textproduct: Sioux Falls

KEY MESSAGES

- Dense fog with visibility 1/2 mile or less is expected to slowly improve through the morning. A Dense Fog Advisory remains in effect for locations along and east of I-29 until 9 am this morning. Patchy slick spots are possible mainly north of I-90 as temperatures fall to near to below freezing.

- Above normal temperatures today will turn sharply colder on Sunday accompanied by northwest winds gusting 30 to 50 MPH. Sub-zero wind chills are expected Sunday night through early Monday.

- Light snow is likely on Sunday. Amounts have trended upwards up to about 1-2 inches with isolated higher amounts up to about 3 inches possible east of I-29. The strong winds with the falling snow will lead to some blowing snow across the area.

DISCUSSION

Issued at 357 AM CST Sat Dec 27 2025

Dense fog persists generally along and east of I-29 early this morning. Low level flow between 0-0.5km is beginning to turn out of the southwest and has begun advecting drier air into the area. Thus, am expecting the fog to continue to erode and also push off to the northeast through the rest of the night. The Dense Fog Advisory remain in effect through 9 am this morning though have trimmed the western extent of the Advisory. However, with temperatures falling to near to below freezing north of I-90, slick spots from the fog is possible this morning. Once the fog pushes northeast/east of the area mid and high level clouds will persist for the rest of the day. Weak warm air advection (WAA) will be in place which will allow high temperatures to remain above average this afternoon, warning to the 40s and 50s, warmest along the Missouri River Valley. Could see some redevelopment of fog and low level stratus late this afternoon and evening mainly east of I-29. A strong cold front will begin to push into the area during the evening hours. A strong shot of cold air advection (CAA) will be delivered to the forecast area in the wake of this strong front. This will quickly ramp up winds out of the northwest while cooling temperatures at a much more rapid rate. Winds look to gust up to 30-40+ mph for the overnight hours, strongest over south central South Dakota.

At the same time, precipitation will begin to return to the area via the elevated front. Precipitation looks to begin around midnight as mixed precipitation across central and south central South Dakota due to initial dry air in the mid levels along with temperatures in this layer being just above freezing. This will result in mixed precipitation as precipitation begins to fall before the strong lift from the elevated front cools profiles to saturation, turning the main precipitation type to snow. This will be driven by the frontogenesis (FGEN) between about 850 to 700 mb. At the same time, sufficient omega (upward motion) will be present in the dendritic growth zone (DGZ) on the order of about 15 microbars/second. This will be a quick moving round of precipitation though as it will quickly race eastwards through the rest of the night and through Sunday morning.

Precipitation will be just about all snow for the beginning of Sunday morning. The snow and the associated strong wind gusts will be quickly progressing eastwards through the rest of the morning hours. The falling snow and strong winds will result in some blowing snow across the area. How low visibilities will get remains somewhat uncertain at this time given how there is little to no snow pack across the most of the area, expect over parts of northwest Iowa and southwest Minnesota. As alluded to in the previous discussion, these winds are still a good bit weaker than out previous blowing snow event. The bulk of the snow will push east of the area by about noon though light snowfall could continue across parts of southwest Minnesota. In terms of totals, snowfall amounts have increased a little bit up to 1-2 inches with isolated higher amounts up to about 3 inches possible east of I-29. However, do want to stress that there remains some uncertainty in this potential as some of the 00z and 06z models have come in with little snowfall. Given this uncertainty, have held off on issuing any Winter related headlines, but will see what the 12z guidance comes in with as Winter headlines may be needed if confidence increases.

The rest of Sunday will be breezy if not windy with gusts remaining strong at 40-50 mph. This will continue blowing snow chances throughout the day along with the potential for wind headlines being needed. Highs will be much colder on Sunday, only warming to the upper teens to low 30s. The winds will be slow to weaken as they will remain breezy through the night. With low temperatures falling to the single digits this will make for cold wind chills down to about -10F to -20F Sunday night.

Monday will be a cold day with a cold surface high in place. Highs will only warm to the teens with lows falling to the single digits overnight. Tuesday will see a brief warm up with highs warming back to the 30s and 40s before temperatures trend back to near seasonable for the rest of the week.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1034 PM CST Fri Dec 26 2025

IFR and LIFR fog/stratus has continued to expand into the James River Valley, and will linger through Saturday morning (longest for areas east of I-29). Although there may be some brief improvements, expect IFR and lower conditions to prevail. VFR conditions are expected to return to end the period, although patchy MVFR and lower fog may redevelop toward late Saturday evening east of I-29.

Southerly winds prevail through much of the period. LLWS is possible around daybreak into mid morning Saturday as a very narrow jet streak moves across the area; maintained mention at KFSD for now. Expect surface winds to shift late Saturday afternoon into the night behind a front, becoming northwesterly through Saturday night.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Dense Fog Advisory until 9 AM CST this morning for SDZ040-055- 056-061-062-066-067-071. MN...Dense Fog Advisory until 9 AM CST this morning for MNZ071-072- 080-081-089-090-097-098. IA...Dense Fog Advisory until 9 AM CST this morning for IAZ001>003- 012>014-020>022-031-032. NE...Dense Fog Advisory until 9 AM CST this morning for NEZ014.