Weathercatch: What are Mother Nature’s plans for December?

Yesterday marked the first day of December and the start of meteorological winter, the initial step toward colder, snowier days and nights.

Astronomical winter begins Dec. 21 this year, but for meteorologists, it always begins Dec. 1. However, since Mother Nature owns the calendar instead of meteorologists, she likes to deliver the unexpected.

Last December is an example.

With the exception of a few intermittent light snowfalls and brisk temperatures, overall conditions were more typical of midfall or spring until a shot of winter finally arrived on Christmas Day. Until then, temperatures were so mild that snow accumulations didn’t stick around. On Dec. 21, the temperature climbed as high as 50 degrees in Spokane and near 60 in the Tri-Cities. (The average high temperature for that date is 35 degrees in Spokane and 40 in Kennewick.)

As December 2021 begins to unfold, here’s what we do know – whether Mother Nature brings surprises or not:

• December is typically the coldest month of the year for Spokane, although January runs a close second. It’s interesting to note January used to be the coldest month in the earlier part of the 20th century, but December surpassed it.

• The average high temperature for Spokane is 35 degrees and the low is 24.

• The average snowfall is 11-12 inches.

• We will lose 16 minutes of daylight between Dec. 2 and the winter solstice on Dec. 21, the shortest day of the year.

• The amount of daylight, which is between sunrise and sunset, on Dec. 21 will be 8 hours, 25 minutes, compared with 16 hours on the summer solstice, which will fall on June 21 in 2022.

• The sun rose at 7:18 this morning and will set at 3:59 p.m. On Dec. 31 the sun will rise at 7:38 a.m. and set at 4:07 p.m.

For the second winter in a row, La Niña conditions are expected to influence our wintertime weather. La Niña is a not-uncommon climate pattern in the Pacific Ocean that affects weather worldwide. It typically fuels cold and wet winters from southeast Alaska and the Pacific Northwest eastward to the Great Lakes, but relatively warm and dry conditions elsewhere in the country.

La Niña’s biggest impact is usually felt in January and February, so it’s unclear how much influence it will exert this month. With the above-average temperatures we’ve had this week, it’s hard to imagine a cold snap anytime soon.

Regardless, the National Oceanic and Atmospheric Administration is predicting fairly average temperatures across the Pacific Northwest this month, along with wetter-than-normal conditions.

This is exciting news because it means plenty of snow is probably in store for the mountains.

As for the Spokane region? At lower elevations, snow can be tricky to predict. What falls from the sky – snow, rain, freezing rain – will depend on temperatures in the column of air as precipitation falls toward ground. What starts as snow can melt into rain when encountering a warmer temperature layer. But if the column of air remains cold enough from top to bottom, then we get snow.

And Mother Nature, not meteorologists, is in charge of that one.