Area Forecast Discussion

KEY MESSAGES

- Near-critical to critical fire danger continues through early this evening with very dry conditions and a gusty south wind. High chance of very high/near critical fire danger returning Wednesday and perhaps Thursday.

- Low to moderate chances for showers and thunderstorms return Wednesday night into Thursday night. Isolated strong to severe storms are possible east of a Spencer to Sioux City line Thursday night. Confidence in severe weather threat is low due to poor model agreement in cold front progression. - 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.

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 /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 206 PM CDT Mon Apr 20 2026

VFR conditions will prevail through the period with gusty winds being the main impact through 00z. South winds will weaken overnight, turning light and variable, then eventually northeasterly with the passage of a front by Tuesday morning. A southwesterly low level jet will trigger low level wind shear overnight near Sioux City and in parts of northwest Iowa.

FIRE WEATHER

Issued at 206 PM CDT Mon Apr 20 2026

As of 2 PM, wind gusts have slightly exceeded expectations this afternoon with occasional gusts of 25 to 35 mph, but dew points have risen slightly faster than expected. This balance has brought occasional critical fire conditions across the region, but most persistently confined to the Red Flag Warning area. Near critical to critical fire danger persists across the region through early this evening due to low humidity and gusty south winds.

High clouds near and east of a Huron to Sioux Falls to Sioux City line have limited heating a bit. Additionally, west of I-29, southerly winds have peaked and begun to weaken. Fire danger lessens considerably with sunset as winds weaken drastically and nighttime cooling commences.

On Tuesday, dry air lingers with abundant sunshine and humidity dipping below 25 percent across the region. Fortunately lighter winds gusting mostly just in the teens should inhibit critical conditions from developing.

Greater concern for fire danger returns Wednesday. The Hot-Dry-Windy Index highlights Wednesday afternoon as the main period of wildfire concern for the week with unseasonable warmth and south winds gusting 35 to 45 mph. Will be closely monitoring this period for potential fire weather headlines. Confidence in fire danger decreases for Thursday with low rain chances and increased cloudiness, but gusty winds and post-frontal dry air may ignite very high fire danger once again.

FSD WATCHES / WARNINGS / ADVISORIES

SD...Red Flag Warning until 8 PM CDT this evening for SDZ039-040- 055-056-062. MN...Red Flag Warning until 8 PM CDT this evening for MNZ071-072- 080-081-089-090-097-098. IA...None. NE...None.