Nation digs out from massive blizzard; Cyclone Yasi rips through Australia

Chicago's third worst snowstorm on record is history, leaving in its wake a remarkable 20.2” of snow, snowdrifts up to ten feet high, and frigid below zero temperatures. Only the January 2 - 4 1999 blizzard (21.6") and January 2 – 4, 1967 blizzard (23”) dumped more snow on Chicago. The Groundhog's Day blizzard of 2011 had stronger winds than either of Chicago's other two record snowstorms, and thus was probably the worst snowstorm ever to affect the city, as far as impacts on travel go. Winds gusted as high as 61 mph at Chicago's O'Hare Airport, and winds at the Chicago buoy, 10 miles offshore in Lake Michigan, reached sustained speeds of 54 mph, gusting to 66 mph. Fortunately, Lake Michigan had so much ice on it that crashing waves were unable to cause significant flooding along the lake shore.

Chicago's 10 biggest Snowstorms:

1. 23.0 inches Jan 26-27, 1967
2. 21.6 inches Jan 1-3, 1999
3. 20.2 inches Feb 1-2, 2011
4. 19.2 inches Mar 25-26, 1930
5. 18.8 inches Jan 13-14, 1979
6. 16.2 inches Mar 7-8, 1931
7. 15.0 inches Dec 17-20, 1929
8. 14.9 inches Jan 30, 1939
9. 14.9 inches Jan 6-7, 1918
10. 14.3 inches Mar 25-26, 1970


Figure 1. A bus jack knifed on Lake Shore Drive in downtown Chicago on the night of February 1, 2011 during intense blizzard conditions, resulting in a dangerous situation where hundreds of cars became stranded behind the bus. Image credit: Viewer uploaded photo from WGN.

The most remarkable feature of this storm was its sheer size. Twenty-two states received snows of five inches or more, and over 100 million Americans experienced snow or freezing rain. Antioch, Illinois recorded the most snow of any location in the U.S., 27 inches. Also hard-hit were Missouri, Oklahoma, Wisconsin, Iowa, Indiana, and Vermont, which all reported more than eighteen inches of snow. Seven states reported freezing rain that left 1/2” or more of ice accumulation, which resulted in power outages affecting hundreds of thousands of people.

The strength of the high pressure system behind the Groundhog's Day Blizzard of 2011 was also remarkable. Pressure readings in Montana at the height of the blizzard were well above 1050 mb, the type of high pressure only seen once every twenty years or so in the U.S. The difference in pressure between this high and the mighty blizzard drove a flood of cold air southwards out of Canada, creating the very high winds that shut down road travel over most of the Midwest during the height of the storm. The unusually strong push of cold air southwards has caused major problems in northern Texas, which is unused to multi-day periods of below-freezing temperatures. Many power plants were knocked off-line by the severe weather, and record electricity demand has overwhelmed the electrical system, resulting in widespread rotating blackouts. A rare Southeast Texas snowstorm is expected today, due to a new storm system moving eastwards across the state. Houston is expecting 1 – 3 inches of snow through Friday. All flights leaving Houston between 3pm today and noon Friday have been canceled, because the airports have no de-icing fluid.

Tropical Cyclone Yasi hits Queensland, Australia
Tropical Cyclone Yasi roared inland over Queensland, Australia at 12:30am local time on Thursday as a strengthening Category 4 storm with 155 mph winds and a 930 mb central pressure. The cyclone missed the most populous cities on the coast, Cairns and Townsville, which experienced wind gusts to about 60 mph. Undoubtedly, tremendous wind damage occurred in the small towns of Tully, Mission Beach, and Bingal Bay where the eye passed. A storm surge of 5 meters (16 feet) was observed at Cardwell, and 3 meters (10 feet) at Clump Point. Townsville received a 2.5 meter storm surge that damaged some sea walls. This was the highest storm surge observed since 1971 there.


Figure 2. Pressure readings from Clump Point on the Queensland, Australia coast during passage of Yasi bottomed out at 930 mb as the storm passed overhead. Image credit: Australian Bureau of Meteorology.

According to an email I received from Blair Trewin of the Australian Bureau of Meteorology, ”Yasi is almost certainly the most intense landfall in Queensland since at least 1918, and possibly since 1899. In 1918 there were two cyclones (at Mackay and Innisfail) with measured pressures in the upper 920s/low 930s but it is quite plausible that the minimum central pressures were lower than that. The 1899 (Mahina/Bathurst Bay) cyclone had a measured pressure (ship near shore) of 914 mb.” However, the number of major tropical cyclones along the Queensland coast has declined since the 1870s, according to recent paper by Callaghan and Power (2010). They found that ”the number of severe TCs making land-fall over eastern Australia declined from about 0.45 TCs/year in the early 1870s to about 0.17 TCs/year in recent times—a 62% decline. This decline can be partially explained by a weakening of the Walker Circulation, and a natural shift towards a more El Niño-dominated era. The extent to which global warming might be also be partially responsible for the decline in land-falls—if it is at all—is unknown.”

References
Callaghan, J. and S. Power, (2010): Variability and decline in the number of severe tropical cyclones making land-fall over eastern Australia since the late nineteenth century, Climate Dynamics. DOI: 10.1007/s00382-010-0883-2


Figure 3. Tropical Cyclone Yasi at 03:35 UTC February 2, 2011, as seen by NASA's Aqua satellite.

Jeff Masters