By Meteorologist Tom Sl=killing
Tuesday’s 38-degree Chicago high temperature would have been right at home in February. The reading equals the “normal” high here on Feb. 22.
But the frigid 38-degree reading, 21-degrees below normal, occurred on “Tax Day” and was the coldest April 15 which has been observed here in the 86 years since 1928!
Daytime highs were actually higher in much of Alaska than in Chicago and adjacent areas of Illinois, Wisconsin and Michigan—reaching levels close to 50-degrees at a number of locations across the 49th state.
Chicagoans didn’t shiver alone; records fell at a number of Upper Midwest locations; frost and freeze warnings issued for 24 states overnight
The abnormal chill wasn’t limited to Chicago Tuesday. Morning readings dipped to new records at International Falls, Minn.( 5 degrees), Sioux Falls, S.D. and Grand Forks, N.D. (11 degrees); Watertown, S.D. (12 degrees) and at both Minneapolis, Minn. and Madison, Wisconsin (18 degrees).
Frost and freeze warnings were hoisted across 23 states south and east of Chicago—from eastern Oklahoma across much of the Deep South to New Jersey, Delaware and Maryland.
Tuesday highs averaged more than 20-degrees below normal south as far as Georgia, Alabama and Mississippi.
Only 4 other days beyond April 15 have generated daytime highs of 38-degrees or lower in over a half century at O’Hare
Weather observations began at O’Hare in 1959. In all that time, temps of 38-degrees or lower have occurred beyond April 15 on only 4 other occasions.
Milder temps Wednesday and Thursday to yield to a chilly, new round of “NE” winds Friday
Temps stage a modest recovery with the arrival of Wednesday’s powerful southerly winds. The “warming” may linger into a second day Thursday. But a thermal downturn, prompted by the re-emergence of northeast winds Friday, is to render the “warming” short-lived.
Daytime highs Friday may remain in the 40s in areas close to Lake Michigan.
South winds Easter Sunday could send temps surging into the 60s
More significant warming is in the offing over the weekend—particularly Easter Sunday. At that time, a new round of powerful southerly winds is to send temps back into the 60s.
Over what period of time have Chicago’s daily normals been calculated? How are the very abnormal temperatures like our very cold winter figured into the normals?
— Tig White, Chicago
The National Weather Service’s National Climatic Data Center in Asheville, N.C., calculates the official normal daily high and low temperatures used in the U.S. By international agreement, normals are simple arithmetic averages of weather variables over 30 years, generally three consecutive decades, and they are recalculated each decade. Normals now in use cover the period 1981-2010.
Unusual temperatures are factored into the calculations just like any other readings.
Don’t overinterpret normal values. They don’t even represent what should happen; they are merely averages.
NASA’s Goddard Institute for Space Studies says March was the fourth warmest globally since records began in 1880. The only years that had a warmer March were 2002, 2010 and 1990. Globally, the average temperature for March was 0.7°C or about 1.26°F higher than the 1951-1980 average. We, of course, were the exception to that warm rule. Notice the shades of blue on the March anomaly map below over Chicago and the upper midwest.
The blues and purples mark areas that were below average during March while the yellows, oranges and reds mark areas that were warmer than average. Much of the eastern half of North America, including the midwest, was much colder than average. March rounded out the coldest four month period (December, January, February and March) on record for Chicago.
Seems like that same cold pattern responsible for our brutal winter has spilled over into spring. After yesterday’s snowfall of up to nearly 3″ in some spots, today will feel more like late February than the middle of April. The image below shows the departures from average expected today. Notice the blob of blue and purple over the midwest. Our high today of 40° will be almost 20° below average.
We should warm through Thursday when our highs get back to about average (59°). Easter weekend will be a bit below average with highs in the lower to middle 50s and cooler conditions lakeside with a wind off the lake.
By Meteorologist Tom Skilling
Snow has historically been no stranger in Chicago during the month of April. Official snow records indicate a trace or more of snow has fallen this late in 86 of the past 129 seasons dating back to 1884-85. That’s 67% of the time.
But the amount of snow which fell Monday and the fact it occurred within 3 days of 80-degree warmth (on Saturday) and on a day which opened in the 60s is without precedent. Neither has occurred before over the 129 year term of official Chicago snow records.
Monday’s preliminary snow totals through 10 pm came in at 1.2” at O’Hare and 1” at Midway.
The 1.2” tally at O’Hare equals the amount of snow which typically falls over the full month of April and was the heaviest official snowfall to occur here so late in a season in 3 decades.
Monday’s snow means April 2014 has become at the 5th month to reach or exceed the city’s normal monthly snowfall.
Heavier snow totals were reported late Monday evening elsewhere across the metro area including 2.5” at Wauconda; 2.1” Huntley; 1.9” Downers Grove; 1.7” Oak Brook; 1.5” Lindenhurst; 1.5” Batavia and 1.4” at north suburban Beach Park.
The 50-degree temp pullback from Saturday to late Monday is the area’s largest to occur in an April in 20 years
The 3-day temperature drop of 50 degrees, which is what occurred in Chicago between Saturday afternoon’s summer-like 80-degree high and the 30-degree reading registered late Monday, was the biggest to occur here in an April over the past 2 decades.
That shift in temperatures was the equivalent of moving from mid-June back late February-level readings in a span of just 72 hours.
Thanks to Valerie Baxter of Elmhurst for sending along this shot of Elmhurst newly-emerged daffodils covered with Monday late-season snowfall.