After a cloudy, chilly and rainy October that failed to produce an official 70-degree high in Chicago for the first time since 1917, the city is finally getting some October-like weather in November. Afternoon highs are slated to break the 70-degree barrier again Sunday as southerly winds carry the late-season warmth into the city. The warm weather is expected to linger into Monday, bringing the city four straight days of 60-degree-plus highs, an occurrence logged this late in the season at Midway Airport only 13 times since 1928. In addition to the return of warmth, Chicago is also drying out after an October that produced precipitation on 23 of the month's 31 days. In contrast, November's opening week produced just one day with rain -- a mere 0.01 inch.
Ida regains strength
Hurricane Ida weakened to a tropical depression after a Nicaragua landfall, but is expected to regain hurricane strength Sunday as it pushes north into the Gulf of Mexico. It could bring rain and strong winds to the Gulf Coast by Tuesday.
Dear Tom,
I was just a kid but I think I remember a big snowstorm that occurred just after Halloween. It must have been in the early 1950s. Am I correct?
Brian Schwartz
Dear Brian,
The year was 1951 and the first week of November featured two major snowstorms. Halloween was a chilly affair with highs only reaching the lower 40s. A surge of cold air followed and held the mercury to just 29 degrees on Nov. 2, setting the stage for a fast-moving Alberta Clipper that dumped 4.4 inches of snow on the city during the afternoon of the 3rd. That was just the beginning as a second, more powerful snowstorm hit on Nov. 6-7, bringing another 9.3 inches of snow. That storm was accompanied by howling northeast wind gusts to 65 mph at the lakefront Meigs Field airport. The winds produced high waves that brought major flooding and property damage along the lakefront.
The warmest weekend in six weeks is underway. Chicago area temperatures broke above 60 degrees for the first time in a week Friday, reaching 62 at O'Hare and Midway airports, and 63 at the lakefront. Among the warmest area highs Friday were 65 degrees at Rockford; 64 at Aurora and DuPage Airport; and 63 degrees at La Grange, Wheaton, Lansing and Plainfield.
Weekend readings look even warmer: A pair of 70-degree highs (or readings awfully close) remain a good bet Saturday and Sunday -- temperature levels not seen here since late September.
Powerful south winds reached speeds of 43 mph in gusts at building-top levels on LaSalle Street Friday and 36 mph at Rockford, Lincolnwood, Burlington and north of the Wisconsin state line in Racine -- and have gusted to 30 mph at times overnight, mixing the air and preventing the usual nocturnal temperature drop. So Saturday's highs build from a higher starting temperature.
The air mass which dominates Midwest weather was so warm to the west of the city Friday it produced a second day of record-breaking highs in the Plains including 81 degrees at Valentine, Neb., 80 at Yankton and 77 at Rapid City -- both in South Dakota. Add to the air mass' inherent warmth the broad subsidence of air which is to occur Saturday beneath the nose of a powerful jet stream -- a process which helps heat the air as the sinking air is compressed in the higher pressures found near Earth's surface -- and there can be little question why weekend temperatures here are headed to levels 20 degrees above normal.
Warm spell to extend to 4 days -- not common this late in the season
With high temperatures exceeding 60 degrees predicted through Monday, this warm spell has only a comparative handful of peers over the term of Chicago weather records. Four days of temperatures 60 degrees or higher have occurred beyond Nov. 6 only once every six years on average. Records at the South Side site record only 13 comparable late-season warm spells in 81 years since 1928.
Dear Tom,
I have seen frost on garage rooftops at sunrise when temperature reports are 38 or 39 degrees. What gives?
Robert Wolfson
Dear Robert,
Frost forms when the shallow layer of air at the ground (or on any other surface such as a rooftop) cools below its saturation temperature (and below freezing) by contact with a cold surface that itself has cooled to a subfreezing temperature. Water vapor in the air condenses directly, in ice-crystal form, onto the cold surface: frost forms.
Under clear, calm nighttime conditions, surfaces like blades of grass (but it works for roofs, too) radiate a great deal of heat and their temperature drops sharply. The cold-air layer can be very shallow, often only a fraction of an inch. Air temperatures in National Weather Service reports are taken by temperature sensors a few feet above the ground and sheltered from radiational cooling.
The Chicago area appears headed for its mildest weekend since September--one which may include high temperatures within striking distance of 70-degrees. The eastbound mild air behind the predicted weekend warm-up sent temperatures Thursday soaring to near 80-degrees in the western Plains. In Denver, where up to 4 feet of snow fell in the mountains to the west of the Mile High City less than a week ago, the temperatures soared to 77-degrees with 81-degree readings at La Junta and Springfield--both in Colorado. Highs in nearby Nebraska included 81 at Sidney, 80 at Imperial and 78 at Chandron while Elkhart and Dodge City in Kansas topped out at 80.
The warming there was produced by air sinking from the mountains into the Plains where it was compressed and warmed as it descended into the higher pressures found at lower elevations. The process is commonly referred to as the Chinook effect.
As that mild air of Pacific origin continues eastward, it won't be quite as warm by the time it arrives in Chicago. But, it is likely to introduce a 15-degrees temperature increase by Saturday afternoon over the levels observed Thursday. Accompanying that warming will be an influx of Gulf moisture in the lowest several thousand feet of the atmosphere--enough to contribute to the "warmer" feel of the air, but, based on present indications from computer models, not deep enough to produce layer of the atmosphere to produce the kind of cloud cover which would block the sun and thwart warming. Arrival of more significant moisture supporting more extensive cloud cover appears the only means of sidetracking what seems on track to become one of the nicest weekends of the fall season--and that's not expected to happen at the moment.
Low clouds forming over western Illinois late Thursday evening were predicted to expand into the Chicago area Friday morning. But, powerful winds Friday are expected to mix down to the surface in the late morning and afternoon allowing clouds to break, some sun to emerge and temperatures to head toward 60-degrees. Gusts in excess of 30 mph appear a good bet once this happens---and, with gusty winds expected to continue Friday night and Saturday, overnight readings should be significantly milder than those of recent nights.
A fascinating weather scenario may unfold in the Caribbean and Gulf of Mexico in coming days and into next week. Minimal Hurricane Ida--with 75 m.p.h. top winds--went ashore in Nicaragua Thursday. The storm, downgraded to a tropical depression late Thursday, threatened torrential rains totaling 15 to 20 inches at higher elevations. But, computer models suggest the storm's northbound remnants are likely to sweep out over the bathtub warm waters of the Caribbean, allowing the system, in the absence of strong winds aloft to regenerate. The re-energized system is then likely to spread north into the Gulf of Mexico where it may threaten sections of the coast--- potentially including Florida with downpours and wind mid and late week.
Thursday's 100 percent cloud -free skies the sunniest in nearly 2 months
Thursday gorgeous, completely cloud-free skies produced Chicago's first 100 percent sunny day in the nearly two months since September 2 and 11.
Dear Tom,
What is the meaning of "northwest winds"? Wind coming from the northwest or blowing toward the northwest?
Ralph Bellendir
Dear Ralph,
By international convention, wind direction always refers to the direction from which the air is moving. The proper interpretation of, say, a northwest wind of 10 mph is that the wind is blowing from the northwest to the southeast at a speed of 10 mph.
While we're on the subject, here's an unusual bit of weather trivia: You'll never hear a reported wind speed of 11 mph. Never. Here's why: Wind speeds are always measured in knots (nautical miles per hour). That's the way it's done, worldwide, and then in the United States that value is converted to statute miles per hour. One knot is 1.1508 statute mph. A value of 9 knots converts to 10 mph and 10 knots becomes 12 mph after rounding to a whole number.
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