Snow is expected to fall Sunday

Moisture will begin to move in to the state on south-southwesterly winds tonight.  The moisture will run in to a cold front that is expected to move across central Indiana Sunday which will cause precipitation to fall in much of the state in the next 24-hours.

Moisture should begin to fall later tonight, initially in the form of rain before changing over to snow around midnight.  The precipitation that falls prior to 2am will be light.

Computer model projection of radar/satellite imagery.

A wave of snow is projected to move in to central Indiana from the southwest around daybreak Sunday.  This should be the main round of snow for Sunday and be out of the area by noon.

Another round of snow will be possible behind a cold front that passes during the early afternoon.

SNOWFALL AMOUNTS

There are factors at play when it comes to how much snow could accumulate around central Indiana.  The biggest – or in this case the smallest – factor is a lack of moisture to work with.  Overall, computer models suggest there is about 0.04″ of liquid available to produce snow in central Indiana.  That isn’t a lot!

Data suggests we could have a couple periods of rain mixed in with the snow.  The first coming this evening/tonight (before midnight).  The second would be late Sunday morning through afternoon before the cold front passes.  While that sounds plausible, there is one problem.  As of 6pm Saturday, temperatures are in the middle 30°s.  That isn’t a problem.  However, dew point temperatures range from the single digits to the teens .  That is a problem!

When moisture arrives overhead and there is enough to fall, it will get soaked up by the dry air.  That will take a chunk out of the amount of liquid available to produce snow.  That being said, as the moisture evaporates, it will begin to cool the air through a process called evaporative cooling.  That could allow temperatures to drop more than computer models forecast, keeping the main precipitation type as snow instead of rain prior to midnight.

The other factor that could impact how much snow accumulates is warmer ground temperatures.

Below is a graph of snowfall projections for Indianapolis by four computer models.  With the exception of the RPM, all the models suggest snowfall totals will be less than an inch.

Computer model snowfall accumulation projections.

I’m factoring in snow to liquid ratios between 8:1 and 16:1 depending on the time of day when precipitation falls.  Overall, I think central Indiana gets less than 1″ of snow through 1am Monday.  More specifically, in Indianapolis, I think we are looking at less than a half inch.

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