textproduct: Sioux Falls

KEY MESSAGES

- Fog, with some dense fog and visibility below one quarter mile, is expected again tonight.

- A strong storm system brings widespread showers and a few thunderstorms to the region Thursday night into Friday. Chances of more than a half inch of rain are over 50% from about Yankton to Windom southeast.

- A few strong to severe storms are possible Thursday night through Friday. Main risk area is south of I-90, with large hail currently the main hazard.

- Temperatures falling behind the cold front Friday night into Saturday causes rain to switch to snow. Light to possibly moderate accumulations possible from south central to northeastern South Dakota. Confidence in exact amounts is low.

DISCUSSION

Issued at 240 AM CST Wed Mar 4 2026

Dense fog with visibility below one quarter of a mile continues to expand this morning. Observations and local DOT cameras show that conditions are quite variable over short distances, so be prepared for quickly changing visibility through the Wednesday morning commute. Temperatures near to below freezing may lead to some isolated slick spots. Dense Fog Advisories are in effect for much of the area through 8 AM CST, but would not be surprised to see continued expansion and extension through the morning hours if trends continue. Fog and stratus may be slower to clear than some of the current guidance suggest, which could lead to temperatures a couple of degrees cooler than current forecast. Highs still warm well above average into the 50s and 60s.

Can't entirely rule out a stray sprinkle this evening south of US Hwy 20 and into northwestern IA; however, confidence is low enough in occurrence with dry sub cloud layer and better forcing to the southeast as the wave moves through IA to keep out of the forecast. Stratus and fog, possibly dense fog, is expected to develop again late tonight into Thursday morning. Temperatures near freezing with fog could again lead to some slick spots into the Thursday morning commute.

Mid and upper level trough ejects out of the Rockies beginning Thursday and through the day Friday. Increasing southerly flow ahead of the cold front allows temperatures Thursday to warm into the 60s. Strong winds especially west of I-29 and dry conditions will lead to some elevated fire danger. Humidity values above 30% should help limit any near critical conditions, but Very High fire danger is expected.

As the trough moves east into Thursday night, chances for convection increases. LLJ strengthens as lee cyclogenesis occurs across the western portions of NE/KS. For us, that means ample moisture advection as southerly flow aloft and at the surface continues. Although we'll have the LLJ in place and strengthening overnight, one question remains is how much instability there will be. Guidance shows most of the area with around 500 J/kg of MUCAPE Thursday night into Friday morning, although there are pockets of over 1000 J/kg early in the overnight across northwestern IA. Given all this, 0-6 km bulk shear around 35 knots, and steep mid level lapse rates over 7 deg C/km, expect storms to be elevated with the main threat being large hail with possibly an occasional severe wind gust. Surface cold front continues to move east through Friday, so may see the severe threat continue into the day. Bulk shear and lapse rates remain fairly similar, but may see instability increase depending on the timing of the front. Both of these risks are covered by SPC Day 2 and 3 outlooks.

As for rainfall amounts, amounts will vary quite a bit with the convection. Ensemble guidance continues to show low to moderate (25- 60%) chances of exceeding 0.5" of liquid through Saturday morning, highest across northwestern IA and east (over 50% along and east of a Yankton to Windom line).

Still some timing differences on the front, but falling temperatures will allow for precipitation to change to snow Friday evening/night with light to possibly moderate accumulations possible - mainly from northwestern NE to south central SD to northeastern SD into MN. Accumulations will be highly dependent on how quickly cold air sweeps in, so definitely keep on eye on things if you have regional travel plans into Saturday. Accumulations may be short lived, depending on how much we recover with a quick surface and thermal ridge sliding through Saturday.

Warmer temperatures and dry conditions continue through the week. Precipitation chances return early to mid next week, although details are still unclear.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1144 AM CST Wed Mar 4 2026

Stratus is beginning to break up and ceilings lift as of TAF issuance. Currently there is a mix of VFR down to LIFR ceilings. These will slowly improve through the early part of this afternoon. Winds are from the south and breezy with gusts of 20-25 kts for areas west of the James River and north of South Dakota 34. Elsewhere winds are generally light. Winds are expected to decrease late this afternoon and become more southeasterly.

Confidence is increasing for stratus and fog redeveloping tonight, the biggest question is where. Current NBM guidance keeps fog along and east of I-29. CAMs guidance and soundings both indicate that fog is possible as far west as central South Dakota. Winds out here will remain slightly elevated, and this may impede the fog development. However, confidence is high enough to have put a mention of MVFR visibility in KHONs TAF for Thursday morning. KFSD and KSUX confidence in fog is moderate to high, and have included mention of IFR ceiling and visibilities.

Southeasterly winds increase through the late morning Thursday, peaking around mid day with gusts of 24-27 kts. Highest gusts will be west of I-29. To the east gusts peak between 18-22 kts.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...None. NE...None.