Fast-moving storm, tornadoes threaten US

A rare and very dangerous late-season severe weather outbreak is underway over the Midwest US, where NOAA’s Storm Prediction Center is predicting a “High Risk” of severe weather–their highest level of alert–over most of Indiana and Illinois, plus portions of Southern Lower Michigan and Western Ohio.

This is just the second “High Risk” forecast for 2013, and the area at risk of severe weather is unusually large. According to a list of all “High Risk” forecasts issued since 1984 maintained at Wikipedia, today’s High Risk area is the farthest north such a forecast has been issued so late in the year.

A 992 mb low pressure system that was over Northern Illinois on Sunday morning will move northeast and rapidly intensify to 965 mb by Monday morning, dragging a strong cold front across the “High Risk” area on Sunday afternoon.

Isolated supercell thunderstorms–the kind most likely to produce strong and violent tornadoes–are expected to form ahead of the front, and the SPC is expecting multiple long-track strong tornadoes to form during the early afternoon.

Any tornadoes that form will be moving at highway speed–50 to 60 mph–and will be under low cloud bases around 2,000 feet, making these storms difficult to see and react to, particularly in wooded or hilly areas. If the sirens sound, seek shelter!

A dangerous day in Chicago

Most of Illinois, including Chicago, has been placed under a special “PDS” Tornado Watch: a “Particularly Dangerous Situation.”

Severe thunderstorms spawning tornado warnings have already erupted over Southern Wisconsin and Western Illinois as of 10:15 am CST.

Severe thunderstorms are likely to sweep through Chicago in the early afternoon during today’s Ravens – Bears game, which starts at noon CST.

According to NBC 5 in Chicago, loose objects are being removed from the stadium in anticipation of high winds, and officials are prepared to evacuate fans, if necessary. An NFL game will stop if there is lightning, and cannot continue until 30 minutes afterwards. Democraticunderground.com