Cold Waves in Minneapolis, Minnesota and More.

Back in mid-December, 2008, I first wrote about cold waves in Minneapolis, MN. Since then, the temperature has managed to creep above freezing for only a few scant hours. So, most Minneapolites remain "in a frozen state." (pun intended!) And, although the mercury hasn't been below zero for too many hours, wind chills have been occasionally brutal.

Record Cold Spells

But the real news is that the current cold spell entered the record books. Not that it's the longest (far from it), but because it became tied for the the 12^th longest cold spell in recent weather records (dating back to 1891). And the streak would have been in reach of shattering others on its climb to the 9^th longest on record (if the temperature on Saturday, January 31^st didn't reach freezing).

Of note is the fact that until this cold spell, only two of these record cold streaks have occurred this century.

Figure 1 is a table showing extended streaks of below freezing days prepared by the Minnesota State Climate office. Note that this year's cold streak surpassed both the ones from 1918 and 1937 at 12:01am CST on January 30. Figure 4 shows the final ranking of this cold wave once it ended on January 31^st .

According to Peter Boulay of the Minnesota State Climate Office (personal correspondence), only whole days are used when tallying the length of below freezing streaks. For below zero periods, hours are used.

So, the most recent extended below zero snap (from 11pm CST on January 12, 2009 through 1pm CST on January 16, 2009) at the Twin Cities International Airport only amounted to 86 hours. This is the longest stretch of below zero readings since 93 hours occurred during the period 5pm CST January 31, 1996 to 1pm CST February 4, 1996.

I have keyed on Minneapolis in my initial climate forays because my son and his family live there. But now that people are recognizing the extent of the cold wave (including myself), other records and descriptions are being posted across the National Weather Service (NWS) and state climatology web pages.

Look for an updated content piece once January climatological summaries become available during the upcoming weeks.

January Thaws

Wherever it is cold, people look forward to a mid-winter warm-up. This is affectionately known as the "January Thaw." And, according to WCAX-TV meteorologist, Gary Sadowsky (Burlington, VT), "... it comes every year whether you like it or not."

I recall that when living in the middle-Atlantic states, the thaw usually occurred around January 20^th. Writing for their book Wisconsin's Weather and Climate, Joseph Moran and Edward Hopkins computed the thaw period for 10 cities in Minnesota, Wisconsin and Illinois. All 10 cities posted climatological warm-ups for the period January 21-24. At LaCrosse, WI, the average temperature jumped almost 7 degrees between January 20 and January 21! As expected, following the warmer period, temperatures dropped.

The Minnesota State Climate Office has been looking into January thaws, too. Climatologically (based on records since 1891), almost every place in the state has a greater than 50% likelihood of experiencing a January thaw (defined in Minnesota as a period of two or more days with daytime temperatures greater than 32^oF). Not surprisingly, the probability is highest in the southern parts of the state (Minneapolis-St. Paul at 92% and St. Cloud at 87%). But even the "Nation's Icebox," International Falls, has a 50-50 chance of having a January thaw.

Even though it warmed to the mid-40's on January 31^st, that was too little and too late for a two-day January thaw in Minnesota in 2009.

For Minneapolis, this means that the city will be experiencing only the 4^th winter in almost 120 years without a thaw. The last time the city went thawless was in 1979. Prior to that, thaw-free January's included 1978 and 1912.

This will likely be the first January since 1979 that there has not been a January thaw in St. Cloud and Rochester, as well. The last time there wasn't a January thaw in Duluth was in 2004.

Causative Weather Pattern

The culprit for such extended cold periods involves a weather pattern that allows a continued feed of arctic air southward into the upper Midwest. A persist upper level low over Hudson Bay and/or eastern Canada, coupled with an upper level ridge over Alaska or the northeast Pacific Ocean ensures this. Figure 2 shows the upper level wind pattern for January 26, 2009. However, when abundant snow cover is present (as it was in the 1977-1979 period and again in 2009), extended cold spells are even more likely.

Back in mid-December 2008, I wrote that folks in Minneapolis and St. Paul would soon be wishing for some of global warmth. About now, I'd say that some are probably ready to pay dearly for it.

Resource links

http://climate.umn.edu/doc/journal/streak0402.htm

http://www.hpc.ncep.noaa.gov/dailywxmap/index.html

http://www.nohrsc.noaa.gov/nsa/

http://www.wcax.com/Global/story.asp?S=7590053

http://books.google.com/books?id=LxajGKR4ZKkC&dq=january+thaw+illinois&source=gbs_summary_s&cad=0