Friday, March 6, 2009

Severe & Winter Storm: Mar. 7-8

As we head into the weekend, showers and thunderstorms are entering portions of western and southern Iowa. These showers and thunderstorms will likely continue across the state throughout the nighttime hours, and through the afternoon tomorrow. Total rainfall amounts may be quite heavy, greater than an inch in most areas, with up to 2-3 inches possible across parts of the state. Due to this heavy amount of rain this early in the spring, the Davenport NWS has issued a flash flood watch across its' entire area. The Des Moines NWS did state that rises in rivers are expected, although they expect it to remain with the banks for most, if not all, rivers.

Overnight tonight, and potentially late Saturday night, there is the potential for some severe thunderstorms. Overnight tonight, the main threat with any thunderstorm will be the potential for marginally severe hail. This has already occurred over northern Missouri, and will not be surprised to see a few warnings across the southern half of the state for some 3/4" to 1" diameter hail. Thunderstorms on Saturday are expected to initiate over Kansas, where clear skies or at least more favorable conditions will give way to new development. This may congeal into a larger complex of storms that will move northeast into the overnight. This complex of storms may reach the far southern counties in the state, giving them the chance at some additional large hail and/or damaging winds.

Another complex situation occurs beginning Saturday night, as cold air enters the state behind the exiting low pressure system that will be over eastern Iowa. This cold air both at the surface and aloft will give way to frozen precipitation over much of northern Iowa. Currently the NWS in Sioux Falls has issued a Winter Weather Advisory for portions of northwest Iowa where a combination of freezing rain and accumulation snow is likely to occur Saturday night and into early Sunday. Some portions of northern Iowa have the potential for 3-6 inches of snow according to the latest models; with some higher amounts even being forecasted in both the NAM and GFS. Expect a combination of freezing rain and snow on Saturday night anywhere north of Highway 20; with accumulations of snow being likely. The amounts are going to be hard to pinpoint, given that the speed and amount of cold air will determine how quickly in changes over and thus how much snow places will see.

Be sure to check out the latest radar image on the Iowa Chaser Homepage: