During this streak, the average high and low temperature in Washington has been 53 and 38, which is similar to normal weather in Sacramento, at this time of year. The period of Dec. 13 to Jan. 2 in Washington ranked as the sixth warmest on record.
The streak of mild weather is likely to continue.
The American modeling system projects above-average temperatures in Washington for the next 10 days, at least. If that holds true, the region will have gone a full month with above-normal temperatures, uninterrupted. If the streak of above-normal temperatures reaches 30 days, it will be the longest in more than a decade (since Dec. 11 to Jan. 9 in 2006-2007).
If you dislike cold, the above-normal temperatures come at a convenient time. This is normally the chilliest time of year, with average high and low temperatures in the low 40s and upper 20s. But the predicted temperatures over the next 10 days are more typical of late February or early March, with highs averaging in the upper 40s and lows in the mid-30s.
The National Weather Service’s eight-to-14-day temperature outlook agrees that warmer-than-normal temperatures are likely to persist, not just in Washington but over most of the Lower 48.
With such an absence of cold air, the prospects of snow are bleak. Washington hasn’t seen a flake of snow since Nov. 15, and there appears to be no credible winter storm threat for the next 10 days. But the big wild card is what will happen during the second half of January. In late December we wrote that the polar vortex was likely to be disrupted by January, and this has just occurred. In fact, the vortex has split in three.
When the polar vortex splits, it increases the likelihood that cold and stormy winter weather will hit the eastern United States. But there can be a long lag between the time the vortex splits and when the wintry weather arrives.
Last year, the polar vortex split in early February, and the effects weren’t felt in the East until March and April. In other words, it could still be several weeks before a pattern shift toward colder, snowier conditions takes place — if it occurs.
A polar vortex split is not a guarantee of wintry conditions, as other processes in the atmosphere and ocean, including those originating from the tropics, can have a significant effect on regional weather.
Model forecasts are decidedly mixed on what will happen during the second half of January into February. Some keep it warm, while others flip it cold.
Nearly all winter outlooks for the Washington region predicted a snowy winter. The polar vortex disruption that just occurred could still pave the way for theses snowy forecasts to come true. But the deeper into winter it stays mild, the greater the chance of an across-the-board prediction failure.