textproduct: Sioux Falls

KEY MESSAGES

- Dense fog will remain a challenge into Saturday morning. The best chance for persistent fog/dense fog will be near and east of I-29, especially northwest IA.

- Above normal temperatures through Saturday turn sharply colder Sunday accompanied by northwest winds gusting 30 to 45 MPH. Sub-zero wind chills are expected Sunday night through early Monday.

- Light snow is possible on Sunday though amounts are favored to remain below an inch at this time.

DISCUSSION

Issued at 341 AM CST Fri Dec 26 2025

Dense fog persists across the area early this morning. Starting to see some erosion on the western side of the fog as a weak front pushes into the area. The front and associated weak cold air advection (CAA) looks to push the fog further eastwards, primarily along and east of the James River. Despite the weak CAA in place, soundings continue to show that a stout inversion above the fog layer will remain aloft for today. On top of that, 0-0.5km winds are out of the northwest this morning but will turn back to out of the south this afternoon as a weak surface high pushes through the area. Thus, think that fog and low level stratus will remain for the day today though do think that the fog will predominately lift to low level stratus by the late morning to afternoon timeframe. Locations east of the James River, and especially along and east of I-29 are most likely to see this continuation of fog and stratus as the best 0-0.5km humidity/moisture will reside in this area. That said, have left the current Dense Fog Advisory in place to account for the potential that new fog develops on its western fringes. Have left the time frame the same with the Advisory expiring at 9 am. Trends will be monitored through the morning hours and adjustments to the headline will be made as necessary. Could also see some slick spots out there mainly north of I-90 where temperatures will lower to near to just below freezing. At the same time, have lowered highs down to the upper 30s, 40s, and even 50s to account for the persistent cloud cover and fog. Temperatures will not move a whole lot during the day, except for locations across south central South Dakota where little if any fog and stratus is expected. This is also the same area that will see highs warm to the 50s. Thus, low temperatures will fall to the 30s overnight. Remaining stratus looks looks to drop back down to fog for locations mainly near and east of a Huron South Dakota, to Freeman South Dakota, to Sioux City, Iowa line tonight but the 0-0.5 km wind will start taking on a westerly component which should finally clear out the remaining fog and stratus overnight.

With low level flow continuing to have a westerly component to it, Saturday is looking to be the first day without widespread fog. That said, mid and high level clouds look to remain in place so skies will remain partly to mostly cloudy. However, with weak warm air advection (WAA) in place, high temperatures will warm to the 40s and 50s. While the day time hours will be dry, a strong cold front will push through the area during the evening to overnight timeframe. A strong shot of CAA will be delivered in the wake of this front while winds strengthen out of the northwest. Gusts look to be on the stronger side, reaching up to about 30-40 mph. At the same time, chances for precipitation look to return via the elevated front. However, precipitation looks to begin falling Sunday morning. With the front through the area by then, low temperatures will fall to the teens to low 20s overnight.

Mixed precipitation is possible though it appears to be most likely across parts of northwest Iowa where thermal profiles will be a bit warmer to start out Sunday morning. Despite a dry wedge of air between about 850mb to 650mb, think the forcing will be strong enough to saturate through this layer. Once profiles are saturated, precipitation will be primarily snow with minor accumulations possible. Currently think that accumulations will be light with most seeing below an inch of snow. The ensemble support this as they only show a 20-60% chance for exceeding an inch of snow. The GFS ensemble has the highest probabilities out of all the ensembles. The post frontal cold advective regime will persist for the rest of the day, continuing stronger northwest winds with gusts slightly strengthening to 30-45 mph across the area. High temperatures will be much colder, with highs only warming to the 20s to about freezing. Winds will be weakening through Sunday night but lows will be much colder, falling all the way down to the single digits. With breezy winds in place, wind chills will fall to about -5F to -15F across the area.

Monday will be the coldest day of the week with highs only warming to the teens and 20s. Temperatures will slowly start moderating to near seasonable beginning on Tuesday as weak WAA strengthens aloft. Broad northwest flow will take over aloft. This will keep dry conditions for the week along with near seasonable high temperatures in the 20s and 30s. Tuesday will be the warmest day with highs warming to the 30s and 40s. Low temperatures will also be near seasonable in the single digits and teens.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1131 AM CST Fri Dec 26 2025

IFR and LIFR conditions will continue, especially near and east of I-29 and particularly in northwest IA. While improvements are expected through the afternoon, IFR and LIFR conditions that do dissipate will likely return tonight as light south and southeast winds help advect back the low level moisture in Iowa. The near surface moisture is a bit more shallow than the previous couple of days, so confidence a bit lower, but still moderate to high for LIFR conditions.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...Dense Fog Advisory until noon CST today for MNZ089-090-098. IA...Dense Fog Advisory until noon CST today for IAZ001>003-012>014- 020>022-032. NE...None.