Longer days, stronger sunlight up against snow-pack and temp-restraining blocking pattern
By wgnweatheron February 16, 2010 11:22 PM | Permalink
With each passing day, the momentum for seasonal warming increases. Days have grown longer by 94 minutes since Dec. 21 and are to lengthen another 79 minutes in the coming month. All the while, the sun's rays arrive with greater energy as it follows a trek across the sky each day higher and higher above the horizon. This shift in the sun's daily trajectory overhead has allowed sunlight intensity in Chicago to more than double since December. But these aren't the only factors pushing toward warming. The sun has risen in the past month across arctic regions of North America after a 2 month absence. This will eventually decrease the supply of available cold air by contributing to warming over the northernmost reaches of the continent.
But even with all these factors at play, formidable obstacles to warming must be overcome---something that's obvious in the fact Wednesday is to mark the 12th consecutive day with high temperatures which fall short of typical mid February levels. The widespread snow pack in place across the 56.3 percent of the country is among them. It reflects incoming sunlight, which might otherwise warm the air, back to space. Clouds also interfere with warming by blocking sunlight. Perhaps most significantly, the intransigent atmospheric blocking pattern at arctic latitudes from Greenland to Alaska, which has forced the reservoir of cold air normally situated from the North Pole into Canada, south into the U.S.---particularly areas east of the Rockies. This blocking shows little sign of relaxing in the coming two weeks. During that period, there may be a few comparatively brief up-ticks in temperature thanks to the growing strength of sunlight---but there's little evidence the overall pattern is likely to undergo a massive change any time soon. This appears to limit prospects for strong warming through the remainder of February and into early March. In fact, colder air may replace the moderately intense chill currently covering Canada in the next week allowing it to extend icy late-season tentacles into the northern tier of states next week, threatening a reinvigorated storm track along its southern periphery.
Chicago in the midst of its snowiest February in 29 years
Flurries are to flutter earthward here in spells Wednesday--- particularly in the Indiana/Michigan snow belt. This takes place in a February which is already the snowiest since 1981---29 years! An official 15.5-inches is on the books at O'Hare--- three times the long term average of 5.2 inches and nearly 78 times the 0.2 which February had to its credit the same time a year ago. A review of seven previous seasons in which February was incredibly snowy reveals five---71 per cent of them---continued on a snowier than normal path. Weather history here reveals a quarter (27 percent) of Chicago's biggest late season snows (6" or more) have occurred beyond Feb. 17.
Beyond Wednesday's Indiana lake snow showers, this weekend is being monitored for a possible snow system
Many questions remain---but there continue to be hints a snow system could sweep northeastward into the Midwest from the Plains this weekend. Much will depend on the track the system ultimately follows and on its strength. Stay tuned.
LOL, J/K. Careful, that's some powerful stuff there. And I'm NOT kidding about that.
