A major winter storm is expected to impact the area beginning later tonight and into early Wednesday morning. Models have come into somewhat better agreement over the last 24 hours on tracking the upper level cyclone out of the southwest and into the central Plains later today via a fast upper level jet at 250 mb. As this system passes by, significant snowfall is expected with high winds across much of the state.

We will likely begin seeing impacts as soon as tonight as light snow is expected to begin as soon as this afternoon south of I-80 and west of I-35 (rain to the east of I-35). Snow will quickly overspread the state by evening with heavy snow developing throughout the overnight hours. The southeast will be a tricky one to watch with a dry slot expected over the area and the 32° freezing line causing havoc on where to sit with the highest snowfall totals. Much of the southeast may end up receiving little-to-no snow at all as temperature profiles remain above freezing here.

By the early morning hours on Tuesday, the heaviest snow will be falling. This will likely be concentrated across northwest Iowa where amounts of up to two inches an hour will be possible. The entire state will likely be completely overtaken by some form of precipitation, with snow for the most part and rain or a mix for the southeast. The worst of the storm will ramp up during the afternoon and evening hours in the northwest part of the state where 20-30 MPH sustained winds with gusts to over 40 MPH will create extremely dangerous to impossible travel. The greatest impacts will be seen here as this is where the heaviest snow will fall and the highest winds will be.

Snow will continue through the evening before snow tapers off through the overnight hours. It would not exactly be surprising to see some light snow remaining through the early morning hours on Wednesday in the northern sections of the state. Nonetheless… any snow that fell the night before will continue to blow as winds continue through the early hours on Wednesday. Along with the presumptuous cancellation of schools and businesses and events on Tuesday, Wednesday may be included in this as well (primarily across the north) where the blowing snow will continue. Details on this will be ironed out as we go through the event.

As far as amounts go… we have gotten a little bit better confidence in totals over the last few days. The preference we have gone with, alongside the local weather service offices and Weather Prediction Center, would be to go with a blend between the American GFS and the European ECMWF. A few other traits from other models were picked out. New with this forecast package as you can see below is that we have expanded the 10-12″ area across much of northwestern Iowa. The eight-to-ten inch area was refined and cut down to mainly the northwestern sections of the state. This is where the Blizzard Warning and Winter Storm Warnings exist.

There are a couple of important notes to go along with this. The first and foremost is that amounts over 10″ are still possible in the area where we have eight-to-ten inches outlined. The primary reason that we did not increase totals for this area is because we were not confident enough with model disagreements over these high totals. Models have generally agreed on the area we’ve outlined to get totals more than 10″. Other areas to the east were not as consistent or disagreements were seen, and we did not add it in.

Another important note would be that amounts can be expected to be locally higher than the area we have outlined. There will be some instability lingering around that will lead to convectively-enhanced snowfall banding which easily causes snowfall totals to rise. Amounts of up to 15 or 16 inches could be possible locally, depending on where this enhancement occurs. Our current idea on where this will occur is generally between north central and central Iowa. It would not be surprising to see snowfall rates of near or above three inches in this area.

The final note of mention would be across southeast Iowa. We currently have a soft gradient going off into the southeast. While models have been trending a sharper gradient… basically a straight cut between the northwest and southeast halves of the state… we are sticking with the European solution of keeping totals farther southeast. We still do believe that temperatures will probably drop at some point during this event to where some snow will be able to fall. In any regard, this is one area that you can expect to be adjusted as we go down the line.

It’s important to highlight the blizzard threat here across northwestern Iowa. 10-12″ is something that is manageable, and it can be expected here once or twice a season. But we have not seen a blizzard of this magnitude for a few years. 10-12″ (potentially more) with 30 MPH sustained winds with gusts to 40-45 MPH is debilitating. Roads will be extremely dangerous to travel on and next to impossible with road closures presumed. Whiteout conditions are likely. You will essentially be stuck at home.

This will effect both the morning and evening commutes on Tuesday and potentially the morning commute on Wednesday. All-in-all… this is a dangerous situation across the Blizzard Warning area. Preparations should be rushed to completion over the 12 hours. If you must travel… please bring a winter survival kit with you. Any events planned for Tuesday should be canceled or postponed.

National Weather Service offices across the state have upgraded Blizzard and Winter Storm Watches to either Blizzard Warnings, Winter Storm Warnings, or Winter Weather Advisories. The worst area right now to be would be in northwestern Iowa where strong winds with 40-45 MPH gusts, in combination with the 10-12″ of snow expected, will create downright treacherous travel conditions across the area. Blizzard Warnings are in effect here for this reason.

In areas where wind is not as much of a threat, a Winter Storm Warning has been issued. Winter Weather Advisories are posted on the southeastern edge of this where the overall threat is lower. The only oddball out of the bunch would be Lyon County in far northwestern Iowa which remains under a Blizzard Watch – the NWS office in Sioux Falls is waiting to become more confident in snowfall totals and wind speeds here before the determination is made on an upgrade.

The bottom line: a major winter storm or blizzard is expected to begin impacting the state tonight through early Wednesday morning. Significant blizzard conditions are expected primarily in northwest Iowa where as much as 12″ of snow and 25-35 MPH sustained winds (gusts to 40-45) will lead to extremely dangerous to potentially impossible travel.

Blizzard Warnings are in effect for the worst impacted areas, Winter Storm Warnings for the areas with less of a wind threat, and Winter Weather Advisories for those with a lesser overall threat.

Any preparations should be rushed to completion today with everyone hunkering down as we weather out the storm.

Stay tuned to the Iowa Weather Network for the latest information throughout this event.