Sunday, December 7, 2008

Winter Storm (Dec. 8-9) Update #1

Well I know the previous post mentioned that a better idea of snow accumulations would be presented in this update tonight, but honestly there can't be that much accuracy stated at even this point. Tonight's model runs at first glance have continued their trend of a north and west movement of the heaviest snow, likely due to the more progressive nature of the system. However, this does not seem to hamper any of the current NWS statements on the winter storm watches currently in effect and it certainly doesn't mean that the new solution will verify either. I am however not going to be able to provide a solid map for your visual reference on how much snow areas are likely to receive.

Precipitation is likely to begin by the evening hours tomorrow, with a few scattered showers during the afternoon hours previous. With the strength of warm-air that is likely to push into the state, it does appear that rain may be the beginning form of precip for much of the southern half if not greater portion of the state. Current surface analysis indicates this warm front is already in the process of taking shape over the southern third of the state. This will provide the good possibility of freezing rain for much of the state on Monday afternoon and into the evening hours. As we head into the heavier precip on Monday night, expect western and northern Iowa to be mainly snow, central Iowa to be mainly snow with the transition a little later in the night, and expect southeast Iowa to be mainly rain; leaving parts of south-central, central, and east-central Iowa with the possibility of continuing freezing rain. All in all, with the amount of precipitation expected with this storm system, a good winter storm is nearly a guarentee, it is just the location that is tricky at the moment.

Latest forecast discussions tend to agree with this detail, with the heaviest band of snowfall possibly falling anywhere between the I-90 corridor in southern Minnesota and northern Iowa, to south-central to east-central Iowa. As mentioned by Des Moines NWS, central Iowa does appear to be in the most likely area for this heaviest band of snowfall to setup during the overnight hours on Monday. Widespread 4-6 inches of snow is likely, with isolated amounts nearing 8 inches. Areas just to the north/south of this heavier band should still see 2-4 inches, with only extreme southeast Iowa perhaps making it out with only an inch or two as they receive more rainfall than snow...

As I type, I figured I might as well make up a map... So it is posted below, notice the area encircled in yellow I believe has the best chance of 4-8 inches of snowfall; while areas outside of the yellow both north and south will be looking at 2-4 inches. The area encircled within blue will see freezing rain with some accumulations possible, while south of the green line you can expect mainly rain with only minor snowfall accumulations.