WGN Weather Center Blog

October-level warmth blows into the city

2009-11-08T04:21:11Z

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.

White Novembers: Getting a jump start on winter

2009-11-08T04:19:09Z

Snowy November of 1951

2009-11-08T04:13:44Z

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.

Temperatures head to 70 for the first time in 6 weeks

2009-11-07T05:15:42Z

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.

Strong winds ease overnight only to resurge with more warmth Sunday

2009-11-07T05:14:17Z

Frost when temperatures are above freezing

2009-11-07T05:12:42Z

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.

Warm 30+ mph gusts set stage for mildest weekend temps since Sept

2009-11-06T04:38:32Z

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.

Only unexpected clouds could interfere with weekend warmth

2009-11-06T04:15:42Z

Explaining wind direction

2009-11-06T03:50:40Z

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.

Spectacular fall colors in the Hinsdale area

2009-11-05T23:10:20Z

Thanks to Kelly Anbach of Bensenville for these spectacular fall color shots taken in Hinsdale. They're beautiful! THANKS for sharing them with us, Kelly!

Tom Skilling

Photos courtesy: Kelly Anbach of Bensenville, Illinois

Mushroom-shaped cloud on the east side of Resurrection Bay in Seward, Alaska

2009-11-05T23:07:31Z

This remarkable picture comes to us from John and Andrea Skillman of Gurnee. It was taken while vacationing in Alaska on the east side of Resurrection Bay in Seward. The Skillman's first spotted this cloud while eating dinner and aptly describe it as a mushroom cloud. It's more technically referred to as an orographic cloud---one which is induced as terrain forces air to rise---a process which leads to cooling and condensation of airborne moisture produces clouds such as this. They report it dissipated a short time later as the sun set. John and Andrea add that Alaska is a great place for seeing weather----which is absolutely true! THANKS SO MUCH to the Skillmans for such a fascinating photo!

Tom Skilling

Photo courtesy of John and Andrea Skillman, Gurnee

Morton Arboretum fall colors update

2009-11-05T22:50:58Z

Allison Phelps, public relations coordinator for The Morton Arboretum in Lisle, give us an update on the fall color display at the arboretum and sent us these great pictures. Allison tells us:

Just to let you know, fall isn't quite over here at The Morton Arboretum. There are still colors to see. Thanks to our expansive collection of exotic trees, visitors can stop in and see the red and yellow leaves of the Persian Ironwood tree or the Paper-Bark Maple with it's bright red leaves accented by the cinnamon-red exfoliating bark!

Thanks again Allison!

-Tom Skilling

Tim's Weather World: Mile High City & Mount Kilimanjaro

2009-11-05T14:55:23Z

Hard to believe that just a week ago Denver was covered in more than a foot of snow. Today they will see sunshine and a high near 80. Snow is also melting on top of Mount Kilimanjaro but at a slower pace. It could be all gone in as little as 22 years though according to a new study.

As the ice melts, more of the darker colored surface is exposed which absorbs more sun and leads to further melting. The people near Mount Kilimanjaro depend on that meltwater for drinking water. Check out this article for more information.

My daughter wants to climb Mount Kilimanjaro with me. She was party inspired by a year of study there and a new book, "Don't Let Her Go". We have a little more than 20 years to make the climb if we want to see the snow on top.

Speaking of snow... We are less than two weeks away from the average date of our first measurable snow, November 16th. No snow in the forecast through the weekend though as we warm into the 60s on both Saturday and Sunday.

It can hit 70 this time of year--it did a year ago

2009-11-05T04:32:55Z

Shorter days and weaker, low angle sunlight make it harder to warm this time of year--but that doesn't keep mild temperatures from happening. The atmosphere just has to work harder to produce such "warmth"--by, for instance, generating stronger winds which blow from warmer regions into the Midwest before the incoming air can cool---or by minimizing cloud formation capable of blocking sunlight. It also doesn't hurt to sit beneath the nose of a pocket of powerful jet stream winds, where air sinks, compresses and warms on a broad scale---a setup predicted to fall into place this weekend. That warmth can occur this time of year was evident a year ago. The area was in the midst of a three day 70-degree spree. Last year's 71 degree high on this date was 18-degrees warmer than the 53 predicted Thursday.

Barring more extensive cloud development Saturday than is currently predicted, readings then could reach 70-degrees for the first time since Sept. 27. Late season 70-degree temperatures aren't common, but they have occurred beyond Nov. 5 an average of one year in three since records began at Midway Airport 80 years ago.

The coming warm-up---likely to produce the first set of back-to- back weekend 60s here since late September---may well be part of a three day spell of 60-degree-plus highs extending from Saturday through Monday. Three consecutive 60s have occurred here this late in the season in 44 percent of years on record.

Frigid arctic air remains trapped in northern North America where temperatures in recent days have dropped as low as 20-degrees below zero. In stark contrast, the tropics remain active. Tropical Storm Ida---with 65 mph winds and gusts of hurricane strength--formed Wednesday off the coast of Nicaragua. The system will lose strength as it punches into Central America on a northward trek. But, it's possible we've not heard the last of the system. It could emerge into the southern Gulf of Mexico off the Yucatan Peninsula in the next week where reorganization would occur.

Humidity surge this weekend will add to mild "feel"---over-development of clouds would thwart warming

Dew points, which reflect atmospheric moisture and have resided in the 30s in recent days, are to take off this weekend as Gulf moisture mixes with mild but comparatively dry Pacific air moving in from the west. They are to reach the 50s which will lead to a noticeably more "humid" feel to the air Saturday and Sunday just as temperatures surge. This should lead a mild feel to the air not experienced here since September.

Mildest weekend since late September ahead; a late season 70 possible

2009-11-05T04:12:37Z