We are continuing to refine our forecast as we go through the day today. Upper-air analysis shows longwave trough currently over New Mexico; this is expected to push eastward. At the surface, the cold front mentioned in forecasts earlier today has setup from a surface low in eastern Ontario to north central Nebraska. Light rain is expected to begin late this evening and push southeast. As the cold front passes by, temperatures will plummet across the state and precipitation will begin to transition to all-snow. This will occur after 1 or 2 a.m. in the far northwest. Eastern Iowa will likely remain as all rain until at least noon or 1:00 p.m. with the far east staying that way until late evening.
There will be potential for some ice formation while precipitation transitions from rain-to-snow. This will be in the form of a flash freeze, where any slush or rain will freeze. Some freezing rain is also possible. This will create a very hazardous traveling situation initially on top of other threats. The heaviest snow will fall between the morning hours, roughly from 6:00 a.m. to noon. Snow will taper off in the early-to-mid afternoon, though wind chills will become a bigger threat towards nightfall, nearing -25° in some areas. It’s important to stress the biggest threat with this system: wind. Sustained winds will become north-to-northwesterly behind the front at 25-30 MPH with gusts to 40 MPH. This will lead to near-blizzard whiteout conditions across the warned area. Travel will become extremely dangerous during the morning hours on Thursday, with blowing snow issues continuing well into the evening hours. This will exasperate the moderate-to-heavy snow threat and potential ice issues.
Our latest forecast has brought the heaviest snowfall totals further eastward. We have removed the six-to-eight inch area, but amended the higher totals to five-to-seven inches from Osage and Cresco to Boone and Clarinda/Shenandoah, including Mason City. Further adjustments may be needed later this evening. A tight gradient will exist outside of this, with 3-5″ expected for Des Moines, Decorah, Carroll, and Council Bluffs, and 1-3″ for Waterloo. Winter Storm Watches have now been upgraded to Winter Storm Warnings from north central to west central Iowa, with Winter Weather Advisories for northwest, south central, and central Iowa. The warnings in the west will go in effect at midnight, east at 3:00 a.m., all expiring at 6:00 p.m. Thursday.
Please avoid driving Thursday if you can and make appropriate adjustments. We may see schools calling things off as early as tonight with businesses closing. If you must venture out, make sure to tell someone where you are going and take a winter survival kit with you. Stay tuned to the Iowa Weather Network for the latest information throughout this event.