2020 First Night fireworks. (Geoff Livingston/Flickr)

Winter, wherefore art thou? With temperatures in the 60s this past Monday and maybe again Friday, it doesn’t feel much like winter right now.

The prevailing weather pattern influences suggest that this warmth should continue for the first half of January, as the main jet stream rockets far to the north over the eastern United States, offering bouts of winter in the West, instead. Some key indicators suggest we could flip to a cold pattern by the second half of January.

With the potential for a mid-month turnaround, our January temperature outlook is a cautious warmer-than-normal projection of about 1 to 3 degrees above normal. Precipitation is forecast to run above normal, too, with snow favored to be below normal, given the very warm first half. It takes only one storm for snow fortunes to reverse, of course, but there’s no significant threat over the next 10 days or so. What happens after that is a wild card.

The recent 1-15 day model forecasts show how warm the next two weeks look for the eastern United States:


(NOAA)

Historical context

The normal temperature average for January in Washington is 36 degrees. Over the past 10 years, we have experienced four years warmer than normal (including 2018) and six years colder than normal (including two years ago). We’re leaning on the warm side this year, given the warmer-than-normal start.

Normal snowfall for January is 5.6 inches, and a major storm last year Jan. 12-13 was able to move the month snowier than normal. This year, we may have chances in the second half of the month, but, given a likely snowless first half of January, it seems more reasonable to favor below-normal snow. Over the past 10 years, we have experienced a snowier-than-normal January 50 percent of the time.

The normal liquid equivalent precipitation (taking into account rain and melted snow) for January is 2.81 inches, which is the second driest month of the year typically (February is normally the driest). The two-week forecast models are projecting about two inches by mid-month, so it seems as though we should get off to a fairly wet start. However, of the past 10 years, only two have been wetter than normal, including last year.

Forecast rationale

The very aggressive warm start to January argues the case for a much warmer month overall, closer to the 6-degree difference from normal seen in 2017; however, the potential for a mid-month pattern shift should offset the warmth some.

A burst of tropical energy tracked via an index known as the Madden-Julian Oscillation (MJO) is forecast to potentially reach colder phases by mid-month similar to a pattern adjustment we experienced in 2019 and also in 2007 (both cases followed warmer-than-normal Decembers, like this year).


Temperature differences from normal for the front and back halves of January in 2007 and 2019, showing the pattern change those years. (Commodity Weather Group)

Some of our more reliable computer model forecasts will be able to project out into the period when this threshold change is possible later this week and will be important to monitor.

The National Oceanic and Atmospheric Administration’s CFS mode has been struggling to get a handle on this possible pattern change, showing lots of variations from day to day. Here is the recent temperature forecast difference from average for the month, which indicates near-normal temperatures when all is said and done (this is suggestive of a cold second half of the month):


(NOAA)

And here is the precipitation forecast difference from normal (favoring wet conditions):


(NOAA)