“January Outlook: More like winter, but still milder than normal with limited snow chances”
by Matt Rogers
1/4/2016
https://www.washingtonpost.com/news/capital-weather-gang
accessed 1/11/2016
After the warmest December on record and conspicuously absent winter weather, a new colder
regime battles for control as we begin January.
Throughout the month, expect a very powerful El Niño, which helped drive mild air into the region
during December, to tussle with a colder pattern with Arctic pedigree.
While January should still be warmer and wetter than normal thanks to El Niño, the odds of a recordwarm month are much lower. Overall, I expect a slightly warmer than normal month with below
normal snow.
Here are the numbers…
I’m calling for the average January temperature to be 37 to 39 degrees, which is 1.5-3 degrees above
the January 30-year normal of 36.0 degrees. My confidence is medium to high that it will be milder
than average, but I’m not as certain about the magnitude.
Our most recent super El Niño of January 1998 was much milder than normal with an average
temperature of 43 degrees (7 degrees above normal), but the next most recent super El Niño in 1983
averaged 38.1 degrees, which is closer to our outlook.
Precipitation (rain and melted snow) should be near average, with approximately 2.5-3.0 inches of
rain (the average is 2.81 inches). Confidence in the precipitation outlook is low
Other super El Niño January periods have produced varying precipitation amounts ranging from 1.69
inches (Jan. 1983, below normal) to 5.43 inches (Jan. 1998, much above normal).
Sorry, snow lovers. I’m calling for just a trace to 3 inches (the normal is 5.6 inches). However,
confidence is just low to medium – meaning there’s a decent chance I could be wrong.
The past super El Niño January periods both recorded just a trace, so there’s little precedent for a
snowy January under such a regime, though the sample size is small.
January snow in the 2000s has ranged from zero in 2006 to 14.5 inches in 2000 with that year’s
surprise snowstorm event. In 2015, we only managed 3.6 inches in this month. With a super El Niño,
the odds seem better for another no-snow result. However, we do have some cold air in the pattern
mix unlike December, so we should at least include the odds of up to 3″inches as a possibility. Half of
the years during 2000s saw 3 inches or less during this month.
“A More Favorable Pattern for a Snowstorm in the East May be Ahead”
by Linda Lam
1/11/2016
http://www.weather.com/forecast
accessed 1/11/2016
An expected change in the large-scale weather pattern over North America and the higher latitudes of
the North Atlantic Ocean may increase the odds for a possible impactful winter storm in the East
during the next week or two.
There is broad support in computer forecast model guidance for colder-than-average conditions
across portions of the East at times over the next two weeks. That forecast is of relative high
confidence.
There are also indications of an increase in storminess, though whether a Southern or East Coast
snowstorm actually forms is of much lower confidence, which is a typical conundrum facing
meteorologists this time of year.
The result could be snow returning to portions of the U.S. which have not seen much in the way of
snowfall so far this season.
One of the factors to examine to determine if the pattern is favorable for an East Coast snowstorm is
the Arctic Oscillation (AO). When the AO is in a negative phase, winds around the North Pole become
weaker, colder air can push southward, and storminess usually increases in the mid-latitudes (the
region south of the Arctic Circle and north of the tropics).
The AO index has been mostly positive since mid-October, contributing to the lack of very cold
conditions and lack of East Coast snowstorms early in the winter season. However, the AO has
become negative, and may continue to be so for the next 1-2 weeks, if not longer.
The North Atlantic Oscillation (NAO), which is closely related to the AO, is another important factor
which can signal the likelihood of an Eastern winter storm. The NAO is a measurement of the
differences in atmospheric pressure between the Icelandic low (an area of low pressure over northern
Iceland) and the Azores high (an area of high pressure located near the Azores). Differences in the
location and strength of these two factors plays an important role in the direction and strength of the
jet stream and consequently storm tracks across the North Atlantic.
The negative phase of the NAO reflects above-normal atmospheric pressure across the high latitudes
of the North Atlantic (Greenland, Iceland, and adjacent regions) and below-normal atmospheric
pressure over the central North Atlantic, the eastern U.S. and western Europe, according to the
National Oceanic and Atmospheric Administration (NOAA). The positive phase is the opposite. The
differences in the jet stream that result from the NAO being positive or negative create changes in
temperatures and precipitation patterns in eastern Canada and the eastern U.S., as well as in
western and central Europe.
The NAO had been positive since October before turning negative within the last few days. It is
forecast to become even more negative as a large low-pressure system east of Bermuda moves
east-southeast into the region that typically hosts the Azores high, potentially becoming subtropical in
the process.
During a negative phase of the NAO in the winter months, below-normal temperatures typically occur
in the East, and there is an increased risk of snowstorms.