With Sunday promising a repeat of Saturday's unlimited sunshine and mild temperatures in the middle 50s nearly 15 degrees above normal, Chicagoans are enjoying a third straight mild weekend.
While this weekend's highs in the middle and upper 50s pale in comparison to the back-to-back 70s on Nov. 7-8 and the 63-degree maximum on Nov. 14, the mild conditions will provide ample opportunity for end-of-season yard work or putting up holiday decorations. The balmy weather should last into Tuesday extending the current string of above-normal days to 21-the longest November stretch since 25 straight days were logged at Midway Airport in 1999.
Brief chill may bring snow
The warmth will not last through Thanksgiving as a cold front sends temperatures plunging late Tuesday. Showers should develop with the front and could mix with snow Wednesday as readings drop into the 30s. Thanksgiving looks to be cloudy with some flurries or mixed rain and snow possible with high temperatures struggling to reach 40 degrees.
Dear Tom,
In July 1987 while driving through the Mojave Desert on our way from Los Angeles to Las Vegas, heavy thunderstorms produced severe flooding and we were ordered off the road. How rare is this?
Kevin Vahey, Evanston
Dear Kevin,
It's not that rare. Rain is limited in the Mojave, averaging less than six inches a year. The desert's western flank receives the majority of its precipitation in the winter, while the eastern desert gets a substantial portion of its rainfall from summer thunderstorms in addition to the amount from winter storms. However, during the summer monsoon season, thunderstorms can form when moist air moves north out of the gulfs of Mexico and California. With ample moisture, strong heating and orographic lift provided by the mountains, the storms can bring blinding downpours.
Nighttime cooling has produced areas of low cloudiness and fog from moisture lingering in the wake of the past week's damp weather system. When temperatures lower at night, air masses grow saturated with moisture at the point readings match the dew point. It's the instant relative humidities reach 100 percent.
Despite areas of clouds, Chicago remains a safe distance from the country's major precipitation-producing weather systems over the pre-Thanksgiving weekend -- one on the Gulf Coast with big rains and another sweeping into the Rockies. It's a situation which should allow the weekend here to remain mild, further extending one of the longest spells of above-normal November temperatures on the books. Highs are to reach the 50s Saturday through Monday -- readings 10 to 15 degrees above normal and more typical of late October than November. The number of consecutive above-normal days reaches 19 Sunday, the 2nd longest such period at Midway Airport since weather records began in 1928. Only 1999 managed more -- 25 of them.
Though winds are light Saturday -- often an impediment to breaking clouds up this time of year -- computer models indicate the layer of moisture supporting Saturday morning's clouds is quite shallow. This should permit daytime heating to mix the air, dissipating the cloudiness and allowing generous sunshine to emerge. Hazy sunshine is likely to return both Sunday and Monday.
As additional evidence of how mild it's been of late, the coldest temperature recorded this fall has been 28 degrees, and the coolest daytime high this month has been 47. A vast majority of years have produced temperatures colder than each of these readings by now: 128 of the past 137 years have recorded a colder autumn low temperature by now, and only one year (1933) has seen its lowest November daytime maximum higher than this year's 47.
Changing pattern to send temps tumbling by Thanksgiving;
potential cold December open ahead
Many indicators continue to suggest large pattern changes loom over the next two weeks -- changes likely to send temperatures broadly lower over the United States. The colder air appears likely to hit in two waves -- and there may be temporary warming between them.
Cold weather surges into the Midwest on gusty winds Tuesday afternoon and Wednesday amid chilly showers. Readings may be chilly enough to allow at least some mixed snowflakes to the reach the ground with the spells of cold rain. The chilly air is likely to hold Thanksgiving temperatures near 40 degrees. Even colder air may hit next weekend and carry into December.
Dear Tom,
On the evening of Aug. 10 I was checking the weather for many cities coast to coast and they were all 79 degrees. Is that rare and is it more likely to occur in summer?
Norman Alexandroff
Dear Norman,
Having a large expanse of uniform temperatures across the nation is quite unusual and would be far more likely to occur in summer than any other time of the year. Temperature contrasts are almost always greater in the winter with arctic air and snow cover much more frequent across the northern states. Summer's sluggish weather patterns are more conducive to smaller temperature ranges -- especially at night when sunshine is not a factor. Conditions that would bring similar temperatures on a regional basis are far more common and can occur throughout the year given the right conditions.
Friday marks the 17th consecutive day of milder than normal temperatures in Chicago--one of the five longest such spells on record in the month of November at Midway Airport. Weather observations there date back to 1928. With above normal readings expected to continue into early next week, the mild spell is on track to become this area's 2nd longest of any November. That so many above normal days have occurred is likely to surprise many Chicagoans. A heavy, week-long overcast peppered with bursts of light rain and, until Thursday, wind chill-generating gusts, have contributed to a much cooler "feel" to the air than readings alone might indicate. The month's 47.5-degree average temperature at O'Hare is the 20th warmest of the past 139 years, placing the month among the Chicago area's 14 percent of mildest Novembers. Estimates based on temperatures suggest furnace usage should be down 25 percent over typical levels up to this point in the month and 18 percent below the same period a year ago.
A stubborn low pressure responsible for five consecutive days of cloudy skies has lifted out of the area--but, moisture lingers in its wake. And, while clouds may break for passing sun in coming days, spells of overcast skies aren't likely to exit the area completely--fitting in a month which is historically the second cloudiest of the year (December is the cloudiest).
Daytime temperatures are predicted to rise several degrees in each of the next three days. But, indications of change in the weeks ahead abound. Two key cold weather indexes, which look at cold air availability in the arctic as well as the predicted buckling of the jet stream over the North Atlantic---a development which frequently ends up sending cold air spilling southward over the eastern U.S., including the Midwest---have turned negative. It's an indication of colder weather on the way. The chill appears likely to hit in bursts---the first to produce a rain-generating disturbance here late Monday into Tuesday. That push of cold air is to last through through Thanksgiving (next Thursday) and may deliver this area's coldest readings of the season to date. There are growing indications flurries or snow showers could sweep at least parts of the metro area Wednesday and Thursday. Still colder air appears a threat as December hits 12 days from now. That chilly spell could allow some sticking snow at some point in December's opening 5-days, according to several preliminary computer forecast scenarios.
West Coast hit by driving rains, huge mountain snows, 100 mph wind gusts
The storm pounding the West Coast Thursday has prompted warnings for all manner of extreme weather---from heavy rain and flooding, to mountain snows measured in feet, and high winds responsible for huge waves lashing the coastline. Gusts hit 103 mph at Rogue Valley International Airport near in southern Oregon near Medford Thursday.
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