Not since 1965 has the first day of astronomical spring in Chicago been any colder. The official Wednesday O’Hare high of 25-degrees was not only the chilliest peak daytime reading here in a month, it was colder than any “normal high” at any point of the year—including those in January, the city’s coldest month. The reading was 23-degrees below the March 20th normal of 48 and 60-degrees colder than the high of 85 on the same date one year ago.
March’s first 20 days an eye-catching 23+-degrees behind same period a year ago
The first 20 days of March are now running 23.7-degrees behind the same period a year ago—a stunning change. 34 of the past 48 days—71 percent of them–have posted temperature deficits, quite a turnaround for a cold season which started comparatively mild and with record-low levels of snowfall!
Huge pool of abnormal warmth aloft draped across the arctic sets up the latest “Greenland blocking pattern”, propelling chill southward into the Lower 48
The unseasonably chilly pattern which has descended on Chicago and the Midwest is being driven by a new round of atmospheric blocking in the arctic. The so-called Greenland block has returned and is predicted by global forecast models to dominate the closing weeks of March and spill over into early April, suggesting the below normal temperature regime in place since February, won’t be leaving soon. The strengthening March sun may contribute to modest temperature increases from time to time, but prolonged warming isn’t yet in sight.
Blocking patterns in the arctic, like the one now in place, occur when vast pools of warmer than normal air take up residence aloft. As the planet ‘s arctic regions have warmed, these blocking patterns have occurred with increasing frequency and with a variety of impacts felt to the south in the mid-latitudes.
Climate researchers point to the growing volatility of mid-latitude weather as examples of the sorts of changes which may be expected to become more frequent in years and decades to come as additional warming takes place.
The vast reservoir of warmer than normal air aloft, which currently covers much of the arctic, extends from northern Russia across the North Pole and into Northeast Canada. Such pools of warmer than normal air act to dislodge the frigid air indigenous to the arctic, sending the chill cascading southward into portions of the Lower 48.
The southward flood of colder air is, in the current situation, being fostered by a northern U.S. snowpack which covers twice the real estate that it did at this time last year, running from the Rockies across the northern Plains and Upper Midwest.
One of the seemingly counterintuitive weather developments which has resulted from the current Greenland block is that, even as Chicagoans and Midwesterners shiver through abnormally frigid temperatures, readings observed far to the north in coastal areas of Baffin Island and Labrador province in northeastern Canada as well as on much of Greenland’s coastline are actually running warmer than those observed in the Windy City.
Storm churning ashore off the Pacific a potential weather threat to the Midwest later this weekend
The latest storm system to churn into the West off the Pacific could impact Midwest weather this weekend. Model forecasts of the track of this system and of the atmospheric flow pattern by Sunday morning suggest this system will have to be monitored carefully across the nation’s Heartland.
A range of model forecasts puts the storm on a track from Texas into the Ohio Valley Saturday night into Sunday. Varied barometric pressures between that system and a huge Canadian high to the north are to set up a broad area of vigorous northeast winds in the region. And given the cold air predicted to hold here into next week, this could set the stage for for lake snow showers and flurries in addition to any “system snow” the storm may end up producing.
The track currently generated by a number of computer forecast models places the system’s heaviest snowfall to Chicago’s south. But, a common bias with a storm like this one is for early forecasts, to send it on a track south of the one it ends up following. That puts the Chicago area close to the storm’s “action zone” and therefore suggests developments will have to be monitored in coming days.
Should system adopt a more northerly track, Chicago could see Sunday wind and snow
A more northerly track could unleash significant snows on Chicago—though this is by no means a sure thing. Getting the system more completely sensed within the U.S. radiosonde (weather balloon) network in coming days is likely to firm forecasts of the new storm’s future path.