Coming off a delightful late fall weekend that brought the city its first back-to-back 70-degree days since Sept. 24-25, prospects for mild weather here loom well into mid-November. With a prevailing west-to-east jet stream promising to spread mild Pacific air across much of the nation for the next two weeks, arctic air should remain bottled up across this continent's polar regions. Readings here should fluctuate through the 50s and 60s -- well above current normal temperatures around 50. While this weekend's 70s did not break any records here, new record highs were established Sunday in areas from Michigan to New York, including 72 at Grand Rapids and 71 at Muskegon, both in Michigan.
Category 2 Ida heading for Gulf Coast
A lackluster 2009 hurricane season has become active in its final weeks. A hurricane watch has been posted for the Gulf Coast from eastern Louisiana to the Florida Panhandle as Ida, packing top winds of 105 mph, approaches the area by Monday night or early Tuesday. Ida's death toll is approaching 100 in El Salvador after three days of flooding rains there.
Dear Tom,
From Nov. 12-14, 1964, Chicago firemen battled numerous multi-alarm major fires. What were the weather conditions like?
Doran Swan, Chicago
Dear Doran,
The weather was windy, dry and unseasonably warm -- perfect conditions for fires to spread rapidly and burn out of control. Chicago climatologist Frank Wachowski found high temperatures reached the 60s on Nov. 11-12 and peaked at 71 degrees on the 14th. Afternoon humidities fell to near 30 percent and winds were strong and gusty from the south and west with a maximum gust to 59 mph on Nov. 12. Three of the biggest fires were at the old Goldblatt's warehouse at 4000 S. Kedzie, buildings near 25th and Michigan, and in an abandoned railroad warehouse near 18th and Clark. Wachowski noted that weather reports from Midway Airport reported heavy smoke northeast of the field.
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.
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