Posted by: JeffMasters
A huge and potentially historic winter storm is taking shape over the Southern Plains today. By the time the storm exits New England on Wednesday night, as many as 50 million Americans may see heavy snows of at least 6 inches or dangerous ice accumulations of 1/4" or more from the massive storm, and 100 million will be affected by the storm. A potent jet stream with strong winds will dive southwards over the central U.S. today, allowing a cold Arctic airmass to spill southwards out of Canada. In front of this cold air, a flow of very warm, moist air from the Gulf of Mexico will surge northwards, providing copious moisture to fuel snowfall amounts that will likely approach two feet across portions of Iowa and Illinois on Tuesday. The storm could be Chicago's biggest blizzard since January 1999, when a storm dumped 21.6" of snow. Accompanying the heavy snow on Tuesday will be strong winds gusting to 40 mph in Northern Illinois and Northwest Indiana, and a blizzard watch is posted for Chicago. Strong winds in Chicago are expected to generate 14 - 18 feet waves on Lake Michigan, with occasional waves up to 25 feet. A significant coastal flooding event is possible for Chicago, with beach erosion and flooding along Lake Shore Drive. Many major cities will likely receive over 8 inches of snow from the storm, including Kansas City, St. Louis, and Detroit. Perhaps of greater concern is the potential for a major ice storm along a swath from Northwest Oklahoma to Massachusetts. Widespread freezing rain is expected to bring over 1/4" of ice to many major cities, including St. Louis, Indianapolis, Columbus, Cleveland, and Pittsburgh. Some regions could see up to an inch of ice, and widespread power outages due to toppled power lines are likely for millions of people. Damages exceeding $1 billions are possible from this ice storm. In addition, the storm's powerful cold front will bring the potential for severe thunderstorms to the deep South. The NOAA Storm Prediction Center is giving Louisiana and surrounding states a "slight risk" of severe weather on Tuesday, and severe thunderstorms with damaging winds are likely Tuesday afternoon in this region.


Figure 1. Probability of receiving at least 1/4" of ice for the 24 hours ending at 7am EST on Wed Feb 2, 2011. Image credit: NOAA.

Very dangerous Tropical Cyclone Yasi headed for Australia's flooded Queensland
With February nearly upon us, the traditional peak of the Southern Hemisphere tropical cyclone season is here, and the waters surrounding Australia have been exceptionally active over the past week. We had the year's first two Category 4 tropical cyclones last week, Tropical Cyclone Wilma and Tropical Cyclone Bianca. Wilma passed over American Samoa as a strong tropical storm, and hit Tonga as a Category 3 storm, causing substantial damage to the islands, but no deaths or injuries. Wilma brushed New Zealand, bringing flooding and landslides to the North Island, and was the strongest tropical cyclone to affect that country in fourteen years, according to weatherwatch.co.nz. Tropical Cyclone Bianca skirted the west coast of Australia and dissipated before making landfall. Tropical Cyclone Anthony hit flood-ravaged Queensland, Australia, over the weekend, as a weak tropical storm with 40 - 50 mph winds. Fortunately, Anthony dropped only modest amounts of rain, and no new flooding disaster occurred in Queensland, which is struggling to recover from record floods. As reported in the latest Australian Bureau of Meteorology climate statement and flood summary, the past four months (September - December) have been the rainiest such period in Queensland's history, and the resulting flooding disaster has been Australia's most expensive natural disaster in history.

Queensland is in serious danger of renewed extreme flooding this week from Tropical Cyclone Yasi. Yasi has intensified to a Category 2 storm with 105 mph winds, and is undergoing a period of rapid intensification that is expected to take it to Category 4 strength. Yasi is expected to hit Queensland on Wednesday, probably as a major Category 3 or stronger storm. In addition the storm's damaging winds and storm surge, Yasi will bring torrential rains. The GFS model is predicting that Yasi will dump 5 - 10 inches of rain over a large swath of Queensland, which would likely cause destructive flooding.

One positive note: the European Center model was remarkably accurate predicting the formation of Yasi over a week in advance, so Queensland has had plenty of time to prepare for the arrival of the storm.


Figure 3. Tropical Cyclone Yasi at 23:20 GMT on January 30, 2011. At the time, Yasi was a Category 1 storm with 75 mph winds. Image credit: NASA.

Jeff Masters