Wasn’t the period from Aug. 17-24, 1947, a very hot one? Didn’t the highs reach at least 95 every day?
Brian Beecher, Villa Park
August 1947 stands out as the city’s hottest August on record, and the Aug. 17-24 period certainly helped it gain its lofty status. The high temperatures did not quite reach 95 every day (Aug. 21-22 topped out at 94) but the other six days recorded highs of at least 97 degrees. The final day, Aug. 24, was the hottest of all with the mercury peaking at 100. Not only were the days hot, the nights were warm and muggy. With the exception of a morning low of 68 degrees on the morning of Aug. 17, overnight lows never dropped below 75 degrees. Four record highs still remain from that period: 98 degrees on the 18th and 20th, 97 on the 23rd and 100 on the 24th.
The summer that wasn’t may end with a record chill. As another shot of unseasonably chilly air settles over the Midwest, clouds will develop across the Chicago area Sunday. Coupled with brisk north winds and temperatures more typical of mid-October, the last Sunday of meteorological summer 2009 will have a definite fall-like feel. Lake-effect showers may bring some light rain or sprinkles to areas near the lake. Sunday’s highs should struggle to reach the middle 60s and with low temperatures expected to tumble into the middle 40s early Monday, one of the city’s longest-standing temperature records (47 degrees on Aug. 31, 1872) may be threatened. Temperatures will slowly rebound to seasonable normals later in the week as winds gradually become southerly. The area will get a chance to dry out after the recent soaking that brought more than 5 inches of rain to the hardest-hit locations. Except for the possible lake-effect showers Sunday, dry weather should prevail until week’s end when the next frontal system approaches.
In a book about the St. Louis Cardinals’ Gashouse Gang, the author mentioned that St. Louis experienced 30 consecutive 100-degree days during the 1934 season. Is that true, and was it also hot in Chicago?
The summer of 1934 was during the “Dust Bowl” and it was beastly hot in St. Louis; but not quite as hot as the author implied. St. Louis officially experienced 23 days of 100 degrees or higher that summer plus many more days in the 90s. There were eight consecutive 100s from July 18 to 25, including the season’s highest reading of 110 degrees on July 24. It was also very hot in Chicago and most of the Midwest. Temperatures at Midway Airport topped the century mark 12 times that summer, including an all-time high reading of 109 on July 23 and six straight 100s from July 20 to 25.
Before this weekend is over, lake-effect rain showers will have swept sections of the Chicago area and a 137-year low temperature record may be replaced.
Powerhouse northwest upper winds–roaring into the Midwest at more than 100 m.p.h. at jet stream level (30,000 feet)–drive a sprawling Canadian high pressure into the area–a development which leads to unseasonably early frosts in northern Minnesota and Wisconsin in coming nights. Air as cool as this often ends up supporting more than the usual amount of cloud cover–especially in the warmer hours of the day. Because of a steep temperature decline with height, generous morning sunshine heats the lower atmosphere which encourages air to rise and cool. Cottony cumulus clouds develop through this process and build into widely scattered shower producers. More numerous showers of the lake-effect variety–expected to first come ashore in southwest Michigan and sections of northern Indiana later Saturday or Saturday night–are likely to gradually build westward into the Illinois/Wisconsin shorelines by Sunday as winds veer north then north/northeast off the lake.
Lake clouds diminish Sunday night as the core of this weekend’s cool air mass settles across the area. Periods of calm and the clearing skies may permit lows to fall below the 1872 record of 47 degrees by Monday morning.
It’s anything but cool in the Southwest where excessive heat advisories are in effect. Temperatures Friday soared to 121 degrees at Death Valley, 118 degrees at Palm Springs, Calif., and Bull Head City, Ariz., 113 degrees at Phoenix and 109 degrees at Las Vegas.
What does a half-inch of rain mean?
When we say that one-half inch of rain has fallen, we mean a blanket of water exactly 0.50 inches in depth would cover all horizontal surfaces if none of the rainwater had soaked in, run off, evaporated or been blocked by nearby or overhead obstructions such as vegetation, wires or buildings.
Rainfall is measured and reported in hundredths (0.01) of an inch, an increment too tiny to measure directly. Rain gauges therefore employ the principle of multiplication. In a standard gauge, rainwater falls into a circular collection area (a few inches in diameter) whose area is exactly ten times that of an accumulation tube into which it drains. Each one-hundredth inch of rainfall therefore stands one-tenth inch deep in the accumulation tube, and that water is easily measured with a ruler graduated to tenths of an inch.