Extreme jet stream causing record warmth in the east, record cold in the west

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.

Extreme January warmth in the East
To compensate for it's southwards bulge over the Western U.S., the jet stream is contorted into a sharp upside-down U-shaped ridge of high pressure over the Eastern U.S. This has allowed mild, subtropical air to flow northwards all the way to Canada, resulting in all-time records for January warmth to be tied or broken for at least eighteen sites over the past week. Notably, Mount Washington, NH (46°), Fayetteville NC (79°), and Bluefield, WV (72°) all tied or broke records for warmest January day over the weekend. In Michigan, the warmth was so unusual on Saturday morning that Traverse City, Michigan tied its record high temperature for January 12 at midnight, when the temperature had already risen to 50°.


Figure 2. The position of the jet stream is marked by where the strongest winds blow in the upper atmosphere. On January 14, 2013, the jet stream dove far to the south over the Western U.S., creating a U-shaped trough of low pressure that allowed cold air to spill southwards out of Canada. To compensate for it's southwards bulge over the Western U.S., the jet stream was contorted into a sharp upside-down U-shaped ridge of high pressure over the Eastern U.S. , allowing mild, subtropical air to flow northwards into New England and Eastern Canada. Image from wunderground's Jet Stream page.

Arctic sea ice loss: a potential contributor to extreme jet stream patterns
We've been seeing an increasing number of situations in fall and in winter in recent years where the jet stream has taken on the sort of extreme configuration that we are seeing today. Dr. Jennifer Francis of Rutgers has published research showing that Arctic sea ice loss may significantly affect the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. High-amplitude loops in the upper level wind pattern (and associated jet stream) increases the probability of persistent weather patterns in the Northern Hemisphere, potentially leading to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions. Arctic sea ice hit an all-time low during 2012 and remains near record low levels, so it is possible that Arctic sea ice loss contributed to the current extreme jet stream configuration, and the past week's spate of extreme temperatures on both sides of the U.S.

Other wunderground blogs: The Climate Lottery, and Easing the Global Water Crisis
Lead Forecaster Guy Walton at TWC keeps diligent track of monthly U.S. temperature records, and posts a regular "Climate Lottery" analysis of monthly and annual rankings of U.S. temperatures. His first wunderground post on the subject, Climate Lottery-Mega Ball Ranking of 2012 is now up in our blog section.

Wunderground's Angela Fritz's blog has a guest post on the global water crisis from Wendy Pabich, author of Taking on Water: How One Water Expert Challenged Her Inner Hypocrite, Reduced Her Water Footprint (Without Sacrificing a Toasty Shower), and Found Nirvana. Wendy holds a Ph.D. in environmental engineering from the Parsons Water Resources Laboratory at MIT, and will be starting a "water challenge" on wunderground in the upcoming weeks to raise awareness of water usage, and to help us all lower our personal water usage.

Jeff Masters