Dreaming of a white Christmas? Maybe the Mayans were, too

Monday, December 24, 2012

Since the Mayans didn't predict anything past 3:11 a.m. Dec. 21, nobody's quite sure how they felt about a white Christmas for 2012.

So whether you want a white Christmas or would just as soon have sunny skies and dry pavement, feel free to go ahead and blame the missing Mayans anyway if you don't get your choice.

After all, they're about as accountable as TV weather forecasters.

The latest information released by the National Weather Service Sunday night indicates a winter storm watch is now in effect for central Indiana from Tuesday evening to Wednesday evening.

Putnam County is included in the watch area, along with all of its contiguous counties.

The Weather Service says the storm system could impact Christmas travel with anywhere from five to nine inches of snow possible.

A low-pressure system is forecast to develop over Texas and track up through the Tennessee and Ohio valleys on Christmas night into Wednesday. Heavy snow fueled by strong winds will be possible across much of central Indiana.

Uncertainty still exists concerning the storm track of the low-pressure system. If it tracks westward, lower snow totals will be the norm as more warm air overspreads central Indiana. Colder temperatures would result in higher snow totals.

The snow is expected to begin falling after 7 p.m. Tuesday (Christmas Day) and continue through Wednesday evening.

So what is the chance of at least a trace of snow falling on Christmas Day?

The National Weather Service has kept snowfall records on Christmas Day in the Indianapolis area since 1871. And in that 141-year period, a trace of snow (or more) has fallen 64 times. That equates to a 45 percent chance of at least a trace of snow falling on Christmas Day.

Of course, there's more than one way to define a white Christmas. For historical purposes, a white Christmas will be defined as any day that has either at least a trace of snow on the ground or experiences at least a trace of snow falling that day.

In more general terms, let's define a white Christmas as any Christmas Day that the Indianapolis area sees snow.

The other possibility of a white Christmas is if there is at least a trace of snow already on the ground. That could be old snow from a week ago, or just the day before.

Snow depth records don't go quite as far back, having been started in 1896. And in that 115-year span, there has been at least a trace of snow on the ground on Christmas Day 57 times. That equates to a 50 percent chance of at least a trace of snow on the ground on Christmas Day.

The last Christmas that saw snow on the ground in Indianapolis was in 2010, with five inches of snow on the ground Christmas morning.

The greatest snow depth on the ground on Dec. 25 came in 2004 when there were nine inches from storms occurring Dec. 22 and 23. In 2002, there were seven inches of snow on the ground on Christmas Day, most of which (5.9 inches) had fallen the day before.

The largest snowfall on Christmas Day ever recorded at Indianapolis was 5.9 inches in 1909. The biggest holiday snowfall in the past 80 years came when 2.6 inches of snow fell in 2005.

So what is the probability of having either a trace or more of snow falling, or a trace or more already on the ground?

Since 1871, it has happened 82 times, where either the snow has fallen or already been on the ground. That's an overall probability of just under 60 percent, meaning that six out of every 10 years, on average, will see either snow falling or snow already on the ground for Christmas Day.

So, much more often than not, there will be at least a few flakes around come Christmas.

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