A strong storm system continues to track across the region and will do so through Thursday. Rain, freezing rain, and sleet over the north part of the state will begin to transition to snow during the overnight hours. The heaviest snow is anticipated over northern Iowa where 8-12″ of snow is possible for some areas. A few tenths of an inch of ice is possible across north central Iowa. The snow combined with strong north-to-northeasterly winds will lead to near-blizzard conditions across the warning area.
We have made a few changes to our snowfall map this evening. The primary change is to add an enhanced snowfall area over far southeastern Minnesota and parts of west central Wisconsin. Snowfall totals of 12 to 15 inches will be possible in this area with Rochester looking at around 13″ and La Crosse 12″. Further refinements were made to the sharp snow cut-off line… as evident in Allamakee where both the 8-12″ and 1-3″ gradients exist. Aside, only minor adjustments were made. The 8-12″ area was expanded slightly to include areas where local totals over 8″ were possible. The heaviest totals are still expected across far north central Iowa, especially north of Mason City, where 9-10″ are possible.
A look at the radar as of 8:00 p.m. shows two distinct areas of precipitation worth monitoring. The first main portion is currently sitting from Colorado to Michigan, in the “deformation zone.” Currently, the only part of the state that is seeing consistent snow alongside this is in far northwest Iowa. Beyond that, much of northern Iowa is currently covered by a freezing rain or sleet – freezing rain accumulations of a couple tenths and a couple inches of sleet will be possible with this. With this area of mixed snow and ice, roads are beginning to be effected, as evident by the road conditions map above from 7:45 p.m. or so. I-29 around the Sioux City area is partially covered with ice with many other roads partially covered with precipitation as well.
To the south, a line of showers and thunderstorms exists from northwest Iowa to the southern end of Kansas City. This activity prompted a Tornado Watch to be issued earlier with a few Severe Thunderstorm Warnings as well (due to some quarter size hail). This convective band is speeding off to the northeast and will merge with the primary arc of snowfall in the deformation zone later tonight. When this occurs, an enhancement of snowfall rates can be expected with the added convective elements and instability. It’s also worth noting that thundersnow or thundersleet will be possible during this period as the band with lightning merges with the primary arc.
Precipitation should continue to be mixed across northern Iowa for a while here this evening as temperatures remain warm aloft. However, as the atmosphere cools tonight, we should see a transition to snow. As the convective band merges in, snowfall rates may approach one-to-two inches per hour.
A Winter Storm Warning remains in effect through Thursday morning for much of northern Iowa, primarily in the northwest. A Winter Weather Advisory is in effect outside of this for areas where the totals will be somewhat lower. It’s important to emphasize that one of the biggest threats with this event will be the continued windy conditions – sustained at 20-30 MPH with gusts to over 40 MPH at times. This will create a dangerous situation with whatever snow falls and will lead to near whiteout conditions. Travel will be extremely hazardous overnight and we would strongly recommending avoiding such travel until the mid-morning.
Stay tuned to the Iowa Weather Network for the latest updates!