The first significant winter storm, or any winter event for that matter, is on deck to affect the state tomorrow night. The primary jet streak, currently positioned from the northwestern United States through the midwestern US, will be aided by another jet streak extending across the Upper Mississippi Valley eastward. These jet streaks will aid in the development of widespread moderate-to-heavy snow across the area. By tomorrow morning, the system should approach the area and saturate the atmosphere and allow snow to begin falling across South Dakota and Nebraska by 7:00 a.m. This should originally by light, but as the day goes on and instability and forcing increases, moderate-to-heavy snow can be expected by mid-morning with snowfall rates of 1-2″ an hour possible.
This activity should continue on through the day. While road surfaces will likely be above freezing, melting moderate-to-heavy snow will cool these roadways and allow things to begin accumulating. The one concern that does exist and there is some uncertainty about is where the rain/snow line to sit. How quick things transition from rain to snow, especially in central and southern Iowa, will fluctuate the totals immensely. By evening, the entire state should be all snow however, with things quickly accumulating. Snow should be widespread and overspreading the state by night. Winds won’t be terrible, in the 10-15 MPH range with gusts to 30 MPH, but this could easily create whiteout conditions, and caution should be exercised.
As far as snowfall accumulations go, the heaviest will likely be on a line from Dubuque to Fort Dodge to Davenport, where 8-10″ is expected. Lighter totals can be expected outside of that. There may be some locally higher amounts and these totals are subject to changes as things go through into the morning.
A Winter Storm Warning has been issued for the majority of areas along and north of Interstate 80 up to Highway 18. These are where the confident high snowfall totals will exist. There are different start and end times for each area, the west starting earlier and the east starting later. Please check your local NWS forecast page for information on specifics in this regard. A Winter Storm Watch remains in effect for areas north of Highway 18 to the border and a little bit south of Interstate 80. Here the snowfall totals are less confident and the decision to transition these areas to a warning or advisory will be made at a later date. A Winter Weather Advisory is in effect for five counties in southeastern Iowa, where lighter totals will fall.
It’s important to emphasize the likely travel impacts that will be seen on Friday night. Snow will likely be falling during rush hour across much of the state, including the Des Moines metro. With this being the first snow of the season, and a significant one at that, people will always “forget” how to drive in the winter and cause accidents. Or someone has a Friday night party that they have to get to, and they go full highway speed, and they go hydroplaning off the road. Or low visibility causes you to miss a street sign and your jackknifed under a semi. It’s happened before, and all more likely to happen as this is the first event. There are some things you can do to help – just remember the three P’s: PREPARE for the trip; PROTECT yourself; and PREVENT crashes on the road. Check this article on OSHA on how you can do this better.
The next big story will be high temperatures in the mid 20s to low 30s behind the system on Saturday. Low temperatures will be brutally cold in the middle single digits to low teens for the state. This is definitely a big change, however it won’t stay like this, and temperatures should moderate later in the week.