For January, we are predicting average temperatures about one to three degrees warmer than the 30-year average of 36 degrees. Rainfall should be one to three inches higher than the 2.81-inch average for the month. However, snow should be near to below the average of 5.6 inches.
A strong Pacific-based weather pattern is poised to send warm and wet conditions into the eastern United States for much of the next two weeks. Computer models are in fairly good agreement that temperatures in the Mid-Atlantic could average about five degrees above average for the first half of January. However, we think this may be overdone.
One reason these models may be overstating the warmth is the presence of a feature known as the Greenland block, which tends to deliver pulses of cool to cold air down the East Coast. Another reason our outlook is not as mild for the overall month is the evolution of an event known as a Sudden Stratospheric Warming (SSW), which is happening this weekend into early next week. It is likely to have influences persisting over the North Pole into the second week of January and probably beyond, though there is considerable uncertainty regarding its long-term evolution.
This event, along with other factors, is already contributing to colder patterns in Western Europe and eastern Asia, and could affect North America by the second half of January.
It will take a few weeks to see how the evolution of this event — one of the strongest in years — unfolds. The extended-range guidance is mixed on how quickly and significantly this affects the East Coast, but the current thinking is to watch for it to alter weather patterns beginning during the third and fourth weeks of January onward.
From a rainfall perspective, the current active Pacific flow is sending storms deep into the South and then toward the East Coast for a wetter-than-average two weeks ahead. The normal January rain total for Washington is 2.81 inches, and the latest medium-range two-week models are favoring us to receive most of that.
This is similar to the National Oceanic and Atmospheric Administration CFS model forecast for January, with a lot of rain across the South and up the East Coast.
This is in keeping with trends seen during December, and as we say in weather forecasting, sometimes the trend is your friend.
What about snow?
If the Pacific influences slow down (and the latest weather models are showing this by middle January), then the active storm track combined with lots of high pressure over the North Atlantic could open the door for more snow chances for the East Coast by mid- to late month.
The NOAA CFS model is slow-moving on those colder, snowier trends, but it suggests we could see at least two to four inches of snow by the end of the month.
Snow is always a huge wild card for Washington.
That one storm in the middle of December could have caused the month to be snowier than average if the main low-pressure center had been just 50 to 100 miles with a w east. With weather, it’s always about probabilities, and our chance for snow events should increase by the second half of the month.
In other words, there’s some hope for snow lovers in this monthly outlook but no guarantee.