|Above: Steam rises from Lake Michigan on Friday morning, Jan. 25, 2019, in Milwaukee, Wisconsin. A cold blast sent temperatures plunging and prompted officials to close dozens of schools Friday. Even colder conditions are expected next week. Image credit: AP Photo/Carrie Antlfinger.|
Midwesterners are in for a dangerous round of bitterly cold air and extreme wind chills as January draws to a close. Temperatures are expected to bottom out from Tuesday to Thursday, hitting their coldest levels in several years in parts of the Midwest and Great Lakes. Less-extreme but still-noteworthy cold will overspread much of the nation east of the Misssissippi by midweek.
This Arctic outbreak—well advertised in long-range weather models—is in line with seasonal forecasts issued as far back as November by The Weather Company. As we discussed in a post on January 18, the outlooks gave increasingly high odds to unusually cold weather in the eastern United States toward the latter half of this winter.
The culprit behind next week’s cold blast is a lobe of the stratospheric polar vortex predicted to set up shop across the Great Lakes, far south of its usual position. The extremely cold upper-level low will pull a frigid dome of surface high pressure from central Canada into the central and eastern U.S. as the week unfolds. On Friday, ahead of the main event, temperatures fell below zero as far south as northern Missouri, with wind chills dipping below –20°F as far south as Iowa, reported weather.com.
|Figure 1. Ensemble forecasts from the European model (left) and GFS model (right), issued 12Z Friday and valid at 6:00 am CST Wednesday, January 30, 2019, are in strong agreement that an intense upper-level low will be centered near Lake Superior. The darkest blue circles in each map show where the height of the 500-millibar surface will be at least three standard deviations below average. Image credit: tropicaltidbits.com.|
Two hammers coming down: advection and radiation
The atmosphere has two main ways to produce cold weather at a given location. One is cold advection, a fancy term for colder air moving in from some other place. The other is radiative cooling—specifically, long-wave radiation heading out to space from Earth’s surface, which typically leads to a net loss of heat near the surface at night.
The initial phase of a cold wave tends to be dominated by advection, as winds from higher latitudes sweep across the landscape and import progressively colder air. In this phase, the impact of the cold is often accentuated by wind chill. The most dangerous aspect of the Tuesday-to-Thursday cold wave in the Midwest may well be the wind chills, which will probably lead to widespread closures of schools and other public entities. In Wisconsin, Minnesota and Illinois, west to northwest winds of 10 to 20 mph will blow, putting wind chills well below the –30°F mark for multiple days.
The Windy City will unfortunately live up to its name, with the National Weather Service office in Chicago predicting wind chills of –35° to –50°F for Tuesday night and Wednesday night. Wind chills this low can produce frostbite on exposed skin within 10 minutes. The NWS in Green Bay, WI, was advising that wind chill values on Wednesday and Thursday morning in Wisconsin would reach –35° to –50°F, and the NWS in Minneapolis was predicting wind chills of –35° to –55°F Tuesday night through Thursday morning.
A long stretch of below-zero cold
The largest number of records next week will likely be for cold daily highs, according to an NWS tool that compares temperatures in the National Digital Forecast Database against existing records. As of Friday afternoon, the NDFD forecast for next week would result in 75 record-cold daily maxima and 24 record-cold daily minima on Wednesday and Thursday. (Local NWS forecasts may differ from the NDFD database.)
Current forecasts have Chicago struggling to reach 0°F on both Wednesday and Thursday. This is an unusually long period of time for Chicago to stay below zero. To put some perspective on this potential cold, only eight times since 1872 has Chicago recorded sub-zero highs on at least two consecutive days, the most recent being early February 1996.
|Figure 2. All-time lowest temperatures recorded across the Midwest. Recordkeeping across this region extends back to the late 1800s. Image credit: weather.com.|
The very coldest temperatures of this outbreak will likely occur on Tuesday and Wednesday nights in the calm conditions right beneath the center of the surface high, wherever that happens to end up—perhaps somewhere in the eastern Dakotas, based on the 12Z Friday ensembles runs of the GFS and European models. The radiational cooling will be intensified by snow cover across the hardest-hit areas; an Alberta clipper is expected to drop several inches of snow from the Dakotas to the Great Lakes early next week, reinforcing the existing snowpack.
As of Friday afternoon, the coldest lows predicted by the NWS include –18°F at Madison, WI (Tuesday night), –12°F at Chicago (Tuesday night), and –21°F at Minneapolis (Wednesday night). As cold as these are, they wouldn’t even be enough to set daily record lows, much less challenge the all-time lows at these locations shown in Figure 2.
Output from the GFS model is running quite a bit colder than the official forecasts. The 12Z Friday run of the GFS suggests that surface temperatures could dip below –25°F at Chicago and below –30°F at Madison and Minneapolis on Wednesday night. However, models like the GFS are often too extreme with their longer-range forecasts of intense surface cold. In its Friday evening forecast discussion, the NWS Chicago office noted that various models do agree that temperatures at the 850-mb level (about a mile above the surface) will be close to all-time lows. The discussion also alludes to the challenge that NWS forecasters face when models project temperatures to be this extreme several days out:
"There is still time for model guidance to back off on the intensity of Arctic air mass. Keeping that in mind, I felt quite comfortable with the more conservative temperature forecast. It is much easier and preferred to slowly trend a forecast closer to all time records this far out, rather than jumping out forecasting all time records only to later have to back off on those extremes if model guidance trends less severe with the cold."
|Figure 3. Predicted temperatures (degrees F) at 6 am CST Wednesday, January 30, 2019, from the 12Z Friday run of the GFS ensemble forecast system (GEFS). Note that temperatures do not always dip to the levels predicted by models during extreme cold outbreaks like this. Image credit: tropicaltidbits.com.|
In general, climate warming from greenhouse gases is making it increasingly tougher to beat the very coldest overnight lows from the 19th and 20th centuries. On top of this, the urban heat island effect (another form of human-produced climate change) has intensified over time in the nation’s largest cities, raising local temperatures by several degrees.
Jon Erdman at weather.com summarized things this way: “For now, [the] all-time cold records appear safe. All this record talk aside, this will be a prolonged bitterly cold outbreak that is likely to be accompanied by at least modest winds at times, which will send wind chills plunging to dangerous levels.”
A blast of generosity from Canada
Along with bitterly cold air, Americans have seen an infusion of warmth from our northern neighbor in the form of surprise meals for staff required to work without pay at U.S. federal agencies during the government shutdown. Employees at several outposts of Environment Canada have donated funds and arranged for pizzas to be delivered to several NWS offices, including those in Glasgow and Great Falls, Montana; Grand Forks, North Dakota; Anchorage, Alaska; and even Norman, Oklahoma, far from the Canadian border. The mini-trend started when air traffic controllers in Edmonton, Alberta, arranged for pizza to be sent to their U.S. counterparts in Alaska.
On Wednesday, CBC News reported that Alysa Pederson, a senior aviation meteorologist in Edmonton, ordered eight pizzas for 15 employees working without pay at NWS Anchorage. "The whole reason we did it was to show them solidarity," Pederson told CBC's Radio Active Wednesday.
Dr. Jeff Masters co-wrote this post.
Huge shout out to the employees of @environmentca (Edmonton office) for ordering pizza for the @NWSSPC and @NWSNorman staff. Your kindness is deeply appreciated! Both operations areas perked up considerably upon the news from our colleagues to the north! #ThankYou— Elizabeth Leitman (@WxLiz) January 24, 2019