Sunday evening, a late-Spring storm system continued to generate severe thunderstorms from the southern Plains, to northwest Wisconsin. At latest count, 21 tornadoes were reported across Kansas, Oklahoma, and Iowa Sunday afternoon and evening. Many other areas were pummeled by large hailstones. This weather system is expected to shift slowly eastward on Monday, spreading the threat of severe weather into the Chicago area. As temperatures soar to the upper 80s Monday afternoon, and dew points approach 70 degrees, the atmosphere will become primed for rapid thunderstorm development. Strong winds aloft are forecast to further increase the potential for damaging winds and hail. The storm prediction center has suggested that our severe weather threat will extend into Tuesday.
Explainer
Thunderstorm clusters roaming the Plains states Saturday evening have re-activated a dormant severe weather season, spawning at least a half dozen tornadoes across Kansas and Nebraska. Storms may reach the Chicago area as early as Sunday night. Southerly winds will bring a surge in dew point temperature. Dew points in the 60s possess sufficient moisture to support severe thunderstorms. These readings are forecast to approach muggy, 70-degree levels on Monday. Along with elevated moisture levels, temperatures are forecast to reach the mid and upper 80s. These conditions, combined with strong winds aloft may bring the area its first organized
severe weather episode. The Storm Prediction Center suggests there is a slight risk of severe thunderstorms across the Chicago on Monday.
Lakeshore cooling persists a second day Saturday. Friday produced a temperature spread of up to 30-degrees between Chicago area beaches and the warmest inland locations.
While Kenosha and Highland Park, on the receiving end of easterly winds coming off chilly lake waters, ended up on the low end of the thermal ledger Friday with highs of 56 and 57-degrees, both Kankakee and DeKalb were warm, posting 85 and 82-degree peak readings respectively.
Saturday highs will repeat that trend with shoreline and beach temperatures holding to the low 60s while inland locations, head toward their warmest weekend temperatures since last September (37 weeks ago). Highs there will reach the mid 70s while near 80-degree readings are likely at the warmest south suburban observation sites.
80s return to the city Sunday, Monday and Tuesday after 2 day absence
Strengthening south to southeast winds return much of the city and inland areas to the 80s Sunday—the beginning of a fresh three-day string of 80s likely to run through Tuesday. It's conceivable a fourth 80-degree high may occur Wednesday.
80-degree or warmer daytime highs Sunday, Monday and Tuesday would mark the 6th, 7th and 8th time this year that temperatures have moved into the 80s.
Isolated thunderstorms unleash Friday’s heaviest downpours south of the city; spotty storm development ahead Saturday and Sunday
Isolated thunderstorms produced by towering cumulonimbus clouds (i.e. thunderheads), which reached heights up to 46,000 ft. Friday according to Doppler radar scans, are likely to re-develop in scattered fashion both Saturday and Sunday.
Though only a fraction of the full Chicago area may see these storms, the moist environment in which they’re developing could produce brief downpours.
Predicted warmth comes as meteorological spring 2013—currently the coolest in 17 years—enters its final two weeks
The predicted weekend warmth comes as the coolest meteorological spring season of the past 17 years moves into its final two weeks.
Since March 1—the start of meteorological spring—Chicago’s temperature has averaged 43.7-degrees. That’s a reading 1.6-degrees below the long term average and 10.4-degrees cooler than the same period a year ago.
"Trying" pollen season produces a 13th consecutive report of “high” tree pollen values Friday
This pollen season has been a miserable one for far too many area allergy sufferers. Pollen counts are generated Monday through Friday. Friday marked the 13th consecutive report in which the tree pollen value taken by Dr. Joseph Leija and distributed by Loyola-Gottlieb Memorial Hospital was categorized as “high”.
Most humid weather so far this year to build in during the days ahead; surging moisture levels to fuel t-storm clusters
The average of a suite of 7-day computer model rainfall estimates through next Friday and centered on Chicago has jumped to 1.80”. Such an average is the product of more than 40 individual computer-generated predictions. Those forecasts included rainfall estimates ranging from as little as 0.93” to as much as 4”.
Mid-U.S severe weather potential on the rise; Chicago area at risk, particularly Monday and Tuesday
Since 2000, May has ranked as the top tornado-producing month across the greater Chicago area—a region which includes 17 counties from southern Wisconsin to northern Illinois and northern Indiana.
Of the 78 twisters which have been logged since the start of the 21st century, 26 of them—33% have occurred in March. That’s why it’s little surprise the area may be headed for some challenging thunderstorm clusters capable of severe weather production in the days ahead. This is particularly true of thunderstorms predicted to “bubble-up” into a vigorous overhead spring jet stream Monday and Tuesday next week.
Waves of severe weather are predicted to sweep the Plains Saturday then extend eastward into the Midwest Sunday.
Chicago is close enough to the area of potential severe weather that any storms which develop later Sunday into Sunday night will have to be monitored. But, it’s the Monday, Tuesday and possibly Wednesday periods which appear likely to warrant the greatest attention.
Temperatures reached the mid and upper 80s across portions of the Midwest, along and south of a frontal boundary draped from South Dakota to Tennessee.
High humidity levels were pooled along this boundary, giving rise to thunderstorm clusters scattered from Texas to the Canadian border. As the front to our south lifts north of Chicago Sunday and Sunday night, similar conditions can be expected to overspread the area. Dew point temperatures which relate to the amount of water vapor in the atmosphere, are forecast to jump into the 60s on Sunday, and approach 70 degrees on Monday. This means that thunderstorm coverage and frequency can be expected to increase Sunday night, and continue into midweek. Rainfall amounts of 1 to 2 inches are forecast during this period.
It’s been quite a run, but it’s over---at least temporarily! The string of three 80-degree and higher temperatures logged this past week has ground to a halt with the arrival of cooler easterly winds off Lake Michigan.
Highs hit 91 Tuesday, 84 Wednesday and 83 Thursday---readings more typical of July than May and well above normal. The warm spell was the Chicago area's longest in the more than 8 months since five 80s occurred from September 2 through 6.
There have been five official 80-degree or warmer highs to-date in 2013 compared to 12 a year ago. Weather records here dating back to 1871 indicate only 37 percent of the 142 years since then have generated five 80s through May 16.
It may be chilly in lakeside areas Friday, and cool there Saturday. But, take heart warm weather enthusiasts. Temperatures resurge later this weekend and into the middle of next week. And that warmth is to take hold in an air mass likely to become quite humid.
With a jet stream predicted by our models to be slicing through Chicago's airspace next week, prospects that severe thunderstorms may break out are to surge. That possibility is driven home by research into what's happened with comparable meteorological set-ups in the past.
O'Hare temps had plunged 25-degrees off the 2 pm Thursday high by nightfall as easterly winds took hold
Temperatures were in a tailspin in lakeside counties of late Thursday. East winds funneled lake-chilled air into much of the area.
O'Hare’s temperature by late evening had plunged 25-degrees off the day’s 2pm 83-degree high. And the WeatherBug sensor at north suburban Kenilworth indicated a chilly upper 40-degree reading had replaced the 77-degree Thursday afternoon high recorded there.
More dry hours than wet ones this weekend
While a scattering of showers and thunderstorms is to erupt over as much as 40 to 60 percent of the metro area later Friday, weekend rains and thunderstorms will be quite scattered and the exception rather than the rule.
Rain coverage Saturday is likely to occupy only a fraction of the metro area with an even lower percentage of the Chicago area getting in on rain Sunday, despite re-surging temperatures and humidities.
Weekend severe storm eruptions in the Plains this weekend could shift into Chicago and the Midwest in the Monday/Tuesday time frame
Several waves of strong and potentially severe thunderstorms are likely to sweep the Plains this weekend then ease eastward into the Midwest next week.
A review of 15 meteorological set-ups similar to the one predicted next week by the Weather Service's GFS forecast model indicates a moderate to high risk of strong thunderstorms could take place across sections of the Midwest in the Monday afternoon and/or Tuesday time frame---a development which will have to be monitored.
Big changes loom which are to bring a jarring but temporary end to the warmth we've enjoyed much of the past week.
Strengthening easterly winds and the chilly waters of Lake Michigan are the culprits. Longtime Chicagoans know the area is just a wind-shift away from a spring chill---and such a wind-shift looms.
Easterly lake breezes are to repeat the localized (i.e. limited coverage) cooling observed in recent days Thursday afternoon. While areas away from the lake head into the 80s for a third consecutive day, easterly winds off Lake Michigan's chilly waters will transport cool air ashore, taking lakeshore and beach temperatures down to the 50s later today. That cooling is to become far wider in scope as easterly winds strengthen Thursday night. It's a development destined to limit Friday highs to the 50s and 60s.
Highs here the past two days the warmest in the over 8 months since last Labor Day
Wednesday's 84-degree high at O'Hare followed the area's earliest 91-degree peak reading in 31 years Tuesday. Together, the past two days' peak readings have been the warmest observed here in the more than eight months since last Labor Day weekend.
Returning warmth, surging humidities could ignite severe weather in the heretofore quiet 2013 severe weather season
The chill of coming days is to be replaced by resurgent warmth and humidity later this weekend into early next week. But with elevated temperatures and dew points on the way as part of this resurgence and a jet stream predicted to take up residence aloft in the Midwest, the stage could be set for an unwelcome awakening of the 2013 tornado and severe storm season.
Chicago's earliest occurring 91-degree high temperature in 31 years followed by less than 36 hours frost and a 36-degree daybreak temperature early Monday morning.
Tuesday’s 91 occurred at O’Hare at 3:22 p.m., close to the time that Midway Airport was logging a 90-degree high. Both readings were more than 20-degrees above the normal of 69. It was a weather turnaround of historic proportions.
Never before in Chicago had a set of May high temperatures increased by 55-degrees in less than 2 days time!
Jarring shift from wintry snows to mid-summer-level heat carries sections of the Plains and western Midwest from a foot of snow to triple-digit temps in under 2 weeks
Even more dramatic were the stunning weather changes which occurred to Chicago's west Tuesday. Soaring temperatures smashed records from Nebraska into western Iowa, Minnesota and western Wisconsin---areas which less than 2 weeks earlier had been crippled by a record-breaking foot or more of late-season snow.
Albert Lea, Minnesota recorded a 100-degree high Tuesday. Only 12 days earlier that city had been buried under a 10-inch accumulation of snow.
Iowa's state climatologist Harry Hillaker reported in a special weather statement out of the National Weather Service Forecast Office in Des Moines Tuesday that 100-degree or higher temperatures have occurred in the month of May on only 11 occasions since official weather records began in the state in 1873. Even rarer have been 100-degree readings two weeks after a major snowstorm. Hillaker reports this has happened only a few times over that period.
Just 17 of the past 142 years have recorded 90-degree temps by May 14 in Chicago
For a 90-degree temperature to occur here by May 14 is a rare meteorological occurrence ---something which has occurred in only 17 of the past 142 years. That puts the climatological probability of a 90 this early in the season in Chicago at just 12%---far from a slam-dunk.
Abnormal heat breaks records across at least 8 states; sends earliest 100+-degree temps into a number of cities to Chicago’s west
For a second day Tuesday, temperatures records fell across a multi-state area as heat spread eastward out of the Rockies.
Omaha and Lincoln, Nebraska each recorded their earliest 100-degree or higher temperatures on record--- with highs of 101 and 100-degrees respectively. The same was true in Sioux City, Iowa where the mercury hit 106-degrees Tuesday---the hottest temperature ever recorded there in May. Sioux City’s previous record May high had occurred 79 years earlier in the Dust Bowl year of 1934 when a 105-degree reading was logged.
In Rochester, Minnesota, Tuesday’s 97-degree high became that city's hottest reading ever recorded so early in the year.
Temps pull back 10-degrees Wednesday but remain well above normal; readings to peak in the low 80s
An unseasonably warm Wednesday is ahead despite a 10-degree pullback in high temperatures. The predicted high of 81-degrees will still be more than 10-degrees above normal.
Lake breezes Thursday and better organized easterly winds off Lake Michigan Friday are to lower temperatures further in the days ahead, especially in lakeside counties.
Predicted onset of warmer, more humid weather this weekend behind higher 7-day rainfall numbers
Warmth and increased humidity stage a comeback this weekend with temperatures returning to the 80s by Sunday and Monday, if current forecast trends continue. The influx of moisture will fuel t-storm clusters expected to occur in scattered fashion and separated by rain-free hours. Nonetheless, cumulative rainfall totals may well surge above normal in the coming week suggesting a wetter overall pattern may be coming together.
A more dramatic warm-up than the one predicted Tuesday has never occurred in Chicago during May. Tuesday's predicted temperature surge to a July-level high of 88-degrees at O'Hare would be a 52-degree increase from Monday morning's chilly, frost-generating 36-degree low. That would be a first here and establish a new record for the largest 2-day temperature surge in the month of May.
There have been past "day-to-next" temp increases of that magnitude at OTHER times of the year here. A 52-degree surge Tuesday would tie with eight other years since 1871 as the city’s 11th- largest increase over a two-day period.
It's been a decade since temps last warmed by that much over two days and that occurred April 13-14, 2003 when readings soared from from 29 to 85-degrees.
Incoming warmth part of a warm surge which broke records across 9 Plains and western states Monday
The pool of abnormally warm air from which Tuesday's warmth emanates generated record-breaking highs across 9 states Monday---from California east to Montana, the Dakotas, Nebraska and Kansas.
Salt Lake City, Utah recorded its earliest 93-degree high on record.
Temperatures flirted with triple-digits in Kansas and topped 100 out West Tuesday
Afternoon highs Tuesday neared triple digits in Kansas and topped the century mark in portions of Utah, Nevada, interior California and Arizona.
Highs of 99-degrees were recorded at Ulysses; 98 at Phillipsburg and 97 at Oberlin---all in Kansas. Farther west, St. George, Utah hit 102-degrees while Fillmore---also in Utah---topped out at an even 100-degrees.
In nearby Nevada, Laughlin reached 109-degrees and Overton hit 108 while Bullhead City, Arizona broiled at 108 and Parker recorded a 106-degree max.
Capped atmosphere means weak cold front to pass precipitation-free here Tuesday night despite influx of Gulf moisture and presence of strong wind shear
The prediction of surging dew points later Tuesday and Tuesday night, a sign of more humid air's arrival, plus forecasts of high atmospheric energy levels and a vigorous shift in wind speeds with height----what meteorologists refer to a vertical shear---would at first glance appear to support the eruption of powerful thunderstorms with a southbound cold front Tuesday night. But computer models depict a "capped" atmosphere---one in which temperatures don't decline with height in their usual fashion, as well Chicago's position under the "nose" of a powerful pocket of upper level winds, as factors predicted to thwart what might otherwise be vigorous thunderstorm development Tuesday night.
This suggests the cold front will do little beyond producing a shift in Tuesday night's powerful ground-level winds here. Temperatures are predicted to hold at unseasonably mild levels 18-degrees above normal overnight,
Influx of Gulf moisture with weekend warm surge could set the stage for several thunderstorms
It's late this week and over the coming weekend which pose the best chance of generating thunderstorms. They're likely to arrive in widely spaced clusters, suggesting many rain-free hours are likely to be interspersed with what looks to be a new round of 80-degree temperatures.
Quietest tornado/severe weather season in nearly 60 years could become more active here Sunday
Sunday afternoon or night could prove a different story. Jet stream winds will be slicing through humid air in place by that time raising the specter of potentially vigorous thunderstorms in a severe weather season which, up to now, has been the quietest across the U.S. in nearly 60 years.
The average date of the latest Spring freeze in Chicago is April 17th. Given year-to-year variations in weather patterns, May 15th is typically considered safe for planting sensitive vegetation. Monday's chilly start is expected to be the last threat of frost for the next 7 days, and possibly for the season. Dramatic warming is due to arrive on Tuesday, with temperatures reaching mid-summer levels. Readings are then expected to turn cooler, but remain above normal for mid May. The latest freezing temperature in Chicago occurred on May 25th, 1992. Frost also occurred over the Memorial day weekend that year, with low temps dipping into the 20s in some suburban locations. Medium range computer forecasts do suggest a return to colder temperatures after the upcoming weekend, but frost is not expected.
Despite ample sunshine, temperatures on Sunday should climb only into the lower and middle 50s making this the city’s chilliest Mother’s Day since 2002 when the high reached just 50 degrees. With clearing skies and light winds expected Sunday night, temperatures are expected to approach the record low of 34 degrees Monday morning with frost possible in areas away from the lake. Warmer air approaches Monday as temperatures rebound into the lower 60s, but arrives in earnest Tuesday and Wednesday as temperatures surge to the highest levels of the year reaching the upper 80s Tuesday and approaching 90 on Wednesday. Some thunderstorms could develop Monday night, but the best chances for precipitation arrive ahead of a cold front late Wednesday or Wednesday night.
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