With all the shifting expected, it is difficult to pin down what December’s temperature and precipitation (and snow!) will be, but we’ll give it our best shot.

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Temperatures for December should end close to normal. The average temperature for December in Washington is 39.7 degrees, so we’re looking for about 38 to 42 degrees by Dec. 31. This would be the coldest December since 2013, when the average was 42.3 degrees, or in 2010 when it was a very cold 34.6 degrees.

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Precipitation is forecast to run near to slightly below normal. Normal is 3.05 inches, so we’re looking for about 2.75 to 3.10 inches of liquid equivalent in this outlook — meaning, if some of it is snow, it would melt down to those totals. This will be much wetter than was autumn, which is good for our drought. Precipitation should turn a corner next week, allowing the area to edge out of its newfound drought status.

Snow is forecast to be near or slightly above normal, if you can believe it. Snow is normally 2.3 inches in Washington for December, so we’re going to lean toward a 2-3 inch total for the month. This is obviously going to require some colder air, and we believe we’ll see some colder periods in the middle to final thirds of the month to offer some lighter coatings. At this point, we don’t see anything close to the crazy December of 2009.

Forecast rationale

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Warmer, then colder. The forecast for the first half of December is topsy-turvy with a warmer lean at the start and then a colder second week of the month. A suppressed jet stream in that second part (Dec. 8 or 9 onward) could help deliver our first flakes of the season, too.

Tough to shake persistence. We’ve been warmer than normal for six straight months now, so calling for a near-normal December might be a bold call and as a result, we are being very cautious with the risk range right around normal, just in case we end up 1-2 degrees above normal still. November was warm, but not nearly as strong as prior months, and the increased variability in late November seems to be a sign that the warmth lingering from earlier this year’s massive Godzilla El Niño is finally fading.

A weak La Niña. The Pacific Ocean continues to run on the edge of a weak La Niña, but the atmosphere has been slower to respond so far. Some trends in the coming weeks suggest some response starting to happen finally and most weak La Niña Decembers tend to lean to the colder side for Washington, but they tend to be volatile.

CFS is slightly warm and very wet. The National Weather Service CFS model did well in predicting the warmer-prevailing November and is leaning warm for December, too, but the average of the past five days of model runs favors just a minor +1 to +2 degree estimate for Washington (which encompasses our forecast range, too). The model also has an active storm track from the south to the east that could really ease our drought concerns, but also perk up some snow sneak attacks later this month.