Jeff Masters on Possibility of Tornadoes 3/2

The winter of 2012 blew out like a lion yesterday, with a massive Leap Day storm that pounded the Midwest with deadly tornadoes and heavy snow. A violent EF-4 tornado with 180 mph winds tore through Harrisburg, Illinois at 4:56 am CST yesterday morning, killing six, injuring approximately 100, and damaging 200 homes and 25 businesses. The tornado cut a path seven miles long and 250 yards wide across the town, according to the NWS damage survey. Another person was killed in southwest Missouri near Buffalo when am EF-2 tornado ripped through a mobile home park late Wednesday night. Twelve others were injured in the mobile home park. Four additional deaths occurred due to tornadoes in Cassville, MO, Smithville, TN, and Monterey, TN yesterday, bringing the death toll of the two-day severe weather outbreak to eleven. An EF-2 tornado also plowed through downtown Branson, Missouri yesterday morning, injuring 33 people. The tornado blew out or cracked windows in 219 of the hotel rooms in the 12-story/295 room Hilton Branson Convention Center, and extensively damaged three of Branson’s 50 plus theaters–Americana Theater, Branson Variety Theater and Dick Clarks’ American Bandstand Theater. The Branson Landing on Lake Taneycomo and the Veterans Memorial Museum were also heavily damaged. An NWS storm survey found the tornado was 400 yards wide and carved a path 22 miles long. An EF-2 tornado also hit the small town of Harveyville, Kansas (population 275), twenty miles southwest of Topeka, at 9:03 pm Wednesday night. The tornado destroyed 40 – 60% of the structures and injured twelve, three critically. Overall, damage from the two-day tornado outbreak will run in the hundreds of millions of dollars, and could add up to be the first billion-dollar weather disaster of 2012 in the U.S.

Figure 1. Damage in Branson, Missouri after yesterday’s tornado. Image credit: BransonRecovery Facebook page.

Yesterday’s tornado outbreak’s place in history
Yesterday was the deadliest day for U.S. tornadoes since May 24, 2011, when 18 people died in a Midwest tornado outbreak–part of the five-day outbreak that brought the deadliest U.S. tornado since 1947, the May 22, 2011 Joplin, Missouri tornado, which killed 158 people and injured 1150. The preliminary tornado total from February 28 – 29 of 2012 is 30, making it the largest February tornado outbreak since February 17 – 18, 2008, when 31 twisters touched down. Yesterday’s Harrisburg, Illinois tornado was the deadliest February tornado since the February 10, 2009 EF-4 twisterthat struck Southern Oklahoma near Ardmore, killing eight. The deadliest February tornado in recorded history occurred on February 21, 1971, when an F-4 tornado ripped a 202-mile path through Mississippi, killing 58 people.

Figure 2. By analyzing both the rotational velocity of the storm systems (the spinning of tornadoes has high rotational velocity compared to the surrounding storms) and presence of hail, scientists at the NOAA National Severe Storms Laboratory have developed a product that approximates the track of tornadoes, shown here for the February 29, 2012 storms. Image credit: NOAA Environmental Visualization Laboratory.

Violent tornadoes in February: a rarity
Violent February tornadoes are rare in February. The Tornado History Project lists eighteen EF-4 and one EF-5 tornadoes in the U.S. during the month of February since 1950–an average of one violent February tornado every three years. Part of the reason for this is the lack of warm, unstable air so early in the year. However, this year’s unusually mild winter has led to ocean temperatures across the Gulf of Mexico that are approximately 1°C above average–among the top ten warmest values on record, going back to the 1800s. Averaged over the month of February, the highest sea surface temperatures on record in the Gulf between 20 – 30°N, 85 – 95°W occurred in 2002, when the waters were 1.34°C above average. Yesterday’s tornado outbreak was fueled, in part, by high instability created by unusually warm, moist air flowing north from the Gulf of Mexico due to the high water temperatures there.

Heavy snow hits Upper Midwest
The same storm system also brought the heaviest snows of the winter to portions of the Upper Midwest, which has received scant snowfall this winter. Widespread heavy snow fell in northern Wisconsin, where Mincqua recorded 18 inches. South Dakota, Central Minnesota, and Michigan’s Upper Peninsula also received snow amounts in excess of a foot. The storm also brought moderate snows to Northern New England, with southern Vermont receiving more than 8 inches. The latest NOAA Storm Summary has detailed storm total accumulation info.

Figure 3. Snowfall amounts for the 3-day period ending at 7 am local time Thursday, March 1, 2012. Image credit: NOAA Southern Region Headquarters.

New tornado outbreak likely on Friday
The storm system that brought yesterday’s tornadoes and snow has moved into Canada and New England, and the threat of severe weather is minimal today in the Midwest. However, a new storm system is expected to form over Missouri early Friday and track northeastward, unleashing a new tornado outbreak over Tennessee, Kentucky, Alabama, Mississippi, Indiana, and Ohio. NOAA’s Storm Prediction Center has placed this region in their “Moderate Risk” area for severe weather Friday, and is warning of the possibility of long-track significant tornadoes. Consult ourSevere Weather Page and Interactive Tornado Page to follow the storms.

Figure 4. NOAA’s Storm Prediction Center has placed much of Tennessee, Kentucky, and portions of surrounding states in their “Moderate Risk” area for severe weather on Friday. This is one level below the highest level of alert, “High Risk.”

Portlight disaster relief charity responds to the Harrisburg, Illinois tornado
Portlight is sending people into the Harrisburg, IL, area at this time in response to the tornado disaster there. They will be assessing needs there and surrounding areas. As usual, they will be focusing efforts on the un-served, under-served and forgotten. Please visit the Portlight Disaster Relief blog to learn more. Donations are always welcome!

Jeff Masters