Wunderground.com - Dr. Jeff Masters, 1/14/13
Los Angeles, California recorded its coldest temperature in 22 years on Sunday, and record daily lows fell across large portions of the Western U.S. over the weekend. But meanwhile, much of the Eastern U.S. basked in record-breaking warmth, with temperatures reaching the upper 60s in New York. What's going on? Well, the jet stream--the upper level river of strong winds that marks the boundary between cold, Arctic air to the north and warm, subtropical air to the south--has worked itself into a very extreme configuration.
The jet is diving far to the south over the Western U.S., creating a U-shaped trough of low pressure that allows cold air to spill southwards out of Canada. The 34°F reading on Sunday morning in Los Angeles was the coldest temperature there since December 23, 1990. (The lowest temperature ever recorded in downtown Los Angeles was 28°F, most recently on January 4, 1949.) The -20°F observed at Grand Canyon, Arizona on Sunday morning tied for the coldest temperature measured there in 37 years of record keeping.
At least three other stations in the West had their coldest January temperature on record over the weekend (January 12 - 13.) And, according to wunderground's weather historian Christopher C. Burt, Lakeview, Oregon hit -26°F on Sunday morning, beating their all-time record low of -24°F set in 1888. This is the first site of the 298 sites that he follows on our Extremes Page to tie or break its all-time cold record since Santa Fe, New Mexico did so on Feb. 3, 2011. Since 1997, only four of the 298 stations that he tracks have recorded all-time lows; 71 have recorded all-time highs.
Figure 1. All-time records for the month of January set so far in 2013, as cataloged by the wunderground Extremes Page. The page is showing that three stations have set new January low-temperature records (excluding a bogus one in Texas), and seventeen have set all-time January high temperature records.
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