textproduct: Sioux Falls

KEY MESSAGES

- Near-critical to critical fire concerns are expected this afternoon/evening as breezy and dry conditions return. Additional fire concerns are expected by Wednesday.

- Shower and thunderstorm chances return Wednesday night into Thursday night. Some hints that much of the area could be split by strong upper level forcing to the northwest and deeper instability south and east, keeping our precipitation more isolated to scattered. - While temperatures will continue to trend above normal through Thursday, a pattern shift will lead more seasonable temperatures into the weekend.

UPDATE

Issued at 359 AM CDT Mon Apr 20 2026

Taking a look across the area, mostly clear conditions continue this morning as most areas sit near to just below freezing as of 3 am. Heading into daybreak, expect a chilly start with wind chills expected to be in the upper teens to 20 degree range for most areas so make sure to take a coat when heading out this morning. The good news is we won't stay cold for long as the combination of increasing southerly surface winds and lingering warm air advection (WAA) help temperatures quickly warm after daybreak. With this in mind, highs will likely peak in the upper 60s to upper 70s for most areas with the potential for a few low 80s across southcentral SD. Otherwise, the combination of breezy southerly winds and low relative humidity values will lead to near critical to critical fire danger from late morning to early evening (more in the fire weather section). Lastly, expect a more mild night with temperatures only decreasing into the low to upper 40s.

DISCUSSION

Issued at 100 PM CDT Sun Apr 19 2026

Cool high pressure shifts east tonight bringing southerly flow back to the area. Lows will mainly be from the upper 20s to lower 30s.

Southerly flow increases on Monday with gusts around 25 to 30 mph likely through the day. With fairly dry conditions expected once again, this creates elevated to near critical fire weather. Afternoon relative humidity should vary from the teens in central SD where winds will be a little lower during the lowest relative humidity with 20 to 25 percent over eastern SD into southwest MN. Will have a fire weather watch out for southwest MN and into Brookings county. If confidence increases enough in higher winds to the southwest of this watch, a watch/warning may be needed there as well. There has been a trend for slightly stronger winds and lower humidities each day for the past few days, so something to take into account.

A weak wave and associated weak cold front at the surface will move through Monday night, bringing weaker northerly and easterly flow into the area for Tuesday. This will bring warm and dry conditions to the area, but with winds mainly below 15 mph the fire weather threat Tuesday will remain muted.

Strong southerly flow returns on Wednesday, gusts 35 to 40 mph, with temperatures sky rocketing into the 80s and 90s. While afternoon relative humidity will be marginal for fire weather, the potential for very strong winds will lead to near critical fire weather conditions.

Low pressure moves onto the Western High Plains late Wednesday night and moves north and deepens over south central SD. This spreads instability into the area Wednesday night but the deeper westerly flow that develops Thursday quickly pushes this deeper instability to the east by mid day Thursday. There may be a small moment on Thursday afternoon near and east of a Marshall to Correctionville line where a thunderstorm could pop, but confidence pretty low. Otherwise colder air will move in Thursday afternoon and evening and like bring some pretty strong winds Thursday night.

Friday through Sunday will see this large low pressure over southern Canada keep generally dry conditions and below normal temperatures in place. Lows in the 30s and highs in the 50s.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 554 AM CDT Mon Apr 20 2026

VFR conditions will continue this TAF period. Taking a look at satellite imagery, mostly clear conditions continue this morning with some high-level cirrus across southwestern MN. Besides a few additional clouds during the day any aviation concerns should be kept to a minimum. Otherwise, light southeasterly winds will become more southerly and should increase through late morning with the potential for gusts between 25-35 mph expected. Lastly, a strengthening LLJ overnight could lead to a few hours of LLWS at KSUX to end the TAF period.

FIRE WEATHER

Issued at 359 AM CDT Mon Apr 20 2026

Near-critical to critical fire concerns are expected today. As mixing increases after daybreak, should see southerly to southeasterly winds quickly follow suit as we tap into a weak LLJ. This will eventually result in gusts in the 25-35 mph range by late morning. While the strongest gusts will likely be north of I-90, lower dew points will result in critical relative humidity (RH) values in the 13-25 percent range for most of the afternoon. Looking at short-range guidance, confidence is high in the strongest wind speeds and lowest RH values be slightly offset from each other. As a result, decided to mold our upgrade to Red Flag Warning to the areas where critical conditions could be truly realized through early evening. Nonetheless, near critical concerns will be possible for all other areas east of the James River Valley so make sure to avoid any outdoor burning and heed your local restrictions! Lastly, RH values maybe a bit slower to recover this evening mainly west of the James River Valley as we hang out to lower dew points in those areas.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from 11 AM this morning to 8 PM CDT this evening for SDZ039-040-055-056-062. MN...Red Flag Warning from 11 AM this morning to 8 PM CDT this evening for MNZ071-072-080-081-089-090-097-098. IA...None. NE...None.