Recently in UNDERSTANDING THE WEATHER Category

This morning's horrific earthquake in Japan and the tsunami that is following it are creating an unfolding and ongoing tragedy of epic proportions. Following are numerous archived Ask Tom Why questions dating back to 1997 dealing with tsunamis and earthquakes.

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

Runaway Runoff

Pavement, buildings and other waterproof surfaces cover a large portion of the land in urban areas like metropolitan Chicago. That means rain water cannot soak into the ground. Instead, it gushes into storm drains that discharge directly to local rivers and streams.

About 55 percent of rainwater that falls on a city runs off (and in intensely urbanized locations such as the Loop, runoff approaches 100 percent); only 15 percent of rainfall sinks in to recharge groundwater supplies. The remaining 30 percent evaporates back into the atmosphere.

For comparison, only 10 percent of rain that falls on natural ground cover (forests, wetlands or other natural areas) runs off, and about 50 percent soaks into the ground.

As rainwater runs over city surfaces, it picks up pollutants encountered along the way -- soil, oil and grease from cars, pesticides and fertilizers, pet waste and much more. Not only do such pollutants harm fish and wildlife, they also degrade drinking water supplies and often require that recreational waterways be closed.

What can you do?
If you plan to replace a walkway, driveway or patio in your yard this spring, consider using water-permeable surfaces such as wood decks, spaced bricks or concrete lattice instead of solid concrete or asphalt. These surfaces allow water to soak through to the ground, thereby reducing runoff from your property and helping to replenish groundwater supplies.

Chicago Midway Airport Summary for February, 2008
Period of record: 1929-2008

Data provided courtesy of Chicago weather historian Frank Wachowski

Total snowfall 22.8", or 221 percent of normal (10.3")
Third-snowiest February on record

Most snowfall in February
1 1994 26.2"
2 1980 23.7"
3 2008 22.8"

Total precipitation (water content) 3.71"
Second-wettest February on record

Most precipitation in February
1 1997 6.76"
2 2008 3.71"

Sunshine in February was 40 percent of possible versus normal of 46 percent

Chicago has a national reputation of being a snowy city, but many U.S. cities routinely receive much more than Chicago's winter average of 39 inches. Here are several cities whose seasonal snow total is at least twice as great as Chicago's:

324" Valdez, Alaska
137" Marquette, Michigan
116" Syracuse, New York
102" Lander, Wyoming
100" Flagstaff, Arizona
99" Juneau, Alaska
98" Muskegon, Michigan
93" Buffalo, New York
92" Rochester, New York
81" Duluth, Minnesota
79" Burlington, Vermont

Chicago snow extremes in February
(1885-2007)

snowiest February ... 27.8" in 1896

biggest February snowstorm ... 13.4" Feb. 6-7, 1895

least snowy February ... 0.0" in 1987 and 1998

Drizzle: Liquid precipitation composed of very small water droplets (0.001 to 0.020 inch in diameter) that appear almost to float while following air currents. Unlike fog, drizzle falls to the ground. It is erroneous to refer to very light rain as drizzle.

Drizzle, fog, mist: All three are composed of tiny water droplets that appear to float in the air. Drizzle droplets are large enough so that they do fall, and therefore drizzle is precipitation. Fog and mist droplets are smaller and do not fall and are not precipitation.

Fog: A visible aggregate of water droplets suspended in the air at ground level. Fog is literally a cloud on the ground. Fog droplets are so tiny that they do not fall through the air, and fog is therefore not considered to be precipitation.

Freezing rain: Rain that falls into a shallow layer of subfreezing air at the ground (usually only several hundred feet deep) and freezes upon impact to form a coating of glaze on exposed objects.

Rain:Liquid precipitation in the form of water drops with diameters greater than 0.020 inch. Drizzle, the only other form of liquid precipitation, consists of droplets 0.020 inch in diameter or smaller.

Sleet: Precipitation in the form of small ice pellets. Sleet forms when raindrops (or largely melted snowflakes), originating in warmer air aloft, fall through a layer of subfreezing air at ground level and then freeze on their way down. Sleet is often referred to as ice pellets in weather observations.

Chicago's snowiest Februarys
1885-2007 snowfall data

27.8" 1896
26.2" 1994
23.7" 1980
22.6" 1900
22.5" 1967

Chicago's biggest February snowstorms
(1885-2007)

13.4" Feb 6-7, 1895
12.8" Feb 18-19, 1908
12.7" Feb 6-7, 1933
12.5" Feb 3-4, 1896
12.2" Feb 3-4, 1901
12.0" Feb 12-13, 1896

Chicago's largest day-to-next temperature changes
In the period Nov. 1, 1870, through Jan. 30, 2008

temperature rises
58º from 0º to 58º February 13-14, 1887
58º from 15º to 73º March 10-11, 1972
57º from 24º to 81º March 31-April 1, 2003

temperature falls
61º from 74º to 13º November 11-12, 1911
58º from 62º to 4º February 8-9, 1900
58º from 49º to -9º December 13-14, 1901

Arctic air: A type of air mass whose characteristics are developed in the cold season over ice- and snow-covered areas of the far north. It has low temperatures, low moisture content, and is very stable. Air masses of arctic origin cover Chicago about six percent of the time.

Arctic outbreak: The rapid movement of a mass of air originating above the Arctic Circle southward to the Gulf of Mexico, or farther. Arctic outbreaks bring Chicago its lowest autumn and winter temperatures; also called "polar outbreak."

Cold wave: In popular usage, a period of very cold weather. Meteorologically, a rapid fall in temperature within 24 hours to temperatures requiring substantially increased protection to agriculture, industry, commerce and social activities.

Norther: In popular usage in the southern United States, especially Texas, a strong cold wind from the northwest, north or northeast. It is the cold outbreak associated with the southward movement of a frigid air mass.

Blue norther: In popular usage in the Southern Great Plains, a blast of bitterly cold arctic air that surges south across Texas during the winter, bringing strong north winds and a sudden, sharp temperature drop.