Wednesday, March 9, 2016   |   Critical Weather

A Typical El Niño? A Meteorologist Examines the Ongoing Phenomenon

Analysis by Kevin Nugent, Forecast Meteorologist, Baron

The El Niño winter of 2015-16 has been both typical for a strong El Niño season, and also atypical. An average strong El Niño winter brings wet and cool conditions for much of California and the southern tier states. It also brings warm and dry conditions for the central and northern tier of states. While these norms for a typical El Niño season have, for the most part, been realized during the months of November through February, one thing is for sure—this has been no typical El Niño season. This year, El Niño has brought high variability and extreme weather.

In terms of high variability and extremes so far this winter, most notable has been the high amount of severe thunderstorm outbreaks and tornadoes, not only across the Gulf Coast region and Florida where you would typically find severe and wet weather, but also further north in the Tennessee River Valley, Carolinas, Mid-Atlantic, and even the Northeast where it isn’t expected. There were more than 100 reported tornadoes in January and February—the second highest amount ever recorded for those two months. They included numerous long-track EF-2 and EF-3 tornadoes, much like tornado that moved across western Alabama near Reform on February 2. During the first two months of this year, there have been deadly tornadoes in Louisiana, Mississippi, Florida and Virginia, and as many as five separate EF-3 tornadoes.

shear_swath_reform

Another example of high variability in the weather took place in California. The winter started out promising for the state, with high amounts of rain and snow to put a dent in the drought conditions. However, the past 60 days have seen a return to very dry and warm weather for California, as well as much of the desert Southwest. Over the past month, much of the southwestern U.S. has received less than 20 percent of normal precipitation, as seen in the Baron Percent of Normal Precipitation product.

30day_percent_of_normal_southwest

As a result, there has been a substantial loss of snow pack in the mountains of the southwestern U.S., including California. This is evident in the Baron Snow Depth product (pictured below).

snowdepth of march

The final example of extreme weather related to El Niño is the relative lack of snowfall across the eastern/northeastern U.S., which is expected in a typical El Niño winter. The exception was the great blizzard of January 23-24, 2016, which buried major eastern U.S. cities of Washington DC, Philadelphia and New York with 18-30” of snow. While that storm produced a season’s worth of snow accumulation, the rest of the winter has been quite warm and relatively snow-free for those areas. This has also translated further to the west, where there have been fewer-than-normal lake effect snow events across the Great Lakes region. This winter, those same areas have experienced very warm temperatures compared to average, with only short-lived invasions of cold Arctic air.

What will the rest of this winter and early spring El Niño bring weather-wise? It’s hard to say, but will likely provide a continued high variability in patterns. The strength of the El Niño has been diminishing since its peak earlier this winter. A weekly analysis of Pacific Ocean temperature anomalies near the equator shows that the large area of above-normal sea surface temperatures has been cooled by 1-1.5 Celsius through the month of February. However, the extent of above-normal temperatures has remained fairly constant.

240hour_accums_forecast

The decline in above-normal sea surface temperatures for that area is expected to continue for the next few months until they lower to near normal along the equator in the Pacific Ocean. However, El Niño conditions are still in place, and a return to wet conditions is expected across California and the southern U.S. over the next one or two weeks. Specifically, numerous strong and wet weather systems are expected to impact the western U.S. and California. All forecast models are predicting heavy amounts of valley rain and mountain snows across much of the state, with the highest rainfall amounts in the 10-15” range, which translates to as much as 10’ of snow in the Sierra mountains. This will help put a dent in the ongoing drought conditions in the state. There are also heavy rain events across the south-central U.S. this week, as well.