all the way towards central Iowa. The ECMWF on the other hand increases mid-lvl ridging through the Central Plains and slows the arrival of upper troughing over the Central and Southern Rockies. This in return forces the boundary further northwest. The GFS splits the two solutions, keeping the boundary nearby and focusing more clouds and occasional spits of rain through the heart of the CWA. Never mind the solution, there may be brief lull in rainfall on Sunday with most guidance suggesting any rain chances diminish during the the first two thirds of the daytime hours.

Aviation

Issued at 645 PM CDT Thu Oct 22 2026

VFR conditions expected through the period. Should see mid to high level clouds spread across the area tonight, with hit or miss showers developing closer to daybreak mainly over southeastern South Dakota and southwest Minnesota. Can't rule out rumbles of thunder with this activity, but looks too isolated to include -TSRA in the TAFs at this time. Southeasterly winds will increase heading into the morning hours on Friday, with peak gusts of 30-35 kts expected by the afternoon mainly along and west of I-29. Near and west of the James River, can't rule out a few gusts to 40 kts.

Fire Weather

Issued at 124 PM CDT Thu Oct 22 2026

Concerning fire weather develops on Friday. After morning sprinkles to light rain move northeast, strong southeast surface winds develop through the day with sustained winds to 20 mph and gust of 35+ mph. Greater wind focus will develop west of I-29, but especially along and west of the James River valley with occasional gusts to 45 mph are likely. While temperatures reach near 80 degrees, dew points may try to pool ahead of a weak front in central South Dakota. This may hold relative humidity values well above critical red flag warning thresholds. However, a special weather statement and other messaging will be considered for this unique scenario.

That said, the combination of strong winds, drying fuels, and abnormally warm temperatures will lead to widespread high to very high GFDI values (along and west of I-29). The greater danger will be in harvest activities, with the GFDIAg values reaching well into the very high category over most of the CWA. Any agricultural activities should use caution and local partners should be aware of the increased potential for fire starts in farm fields.

Light rain begins to move into the area by Saturday, with chances increasing for a widespread wetting rain into early next week.