The area’s warmest weather in over half a year arrives Wednesday—the beginning of a multi-day warm spell expected to send temperatures surging to within striking distance—but probably a degree or two short of—record highs in the low 80s Thursday and Friday. The warmth’s arrival coincides with March’s close. The 75-degree high predicted here Wednesday would become 2010′s first 70+ reading while 81 degree highs forecast both Thursday—April Fool’s Day, but NO joke—and Friday are at levels 30-degrees above normal. Those high temps are more typical of June than early April and eclipse 53-degree highs on the same dates a year earlier.
The incoming warm spell continues an above normal temperature trend which has dominated March and pushed readings 1.5-degrees above a comparable period a year ago. The month’s 2010 average of 40.9-degrees is 4.5-degrees above the long term average of 36.4-degrees, making it the 25th mildest Chicago March of the past 139 years.
An air mass responsible for 80s from western Iowa into the Plains Tuesday, is behind the warmth. Gusty southerly winds stacked vertically tens of thousand of feet into the atmosphere are helping propel the temperature surge.
March rainfall lagging the same period a year ago as area farmers plan for planting
With a new planting season just around the corner for area farmers and gardeners, soils remain a bit wet in the area—but possess a fraction of the moisture which saturated them a year ago. March has generated only a third of the rain observed a year ago to date—1.55 inches versus last March’s full month tally of 5.20 inches. Last year’s regular March downpours led into an incredibly challenging growing season which was so wet, many Illinois farmers were months late in getting crops into the ground.
Soil moisture is monitored carefully by long-range weather forecasters because of its potential to impact warm season temperatures. In-house analyses of Chicago’s summer temperatures in the seasons which have followed 21 drier than normal Marches since 1871, indicate a slight majority (62 percent of them) went to produce above average June through August temperatures.
Last summer’s abnormally cool temperatures and, in the eyes of the area’s hot-weather enthusiasts, its dismal four-days of 90-degree temperatures—17 such days are considered typical—was likely a by-product of prolific precipitation which began in February and continued through June. The precipitation soaked area soils, a development which makes it hard for really hot weather to gain a foothold. As temperatures warm over wet soil, evaporation rates increase and the moisture which returns to the atmosphere is available to produce more than the typical levels of cloud-cover and precipitation. Both impede warming and often lead to cooler than normal summer temperatures.
Though soil moisture isn’t as extreme in the Chicago area as a year ago, a large area of the Midwest to Chicago’s west remains wetter than normal. It will be interesting to see if this ends up affecting the region’s warm season temperatures.