Forecasters expect rain today, changing to snow this afternoon and evening in northern Indiana, southwestern Lower Michigan and northwestern Ohio, according to various text products from the northern Indiana office of the National Weather Service (NWS) (Facebook, Twitter).

They expect the change to snow to begin this afternoon in the western counties of the office’s 37-county warning area (CWA) and progress to the eastern counties by this evening.

The office has issued a Winter Weather Advisory for counties along the western edge of its CWA (see graphic above), where meteorologists expect one to three inches of snow with locally higher amounts. The winter weather advisory is in effect from 4 p.m. to midnight.

They issued a Wind Advisory for most of the CWA’s Ohio counties from 4 p.m. this afternoon to 3 a.m. tonight. There, they forecast sustained winds of 20 to 30 mph, with gusts up to approximately 45 mph.

The NWS issued a Special Weather Statement for the rest of the CWA that alerts readers to potentially difficult driving conditions by this evening, due to slushy roads and reduced visibilities.

Believe it or not, there is still some uncertainty regarding when the change from rain to snow will happen and therefore, how much snow will fall. That’s because there’s still a chance that the low pressure system that will be responsible for all this weather could follow a different path than forecast. “Just a 20-30 mile shift west or east will make all the difference,” writes NWS meteorologist Mark Steinwedel in an Area Forecast Discussion the northern Indiana office issued this morning.

As of 7 a.m. EST today, that area of low barometric pressure was just south of Indiana (see map above; black arrow points out the low). When meteorologists see what path the low actually takes, they’ll be better able to forecast snowfall timing and amounts.

“Uncertainty.” If you’ve been following this blog (or any other information sources) for information on a winter storm forecast for Christmas Eve, you’re probably growing weary of that word.

But “uncertainty” remains the key word, because the low pressure system that will be responsible for the storm is just beginning to form in the area of the Gulf of Mexico this morning.

Currently, that low pressure system is forecast to move straight up through Indiana. Most of the snowfall will be to the west of the low. That means if the low goes right over you, you won’t get as much snow as you will if it goes east of you.

Meteorologists use a suite of computer forecast models to predict things like where that low pressure system will go. Different models calculate things differently, so meteorologists don’t rely on a single model, they look at several. Agreement between the outputs of several models helps them forecast confidently.

Unfortunately, as of this morning, the range of storm tracks provided by those models “remains a bit wider than one would like to see at this time,” writes meteorologist Sam Lashely in an “Area Forecast Discussion” that the northern Indiana National Weather Service office issued.

Lashley continues, “The details with where any accumulating snowfall will develop remain in question,” and “we continue to stress the uncertainty and need for people traveling to continue monitoring forecasts and remain aware.”

The northern Indiana office of the National Weather Service sent an email message to emergency managers in its forecast area this afternoon that included a map (above) showing a very preliminary snow accumulation forecast for the coming winter storm.

The NWS wrote:

• Rain is expected to change to snow from west to east across the area Wednesday evening.
• Snow accumulations of one to three inches along with slick roads are possible from this system.
• Confidence in the snow accumulation forecast is low at this time, but since the snowfall could impact the busy Christmas Eve traveling period, the NWS wanted to make sure emergency managers are aware of the potential.