textproduct: Sioux Falls

KEY MESSAGES

- Strong southerly winds and unseasonable warm temperatures will promote dangerous fire weather concerns on Wednesday mainly west of the James River Valley. Additional concerns will be possible by Thursday.

- Low to moderate chances for showers and thunderstorms return Wednesday night through Thursday night. Scattered severe storms will be possible east of a Yankton to Hartford to Brookings line. However, some uncertainty remains due to poor model agreement with the progressing cold front. - Above normal temperatures persist through Wednesday, when highs of 80 to 95 degrees are expected. A pattern shift means cooler weather returns for the weekend with highs dropping back into the 50s and 60s.

UPDATE

Issued at 420 AM CDT Tue Apr 21 2026

Taking a look across the area, mostly clear conditions continue this morning with many areas reporting temperatures in the 40s to low 50s. The forecast remains on track with warmer and quieter conditions expected today as highs approach the upper 70s to mid 80s. While we once again will be dry this afternoon, light northeast winds in association with a weak surface low will keep any fire weather concerns at bay for the day. Looking ahead, Wednesday continues to look like our warmest day of the week as a surface warm front passes through the area. This combined with increasing southerly winds will not only lead to dangerous fire weather concerns but also highs in the 80s to low 90s (more in the fire weather section). The breezier conditions will likely carry over into Thursday as a cold front swings through the area. While there is still some uncertainty with the progression of the cold front, scattered showers and thunderstorms will be possible by Thursday afternoon especially east of I-29.

With the temperatures expected to be in the 70s to low 80s, a few developing storms could become severe east of I-29 with damaging winds and large hail being the primary threats. Upon an initial look at the environment, damaging winds looks to be the more prevalent threat as semi-discrete cells grow upscale into a line with eastwards extent ahead of the cold front. However, there is still some uncertainty on if things will get going in our area (Euro/Canadian) or just east of us (GFS/NAM) and this is currently depicted in medium-range guidance. With all this in mind, SPC has now outlined areas along and east of a Yankton to Hartford to Brookings line in a Day 3 Slight Risk for severe weather (Level 2 of 5). Remember these details are subject to change so make sure to follow your local forecast and have multiple ways to receive warning information!

DISCUSSION

Issued at 206 PM CDT Mon Apr 20 2026

LATE THIS AFTERNOON: Looking across the region, temperatures range from the low 60s to around 70 degrees as of 2 PM. Deeper mixing than models expected has yielded gusts peaking 25 to 35 mph, but warm air advection has brought rising humidity (currently 21 to 35 degrees) and slow-to-warm temperatures. Dew points remain near the NBM 25th percentile. Periods of near-critical to critical fire danger will persist through sunset. See the Fire Weather section below for more details.

TONIGHT AND TUESDAY: Winds weaken tonight as a dry, weak sfc trough slides in northwest flow, reducing fire danger. Mostly clear skies will pave the way for another chilly night, but a steep near-sfc inversion will keep lows a bit warmer than previous nights. Expect temperatures to bottom out in the mid 30s to mid 40s.

Meandering on the dry side of a quasi-stationary front near the I-80 corridor means continued very dry conditions for Tuesday. Efficient mixing quickly through the nocturnal inversion into light winds aloft will make for a sunny, warmer spring day with high confidence highs ranging from the mid 70s (southwest MN) to mid 80s (Hwy 20 corridor and south central SD).

WEDNESDAY: Notably hotter, windier, and dry conditions develop Wednesday in response to a 90th percentile (of NAEFS climatology) upper ridge building through. Currently have forecast high temperatures ranging from the lower 80s (east of I-29) to the lower 90s (west of the SD James River Valley), but see potential for temperatures to tick up a few degrees based on recent blend biases. A south wind mixing into a strong low level jet lends high confidence to gusts peaking in the 30s. Model forecast profiles show potential for some lower 40s gusts in south central SD. Higher winds combined with hotter weather brings high confidence in fire weather headlines across at least a portion of the area Wednesday and low confidence in fire danger on Thursday. See Fire Weather section for details.

WEDNESDAY NIGHT THROUGH THURSDAY: A progressive upper low treks east into the Upper High Plains Wednesday night, introducing a low to moderate (<60%) chance for isolated showers and storms in central SD. This activity may progress eastward leading to some scattered showers and/or storms for the day Thursday. While agreement in a mid level speed max in the area is sufficient to warrant isolated severe storm threat, moisture and instability may be weak enough to prevent organized convection. Portions of northwest Iowa are currently highlighted in a SPC Day 4 Severe Weather Outlook, but will need to continue to monitor model trends as models differ greatly in the residence time in the warm sector and the speed of the associated cold frontal passage (slower Euro vs faster GFS/NAM).

FRIDAY AND BEYOND: Behind Thursday's front, temperatures will be much cooler for the weekend with highs again dropping to the 50s and 60s and nightly lows near to below the freezing mark. The mid week upper low closes off over the Canadian prairie favoring below normal temperatures at least into early next week. The resultant zonal flow aloft brings lower confidence in next week's forecast with a moderate (20-40%) chance of at least some light rain (or rain/snow mix) Sunday night into Monday with a passing wave.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 630 AM CDT Tue Apr 21 2026

VFR conditions will persist this TAF period. Besides a few mid- level clouds, no significant aviation concerns are expected. Otherwise, light and variable winds in the morning will become more northeasterly to easterly for most of the day before becoming more southeasterly overnight.

FIRE WEATHER

Issued at 450 AM CDT Tue Apr 21 2026

A brief break from fire weather concerns is expected today as light northeasterly winds persist for most of the day. With this in mind, low to moderate fire danger is expected although it will be quite dry this afternoon. This will change into Wednesday as deeper mixing and a tightening surface pressure gradient leads to strong southerly winds withs gusts between 35-45 mph by early afternoon. Combine this with critical relative humidity values in the 15-30 percent range and it becomes quite the dangerous set up for fire concerns especially along and west of the James River Valley. With this in mind, decided to issue a Fire Weather Watch for the previously mentioned areas since this is where the highest confidence for critical conditions are. While the fuels are a bit greener across southcentral SD, the stronger winds and warmer/drier conditions will create a favorable environment for fire spread. Nonetheless, this isn't the only area of interest. Near-critical fire concerns could stretch as far east as the I-29 corridor so make sure to avoid any outdoor burning and to head your local restrictions.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Fire Weather Watch from Wednesday morning through Wednesday evening for SDZ038-050-052-053-057>060-063>065-068-069. MN...None. IA...None. NE...None.