It’s complicated…

5 P.M. Monday, Jan. 30, 2023

General situation shows a large cold air mass over the midwest slowly dropping southward. Temperatures today have been slowly falling and will continue tonight as temperatures drop into the upper 20’s by morning. Meanwhile, a small upper level disturbance in the jet stream flow will move rapidly ENE over the area tonight. It’s not much of a system, but it does have enough moisture to bring us some icy weather tonight.

That’s where the forecast trouble starts. The lower atmosphere (up to 5,000 feet) is definitely cold enough to support an inch or two of snow overnight along the Ohio River. But, it’s not that simple.

There’s a pocket of slightly above freezing air roughly between 5,000 and 10,000 feet above us. That will be slowly cooling overnight but should still stay slightly above 32 degrees. That’s the fly in the ointment.

The primary consequence will be that some of the snow falling through this warm layer will melt, then refreeze into sleet before hitting the ground. That sets up a very subtle balancing act between snow and sleet for our overnight entertainment.

In general, the whole atmospheric column will be slowly cooling, so snow becomes the most likely result as time goes on. The onset is trickier. Everything depends upon just how thick that warmer air is and how much cooling it will get from evaporation of precipitation aloft.

The models are consistant on two things. First, the amount of moisture falling will be small. Probably between .1″ and .2″ of water. That would be a 1″-2″ snowfall but only about a quarter-inch of sleet. Second, the location of the maximum precipitation will be about roughly 30 miles north and south of the Ohio River.

After putting all those variables into a big pot and letting them simmer, here’s what I think will happen tonight. Precipitation should begin around 8 P.M. in Louisville. At first, it’ll be mostly sleet with a little snow mixed in. As the night goes on, the mix will gradually change to mostly snow with a little sleet mixed in. Any significant snow/sleet will end by 3-4 A.M. The Louisville area should end up with a snow/sleet total of up to one inch.

North of Louisville snow totals could get up to 1″-2″. South of Louisville will see a snow/sleet accumulation up to one-half inch.

By morning rush hour, treated roads should be in fairly good shape with icy spots. Meanwhile, non-treated roads should be mostly snow/ice covered.

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