textproduct: Sioux Falls

KEY MESSAGES

- Dense Fog This Morning: Areas of dense fog will impact the morning commute across the Coteau and Buffalo Ridge (east central SD/southwest MN) and south-central South Dakota with visibility 1/4 mile or less at times. Fog should improve from south to north after 9-10 AM, persisting longest across the Buffalo Ridge.

- Extreme Temperature Ranges Today: A stalled cold front will create a sharp contrast in temperatures today, ranging from 50s near Huron/Chamberlain, to 80s east of IA/MN Highway 60.

- Dry Mid-Week With Rain Returning Thursday: Near normal temperatures and dry conditions likely through Wednesday. Scattered rain by Thursday with a 60% probability of greater than 0.10" of rain by Friday.

- Turning Colder: Temperatures into next weekend fall below normal into the 50s.

UPDATE

Issued at 435 AM CDT Mon Oct 12 2026

Observations/web cams show dense fog becoming more widespread across the higher elevations of the Coteau des Prairies/Buffalo Ridge in east-central SD/southwest MN early this morning. Fog is likely more prevalent in these areas due to stratus lowering to the ground beneath a strengthening surface-based inversion, and thus it may persist a bit longer than standard radiation fog, especially in the highest elevations between Brookings and Marshall/Tracy. As such, have issued a Dense Fog Advisory for these 3 counties through 1 PM this afternoon, and buffered this area to the west and south with an advisory through 10 AM. Will continue to monitor areas west of the James River Valley as some guidance suggests dense fog will develop in higher areas west of Mitchell to Tyndall. Seeing isolated low visibility on web cams, and if this persists and continues to expand, may need to expand the advisory into this area as well.

Otherwise, cloud cover and associated temperature trends will be the main focus today. Subtle surface low located between Sioux Falls and Sioux City early this morning with a frontal boundary extending northeast near the IA/MN state line into south-central MN. Models suggest this will remain nearly stationary or perhaps retrograde a bit to the northwest this morning in response to a mid-upper level wave lifting northeast across the Dakotas. The eventual location will determine where a very tight temperature gradient will be located by midday/early afternoon, before the system makes a more pronounced eastward progression and brings falling temperatures to northwest Iowa later in the afternoon. Currently have highs ranging from near 60F Huron to Chamberlain, to lower-mid 80s near and east of IA/MN Highway 60. However, for many locations, this is a lower confidence temperature forecast with a tighter-than-advertised gradient expected but difficult to place.

Lift from this wave will likely trigger areas of drizzle in the thicker stratus across our northern counties today, with higher chances for appreciable rainfall remaining north of our CWA.

DISCUSSION

Issued at 1242 PM CDT Sun Oct 11 2026

THIS AFTERNOON: Another very warm day across the Tri-State area as temperatures continue to rise into the 80s. Further west however, a frontal boundary has stalled from Gregory to near Huron and north of Watertown. Northwesterly drainage winds are doing what they like to do and keeping temperatures cooler with considerable stratus through central and northern South Dakota. This front will stay nearly stationary into late afternoon, perhaps sliding a bit further southeast into the MO River valley. Temperatures will likely fall short of records in most locations, however gusty winds greater than 25 mph in NW Iowa could promote elevated agricultural related fire risks to sunset.

TONIGHT: My confidence is rising that the cold front will continue slipping southeast through the overnight hours, though just how far southeast is still in question. Should the front reach into NW Iowa and NE Nebraska, then a significant amount of cooler air may drain southeast knocking temperatures further into the upper 40s to lower 50s. Anticipating stratus to reform late tonight, especially in areas from Gregory to Brookings and Marshall where cool air will continue to drain.

MONDAY: We're likely to start the day with quite a bit of stratus in the CWA, potentially as far SE as Sioux Falls. A mid-lvl shortwave tracking through the Dakotas mid-morning to mid-day will accomplish two tasks, lifting the cold front very slightly back northwest, but also pinning in cooler and moist air in the drainage flow on the backside of the front. The end result may be an extreme temperature gradient of the 80s in Sioux City and Storm Lake/Spencer, to the 50s in Huron. Latest NBM will not catch these mesoscale temperature gradients, so have adjusted and blended in higher resolution guidance. However the gradient may still be more defined than the current forecast suggests. While moisture is lacking aloft, a few sprinkles to light rain showers could develop through central and northeastern SODAK in the day. Have also manually pushed up stratus through mid-day west of I-29.

MONDAY NIGHT: Northwest winds continue through the overnight hours into Tuesday as quite a bit of cooler Canadian air filters southeast This will push overnight lows into the 40s in several areas with some questions on cloud cover potential lingering.

TUESDAY-WEDNESDAY: Latest forecast guidance continues to trend drier with precipitation chances during the middle of the week. The amplitude of mid-lvl ridging through the Central and Southern Plains may be strong enough to prevent any cut off energy in the Four Corners from moving eastward as quick as guidance hinted yesterday. The end result will be dry conditions Tuesday and Wednesday with highs near or even slightly above seasonal normals.

THURSDAY-SATURDAY: The cutoff energy in the Four Corners may eventually phase with a secondary northern stream trough crossing the Canadian Rockies by Thursday. Increasing warm advection and moisture return ahead of this trough combined with mid-lvl dPVA may result in the development of scattered rain by Thursday. Latest ensemble probabilities continue to suggest light rain amounts with 60-70% probabilities of >0.10", but only 30% probabilities of more than 0.50". High pressure will quickly swing southeast into the Plains for Friday and the upcoming weekend. Temperatures for at least a couple days may cool below seasonal normals, but only slightly.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1250 PM CDT Mon Oct 12 2026

VFR conditions prevail east of I-90 to start the period, while IFR/LIFR persist to the west, separated by a frontal gradient. The front continues a slow eastward push bringing MVFR across eastern areas. Localized IFR remains possible post-front if westerly flow does not break up the cloud deck. Winds will remain variable along the boundary before shifting to a broad northerly flow across the CWA by the end of the period.

FSD WATCHES/WARNINGS/ADVISORIES

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