textproduct: Des Moines

KEY MESSAGES

- Strong, gusty winds developing tonight with wind gusts over 50 to around 60 mph likely. High Wind Warning and Wind Advisory in effect.

- With reported snow pack character being generally wetter, blowing snow chances are lower, but not zero. Winter Weather Advisory covers blowing snow as well as the chance for narrow bands of snow, which are most likely over northern into eastern Iowa overnight.

- Active pattern continues through the rest of the week with additional snow chances and colder air returning.

DISCUSSION

Issued at 304 PM CST Tue Dec 9 2025

While the forecast through the weekend remains active beneath the northwesterly flow with plenty of shortwave energy, the next 18 hours or so will feature a plethora of sensible weather conditions. The shortwave trough, or clipper, that will bring these conditions is moving over North Dakota this afternoon with a surface low pressure over eastern North Dakota. This has led to strong low level warm air advection over our state, which has lifted temperatures above freezing at all but our far northeastern forecast area at this hour. This warming is outpacing our forecast highs from yesterday afternoon and this morning, which will be important to discuss later. Cross sections show that the column is trying to saturate over northern Iowa, and this is also apparent in the low dBZ radar echoes there with no surface observed precipitation. There still remains a low risk of freezing rain over far northern Iowa, but temperatures will be warming into this evening so expect a transition to rain. While road temperatures and surfaces are below freezing, which may allow for a light glaze, again temperatures should be rising above freezing mitigating widespread impacts.

As the surface low moves to near the western shores of Lake Michigan this evening, a cold front will plow through the state. The low level cold air advection right behind this front along with the stronger kinematics from the passing low will yield to quickening winds this evening from northwest to southeast as winds become from a northwesterly direction. Looking at a variety of models, winds at 850mb do not look nearly as strong as yesterday at this time so the ceiling of max winds is lower. The 0z HREF 10m ensemble mean showed wind gusts of 50 to 55 mph from roughly Highway 63 westward with the core of gusts of 55 to 60 mph west of Highway 71. A westward trend in the core of the strongest winds did continue in the 12z HREF data. Further, 12z HREF showed a 12 hour probability of winds of 50 mph or higher at 90 to 100% over almost our entire forecast area of central Iowa with a probability of gusts of 58 mph or higher at 50% or higher north of roughly I-80 and generally along and west of I-35. Given the location of the core of the strongest winds and gusts, have issued a High Wind Warning for roughly the same area with at least a few gusts over 60 mph expected. South of the I-80 counties and near Highway 63 eastward, confidence in wind gusts over 58 mph is lower, and have opted for a Wind Advisory for those areas.

The concern yesterday and this morning on the forecast desk was to what degree would these winds be able to unlock the snow pack causing blowing snow and possible ground blizzard conditions. As mentioned earlier, temperatures are higher than forecast and with wet bulb temperatures above 32 degrees already from Algona to Marshalltown and points southwest, this is changing the character of the snow pack on the ground. With low level WAA continuing into this evening, this should make it to maybe all but the far north or northeast forecast area. So, how has the snow pack changed? Yesterday, the snow was powdery at our office, but at noon today, the 4" snow depth was overall wet throughout and unlikely to blow. The Waterloo snow observer stated the snow was sticker than yesterday. USGS field crews in New Providence/Hardin County reported an 8" snow depth with a 'wet texture' and 'firm when you step on it'. As they returned to their office in Fort Dodge, the remarked that the fields are a little barer and the snow has a 'polished look to the top'. At the USGS Fort Dodge field office, snow depth was 15" and a 'lot of it has melted and refroze on top...current conditions are super wet feeling snow.' The emergency manager in Webster County also stated that just below the wet layer it seemed 'light and fluffy'. In Crawford County, the emergency manager relayed from their secondary roads that the snow is 'wet and heavy due to some melting' and thinks it will 'crust over and not blow much'. Now, farther north, the snow character seems a bit more blowable. The Emmet County emergency manager report a 8" snow depth with the snow character powdery. This is not surprising given the warmer air is just starting to reach this area. Our expectation is that with so many hours with temperatures and wet bulbs above freezing, the depth of crust will largely keep the snow pack locked in and/or too wet to be able to be lofted. While some surface blowing or perhaps drifting snow is possible, the chances are too low to raise a Blizzard Warning at this time. There is a chance that a few areas may not have as deep of a crust and may allow for the snow pack to be released. This would most likely be in the deepest snow pack, which is roughly along the Highway 20 corridor per NWS COOP observers and NOHRSC snow analysis, or over far northern Iowa where the duration of above freezing conditions will not be as long. This is roughly the area highlighted by the Winter Weather Advisory. For the Waterloo/Cedar Falls area, have grouped in wind advisory like wording in collaboration with La Crosse and Quad Cities offices to try to keep headlines simpler over that DMA.

The Winter Weather Advisory also covers the potential of convectively driven snow showers. As the second push of cold air advection arrives about 6 hours after the first - roughly after midnight - along with a strong pressure rise couplet, low level lapse rates will steepen. While models pushed the low level instability and saturation into the dendritic growth zone (DGZ) yesterday and last night, today's data is less certain on how widespread this potential will be. The NAM's traditional snow squall parameter is not pinging at all, which is in contrast to yesterday, but does still shows potential in the 1km version. The FV3 cores are more aggressive in the snow squall potential farther south, but overall models point to northern into eastern Iowa as the area if snow squalls are to occur.

As this clipper departs Wednesday, winds will diminish, but a stream of energy in the northwesterly flow will reside over the area. Thus, the next clipper will be approaching by the day Thursday with low level thermodynamic forcing moving over the region. With the surface low tracking over southwest Iowa, this will place Iowa on the cold and snowier side of the clipper. Cross sections show moderate lift up to and into the DGZ. This may bring a few inches of snow to north central into eastern Iowa later Thursday into Thursday night. Colder air will follow behind this clipper with yet another clipper bringing accumulating snow into the state by Saturday.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1148 AM CST Tue Dec 9 2025

VFR conditions are forecast to deteriorate later this afternoon into this evening across the terminals. First, there is light precipitation that may pass over northern Iowa with highest chances at MCW, including a low chance of a short period of freezing rain with temperatures rising causing a transition to rain. At FOD and ALO, just light rain, if anything, is forecast. As the precipitation slides out this evening, very strong and gusty winds from the northwest will spread over the state along with MVFR ceilings tonight. Wind gusts over 40 knots are likely at all terminals and a few gusts to or a bit over 50 knots are possible, especially over western and northern Iowa. Low level wind shear may result and have left previous forecast LLWS; however, the vector difference may not be great enough for true LLWS and this may end up being more turbulence. With the strong winds, visibility restrictions may occur if the snowpack on the ground is able to be unlocked and blown and have this advertised at MCW, FOD, and ALO to varying degrees. Narrow, intense snow bands, or snow squalls, may develop after 6z until around 12z, with this shown at PROB30 groups over northern Iowa. Ceiling restrictions will persist through the end of the period.

DMX WATCHES/WARNINGS/ADVISORIES

High Wind Warning from 9 PM this evening to 9 AM CST Wednesday for IAZ004>007-015>017-023>026-033>037-044>049-057>060. Winter Weather Advisory from 9 PM this evening to 6 AM CST Wednesday for IAZ004>007-015>017-023>028-034>039-048>050. Wind Advisory from midnight tonight to 9 AM CST Wednesday for IAZ061-062-070>075-081>086-092>097.