Of all months, few have a wider meteorological repertoire than April. It’s a characteristic evident in the predicted weather swings of the next two weeks. The cool temps of coming days yield to milder readings and bursts of thundery weather by next Tuesday and Wednesday. Chicago’s “normal” (most recent 30-year average) daily high temps rise over the coming 30 days from 53° on April 1 to 64° on April 30—an 11° increase! Only March boasts a more significant monthly surge in daytime highs.
Chicago has experienced everything from snowstorms to tornadoes and occasional 90° temperatures in April.
April 1-2, 1970 hosted a crippling 10.7” snowstorm. Only three years earlier, the infamous Oak Lawn tornado dipped from area skies on April 21. Other twisters occurred in Belvidere and Lake Zurich. That April 1967 tornado outbreak remains Chicago worst on record.
-Tom Skilling
March 2005 Archives
Hail, and lots of it, accompanied the Chicago area's first outbreak of severe weather Wednesday afternoon and evening (March 30). More than six dozen reports of hailstones 0.75" in diameter or greater were logged by the National Weather Service (NWS)-Chicago Forecast Office.
Several of the t-storms moved along at speeds as high as 64 mph. Little wonder a 62 mph wind gust was reported at DuPage County Airport in West Chicago--and it's likely, given the speed at which these storms moved, that even higher gusts may have occurred in parts of the Chicago metro area but, because they occurred in unmonitored areas, speeds were unavailable. NWS Meteorologist Nathan Marsili at the Chicago office tells us the so many hail reports flooded the office in such a short period of time during Wednesday's severe weather assault that some duplicate observations weren't listed when they occurred in areas already logged as having received hail.
The NWS-Chicago office issued 23 timely severe weather warnings during the outbreak: 16 severe t-storm warnings, 4 marine warnings and 3 tornado warnings. The area was placed under a series of tornado and severe t-storm watches by NOAA's Storm Prediction Center.
--Tom Skilling
Pictures of Chicago's Hail Courtesy of Brad Sowers and Dan Hanson:
Photos by Brad Sowers
Photo by Dan Hanson
One of Chicago’s five warmest late March periods in more than a century ended with powerful wind and hail generating t-storms late Wednesday. The day’s official high temperature of 77° was 25° above normal! Readings that warm typically occur three weeks later around April 19.
Late day t-storms took advantage Wednesday of a lower than average freezing level in the atmosphere, generating more than six-dozen reports of hail 0.75” in diameter or greater across the metro area. Will County alone logged 23 such reports followed by Cook County with 12. Firefighters at Engine 127 near Midway Airport reported hail covering the ground around 6:45 p.m. Hailstones in Lemont reached 2.75” in diameter—the size of baseballs. And Joliet, Romeoville and Woodridge were hit by 1.75” hail. It was the first time since 1992 March t-storms in the city have been hail producers. More than 400 cloud-to-ground lightning strokes flashed across the area in one ten minute period around 6 p.m.
Photo by John J. Kleeman
Wednesday's powerful t-storms, which exploded to life in the day's near
record warmth, produced more than large hail. Mammatus clouds, observed
and photographed by J. Kleeman in Chicago's northern suburbs and Ron
Donais in far west suburban DeKalb, graced the underside of towering
cumulonimbus (thunderhead) cloud anvils. This type of cloud formation
often denotes extreme turbulence. Strong surface wind gusts with the
t-storms underscored power of the storms, which radar tracked moving at
speeds up to 64 mph.
THE CHICAGO AREA'S
PEAK WEDNESDAY T-STORM
WIND GUSTS:
Aurora: 47 mph
DuPage County Airport: 62 mph
Kankakee: 44 mph
Midway Airport: 43 mph
O'Hare International: 43 mph
Rockford: 47 mph
Waukegan: 46 mph
Photo by Dan Lauer
This ominous WALL CLOUD, an isolated lower of the cloud base near the
rear southwest quadrant of a t-storm indicating a region of strong
upward vertical motion and an area to be monitored for possible tornado
development, was captured by storm chaser Dan Lauer west of the city
near Northern Illinois University in the DeKalb area.
Photo by Deborah Pitstick
Here is a picture of a double rainbow (second one is pretty faint) as
seen this evening at 5:30 in Geneva, IL.
Many thanks to all for the wonderful photos!!
Warm weather isn’t over yet. A second day of 70s appears a good bet Wednesday amid strengthening south winds likely to gust over 30 m.p.h. by afternoon. An intense spring storm in the Plains is responsible for the wind and warmth. And, the system could spin up even stronger gusts Wednesday night once a wave of potentially severe late afternoon or evening t-storms sweeps across the area. The powerful, post squall line winds tonight are to be associated with a storm feature known as the dry slot—a region within which air sinks vigorously, producing the narrow cloud-free corridor or indentation in the cloud mass which lends storms their comma shape when viewed on satellite imagery. This wedge of dry air can host particularly powerful winds, because it marks a region in which the air flow through a deep layer of the atmosphere is moving in the same direction. That’s a formula which could lead to overnight gusts of 40 m.p.h. or higher at times.
The year’s first 70° high—the mildest reading here since 72° on Oct. 30—is a good bet Tuesday. Sun-filtering high clouds may well shave a few degrees off temperatures at some locations, restricting highs there to the mid/upper 60s. And, in communities closest to Lake Michigan’s northeast Illinois shoreline, an easterly component to Tuesday’s dominant southerly winds is likely to restrict highs to the low/mid 60s. But, for the rest of the metro area, readings Tuesday will surge 5-10 degrees above Monday’s. An official 70° high Tuesday would nearly match the 134-year average date for the region’s opening 70° reading of the year, which is March 31. Normal highs of 70° don’t occur here for another month and a half (May 16). The 60° high at O’Hare was the city’s highest in three weeks.
Big rains flooded parts of the East Monday, establishing daytime rainfall records at New York’s Central Park (2.94”) and in parts of five states from Florida north to Delaware.
After a month-long chill, March will exit on a significantly warmer note. Today’s highs near 60º are just a precursor to a surge of warmth that should send temps into the lower 70s Tuesday. Even lakefront areas should enjoy the warmth Tuesday as brisk southwest winds overcome the lakeside cooling that will rob those areas of today’s warmth. Clouds and showers will limit highs to the 60s Wednesday before the chill returns by week’s end, accompanied by clouds, rain and gusty northeast winds.
Most of the nation enjoyed a mild and tranquil Easter except for the Southeast, where warmth and humidity fueled severe thunderstorms. Tornadoes were sighted in south-central Alabama near Montgomery, and hail and high winds blasted areas of Georgia, Tennessee and Kentucky. Florida basked in warmth with a record high of 89° set at Vero Beach.
After seemingly endless weeks of clouds, cold and snow, spring weather will finally arrive in Chicago early this week, though albeit, its stay will be short-lived. The mercury will rise in leaps and bounds with highs increasing around 10 degrees each day after today’s 50º high reaching the balmy 70º mark by Tuesday. Spring warmth should continue Wednesday with readings in the the middle and upper 60s, but a round of active thunderstorms will signal the death knell for the brief warm spell as a return to northeast winds sends temperature tumbling even faster than they rose, falling back into the lower 40s by Friday with the possibility of wet snow mixing in with a cold rain.
This week’s brief flirtation with spring warmth may come with a severe weather price tag, a weather feature that has been totally absent from the Chicago meteorological scene so far this chilly month.
Wet snow dusted colder outdoor surfaces Friday in parts of the Chicago area—at times reaching a depth of 0.5”. But, it didn’t last long. Total snowfall in south suburban Plainfield reached 1.5”—the heaviest reported in northern Illinois. But, the warm ground and above-freezing temperatures meant the snow melted nearly as fast as it fell. The same was true at Midway Airport where little of the 0.7” stuck. Chicagoans have shivered through one of the 32 chilliest March 1-25 periods on record, boosting the need for home heating by an estimated 27 percent over the same period last year. Seventy-six percent of days this month have been below normal, and only five Marches have been cooler to date since 1970.
Meteorological springs in Chicago have warmed slowly but steadily since the 1930s, according to March-May readings by decade at Midway Airport. Springs in the 1990s averaged more than 2-degrees warmer there than those in the 1930s.
Wet snow is in the air again Friday. But, above freezing ground temperatures are likely to limit accumulations to colder outdoor surfaces, i.e. grassy areas, some sidewalks, less traveled roads, etc. And, even these accumulations should be marginal—a far cry from the 70” of snow measured with this storm since Saturday at the 9,600 ft. level near Alta Collins, Utah. The system’s snowfalls topped 20” in parts of Colorado, Wyoming and Utah.
The long spate of cold days here this month has pushed thoughts of thundery spring weather aside. It’s one reason many Midwesteners may be surprised to learn that the 2005 U.S. tornado and severe weather season is off to an active start. Reports of twisters across the country are nearly twice those recorded by this time a year ago. History indicates April often marks the beginning of Chicago’s highest severe weather risk period.
-Tom Skilling
Temperatures Thursday may surge to 50° briefly over parts of the Chicago area—but the mild readings won’t last. A windshift to the NE is predicted this afternoon as the circulation of an approaching storm system takes hold. The storm produced huge snow accumulations out West Wednesday. Solitude, Utah was buried beneath 20” and nearby Deer Valley measured 16”. Rocky Mountain residents aren’t alone. Winter-weary residents of the Northeast are battling wind-driven snow again. From northern Pennsylvania east to southern New England, 10-12” totals are likely before an oceanbound storm departs Thursday night. Parts of that region are reeling with 90-100” seasonal snow tallies.
The Chicago area is in for an additional snow this week too. Rain falling into dry air Thursday night will evaporate—a process which produces cooling, switching rain to snow from NW to SE by Friday.
March, a month known for putting all of its meteorological wares on display, certainly lived up to its reputation across the U.S. Tuesday. While one storm—responsible for a record-breaking 18” of snow over northern Nebraska and a swarm of twisters in its warm southern flank from Arkansas to Florida churned east—a new Pacific storm raced ashore. It prompted winter weather warnings across the mountains of 12 Western states. Snowfall on Utah’s hardest hit slopes through Wednesday was predicted to hit 1-2 feet, with 3 ft. tallies not out of the question.
Though the latest western storm produced only modest rainfall in Los Angeles proper Tuesday—much heavier amounts fell in the surrounding mountains—it was enough to push the area’s precipitation since last July to 34.85”. The wettest since 38.18” fell during the same period in 1889-90.
-Tom Skilling
For a tornado to dip from the skies over San Francisco is an uncommon meteorological event. But, that’s what happened Sunday afternoon. Twenty homes and businesses in the Bay area were damaged by the twister which formed above the Westborough Hills before heading over Interstate 280. The tornado was the first sign that an eastbound Pacific storm system was to mean trouble for other parts of the country. Fueled Monday by the northward rush of 70°/80° temps and humid Gulf moisture, the same storm generated eight twisters from powerful thunderstorms which swept sections of Texas, Oklahoma and Kansas, and threatened an even more potent severe weather outbreak Tuesday. But, storms in spring are products of huge temperature variations in the atmosphere—and this system is no exception. While thundery weather and large hail pummelled areas to the south, 6-8” of snow buried sections of western Nebraska. And another western storm threatened new snowfalls up to 16” farther west in Montana’s mountains.
Northern Illinois and Chicago will have their fill of easterly winds this week. A series of low pressure centers will parade from west to east through central Illinois. Counterclockwise flow around the low pressure systems will keep a steady diet of easterly winds off Lake Michigan over the metro area. Persistent cloudiness is in store, with any breaks diluted by the reinforcing moisture flow off the lake.
Rain will not be continuous, but computer models indicate he period from Thursday through Saturday will see more rain than not. The low pressure track means that further south, in the lower Mississippi Valley and along the Gulf Coast, convective storms are likely to develop in warm, humid air with an area of strong severe weather potential in eastern Texas and Louisiana today. Northern California is bracing for frequent bursts of rain again this week.
Despite some sunshine today, mostly cloudy skies and cool temperatures are expected for much of the week ahead. Should forecasts materialize, six out of the seven days this week will have below-normal readings—giving a total of 19 out of 26 days for the month.
Rain is forecast for four consecutive days, with the heaviest amounts expected later Thursday into early Friday.
By next weekend, computer models have the polar jet shifting north into Canada, allowing surface low pressure systems to track out of the Rockies along the U.S.-Canadian border. A large high pressure area will then develop over the southeastern United States.
Should this situation be established, a strong southwesterly flow from the southern and central Plains into the western Great Lakes will evolve, resulting in a significant warm-up for northern Illinois and the Chicago area early next week.
Spring, 2005 officially arrives at 6:33 a.m. Sunday morning. That’s the moment the sun’s most direct rays fall on the equator. For three months, these rays have been creeping northward, a process which has allowed days in the Northern Hemisphere to lengthen slowly. But, as is so often the case this time of year, truly springlike weather isn’t here yet. Saturday’s damp, occasionally rainy pattern—which may well include wet flakes of snow, especially in the Illinois counties adjacent to Wisconsin—will have exited. But the sun which breaks through the overcast Sunday afternoon is only likely to warm temps to seasonable levels—not the 60s which dominated Chicago’s far southern suburbs Friday.
Saturday’s rain isn’t all bad news. The first 18 days of March have ranked 10th driest of the past 134 years here. Late Friday’s 0.33” monthly rain tally was just 24 percent of normal and the driest March open here in 11 years—since 1994.
More than a foot of wet snow is headed for southern Minnesota Friday into Saturday. But, other areas of the Midwest are targeted as well. Heavy 4-8” totals are predicted to extend into sections of southern and central Wisconsin. Low dewpoints, indicating exceptionally dry low level air ahead of this storm, present a forecast challenge. As precipitation falls into a layer of such dry air, it evaporates—a process known as evaporative cooling. Many a March storm has produced accumulations south of the area initially predicted despite above-freezing temperatures at the start. Rain may arrive in the Chicago area late Friday. But, precip is to mix with or change to wet snow near the Wisconsin line toward morning, then continue as snow or a rain/snow mix Saturday. Should this switch occur sooner or farther south, snowfall could cover more than just the northern half of the metro area.
Lake Arlington in Arlington Heights after today's 1.5 inch snowfall
Memories of a White St. Patrick's Day-- March 17, 1965 in Madison, Wisconsin
Today's white St. Patrick's Day in portions of the Chicago area brought back memories of a St. Patrick's Day in 1965 when I was an undergraduate meteorology student at the University of Wisconsin in Madison. It had snowed hard all night and about 6 inches of snow was on the ground at 6 a.m. on March 17. The forecast called for another 6 inches of snow with storm totals of more than one foot expected, so the university canceled classes for the day. Well, by 8 a.m. the snow had ended and skies cleared after a snowfall total of only 6.9". With no classes to attend, partying began early making for a very memorable St. Patrick's Day. That same storm system brought 3.7" of snow to Chicago, but much of the precipitation here fell as rain.
Steve O'Kahner WGN-TV/Chicago Tribune Meteorologist
Wednesday’s readings in the lower 50s marked only the fourth day this month (out of 16) on which Chicago’s daytime temperatures managed to climb above normal. That raises the month’s tally of 50° days to three—half the total that climatology tells us to expect.
It will come as no surprise to Chicagoans anxious for spring warmth that the month thus far has been on the chilly side—in fact, among the coolest 25% of all March 1-16 periods since 1871. An altered wind and jet-stream pattern across North America suggests the persistent chill of recent weeks has ended, but the new regime might not be much more pleasant: Computer models indicate heavier rainfall and considerably more temperature variability during the latter half of the month. But we can use the rain. Through March 16, we have recorded only 23% of normal rainfall for that period.
Twelve of this month’s first 15 days featured below-normal temperatures here, a fact not lost on Chicagoans displeased with the persistent chill. An evolving weather pattern now suggests the cold regime is ending, but the price to be paid for milder temps is unsettled weather in upcoming days. A western U.S. storm system has begun to eject pieces of energy into the Southern Plains, one manifestation of which is heavy snow across the Texas Panhandle. Consider Amarillo, Texas. On average, that city receives 2.5 inches of snow in March, but with an expectation of ten inches of snow before the storm ends early Wednesday, Amarillo will record, in one storm, four times its entire normal March compliment of snow. It was enough to prompt meteorologist Matthew Kramar of the Amarillo National Weather Service Office to cry, “Fie! Contemptible white snowbeast...begone! Thy icy core doth reek of rank treachery.”
“When will it finally get warmer?” It’s a question being posed more and more often by Chicagoans growing increasingly impatient with the area’s lengthy spell of chilly temperatures. Computer models suggest a pattern change that heralds moderating temperatures, though not a return to above-normal readings.
Today is the anniversary of the world’s greatest single-day rainfall: 73.6 inches of rain poured down on Cilaos, La Réunion, in the Indian Ocean during a 24-hour period on March 15-16, 1952. Incredibly, this amount is more than twice Chicago’s annual precipitation total (36.27 inches), and it was but one 24-hour period within an eight-day spell of intense rainfall occurring in association with the passage of a tropical storm across La Réunion. Total precipitation during that period, Mar. 11-19, 1952, was a phenomenal 162.59 inches. That’s over 13 feet of water, and also a world record for that time interval.
Our 25th annual Fermilab/WGN-TV Tornado and Severe Storms Seminar is fast approaching and we hope many of you will be able to join us there on Saturday, April 9. Our seminars run approximately 3-4 hours and are completely free of charge. Seating is on a first come, first served basis and the first seminar gets underway this year at Noon on Saturday, April 9. The entire program is repeated beginning at 6 p.m. Saturday, April 9. Feel free to join us for either one. Hope to see you there and thanks for your interest and continuing support of our annual programs! For more information, go to http://www.crh.noaa.gov/lot/severe/Fermilab05.php
Here's this year's line-up of speakers. Warning Coordination Meteorologist Jim Allsopp of the National Weather Service-Chicago Forecast Office was kind enough to put the list of our speakers together:
The 24th Annual Fermilab Tornado and Severe Storm Seminar
Saturday April 9, 2005, Noon - 4 p.m. and 6 p.m. - 10 p.m.
Ramsey Auditorium, Fermi National Accelerator Laboratory, Batavia, Ill.
Speakers:
Tom Skilling, Chief Meteorologist, WGN-TV - 15th Anniversary look back on the 1990 Plainfield Tornado disaster and the heart-wrenching coverage of that disaster on television. Plus the report which aired only days later of Paul Sirvatka's stunning storm in progress tornado chase video of the wall cloud which was to go on to become the devastating Plainfield tornado.
Paul Sirvatka, Meteorology Professor, College of DuPage - Post-Plainfield moves to enhance area storm spotter training plus Paul's encounter on a storm chase with the wall cloud which was to become the infamous Plainfield twister. Also, the COD Storm Chase program which has been opened to the public this season.
Jim Stefkovitch, Meteorologist-in-Charge of the NWS Chicago office - Doppler radar's role in the tornado and severe weather warning process. Also a look at the new "polygonal" NWS warnings, which begin in the Chicago area this year, which will better and more precisely target the areas most at risk from incoming severe weather.
Paul Merzlock, Lead Forecaster, NWS Chicago - A look back at the meteorological environment which spawned the deadly 1990 Plainfield tornado and stunning similarities between that tornado and last year's damaging Roanoke, Ill., twister.
Dr. Joe Schaefer, Director of the Storm Prediction Center, Norman, Okla. - Important changes, which become operational for the first time this year, in the way severe weather watches outline the area at risk for severe weather - a county watch system which will more precisely designate areas at risk than the long employed box-shaped watches.
Dr. Mary Ann Cooper, MD, University of Illinois, Chicago - YOU Can Make a Difference in Lightning Injuries. Recent studies have shown that the lightning safety message is being heard by more people and that lives are being saved. Lightning injuries and how they occur, and what you can do to prevent lightning injuries in your own neighborhood.
Brian Smith, Warning Coordination Meteorologist, NWS Omaha - It Doesn't Always Look Like a Tornado. Brian will talk about the 2-1/2 mile wide monster storm that struck Hallam, Neb., as well as other tornadoes that did not look like tornadoes including the Tri-state tornado in 1925, the Lemont, Ill., and Jordan, Iowa, storms in 1976, and the Plainfield tornado in 1990.
Al Pietrycha, Forecaster, NWS Chicago – A brief overview of the April 20, 2004, northern Illinois tornado outbreak, including the deadly Granville-Utica tornado.
Jim Allsopp, Warning Coordination Meteorologist, NWS Chicago - Tornadoes and severe weather hazards - understanding the risks and spotting suggestions.
Although the origin of the word “blizzard” is obscure, the term appeared in the United States 135 years ago and its first use was possibly on March 14, 1870, to describe a storm that produced heavy snow and high winds in Minnesota. Technically, a blizzard is an intense winter storm with sustained winds 35 m.p.h. or higher and sufficient falling and/or blowing snow to reduce visibility below one-quarter mile for at least three hours. Colloquially, the term is loosely applied to any heavy snowstorm. Blizzard conditions figured prominently in one of the worst-ever U.S. winter storms, the “Storm of the Century” that raked the eastern quarter of the nation on March 13-14, 1993. It impacted 100 million people in 26 states from Florida to Maine and claimed 270 victims. The storm produced 11 tornadoes in Florida, a 12-foot storm surge on Florida’s west coast, 20-40” of snow and whiteout conditions from Atlanta to Maine, and winds gusting to 101 m.p.h. in Fairview, N.C.
Memories of Chicago’s mild winter are fading as the city slips ever deeper into unrelenting springtime chill. Sub-normal temperatures began nearly a month ago and now, with daytime readings projected to run 8-15º below normal through the upcoming week, there’s no apparent end to the ongoing and lengthy cold spell.
Computer models indicate that the jet stream, anchored to our south, remains in a position that favors the southward movement of cold air from northern and central Canada. That means continued, persistent cold weather for Chicago and the Midwest, as well as the Ohio Valley and the East.
A burst of light snow (such as the dusting Friday evening) has accompanied each new surge of cold air, and that scenario will dominate area weather this week. However, a stronger storm system, possibly with the ability to tap deeper moisture from the Gulf of Mexico, threatens the area with a significant rain/snow event this coming Friday and Saturday.
On a stormy day 82 years ago—March 12, 1923—Chicago recorded its all-time low air pressure, 28.70 inches.
As provided by Chicago weather historian Frank Wachowski, the following annotation appears in Chicago Weather Bureau (now the National Weather Service) records on that day: “The lowest barometric pressure in the history of the Chicago office was registered on March 12th in connection with a thunderstorm, sleet and snow and strong gales. The reading, reduced to sea level, being 28.70 inches.”
Wachowski provides this additional information: The record low air pressure value occurred at 7 a.m., with the wind roaring in from the northeast with gusts to 60 m.p.h. High and low temperatures that day were 41º and 31º and water content of precipitation was 0.67 inches, along with 0.2 inches of glaze.
After a long winter—and all Midwestern winters are long, even the mild ones—we impatiently anticipate the arrival of mild temperatures when March appears on our calendars. But lost in the lament over this spring’s persistent snow and chill is this crucial climatological fact: March is the beginning of Illinois’ tornado season, but low temperatures suppress severe thunderstorms.
The nation’s most deadly tornado, the great Tri-state tornado, killed 695 people (606 in Illinois)—and it was a March event: March 18, 1925.
So, the cliché that every dark cloud has a silvery lining is valid, and it’s applicable to the current cold spell. Consider this: The kind of upper-air wind pattern responsible for our current cold spring weather, when it occurs in January, brings sub-zero temps. In short, it’s far less painful to experience sub-normal temperatures in March than in January.
Chicago and the eastern third of the country better get used to Wednesday’s chill, since overwhelming forecast evidence points to a prolonged cold spell. With the jet stream locked south of Chicago for at least two weeks, temperatures should remain below normal through the period. Extended strings of cold, cloudy weather with flurries are not unusual in March, the most recent occurrence was just last year.
In the current regime, our jet stream remains well south, and begins to sink southward across the West, replacing the several weeks of warm weather there. The resultant cool pattern across the lower 48 is a difficult one to dislodge, hence the high confidence in extended chilly weather.
Snow Thursday could total an inch or more, and a new system with lighter amounts on Friday. The bulk of the energy with future systems should track south of Chicago.
The system that brought the cold air to the Midwest on Monday developed into another big nor’easter off New England, with interior Maine can expect over a foot of new snow. Meanwhile, frigid air by March standards settled into the Midwest. Embarrass, Minn. recorded a low of -30° Tuesday morning, with below zero readings speckled across the north.
This cold pattern is now well established across the northeast quarter of the country, and Chicago will remain along the western flank of this frigid air mass until further notice. However, just a few hundred miles to the west, more spring-like temperatures are in control, and some of this mild air approaches by early next week. Before then, the only weather maker of the next week races southeast from the Canada for some snow here on Thursday, before developing into the next big winter storm off the northeast coast on Saturday.
After a brief fling with spring on Sunday, cold air returned with gusty northwest winds and a temperature drop of 21 degrees between 9:00 a.m. and 6:00 p.m. Monday. With the return of cold weather, the connection was re-established between the Arctic and the eastern half of the country. At upper levels, the jet stream has once again slipped south and west of Chicago, bringing in northerly flow from the coldest regions of the hemisphere. The bitter cold that had blanketed that region for much of the winter has eased in recent weeks, so the extended cold spell under way here should not be that extreme. Meanwhile, the coldest air in this regime should settle east of Chicago. Nonetheless, temperatures will remain below normal for the next week, with occasional bouts of light snow from Thursday through Saturday, and another brief warm-up possible early next week.
Gusty west and southwest winds drove temperatures in Chicago higher all afternoon, topping out at 64° at both Midway and O’Hare airports. Even Northerly Island along the chilly lakefront reached 63°, making Sunday the warmest day in four months—since the 65° Nov. 6.
But the party’s over for the mild spring weather. A sharp cold front will sweep south through the region Monday morning with temperatures falling all the way to the teens overnight into Tuesday. Northwest winds gusting past 30 m.p.h. will add intensity to the temperature drop.
This front signals the beginning of a long string of below- normal days as a powerful northerly jet stream locks in place along the western edge of a blocking pattern that stretches all the way to Europe. Stellar upper air credentials suggest it will be even colder than forecast, with a major storm late in the week—but computer models vary wildly on its timing and location.
Saturday temperatures soared into the 60s and even 70° in snow-free areas of the Dakotas. This surge of warmth, headed toward the Midwest Sunday, pooled ahead of a cold front gathering strength in southern Canada. As a result, Sunday’s highs around Chicagoland should easily make it into the mid 50s with breezy west to southwest winds, and rain holding off until the wee hours of Monday.
But the shoe drops when that cold front sweeps through Chicago around noon on Monday. Falling afternoon temperatures turn the widespread light rain to snow as evening temperatures plummet and overnight lows bottom out around 20°. This return to chilly winter weather is a result of the blocked pattern in the Atlantic, one which appears locked in place for the next two weeks. Chicago sits towards the western edge of the cold air, with the brunt of the chill destined for New England.
As successive low pressure systems track east across Lake Superior through northern Lower Michigan later this weekend, strong westerly winds tug on warm air in the plains pulling it into the Midwest. High temps will reach well into the 60s just to the west and south Sunday, while the Chicago metro area flirts with 50° highs. Under the influence of gusting SW winds, temps will hold in the 40s Sunday night and might even reach 50 again Monday despite a heavy cloud cover and liklihood of rain. Later Monday temperatures will fall into the 30s, never to see 40° levels the remainder of the week. By Tuesday, upper level Jet stream winds will take a position that may be relatively unchanged for the following 10 to 14 days—with northwest flow over the northern Plains directing the southern portion of the coldest Canadian air directly into the western Great Lakes. Starting Tuesday for the remainder of the week, daytime highs will average in the late-January-like lower 30s.
The recent cold snap moderates over the weekend as the chilly Canadian high of recent days edges east and moderates under increasingly potent March sunshine. In its wake, several disorganized weather systems follow, none of which develops with any Gulf moisture to employ. As a result, the overall pattern should be dry, but with good enough precipitation credentials to keep at least a chance of rain or snow with each frontal passage.
By Sunday, retreating high pressure leaves somewhat of a void in weather systems, leaving the default winds southwest with origins in the toasty southern Plains. Thereafter, a reinforcing northwest jet stream brings several intrusions of weak arctic air, each colder than its predecessor, with the end result of some very cold air over the Midwest by Wednesday and Thursday.
Residents of the East Coast weren’t the only ones dealing with piles of snow Tuesday. (As much as 16” fell in interior New England and Boston was hit with 8.5” increasing its seasonal total to 78.1”—the 6th snowiest since 1920). Heavy lake snow squalls swept into north-central Indiana and southwest Lower Michigan much of the day. By late evening, 12” had fallen at Buchanan, Michigan and 11.9” covered nearby Niles. 11.0” was down at Granger, Ind. South Bend, where visibilities dropped under a quarter mile earlier in the day amid 30+ m.p.h. gusts, sat beneath 6.5” of new snow. Snow intensities had dropped there by late in the day thanks to a minor windshift to the “NW”—rather than the NNW. The change in direction slashed the “fetch” (distance traveled by the wind) over Lake Michigan. But, winds may alter direction again Wednesday, increasing lake-effect snowfall and forcing it to shift west.
