New Blast of Cold Air Invades Midwest U.S.

A frigid blast of Arctic air will bring some of the coldest late February temperatures seen in decades to the eastern 2/3 of the U.S. this week, with temperatures 15 - 30° below normal commonplace. The cold air isn't going anywhere fast, and will stick around through early next week. The cold blast is due to an extreme jet stream pattern we have seen before this winter--a sharp ridge of high pressure over California, and a large trough of low pressure over Eastern North America. This upper air pattern was described by the National Weather Service in Buffalo, New York on Tuesday as one that occurs less than once every 30 years in late February. The intense cold is already affecting the Upper Midwest this Wednesday morning. My vote for worst winter weather of the day goes to Central Minnesota at Alexandria, where a temperature of -8°F this morning combined with winds of 14 mph to make a wind chill of -28°. The winds are expected to increase to 25 - 30 mph Wednesday afternoon with higher gusts, creating blizzard conditions. In Chicago, the intense cold is expected to put the December - February average temperature for this winter below 19°, making the winter of 2013 - 2014 the 3rd coldest winter in the Windy City's history. Only the winters of 1978 - 1979 and 1903 - 1904 were colder.


Figure 1. Great Lake ice cover as seen on February 19, 2014, by the MODIS instrument on NASA's Aqua satellite. Ice cover on North America’s Great Lakes reached 88 percent in mid-February 2014—levels not observed since 1994. The average maximum ice extent since 1973 is just over 50 percent. It has surpassed 80 percent just five times in four decades. The lowest average ice extent occurred in 2002, when only 9.5 percent of the lakes froze. Image credit: NASA Earth Observatory.

Rain coming to California
Unlike previous versions of this extreme jet stream pattern, though, the ridge over the Western U.S. will not be very persistent. The ridge of high pressure over California, which brought numerous record high temperatures for the date on Tuesday, will get broken down by a weak low pressure system on Wednesday and Thursday. On Friday and Saturday, a more intense storm system will smash through the ridge, bringing moderate to heavy rain to much of drought-parched California. This storm will then track eastwards, potentially bringing a major snowstorm and destructive ice storm on Monday to Illinois, Kentucky, Indiana, Ohio, West Virginia, and portions of the Mid-Atlantic and Northeast U.S.


Figure 2. Departure of temperature from average at 2 meters (6.6') as diagnosed by the GFS model at 00 UTC February 26, 2014. A negative phase of the Arctic Oscillation (AO) created a sharp kink in the jet stream (Figure 3), which allowed cold air to spill southwards out of the Arctic over the Eastern U.S. Compensating warm air flowed northwards into the Arctic underneath ridges of high pressure over Alaska and Europe. Data/image obtained using Climate Reanalyzer™ (http://cci-reanalyzer.org), Climate Change Institute, University of Maine, Orono, Maine.


Figure 3. Winds at a height where the pressure is 250 mb show the axis of the jet stream, seen here at 00 UTC February 26, 2014. A sharp trough of low pressure was present over the Eastern U.S., and unusually strong ridges of high pressure were over the Western U.S. and the North Atlantic. Data/image obtained using Climate Reanalyzer™ (http://cci-reanalyzer.org), Climate Change Institute, University of Maine, Orono, Maine.

Wanted: professionals willing to speak about climate change to local groups
If you are a professional or graduate student with a strong background in climate science, the world needs you to reach out to local audiences at schools, retirement homes, the Chamber of Commerce, etc., and share your expertise. A new initiative by the University Corporation for Atmospheric Research (UCAR) and the United Nations Foundation called climatevoices.org is launching a Science Speakers Network this spring, with the goal of bringing scientists and their local communities together for real dialogue on climate science that speaks to citizens’ current and future well-being and responsibility as members of a community and democracy. Materials for context-setting presentations will be offered as will coaching regarding how to begin conversations about climate change with fellow citizens. If you are interested in volunteering for this network, please go to climatevoices.org and create a profile.  Profiles will “go public” when the full web site is launched in April. Once you create a profile, you will be kept up to date on Climate Voices progress including construction of the full web site, availability of presentation materials, webinar coaching, and plans for project launch. For any questions, please contact: Cindy Schmidt (UCAR), cschmidt@ucar.edu. I have my own set of slides I use for such talks that anyone is welcome to borrow from, available at http://www.wunderground.com/hurricane/2013/climatetalk.ppt.

Jeff Masters