We are continuing to monitor the potential for a winter storm to impact the northern portions of the state beginning from late tonight and continuing through the overnight hours Wednesday.
At the surface, a low pressure center currently located over Wyoming is expected to deepen and shift east, locating itself over the Central Plains later this evening, and eventually into southern Iowa by Wednesday night. A cold front will overtake a dry line to the south of this system, with a northward-facing warm front extending off to the east and a trough to the northwest. In the upper-levels, a longwave trough entering the Plains this evening will deepen into a closed low by tomorrow morning over northwest Iowa. Deep-layer lift into the mid-levels will support widespread snow to the Highway 20 corridor. These synoptic features, as always, will play a role into the forecast at hand.
Precipitation will begin falling over northwest Iowa in the late overnight hours tonight, likely around the 2:00 to 3:00 hour. This will be in the form of freezing rain or sleet initially before precipitation gradually changes over from a mixed form to all-snow from north to south. The early morning commute will be impacted over our northern counties with a variety of light snow to a wintry mix of ice and sleet potentially on roadways. The heaviest snow will fall from north central to northeast Iowa from the mid-morning to early afternoon hours with snowfall rates up to an inch possible. It’s important to note that with some instability at play aloft, snowfall may be much higher in a localized setting, depending on where this all sets up.
Farther to the south, icing may be the bigger issue along the Highway 20 corridor during the commute periods as the mix-to-snow changeover will happen last here. A few factors hamper this, however. The first is that road temperatures are sufficiently warm enough to melt any precipitation initially. The second is the overall timing and extent of this icing may not be long enough to provide any substantial icing. Regardless, everyone along and near these areas should use a little extra caution and check road conditions before heading out Wednesday morning.
Our latest snowfall map has changed quite a bit from our first run on Monday. The overall axis of totals has been shifted on more of a west-to-east approach with a more defined and higher confident area of five-to-seven inches from north central to northeast Iowa. These amounts will still need to be revised tonight with locally higher amounts possible, but we are more confident with these than our last time around. Further in other areas north of Highway 20, three-to-five inches will be possible, with one-to-three north of Highway 30.
A Winter Storm Warning is in effect for much of north central Iowa from the early morning to overnight hours tomorrow. A Winter Weather Advisory is in effect for areas along and north of Highway 20. Winter Storm Watches remain for northeast Iowa where high confidence still does not exist with snowfall amounts. It’s important to note as well that blowing snow will be possible on the back-end of the system. Hazardous travel will continue into the evening commute for much of this area.
Stay tuned to the Iowa Weather Network for the latest information!