Confidence is increasing in a significant winter storm on Tuesday and Wednesday of next week. Heavy snow is most likely across parts of Nebraska, Iowa, South Dakota, Minnesota, and Wisconsin. It is still a little too early to know exactly where the heaviest snow will fall, but more than 6" is likely in some areas with some areas seeing up to a foot of snow. Models continue to change, and we will continue to monitor them. This is our best guess as of right now. Freezing rain will be possible from eastern Kansas and southeastern Nebraska through northern Missouri and into Iowa and Illinois. Severe Thunderstorms are likely on Wednesday and Thursday across south-central CONUS along the Gulf Coast. ells that initiate well to the east of the front across the moist sector will have the potential to become supercells. The main threat would be for a few tornadoes and isolated wind damage.
A wave of low pressure is likely to move from IL to WI and across
Michigan today. Behind this low, another system over the SW will begin to move its way eastward across the SW CONUS, eventually crossing the Rockies into the Great Plains where the low will begin to deepen and intensify. This feature will be accompanied by persistent jet energy crossing central to southern CA inland across central to southern NV/UT, then CO. Upper-level divergence combines with topographically forced ascent will produce snows across the central to southern CA Sierra Nevada mountains, followed by the Transverse Ranges of southern CA. As the longwave trough moves east across the Plains, low-mid level southwest flow increases. The increased low-level jet drives warm/moisture advection (MAA) with an 850mb front moving northeast across Nebraska and Kansas through eastern South Dakota, Iowa, southern Minnesota, Wisconsin, and northern Illinois.
The combination of the front and warm advection, this will produce ascent/forcing across this region with snow across northeast Nebraska and southeast South Dakota and across southern Minnesota, northern Iowa, and into southern to central Wisconsin. We will need to be aware of where the 850-700mb frontogenesis band sets up as this is where we could see some of the highest snowfall amounts with this increased isentropic ascent with the MAA in the warm sector.
There remains considerable spread in both the placement and timing of the 700 mb low and resultant Quantitative Precipitation Forecast (QPF) and where the precipitation type transition zone sets up across the upper MS Valley to the Upper Great Lakes. Where that zone sets up could cause varying snowfall totals across that zone. The GFS/GEFS differ from the ECMWF/ECMWF Mean, UKMET as noted in the video above. South of this area, warm advection turns snow to sleet and freezing rain across northern Kansas to northern Missouri and Illinois, continuing into Iowa and southern Wisconsin. WPC probabilities indicate a low risk for 0.25" of freezing rain accretion in northeast KS to northern MO and southern IA. This will create hazardous and slippery road conditions across this region.