textproduct: Sioux Falls

KEY MESSAGES

- Growing potential for areas of fog and drizzle today through Christmas Day, mainly along/east of MN/IA Highway 60 today, then expanding as far west as I-29 tonight into Thursday. A light glaze of ice is possible near to north of I-90 tonight into Christmas morning as temperatures fall below 32F.

- Temperatures remain above normal through the end of this week, but we turn windy and colder this weekend, with wind chills likely dropping below zero by Sunday morning.

- Precipitation chances Friday-Saturday are low, but may have to watch for scattered flurries Sunday as colder air moves in.

- Elevated fire danger will be possible on breezier days in snow- free areas, mainly across south central South Dakota through the Missouri River Valley.

DISCUSSION

Issued at 335 AM CST Wed Dec 24 2025

Main focus for this forecast period will be today into Christmas Day, which has turned a bit more challenging due to a growing potential for fog and drizzle. Increasing low level moisture looks to become trapped beneath a strong temperature inversion, mainly in our eastern counties today ahead of a subtle boundary which moves east toward the MN/IA Highway 60 corridor by sunset. The more abundant low level moisture is already present in our far east where we have some dense fog early this morning. The Dense Fog Advisory has been extended through 8 AM CST, but weak mixing ahead of the boundary should allow this fog to lift a bit after sunrise.

Increasing moisture advection in a southerly flow beneath the continued warm advection aloft, combined with additional snow melt moisture from our remaining deeper snow-pack in northwest Iowa, will serve to reinforce this low level moisture through the afternoon, which is then expected to expand toward I-29 and perhaps beyond tonight in a prevailing easterly flow. Areas of dense fog could again develop tonight into Christmas morning, though this is a lower confidence forecast than the more general fog/stratus which is expected.

Also a lower confidence forecast is the potential for drizzle, mainly due to uncertainty in the thickness/depth of the low level moist layer. However, several CAMs show spotty light QPF this afternoon through Christmas Day with forecast soundings supporting a moist layer depth approaching 1KM. As such, felt it prudent to introduce some low pops and drizzle mention given potential impacts on holiday travelers. This is especially a concern by late evening through midday Christmas Day when areas near to north of I-90 should see air temperatures drop to near or below freezing. As we saw with our light rain event earlier this week, even if air temperatures are just above freezing, road surface temperatures could still be cold enough to allow for light icing. Those with travel plans tonight into Christmas Day will want to monitor weather and road conditions before heading out, especially if heading north where sub-freezing temperatures are more likely.

This moisture should slowly be scoured out west to east Thursday night as another weak boundary and associated mid-level wave move east across the Dakotas/Minnesota. Unlike today and Christmas Day which have trended cooler over the past several days, forecast temperatures for Friday and Saturday are trending upward with highs in the 40s and 50s.

This is ahead of a very strong cold front and its associated upper trough which pushes across the region Saturday night. Post-frontal northwest winds will become gusty, but not as strong as we have seen with the past couple of potent cold fronts. Soundings suggest winds at the top of the mixed layer are in the 40-45kt range, which could support isolated advisory level winds. Nighttime temperatures fall back into the teens and single digits early next week, with gusty northwest winds pushing wind chills into the single digits and teens below zero. Temperatures only recover into the teens/20s for highs Sunday and Monday, and if we have any stratocu development, 925MB temperatures of -10 to -18C could support scattered flurries.

This cooldown looks to be rather short-lived, though, with warmer air returning to the forecast area by the middle of next week.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1137 AM CST Wed Dec 24 2025

An IFR stratus deck is located along a KMDS to KFSD to KSUX corridor and points east, with patchy dense fog underneath. This area of stratus will largely stay put through the afternoon, though it currently looks like the western edge of it near KSUX will erode enough late this afternoon to allow for a brief return to VFR conditions there, with chances of this occurring around 50-55% at KSUX. This area of stratus will expand westward tonight and cover much of the forecast area through tomorrow morning before moving eastward by the end of the period. Dense fog will also expand especially across northwest Iowa and adjacent parts of southwest Minnesota tonight, but dense fog is not expected at the TAF sites at this time.

Any area under stratus looks to be capable of some drizzle, especially along and east of US Highway-81. With temperatures dropping to freezing tonight mainly north of I-90, some freezing drizzle will be possible that could result in a light glaze of ice. Right now, this threat looks to stay north of KFSD and east of KHON, but trends will be monitored. Winds will be light for the remainder of today into tonight, with southeasterly winds increasing through tomorrow morning.

FSD WATCHES/WARNINGS/ADVISORIES

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