December 2004 Archives

Sunday's earthquake and following tsunamis were great tragedies. Here are three archived Ask Tom Why questions dealing with tsunamis and seiches.

July 28, 1998
Dear Tom,
Could an earthquake in Lake Michigan cause a catastrophic tidal wave to hit Chicago like the one that happened at Papau, New Guinea?
MTM, Bartlett

Dear MTM,
There is no known historical precedent for a tsunami even remotely close to the magnitude of the Papau, New Guinea, event on the Great Lakes. The probability of such an event here has to be considered exceedingly low. says Guy Urban, geophysicist at the Palmer, Alaska, based West Coast and Alaska Tsunami Warning Center.
Urban does add that several catastrophic, rare and rather improbable occurrences would be required to set up a tsunami here. He’s quick to point out the near impossibility, absent careful modeling of such an event, of even beginning to speculate on the dimensions of such a wave. Only a direct asteroid strike, a huge thermonuclear explosion beneath the lake or a massive earthquake might initiate one, and while not impossible, the odds are not high.
Copyright © 2004, WGN-TV

March 18, 2003
Dear Tom, When and where was the most recent destructive tsunami? Shaqueda Green

Dear Shaqueda,
Tsunamis are ocean waves generated by undersea earthquakes, landslides or volcanic eruptions. They can be only a few inches high in the open ocean, but steepen and rise as they approach shallow water, reaching heights of 200 feet in extreme cases. Last year on Sept. 8, an earthquake with a Richter scale magnitude of 7.6, centered off the coast of Papua New Guinea, generated two tsunamis with heights up to 7 feet that caused two fatalities. The most recent devastating tsunami also struck Papua New Guinea, occurring on July 17, 1998, following a 7.1 magnitude earthquake. The resulting 30- to 50-foot-high wall of water struck a 25-mile stretch on the island's north coast, killing nearly 3,000 people.
Copyright © 2004, WGN-TV

May 17, 2004
Dear Tom, I once read that a tsunami wave hit Chicago in the 1950s. Did this actually happen? Anne Violante

Dear Anne,
On June 26, 1954, the Chicago lakefront was hit a 10 foot wall of water called a seiche (pronounced saysh) that swept eight unsuspecting fishermen off the Montrose Harbor pier to their deaths. While a tsunami or seismic sea wave is generated by underwater earthquake or volcanic activity, Chicago's 1954 seiche was caused by line of thunderstorms racing southeast across Lake Michigan at speeds in excess of 50 m.p.h. The cold downdrafts of air flowing out of the thunderstorms caused a rapid rise in air pressure that pushed a building bulge of lake surface water toward the southeastern shore. This surge of water then reflected back to the Chicago shore as a large wave, taking nearly 90 minutes to make the return trip.
Copyright © 2004, WGN-TV

Steve Kahn

At 6:58 a.m. Sunday in Indonesia, an earthquake of epic power rumbled deep beneath the waters of the Indian Ocean in a location near the juncture of three tectonic plates. U.S. Geological Survey geophysicist Julie Martinez said a 620-mile section along the boundary of the plates shifted, triggering ocean waves that spread outward at speeds in excess of 400 m.p.h.
Unnoticeable in the open ocean because they are only a few inches high and 10-40 miles wide, those waves steepen and rise in shallow water and surge ashore as tsunamis (literally, “harbor wave” in Japanese) sometimes 200 feet in height. Their destructive power is immense, and the havoc wrought along densely populated shorelines is mind-boggling.
Earthquakes and tsunamis are not meteorological events; they are not caused by, nor do they affect, the Earth’s atmosphere.

Massive rainfall totals are likely to accumulate across much of California by Wednesday as a powerful, moisture-laden storm system lingers just off the coast. Snow—perhaps accumulating 5 feet—will fall above 7,000 feet in the Sierra Nevada Mountains.

Light snow across the area yesterday evening was just enough to add a final Christmas touch to the holiday but not enough to cause great inconvenience. An inch of fluffy, low water content snow fell within a few miles of Lake Michigan but only 0.1” was reported farther inland.
The snow heralds the onset of a multiday period of moderating temperatures that will culminate in readings breaking 50º toward the middle and end of next week, along with a good deal of rain.
Yesterday’s snow notwithstanding, snow production this month has been meager, and moderating temperatures suggest the remainder of December will be free of accumulating snow. Chicago’s normal December snowfall is 9-10”.
Snow was anything but scarce in southern Alaska on this date in 1955 when that state’s biggest snowstorm on record began. When the last flakes fell on Dec. 31, 175.4”—more than 14.5 feet—had fallen at Thompson Pass.
By Richard Koeneman, WGN-TV Meteorologist

The season’s first sub-zero blast Friday morning delivered temperatures locally as low as -6º (Lake Villa, Mundelein, Streamwood)—cold, to be sure, but far from the record lows registered at International Falls, Minn., -35º, and Rhinelander, Wisc., -29º. The arctic chill even pushed to the Gulf: Sleet and snow fell at New Orleants Friday morning.
But the arctic surge is departing as quickly as it arrived. A multi-day warm-up that begins today in Chicago will culminate with 50º+ readings by next Thursday.
While winter is in progress here, it’s summer “down under” and today marks the 30th anniversary of Australia’s worst ever hurricane (Australians call them “cyclones”). On Christmas Day in 1974, Cyclone Tracy roared through Darwin with 150 m.p.h. winds and a 19-foot storm surge that claimed 64 lives and injured thousands.
By Richard Koeneman, WGN-TV Meterorologist

The season’s first taste of sub-zero cold is to be a one-day affair, and a substantial warm-up lies immediately ahead. Warmer air heading this way from the Plains might put down an inch of snow on Christmas—it’s called warm advection snow—but the snow, like the arctic chill, won’t last. Upper level winds turn southwesterly by Sunday, and will remain that way well into next week.
The arrival of warmer air will finally turn off the lake-effect snow machine that has dumped more than two feet of snow across Northwest Indiana in recent days.
But that’s nothing compared to the five-day lake-snow event that buried Buffalo, N.Y., in December 2001. Beginning on Dec. 24, snow squalls brought whiteout conditions that delivered a staggering 81.5 inches of snow (an equivalent water content of 4.49”) over a five-day period—more than twice Chicago’s 40” annual snowfall.
By WGN-TV Meteorologist Richard Koeneman

It’s an arctic outbreak reminiscent of the some of the colder surges in the barbaric winters of the mid and late 1970s—though it’s unlikely to last quite as long. Brutally cold air has spilled off the Canadian tundra and is to tighten its grip on the Chicago area in coming days. The fluffy lake snowflakes, which are falling in the cold air have a volume up to four times the snow which accompanies classic, large-scale winter storms. This means the gusty winds drift such snow easily, making it an especially insidious travel hazard. But, the bitter chill which follows is the real story.

It promises a series of sub-zero nights and the coldest daytime temp readings here since January of 1997. Lows Thursday night dip to -13° in Chicago’s far western suburbs (i.e. the Fox Valley and areas toward DeKalb and Rockford), struggling there just to reach 0° Friday. The chill’s strength is remarkable because it is arriving over bare ground.
-Tom Skilling

Mark Walther sent us these incredible shots of altocumulus clouds bathed in color by the low angle winter sun. Mark captured the clouds near the College Avenue Metra stop in west suburban Wheaton. Thanks Mark!

-- Tom Skilling, WGN-TV Meteorologist

If you've ever wondered about the hearty folks who take on one of the most challenging winter weather regimes in one of the most stunning arctic regions on this planet, you'll have a chance to meet some of them when we re-air our "Alaska: Where Winters are Really Winter" special this Saturday night (Christmas night, Dec. 25) at 9:30 pm (CST)--in the back half of our Nine O' Clock News program. We shot the program last January. What an incredible experience it was for Pam Grimes, videographer Kevin Myers and yours truly!

Our webmaster, Amy Mowery, is including a link here which will take you to a series of photos from the program. This was a project I'd always hoped to do. I first visited Alaska in 1980 and in my many trips back since then, I've always appreciated the way Alaskans approach the winter season. We focus on that in our program and visit with a number of folks who have moved from the Midwest to Alaska and love that incredible land--even in winter!

We were treated to an incredible northern lights display, which we share with you during the program as well as a discussion on aurora borealis with a University of Alaska geophysicist. We also spend time at Alaska's incredible Ice Hotel 70 miles northeast of Fairbanks in the heart of the state's Interior. It--and all of its contents---are made entirely of ice.

And, although it melted in this past summer's heat, it's being rebuilt again this winter. The hotel in part of Chena Hot Springs Resort and sits next to geothermal springs which bubble from the ground and which and remain incredibly warm (like the water of a warm bathtub) despite air temps of -20 to -30-degrees. The time we spent with Jon and Karin Nierenberg and their sled dogs in Healy, Alaska near Denali National Park and with veteran Alaska meteorologist Tom MacPhail, who invited us to his cabin within sight of the Alaska Range on a blustery winter day (the daytime temperature was near +5-degrees and the winds were gusting to 35-40 mph), was memorable. All these moments and our time in Girdwood with Chris Von Imhoff and Larry Daniels and the Alyeska Resort's avalanche control team in Girdwood, Alaska are included on the program. Hope you have a chance to check it out Christmas Night (Saturday) at 9:30 pm on WGN-TV.

-- Tom Skilling

The Midwest is bracing for a one-two punch beginning Wednesday night; lake-effect snow followed by one of the coldest surges to occur in a December here since 1989. A powerful storm lifting out of the Gulf threatens the southeastern Midwest with heavy snows in coming days—burying an area from Paducah and Louisville, Ky. NE to Cleveland, Ohio beneath as much as a foot of snow. The storm’s circulation is to tug intensely cold air south the length of Lake Michigan into the Chicago area—a set-up expected to ignite heavy lake snows across Indiana—and, ultimately lower Michigan. These snows could, for at least a time late Wednesday night/Thursday morning, build westward into sections of NE Illinois. This may include eastern Lake, Cook and Will counties. Some computer models suggest as much as 0.20” water equivalent precip may fall in these areas by/during the a.m rush hour Thursday, which at the temp levels predicted then could fluff up into 3 or 4” of snow.
-Tom Skilling

Tuesday’s temp. moderation is just a breather. A more intense arctic outbreak—one likely to cover more of the country and settle out of Canada well west of its predecessors—is already oozing south into the Lower 48. It’s the first arctic blast this season likely to “bank” up against the eastern slopes of the Rockies while plunging south with vigor all the way to the Gulf of Mexico. The bitter air mass promises round the clock subzero readings over the Upper Midwest much of the remainder of the week and promises Chicago its most frigid daytime December temps in 15 years by week’s end. It sets the stage for the second coldest Christmas Eve daytime high on record since 1870. To date, the -11° in 1983 is the coldest Dec. 24 high on the books; 5° is the second coldest set back in 1972.
The forecast, dependent upon some snow on the ground, is for a 2° high Friday, a reading 30 degrees below normal.

WGN-TV Meteorologist Richard Koeneman sends us this photo to remind us that winter snow isn't limited to the Midwest: The view in the image below is to the southwest from Fairview, N.C., looking toward Mt. Pisgah in the Blue Ridge Mountains of western North Carolina.

The view from Fairview, NC 
 
The arctic chill of the last few days was not limited just to Chicago and the Midwest. Frigid air plunged southeast all the way to Florida, and it deposited up to five inches of snow in its transit across the Appalachians of western North Carolina. Pictured here is Mt. Pisgah (elevation 5,721 feet) in the Blue Ridge Range of western North Carolina on Monday morning.
 
The view is from the mountain community of Fairview, NC, southwestward toward Mt. Pisgah, 25 miles distant. The Monday morning low temperature at Fairview (elevation 3,650 feet) was a nippy -1ºF.  At Asheville, five miles to the northwest, the overnight reading was +7º. a record low for the date.
 -Richard Koeneman

As much as 26" of snow fell near Michigan City, Indiana Sunday--coming down at the rate of 2-3" per hour there at the height of the storm--and whipped into drifts of 3 feet by powerful winds. While much of the northern Indiana/western Lower Michigan snowbelt received snow, it was a small area centered on western LaPorte and eastern Porter County which was hardest hit. Explosive instability, created as bitterly cold arctic air came in contact with the warmer than normal, ice-free Lake Michigan waters plus a full fetch wind, which traveled the length of the lake into the hard hit area, were behind the Sunday mega-snow. Follow this link to pictures of the snow from Michigan City, Indiana, from meteorologist John Dee's website--with thanks to John for the heads up on this. Overnight cooling over the fresh snowpack led to subzero temps Monday morning. New lake snows and a fresh round of bitterly cold arctic air are in store for the Indiana/Michigan snowbelts later this week.

Some of the heavier snow totals:
Michigan City 26.0"
Westville 20.0"
Wanatah 12.0"
LaPorte 9.5"
South Bend Airport 8.0"
Berrien Springs 8.0"
Benton Harbor 7.8"
North Judson 6.0"
Rolling Prairie 4.8"

Snow reports: Courtesy National Weather Service COOP observers

Tom Skilling-WGN-TV Meteorologist

Lisa Wilson of Bristol, Wis., took these photos in late November of Lake Shangri-La in Salem, Wis. (near the Illinois border). It's a reminder of how beautiful winter weather can be. Thank you Lisa for sharing your photos with us!
-- Tom Skilling, WGN-TV Meterorologist

As residents of northern Porter and La Porte counties in Northwest Indiana dig out of up to two feet of lake-effect snow, northeast Illinois will experience a period of lighter snow today that might accumulate an inch or so, primarily in areas north and northwest of the Chicago metro area.
Low pressure will move northeast up the Mississippi and Ohio valleys midweek, spreading cloud cover over Chicago with a chance that at least the eastern portion of this area might pick up some snow. As the low center pulls away, gusting northwest winds and the coldest air of the season will flow into northern Illinois. If an inch or two of snow cover is on the ground, Friday morning lows could be well below zero and daytime highs restricted to single digits, resulting in dangerous wind chills in the -20° to -30° range.
Paul Dailey, WGN-TV Meteorologist

The week before Christmas has been mild the last three years, but this year, last minute holiday preparations will be carried out under the added strain of cold weather and the threat of some snow. The first arctic blast is hitting the city today with wind, below-zero wind chills and some passing flurries, but the city is escaping the heavy lake effect snow that is targeting areas to the east in northwest Indiana. After a brief rebound above freezing Tuesday, a second onslaught of cold will arrive, keeping the city cold right through Christmas. While a significant snowfall does not appear to be in the cards for Chicago, a threat of snow on Monday and some passing flurries during the upcoming week may be just enough to whiten the ground for some holiday atmosphere and help send temperatures into subzero territory on both Christmas Eve and Christmas Day- the city’s first subzero readings since late January.

Wind-whipped lake snow in the Indiana snowbelt is but one facet of the season’s strongest blast of cold air expected to hit later Saturday night and Sunday. Temps here are to descend to the lowest December levels in four years—hovering between 10-15° Sunday as 20-30 m.p.h. winds send windchills tumbling below 0°. Bears fans at Sunday’s game face the coldest temps at a Soldier Field home game since 1993. Cold temps have been in stunningly short supply to date. Just one day since autumn began has failed to warm to at least 30°. That’s something that’s occurred remarkably infrequently by Dec. 18—just 20 times in 134 years of official records.
But what happens next week may be even more bonechilling—and may cover a greater swath of the U.S. A second bitterly cold outbreak—stronger than Sunday’s—could see nighttime lows near -30° from northern Montana east to northern Minnesota beyond midweek. Readings there will likely remain below 0° all day. And, the same air mass all but assures Chicago’s first subzero temperature by Friday morning.
— Tom Skilling, WGN-TV Meteorologist

The recent cold snap has taken its toll on the water temperature of area inland lakes. This morning after a frosty low of 20º, Lake Arlington, a 50-plus acre man-made lake in the northeast section of Arlington Heights, was almost totally ice-covered for the first time the season.

Note: If you look closely, you can see ducks standing on the ice.

The mild, comparatively sanguine weather pattern which has dominated since September, producing a string of large monthly temp surpluses, is coming to an end. Huge atmospheric changes in coming days over North America will drive a series of bitterly cold arctic air masses into the U.S. in the week ahead, each colder and more expansive than than its predecessor. The first hits Sunday, arriving on powerful north winds expected to limit daytime temps to the teens while generating sub-zero windchills. It hasn’t been that cold in December since 2001. A chill of that intensity would make the Bears game the coldest at Soldier Field in 11 years—since Dec. 26, 1993 with its 13° high.

The chill isn’t occurring everywhere. Powerful, downsloping Santa Ana winds roared across sections southern California’s Ventura County Thursday at speeds of 120 m.p.h. Temps there soared into the upper 70s. And in Alaska, record highs were set at Yakutat (47°) and Juneau (46°).
-Tom Skilling

Chicagoans have weathered the season’s first punch of true arctic air, including the area’s coldest daytime and nighttime autumn readings to date. Our descent into wintry weather regime has also officially produced the area’s longest period of sub-freezing temps. Readings here dipped below freezing at 11 p.m. Sunday evening and didn’t break above 32° until noon Wednesday—61 hours below freezing. Still colder weather’s ahead. A new push of chilly air Friday restricts highs to the 20s for only the second time this cold season—and, a more brutal brand of cold hits Sunday.

But, that’s not the last of it. Computer projections suggest another powerful cold surge could set the stage next week for a snow toward Christmas Eve—a week from Friday. With at least single digit readings a good bet Sunday night, it’s worth noting last season’s first single digit reading (+4°) didn’t arrive until January 5.
-Tom Skilling

The lack of snow here is turning into one for the books. Only 0.1” has been logged in the city in the month’s opening 15 days, little enough to rank among the least snowy 14% of all December opens on record since 1884. Over the past three decades, the period has averaged 42 times that amount (4.2”)!
Heavy snows shifted into the eastern Great Lakes Tuesday, accumulating abundantly. Cleveland, Ohio has measured 11.7” since Saturday. But, that amount paled in comparison to the 23.2” which has been measured since Saturday to the east at Pierpoint in northeast Ohio’s Ashtabula County. The region is well know for its heavy lake effect snows.

Chicago’s 28° high Tuesday was the coldest here since February 15 when readings peaked at 22°. Powerful SW winds Wednesday are to override some of the warming effect of the predicted 17° temps increase. Winds chills are likely to hover by afternoon in the low/mid 30s.
-Tom Skillling

Just months ago, hurricanes dominated the news in Florida. But, Monday night, cold air was on Floridians’ minds. The deepest penetration into the U.S. of early season arctic air prompted wind chill advisories over the same sections of east central Florida which served as ground-zero in August and September for Hurricanes Jeanne and Frances. And Florida wasn’t alone with the chill. Not only did Chicago and the Midwest shiver in the midst of the first really wintry air of the season, sub-freezing temperatures threatened to reach much of the Deep South overnight, extending from eastern Texas to Georgia.
Chicago’s 30° high at midnight Monday morning was the coldest daily maximum temp here in 10 months (since 24° back on Feb. 16).
Lake snows produced by the cold air across Lake Michigan were significant—but less extreme than in areas farther north. Hartford, near Benton Harbor, Mich., was hit by 7” in just four hours Monday. But snowfall more generally ranged from 2-5”.
--Tom Skilling, WGN-TV Meteorologist

For the full seven day forecast associated with the maps below, click here

Sunday’s highs in the middle 40s will soon be a distant memory as the continuing strong wind assault on Chicago brings in the coldest air to date this season. Temperatures today will hover in the middle and upper 20s, and slowly fall off into the teens by this evening. And though diminished from Sunday’s 40-50 m.ph. gusts, today’s still-strong winds will send windchills down into the teens. Only passing flurries will be seen in Chicago, but the lake-effect snow machine will rev into high gear downwind of the Great Lakes with up to 18 inches of snow expected in portions of Michigan by tonight.
This first real cold snap will quickly moderate with readings rebounding back to the middle and upper 30s the rest of the week. Except for a few passing flurries or showers, no significant precipitation is expected in Chicago this week, allowing holiday preparations to continue without significant meteorological interference.

An annual celestial spectacle. the Geminid meteor shower will peak tonight and Monday night and will be visible in the Chicago area away from the bright lights of the city if skies are clear. Clouds are expected to limit viewing tonight but current forecasts give hope for at least some clearing on Monday night. However, star gazers will have to brave strong gusty winds and chilly temperatures tonight. Winds should be much lighter on Monday night, but temperatures are expected to be well below freezing.

GEMINID METEORS: The 2004 Geminid meteor shower is underway. Midnight sky watchers this weekend can expect to see bright meteors shooting out of the constellation Geminid--at least a few per hour. Rates will increase many-fold on Dec. 13th when the shower peaks.
Space Weather News for December 11, 2004 http://spaceweather.com
Because this meteor shower has such a broad peak, a good display is possible twice: on Monday morning, Dec. 13th, during the dark hours before sunrise and again on Monday evening, Dec. 13th, especially during the hours around midnight.

The season’s first encounter with arctic air will jar Chicagoans with a one-two punch today and tonight—first strong winds and then near zero chills. Low pressure centered over Lake Superior will intensify as it moves east swinging a strong cold front through northeast Illinois. Winds become northwest behind the front this afternoon and strengthen to gusts possibly reaching 50 m.p.h.

Temperatures will fall out of the early morning 40s through the 30s this afternoon and the 20s tonight. Wind chills will drop into the 20s later this afternoon, the teens during the evening hours and into single digits after midnight approaching zero by Monday morning. Children should bundle up if they have to brave the elements Monday morning walking to school or waiting on a bus. Monday will be a raw day with strong northwest winds continuing and highs in the 20s with frequent snow showers. Lake effect snow accumulation is likely in northwest Indiana.

It’s been incredibly mild here this month. Even with Saturday’s modest 5 degree temp. downturn, the day is likely to produce December’s eighth consecutive above-normal temperature. Only gusty NW winds will add a chilly feel to the air, restricting windchills to the upper teens or mid 20s this morning.
Near-record warmth is predicted in the Plains this afternoon—including near 70° highs over western South Dakota, parts of Nebraska and eastern Colorado Saturday. To the north, residents of northwest Minnesota and eastern North Dakota are being warned by forecasters that the season’s first winter storm is on the way.
Chinook winds produced gusts to 85 m.p.h. in Montana Friday. Farther east, damaging thunderstorms, including a pair of twisters—one of F3 intensity (indicating 158-206 m.p.h. winds)—hit near Orangeburg, South Carolina, as a squall line passed early Friday.

It's always such a pleasure to hear from those who watch our WGN weather programs. That's why I was thrilled to receive these photos from Carole Edwards, who's cat Simba is apparently quite a fan---in fact, says Carole, "one of your biggest fans!" Thanks for sharing the pictures with us Carole! Happy holidays to you and Simba!!
-- Tom Skilling, WGN-TV Meteorologist

Chicago’s first truly wintry weather is in sight. Though the season’s first blast of pure arctic air isn’t to arrive until Sunday night, a modest temperature downturn later Friday signals the beginning of the transition to colder weather. A storm, spawned by the first stage of this pattern realignment, is spinning up directly over the Midwest. As it intensifies, the strengthening rush of air into the system is to produce a noteworthy increase in wind velocities here this afternoon, importing enough cold air to introduce wet snowflakes to at least parts of the area Friday night.

Thursday’s 50° high—the third of the week and a reading 13° above normal—is only the 17th to occur on Dec. 9 in 134 years. Record warmth was reported in Texas Thursday. Temps reached 81° Austin and 78° in Galveston. 95 m.p.h. wind gusts blasted sections of Montana. Gusts farther east on Mt. Washington, N.H. reached 133 m.p.h.
-Tom Skilling

Try to tell residents of Yellow Pine, Idaho or the other snowbound, wind-whipped communities scattered across 11 Western states, that the remnants of a typhoon are behind their wintry meteorological woes and you might get a look of surprise. But it’s true. Deadly Typhoon Nanmodal, which developed a week and a half ago (Nov. 28) over warm equtorial Pacific waters northeast of Australia, slammed into the Philippines four days later (Dec. 2), killing hundreds, and also swiped Taiwan and parts of Japan before embarking on a long trek across the Pacific.

Remnants of hurricanes and typhoons are saturated with tropical moisture, making the systems huge precip producers. The 6.16” of rain at O’Brien, Ore. Wednesday illustrates the point. California was also hit, with 3.31” at Mt. Shasta, Calif., 2.68” at Redding and 2.49” at Santa Rosa. Wind gusts hit 88 m.p.h. at Los Gatos, Calif.

The stinging chill of winter remains on hold. December, 2004 may be only 8 days old, but the month already boasts an impressive 4.5° temperature surplus. That’s warm enough to rank among the mildest 36% of Dec. 1-7 periods here in the past 135 years.

Temperatures both Monday and Tuesday surged past 50°—and another 50-degree day appears a good bet Thursday. Back to back 50s aren’t as unusual in the Chicago area as December’s cold reputation might make you think. 82 of the past 134 Decembers (61%) have hosted sets of consecutive 50° days.

Generous precipitation over the past 2 weeks has been unusual in its own rite. When Tuesday’s 0.82” at O’Hare (1.20” fell at Midway) is included, the period since Nov. 24 has generated more than twice the official rain and snow (3.11”) making the period this area’s 5th wettest since 1870.

-Tom Skilling

Tuesday’s downpours threaten to generate the Chicago area’s heaviest rain totals since the 1.08” which fell on Nov. 1. Only two systems since Sept. 1 have produced over 1” of rain. The wind-driven precipitation is the product of an intensifying storm which is to sweep rapidly across the south end of Lake Michigan Tuesday morning. The system unleashed damaging 70 m.p.h. wind gusts and at least one twister in a swarm of north Texas thunderstorms Monday. The storm’s snowy, cold northern flank produced 12” accumulations in southern California’s mountains outside San Diego Sunday and went on to bury southern Colorado’s peaks beneath more than a foot of snow.
Powerful northeast winds accompany today’s rainfall. Big rains are fairly common this time of year. Storms here produce 1”-plus totals (water equivalent) on average once every other December.

With nearly all of last week’s snowfall melted, the second week of December is setting up to be a relatively mild one for the Chicago area.
The warmest weather will occur today and early Tuesday when highs are expected to top out in the upper 40s and lower 50s. But even when colder weather moves in for the rest of the week, daytime highs are still expected to remain above the mid 30s readings typical here this time of the year.
Precipitation is forecast to be primarily liquid with rain expected today into Tuesday and again toward the weekend. And though some light snow or flurries can’t be ruled out, no significant snowfall is in sight.
In contrast, cold and snow continue to plague the West. Las Vegas could only muster a high of 46º Sunday and has not recorded a reading higher than 54º in more than a week. Heavy snow warnings are posted for the higher elevations of southern Arizona with up to 12” of snow expected.

Pacific-origin air surged into the Dakotas Friday with Bismarck, North Dakota hitting 51° and Pierre, South Dakota topping out at 53°—readings some 20° above normal. Westerly flow will bring that same air mass into northern Illinois this weekend. Some of the warmth Saturday will be used to melt the remaining snow cover, but high temperatures will still end up some 10° warmer than Friday.

A cold front will move out of Minnesota, sagging to the south end of Lake Michigan before becoming stationary later tonight, and then moving slowly north on Sunday. Cloudiness and scattered showers will be associated with this frontal boundary. Southerly winds will eventually pull very moist, high dew point (50°) air into this area Sunday into Monday giving a mild humid “feel”. Clouds and showers will keep temperatures from approaching the 60° mark.

Mild, downsloping winds—the so-called Chinooks—were in fine form late Thursday, roaring out of the Montana mountains and the Black Hills of western South Dakota. Wind advisories were issued for gusts to 70 m.p.h. The mild air these powerful winds are delivering to the northern Plains Friday is headed for Chicago. Temperatures may flirt with 50° this weekend. Of all the Decembers since 1990, only 2000 failed to produce at 50° high. Readings at such mild levels are hardly a novelty this month. In 134 years of official weather observations, 111 (83%) of them have generated December 50s.

It’s snow making news in the Upper Midwest. Snowfalls reached 6” near Duluth—that area’s first major accumulation this season (a storm last week whitened areas farther east in northern Wisconsin and the Upper Peninsula). Nearby International Falls reported its first sub-0° (-4°) this season.
-Tom Skilling

Meteorological winter (Dec 1-Feb. 28) certainly started off on a “wintry” note with a blanket of snow cover over the area and an official high temperature of only 32°—the coldest high since last February 16th! A return to southerly flow starting later tonight will bring milder readings back this coming weekend and wipe the snow cover slate clean. November finished up as a month of contradictions—temps averaging 4.4° above normal and yet the 5.1” snowfall total (thanks to two storms in the final week) was the 14th snowiest of 121 Novembers since 1884. The last time November had more snow was in 1978 when 7.1” was recorded.

Pacific-origin air will continue to flow across the northern half of the country well into the middle of next week, but at that point computer projections tilt the polar jet allowing an arctic cold air mass to invade the central Plains and Midwest by mid-December.