With the winter of ’16-’17 closed, various methods used to forecast the season ahead of time are being explored; one such method includes this review of the Bering Sea Rule.
The Bering Sea Rule was founded by Joseph Renken. Renken’s credits include presenting the BSR to both National Conferences of the National Weather Association (NWA) and the American Meteorological Society (AMS), submitting two BSR research papers to the National Oceanic and Atmospheric Administration (NOAA) , and making numerous presentations to local chapters of the AMS. Renken has also provided advice to organizations such as the National Weather Service and private weather forecast firms with insights on how to utilize the BSR.
During the 2016-2017 winter season, the BSR has many highlights and some lowlights in forecasting future conditions.
After a rough start, the BSR was very reliable from mid-December through February. In the Northeast, it foretold the cold snap 10 days or so before Christmas, predicted a mild stretch from Christmas lasting into the New Year, saw January being changeable temperature-wise but with no big cold snaps, foresaw the pattern change to colder in early February and then finally, envisioned the tremendous stretch of warm weather in mid-to-late February.
As the calendar flipped to March and April, the BSR continued to rack up victories. It foretold several severe weather outbreaks across the Plains and South and also predicted an early April snow, as well as the chilly temperatures, for the interior Northeast.
However, in the transition period between winter and spring, the BSR struggled. The BSR anticipated a massive warm-up in the Northeast in the middle of March, similar to the previous mild stretch in February. This warm-up never materialized in the Northeast.
Across the country, the winter of 2016-2017 was quite remarkable and memorable. The Northeast blizzard in early-to-mid March, the tremendous coastal rains and mountain snows in California,and the tremendous warmth all winter long in the Deep South were all noteworthy.
Michael Vuotto, lead forecaster at FleetWeather, reflected on the major factors of the winter of extremes experienced across the US. “A stronger than normal Pacific jet sent storm after storm into the West Coast and thus sent the energy and mild Pacific air into the Plains and then the East. At times, this factor effectively eliminated the southward transport of arctic air into the Continental US. This factor also dumped mountain snows and low elevations rains into California, a wet and white winter they sorely needed and one that had seen for about 20 years.” Vuotto added, “A strong southeast ridge helped to keep the East Coast warmer than normal for most of the winter. This factor also was responsible for the nearly snow-less winter for portions of the mid-Atlantic and the abnormal warmth the Deep South and Southeast experienced. Warm Gulf of Mexico waters also helped to contribute to the warmer then normal conditions across the eastern and southern United States.” Viotto also gave his reason for the lack of cold air in the eastern US. “A polar vortex, which remained strong up around the North Pole and combined with the strong Pacific jet, inhibited real arctic air from flooding into the United States besides one period in December and then again in March. Both of these times, the vortex got slightly displaced and/or stretched and was centered over northern Hudson Bay, allowing for a consistent source of cold air to move into the northern United States. This flow was missing for the entire January into February stretch of time.”
As with any newer theory, it is not widely accepted and not everyone in the meteorological field uses it. Paul Pastelok, lead long-range forecaster at AccuWeather said, “I did not follow the BSR too much this winter because it was not very good in the beginning (of the winter). I think more studies have to be done on the magnitude of the features that move across this area along with other teleconnections going on.” Pastelok also shared Vutto’s thoughts on the Pacific’s influence on the winter weather across the country. “I believe the dominant feature this year was the SST (sea surface temperature) anomaly that set up over the Pacific with a strong jet smack over the strong contrast from cooler waters to warmer waters. An avenue of storms set up and followed the same path along this contrast sending mild Pacific air across the nation…”
BSR founder Renken agreed with Pastelok. “The BSR did indeed struggle in the early part of this past cold season. This struggle period was well documented in my December verification write-up . What needs to be kept in mind when using the BSR is that it is not a 1-to-1 direct correlation. It needs to be used as a tool in a whole toolbox of other long range teleconnections when making a long range forecast.” Renken has stressed that the operation time that BSR operates in is 17-21 days. Sometimes the BSR even operates outside of this window of time; this time span can often be responsible for perceived errors in the BSR’s forecasts.
A fair way to use the BSR is to get an idea of what the upper-air pattern has been doing over the Bering Sea and 2-4 weeks later the same pattern can be expected somewhere over the middle of the United States. As long as you do not get too detailed with your forecast of what is going on at the surface, more times than not the BSR will give you a ballpark idea of what will be going on. The major hiccups the BSR had in the beginning of the winter and then again in the transition period between winter and spring wasn’t that big of an error when you look at it via the upper-levels. The pattern was forecast correctly but the BSR’s position and timing of the pattern was off.
Sometimes, major seasonal events, like an on-coming strong El-Nino or large ridge of high pressure developing over warmer than average water in the North Pacific, can be forecast well in advance and used to make a seasonal forecast that shows high levels of accuracy. At other times, factors arise that are nearly impossible to be foreseen in advance and can destroy a seasonal forecast. This past winter falls into that latter category in many ways. The stronger than normal Pacific jet was difficult, if not impossible, to predict in advance and there were few, or no, long range forecasting tools that saw it. At times, this factor completely dominated every other meteorological variable and set the stage for the Winter of 2016-2017.