January 2, 2019
New hope for some actual “winter weather”
Sudden Stratospheric Warming (SSW). I first became familiar with that term in early 1977. For those of you with good memories, you’ll remember January 1977 as the coldest month in Louisville’s recorded weather history. And it featured a good bit of snow as well. At the time, the reason was given as rapidly warming stratosphere temperatures over the Arctic. Some studies of the stratosphere began in the 1950’s, but it remained a rather esoteric field until 1977 when Mother Nature decided to put on a demonstration of the full effects of SSW. January started normally, but by the second week we were covered with snow and extreme cold. The cold air just kept on coming. The average temperature for the month was 18.6 degrees – far below the previous record. In early February, warmer weather returned and dominated the rest of the month. That was it. Four weeks of the coldest weather we’ve ever seen!
Today, many people enjoy walking over the Ohio River on the Big Four bridge. Back in 1977, however, many people walked to Indiana across the frozen Ohio River.
What brings up this discussion about the SSW is that we’ve just experienced another one. As far as I can tell this warming event is not nearly as strong as the 1977 event. Even so, the general consequences of a SSW remain the same. The sudden warming fouls up the circulation of the now commonly-called Polar Vortex. In recent years, the media have blamed the Polar Vortex for just about every moderate to strong winter storm. True, but somewhat misleading. Usually the storms are created by a strong pocket of atmospheric energy which breaks off the Vortex and digs south into the U.S. During a SSW event, however, the warming actually breaks up the vortex into two (rarely three) major troughs which drop out of the Arctic into the middle latitudes. Usually, the strongest cold weather hits Europe while the weaker one sets up over eastern North America.
Normally, the time between the appearance of the SSW until the consequences reach our surface weather is two weeks. So, right about the middle of this month, our mild winter will vanish for about four weeks. Cold, and probably snow, should be plentiful during that time.
Don’t give up on winter yet!