We have made it through another meteorological winter, though it may not seem like it east of the Rockies for a while longer. With meteorological spring right around the corner (March, April and May), it is time once again to inspect the long range forecast to try to infer how active the spring tornado season may be.
For March, we are able to use more of the traditional medium and long range tools like the Pacific-North American Pattern (PNA) and the Western Pacific Oscillation (WPO) in addition to the more seasonal signals like ENSO, PDO and AMO, many of which I referenced in last year’s spring tornado outlook. The two most commonly referenced global forecast models, the GFS (American model) and ECMWF (European model, or Euro), help paint the picture on how the first half of March will turn out.
In the near term, there is a low tornado threat in the South, but weak low-level and mid-level lapse rates will inhibit tornado development.
It’s almost that time of year again. Sure, it’s always that time of year to some degree, as we’ve detailed in length here and the map animation above shows.
In a winter invaded so frequently by Arctic outbreaks as the one currently heading toward its end, 2014 is off to a historically slow start (seems to be the story of late?). While any uptick in activity will sure to be noticed, it’s of course early in the year to think too much about deficits. And watching the animation, you can certainly see why the main focus is typically on April through June.
A general under-performance of tornado activity continued for the second straight year across the United States during 2013. But what the country missed in pure numbers, it made up for in powerful events.
While the largest tornado outbreaks occurred in times typically not noted as the main tornado season, spring was full of dangerous days, with the majority of the violent tornado activity centered on May.
In a number of instances below, there may have been several top videos that could have been selected. Rozel, Moore, Bennington, El Reno and the November 17 outbreak in particular all had their fair share of striking videos.
February 10, 2013 – EF4 in Hattiesburg, Mississippi
by Basehunters via TVN
A major “second season” tornado outbreak struck parts of the Midwest, Tennessee and Ohio valleys on Sunday. The outbreak will likely go down as the largest of 2013.
The event contained at least two confirmed violent tornadoes that passed through New Minden and Washington, IL. These are the first violent tornadoes in November since 2011 in Oklahoma. They’re also the only violent tornadoes on record in Illinois during the month.
New Minden IL (prelim EF4) is the first violent tornado in Illinois in Nov during modern record. Prior ones: pic.twitter.com/FWSniysVXg
— U.S. Tornadoes (@USTornadoes) November 17, 2013
Here are some of the most intense tornado videos from the event…
A strong disturbance will work into the Midwest today into tomorrow, with the threat of a tornado outbreak looming on Sunday. As is typical with these cold season threats, this system has a high shear/low CAPE environment with conditional risks to both sides. Regardless of the risks, tomorrow’s setup looks prime for widespread severe winds and some tornadoes.
Central Mississippi Valley — POTENTIAL: Low — CONFIDENCE: Normal
Pros: Strong shear (both directional and speed), left-exit region of an upper-level jet.
Cons: Very little instability, weak lapse rates.
Midwest, Tennessee Valley — POTENTIAL: High — CONFIDENCE: Normal
Pros: Very strong speed shear, good directional shear, very strong forcing, improving mid-level lapse rates, surface dewpoints in the 60s, pre-frontal supercells possible.
Cons: Instability could be limited by widespread cloud cover and rain in the warm sector. Storms could turn linear faster, which would limit the supercell potential.
I’m back with a forecast finally! It has been awhile since we have seen a storm with good enough potential for an update.
Eastern Nebraska, Iowa — POTENTIAL: Low — CONFIDENCE: Normal
Pros: Good directional shear, moderate instability, left-exit region of approaching jet streak.
Cons: Storm initiation/coverage is questionable with somewhat-capped atmosphere, no notable vort. max to help forcing.
Central Plains, western Midwest — POTENTIAL: High — CONFIDENCE: Normal
Pros: Strong shear, moderate to high instability, strong vort. max and good surface convergence along two frontal boundaries.
Cons: Uncertainty with storm coverage in the area of greatest potential, which is basically Iowa. Storms may line out early and would shorten the window for supercells. High LCLs could limit initial potential, especially in the southern areas.
The United States experiences approximately 75 percent of the world’s known tornadoes and thus is notorious for its tornado climatology in terms of frequency, intensity, and destructive outbreak events. While it is appropriate to focus on tornadoes across the United States, it is important to recognize that tornadoes also happen in other countries of the world.
This article investigates where many of the other 25 percent of the world’s tornadoes occur, with a specific emphasis on our North American neighbors of Canada and Mexico. How do other countries match up against the United States when it comes to tornado climatology? You’re about to find out. (Hint: The U.S. is the uncontested heavy weight champion of the world.)
The pattern looks pretty quiet for the next week, so I’m going to go back to what we did last year and just do special updates when the more notable disturbances show up. As you can see on this inflation-adjusted graph, the tornado count has really flat-lined recently in this already quiet season:
Needless to say, I am very fortunate to have picked a two-week period months in advance that would end up being the only active period in the Plains! I hope all the chasers were able to get what they could out of this paltry tornado season.
If you’re into finding a holiday tornado, July 4 is likely one of your best bets given its residence in the center of the warm season. Since 2000, only 2005, 2007, and 2008 have seen no tornado touchdowns on the Fourth. In the most recent 20 years, 85 percent of Independence Days saw at least one.
222 tornadoes have been documented on the day since 1950. As we might expect given July’s tornado climatology, parts of the northern and central Plains, as well as the Great Lakes region, appear “favored” to see a July 4 tornado.
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