A powerful storm system is currently on track to affect the region beginning Wednesday morning and continuing through Thursday morning. Significant snow totals are possible over far northern Iowa, potentially along the lines of up to 12 inches. A marginal risk of severe weather also exists for southeastern Iowa for Wednesday evening.

A closed upper-level low will move eastward into the area over the next 24 to 48 hours with a deepening surface low. A boundary will be draped across the central part of the state on Wednesday, allowing for a sharp temperature gradient, potentially along the lines of 30-40° or so. Low-to-mid 30s will be seen for highs north to nearly 70 in the south.

Models have come into a much better consensus with the last several runs, as far as the track of the storm goes. Previously, over the past couple of days, there have been two tracking possibilities – one that’s more to the northwest, as suggested by the American GFS, American NAM, and Canadian GEM models. Another, the European ECMWF, has been more to the southeast. With the European being one of the larger models, we could not discount that possibility, though we were heavily leaning away from it under the consideration that it was the only outlier of the suite. However, one thing that is boosting our confidence this morning is that the ECMWF seems to be shifting further northwest, in line with the three models mentioned earlier. This is giving us medium-to-high confidence in the forecast track that we currently have, with the low navigating farther northward.

Rain will likely begin developing across the state early Wednesday morning and overspread the state by early afternoon. Some scattered strong thunderstorms may develop across southeastern Iowa where a marginal risk of severe weather exists. Strong shear and forcing will be flowing into the area from the southwest with some limited instability available. However, the overall severe threat will be minimized by the lack of moisture available, with surface dew points being in the 40s and 50s for most. This takes away a big component needed for severe weather to occur. Although…with any elevated stronger cells in the region in the late afternoon and early evening…isolated cases of large hail and some gusty winds will be possible. A tornado or two also cannot be ruled out with low-topped thunderstorms. In any case, keep an eye on the skies and be prepared to take action should warnings be issued.

Back to the winter side. In the mid-morning, a quick changeover from rain to snow should begin occurring across northwestern Iowa. By 3:00 p.m,  areas north of Highway 18 and west of Interstate 35 will be completely changed over to snow. This should be expanded to areas west of Interstate 80 by rush hour with the whole state under light-to-moderate snowfall by late Wednesday night (the exception being southeast Iowa). A period of a snow/sleet mix will be possible across eastern Iowa in the evening. Light snow will continue falling through around noon Thursday statewide, heaviest areas being in eastern Iowa. By evening, the entire state should be clear of precipitation.

There is currently low-to-medium confidence in regards to amounts across the area. Models are in fairly decent agreement now on a convectively-enhanced snow band that will kick up totals across the area. Where this exactly sets up is up in the air at this time. There are a few other wild cards that will be fluid over the next couple of days… the quick changeover in northwest Iowa being one of them. This can easily influence snowfall totals – if the precipitation-type remains as rain longer than anticipated, lower totals are possible, and vice-versa. One thing is for certain… totals of at least 6-8″ are expected across the Winter Storm Watch area. These totals may end up being higher. However, until predictability improves in that regard, we are leaving things as 5-8″. A 8-12″ area was added where models are in general agreement of higher amounts… primarily across Kossuth, Winnebago, Worth, and the northern portions of Cerro Gordo and Hancock counties. Most models do not go farther south than this, though it will have to be monitored and is subject to change.

Our forecast currently has the heaviest of snow centered across extreme north central Iowa – eight-to-twelve inches is possible in this area, including Rochester and La Crosse. Five-to-eight inches is anticipated outside of that in much of northern Iowa, including Estherville, Storm Lake, Sioux City, Mason City, and Decorah. The cut-off line is very short beyond this – three-to-five inches is expected in Fort Dodge and Waterloo, with one-to-three inches in Carroll, Harlan, Ames, and Dubuque. The remainder of the state will see a dusting to an inch or so. Keep in mind that these amounts are subject to change as we get new data and information in. Models have been showing potentially higher amounts than what we are showcasing here, so make sure to stay tuned to the latest forecast.

One area of major concern is the expected winds in the evening on Wednesday, in the likely peak of the storm. Sustained winds of 20-30 MPH with gusts to over 40 MPH in many spots, worst being in the west. This will lead to dangerous, near-blizzard conditions with zero visibility and whiteout conditions possible. It’s especially concerning with the convectively-enhanced snowfall rates – if you have heavy snow falling with 40+ MPH wind gusts, travel will be next to impossible. The worst of the effects will be felt in rural and open areas. If you have to travel at all Wednesday or Thursday in the affected area… be prepared to change plans.

Due to the significant accumulations and near-blizzard conditions, a Winter Storm Watch has been issued for essentially the northernmost two rows of counties of the state. For northwest Iowa, this will go into effect early Wednesday morning and remain until late Wednesday night. For north central and northeast Iowa, this will go into effect Wednesday afternoon and remain through Thursday morning. I would anticipate that this potentially gets expanded southward slightly (especially in northwest Iowa) and eventually upgraded to Winter Storm Warnings and Winter Weather Advisories this afternoon. We should have a clearer picture by then as far as model data goes, so check back for the latest updates. Travel difficulties can be expected throughout Wednesday and early Thursday and you should begin making preparations for this now. Fill any prescriptions before Wednesday…double check your winter survival kit…stock up on essentials…etc. If you have events or anything planned for Wednesday afternoon, be prepared to make changes due to inclement weather.

Stay tuned to the Iowa Weather Network for the latest updates.