Tim's Weather World: Serene Severe Weather Season So Far

March, April and May are usually the worst months for the Chicagoland area in terms of severe weather but so far, so good.  There has not been one single report of severe weather in Illinois so far this year.  There have been only four reports in Indiana.  A thunderstorm is considered severe if it produces either 1″ diameter hail or larger, and/or wind gusts of 58 mph or stronger, and/or or a tornado.

Nationwide, it has been relatively quiet too.  There have been 710 reports of severe weather which includes 78 tornadoes.  Last year we had over 2000 reports of severe weather by this date and more than 150 tornadoes.  On average, the United States sees about 225 tornadoes by now.

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The influence of this year’s El Nino has a lot do with the quiet start to the severe weather season.  The jet stream has been a bit further south than normal and the water in the Gulf of Mexico is a bit cooler than average.  Both of these factors have mitigated severe weather.

Don’t be lulled into a false sense of security though.  We will have severe weather this season.  It is not a matter of if but when. 

Click here to download a brochure with severe weather safety tips.

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Warmth of this intensity at such an early date is rare; new records possible

If at some point in the past 24 hours you’ve asked, “isn’t weather as warm as THIS unusual? Temperatures aren’t typically anywhere near 80-degrees on April 1, are they?”, then pat yourself on the back!  Your “read” on the unusual nature of this warm spell is right on and very perceptive. Thursday’s predicted 82-degrees high is nearly 30-degrees above “normal” early April levels and would tie the 64 year old record for this date set in 1946. Such a high would be 29-degrees above the 53 recorded a year ago.

An analysis of Chicago’s observational weather record, which dates back to 1871, reveals only 11 of the past 140 years–8 percent of them—have managed to produce an 80-degree temperature by the close of April 1. A reading at or above 80 degrees Thursday would become only the 12th time since records began that the city’s official temperature has reached or exceeded 80 at such an early date!

It wasn’t until April 24th a year ago—more than three weeks from today—that the mercury first made it to 84-degrees in 2009.  The year’s first 80-degree reading typically occurs on or about April 22 at Midway Airport, and April 25 at O’Hare.

Wednesday’s 77-degree high beckons Chicagoans outdoors in droves

 
Temperatures Wednesday broke above 70 just after the noon hour—the first 70-degree reading here since early November and 2010′s warmest. Other area highs Wednesday included 81-degrees at Itasca and 80-degrees at Weather Bug sensors at Buffalo Grove and Aurora. High temperatures at Waukegan and Gary—both on the shores of chilly Lake Michigan—made it 79-degrees.

Wind trajectory forecasts produced by one of Environment Canada’s computer forecast models, which offer an indication of the source of Thursday’s warmth in Chicago, predicts the air over the city by mid and late afternoon was over Texas Wednesday.

 
Brush fires erupt in the wake of the sunniest March in 9 years; driest in 5 years
 
The remarkable warmth comes on the heels of Chicago’s sunniest March in 9 years and its driest in 5 years. The month’s 1.55 inches at O’Hare was a fraction of the 5.20 inches recorded last March. It’s little wonder a series of small brush fires have erupted in recent days. A combination of strong winds, low humidities and warm temperatures Wednesday proved the perfect combination for the eruption of fires at Lake in the Hills, Vernon Hills and Willowbrook. Some roads in the Willowbrook area had to be closed for a time Wednesday evening. 

The Chicago area’s precipitation trend is sure to be monitored closely in coming months as spring planting nears. Several 2-week computer rainfall projections generated Wednesday hint elevated rainfall is possible over the period. The first rains and even some thunderstorms are possible Saturday and several additional waves of rain could occur next week. 
 
 
Boston records wettest March; some suburban totals top 20 inches
 
Rivers continue to rise in the Northeast where historic flooding is on the way. Boston recorded 14.87 inches over the past month making it the wettest March on record and the 2nd wettest single month ever.  A typical March produces 3.85 inches there. Rainfall tallies in some surrounding communities topped 20 inches.

What's the difference between scattered and isolated thunderstorms?

Dear Tom,
What’s the difference between scattered and isolated thunderstorms?

-Joann Spencer

Dear Joann,
When applied to thunderstorms, “scattered” and “isolated” refer to the amount of the forecast area experiencing random, disorganized thunderstorms.
Scattered thunderstorms have an areal coverage at any moment of 10 to 50 percent and whose occurrence is random — that is, displaying no organization such as lines or clusters. Isolated thunderstorms are “loners,” well removed from any other thunderstorms and affecting less than 10 percent of the area.
“Scattered” and “isolated” refer only to areal coverage and do not address other thunderstorm issues such as severity, lightning intensity or flooding. The parent thunderstorm of the devastating Plainfield tornado of Aug. 28, 1990, that claimed 27 lives was an isolated storm.

Warmest temps in a half year on the way here even as record rains drench the Northeast

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.