Author Topic: Musings: Meteorologists At A Loss to Explain The Winter Weather  (Read 1211 times)

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Offline donnay

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Musings: Meteorologists At A Loss to Explain The Winter Weather
« on: February 06, 2011, 07:53:16 pm »
Musings: Meteorologists At A Loss to Explain The Winter Weather

Another huge snowstorm moved through the mid-Atlantic and Northeast states last week, and forecasters are calling for more snow this week and possibly next. In New York City last Thursday, 19 inches of snow landed in Central Park. That snowfall brought the city's January snowfall total to 36 inches, well above the 1925 record of 27.4 inches. The snowy winter has people upset because previous winters have not been so bad, although last year when a blizzard descended on Washington, D. C., President Obama was moved to describe the storm as a "snowmageddon." He was quick to point out that his daughters didn't quite understand why school was cancelled since in Chicago this was a normal winter experience.

This winter has brought 51.5 inches of snow to Boston, easily topping the city's winter average of 42.3 inches. The record snowfall for the city was experienced during the 1995-1996 winter when Boston was buried under 107 inches of snow.  New York so far this winter has experienced 56 inches of snow, although its record was also experienced in 1995-1996 when 75 inches fell.

Besides the dramatic snowfall records this winter, average temperatures also have been colder than normal. Importantly, the winter weather has impacted much more of the United States than normal. On January 11th, every state except Florida had snow on the ground, including Hawaii where there were seven inches atop the dormant volcano Mauna Kea on the island of Hawaii. Slightly over 70% of the nation's areal extent was snow covered that January day as shown in Exhibit 6.



Source:  NOAA

Recent media articles have focused on the altered weather pattern that has been impacting Northern Europe and North America along with the Arctic for the past two winters. As we have written about, the polar vortex, a weather pattern that influences the location and movement of the jet stream, seems to have shifted bringing the cold weather. When there is a strong pressure difference between the polar region and the middle latitudes of the planet, the jet stream, a wind pattern that moves from west to east and normally across Canada, shifts into a tight circle around the North Pole and contains the frigid winter air at the top of the world.  When that pressure differential shrinks, the jet stream weakens and drifts southward bringing cold air into the middle latitudes (the United States and Europe) and allowing warm air to move into the polar region. This pattern shift has happened intermittently over many decades; however, it has been unusual for it to weaken as much as it has in recent winters.  Last year, one index had the vortex hitting the lowest winter-time value since record-keeping began in 1865. It was nearly that low last December.

Throughout the decade ending in the mid 1990s, the polar vortex was strengthening resulting in much warmer winters on average in Northern Europe and North America. This pattern led some climate change supporters to claim that global warming was responsible for the near end to traditional winter weather. Now that the pattern has reversed, and in a big way, climate change supporters are claiming that global warming is impacting the Arctic and is shrinking the Arctic sea ice cover, which contributes to the weakening of the pressure differential and the shift in the jet stream. Smarter climate change supporters are beginning to say it is too early to tell whether these weather changes are related to global warming, and certainly a two year timeframe is insufficient for overthrowing previous climate change theories dealing with the polar vortex.

AccuWeather.com's severe weather forecaster, Joe Bastardi, recently produced a video in which he offered an explanation for why his winter weather forecast missed the record snow and cold.  He is both an entertaining and smart weather forecaster in our judgment.  He firmly believes that natural forces help determine the weather and by seeking to find analog patterns in history is a way to understand the development and path of weather and storms.

According to Mr. Bastardi, the changed weather pattern has a lot to do with La Niņa, a weather pattern in the South Pacific Ocean that is associated with the cooling of the surface water and can alter the Northern Hemisphere's wind patterns bringing cooler and wetter weather to the U.S. and the Atlantic Basin. Mr. Bastardi has found that when there are back-to-back La Niņa years, temperatures across the United States get progressively cooler. If the La Niņa period is then followed by an El Niņo, winters get even colder. He bases his conclusions on looking at the analog years for back-to-back La Niņa years such as were experienced in 1949-50, 1954-55, 1973-74, 1998-99 and 2007-2008. In his view, "something is going on that is bigger than we understand."

The original AccuWeather.com winter weather forecast for 2010-2011 called for winter to be focused primarily in the Midwest and Northeast. The severity of winter would be contested in the southern portion of these various states. It was expected that the southern tier of the U.S. would not experience much of a winter and that Florida would be warm.

Exhibit 7.  Original AccuWeather Winter Forecast

Source:  AccuWeather.com

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