Christmas day turned out to be one of the strongest tornado outbreaks of the 2012 season, in ‘Dixie Alley.’
Yesterday, December 25th, provided intermittent and diminishing snow showers and cold temperatures, resulting from a strong 500mb jet descending from the north and down over the Colorado Rocky Mountains. The cold jet dipped and extended eastward, helping to produce heavy snow falls and blizzard conditions in northeastern states. A low pressure system intensified over Mississippi and progressed eastward overnight through Alabama and Georgia, and was assisted by this strong jet flow to produce convective storms. The powerful jet then progressed eastward and up in-front of a low pressure trough over Alabama, and helped to create an historic Christmas day tornado outbreak.
The backside of the trough (See slide show) brought down cold air and precipitation from the northeast, while in-front of the low pressure trough, the strong system, assisted by a powerful mid-level jet, also drew-in warm moist air and high dew points up from the Gulf of Mexico, spawning surface-based conditions, and resulting in a record number of Christmas day tornadoes (40 at present count).
The following is a video link to a powerful tornado that went through Mobile, Alabama, yesterday on Christmas.
The 2012 Christmas day tornado outbreak spanned States from Texas, through Louisiana, Mississippi, and over night into Alabama. A number of Christmas day tornadoes were large and violent in Mississippi and Alabama. There were a number of tornado injuries from Louisiana through Mississippi, but the injury count is ‘so far’ reportedly low, considering the large number of violent tornadoes that moved through fairly populated areas, and the high amount of property damage. Some of this low injury count can be attributed to advance warnings made by NOAA National Weather Service (NWS), Storm Prediction Center (SPC), and the Weather Channel (TWC).
Recapping the 2012 tornado season, this year started off early with strong powerful tornadoes in Kansas and Oklahoma on April 13-14th. Fortunately, on April 14th, a number of very strong long-track EF4 tornadoes moved mostly over open range lands, but there were deaths unfortunately reported in Woodward, Oklahoma.
According to preliminary data from the SPC, the highest months for tornadoes ‘in 2012’ were: March, April, May, and June. This year, SPC reported 154 tornadoes in March, 206 in April, 121 in May. Comparing the same three months last year in 2011, there were 75 tornadoes in March, a whopping 758 in April, and 326 tornadoes reported in May.
The 2012 tornado season is statistically lower than average, up until yesterday on Christmas day. However, estimating with an additional 40 tornadoes added to the total count in 2012, the number of tornadoes for this year will still likely fall below average, and annually is far less than the overall number of torandoes that occurred in 2011.
This year of violent weather has been somewhat perplexing, as we have seen tornadoes and forest fires initiate in Colorado, within the same day, and in a relatively close geographic region. A considerable number of tornado outbreaks have also occurred, along with heavy snowfalls and blizzard conditions. While snowfall on the backside of a northeastward progressing low pressure trough is not uncommon, the concurrence of mesocyclone-based tornadoes and major forest fires in the same day is not typical, as low dew points (dry air) conditions that create wildfire dangers also tend to discourage surface-based conditions needed to initiate tornado genesis. However, up slope conditions, along the Colorado Front Range and the Denver Cyclone, formally known as the Denver Convergence Vorticity Zone (DCVZ), has allowed for both wildfires and tornadoes this spring, partly due to upslope conditions that drew-in adequate dew points from the southeastern plains to produce supercell thunderstorms, while mountain forest areas of the Front Range, also remained critically dry.
Given the Mayan calendar officially ended on December 21st, 2012, and the earth still exists, we at least can rely on advancing meteorological systems and better background knowledge of events leading to conditions that produce violent storms, but there remains many unanswered questions about exactly when and where dangerous weather will hit a local community, so both emergency preparation and further research are important.