Looking back at the week of April 6-12.

Tornado watches, warnings and reports the week of April 6-12, 2014.

Tornado watches, warnings and reports the week of April 6-12, 2014.

April can be volatile, but lately it seems we talk more about lack of tornadoes and/or tornado droughts than anything else.

The week was dominated by a system that rolled through the south to start the period — Sunday into Monday, April 6 and 7.

As the week closed, some storminess resumed across the Plains, but nothing to write home about at this time of year.

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Tornadoes with a track length of 25 miles or greater ranked by strength grouping. (Ian Livingston/SPC Data) *select for larger*

Tornadoes with a track of 25 miles or greater sorted by strength grouping. (Ian Livingston/SPC Data) *select for larger*

Long-track tornadoes are unusual in the tornado world.

Using a moderately restrictive 25 mile or longer path as the definition, they’re about 2.5 percent of all twisters. In a more stringent 100 mile or longer path length, we’re looking at about 0.1 percent of the full modern record dating back to 1950.

Here, we’ll use 25 miles as a base, with additional looks at 50 miles or longer and 100 miles or longer tracks. In today’s lingo, you may hear the term referring to even shorter tracks, but we begin to wash the idea down heading much lower than 25 miles.

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(SPC)

(SPC)

If you’re a regular follower of our blog or of U.S. weather in general, then it’s no secret that this tornado season has been even quieter through early April than 2013 was.  But back on March 31, the 2014 tornado season actually broke a record for the latest in the year with no F/EF3+.

March 30 (local time) was previously the date of the latest F/EF3+ tornado on record in the U.S. since 1950, and it happened in 2002.  As of publish, there has not yet been a single EF3+ rated tornado in the United States during the 2014 calendar year. Caveat: There was a fairly large tornado in eastern North Carolina during the afternoon of April 7 that has yet to be rated.

If that tornado is not rated EF3+, then the streak will likely continue until at least Monday, April 14, when the next significant trough ejection is modeled to occur across the central U.S. If the NC twister does attain the rating in question, we still have set the record by over a week.

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Looking back at the week of March 30-April 5.

Tornado activity the week of March 30 - April 5, 2014.

Tornado activity the week of March 30 – April 5, 2014.

It was a wild week of weather, with even a predominantly cold storm producing some action. Two significant systems rolled across the country. The first was the cold one, with blizzard conditions spread across the north central U.S.

The second, while also featuring snow in the northern Plains and Midwest, promised to be the first legitimate tornado event of the spring. While it did produce, it may be said it did so on the lower end of potential.

Still, a number of tornadoes occurred on multiple days, with a focus on the Ozarks and mid-South, but also targeting the broader Dallas-Fort Worth metroplex.

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Tornadoes will threaten the South today and tomorrow as a high shear, low instability environment develops over the region. The environment for tornadoes will be fairly conditional, but with the strong shear, some upside risks are in play for areas that might get greater daytime heating, but the chances of that happening are low.

Just a reminder that for 2014, we have changed up the forecast format a bit, and the details can be found in our forecast from last week.

20140406_update
Sunday

Western and central Gulf — TORNADO RANGE: 2-7 — CONFIDENCE: Normal
Expected Tornado Hotspot: Southern Louisiana, southern Mississippi
Pros: Strong speed shear, good directional shear, good upper-level forcing, height falls moving in late
Cons: Low instability, okay/poor lapse rates, widespread cloud cover minimizing any chances for pockets of greater instability, greatest potential appears to be in the overnight hours

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During a period of just 18 hours between April 3rd and 4th, 1974, the so-called Super Outbreak dropped 147 tornadoes across 13 states. This was the largest and most violent tornado outbreak of the 20th century, and likely only matched in scale by the outbreak of 2011. In all, there were 30 F4 and F5 tornadoes recorded during this period, and over half of the tornadoes recorded were classified as F2 or higher.

Related: Looking back and recreating the maps | A Numerical Comparison of 1974 and 2011

Forty years later this outbreak continues to be an important case study for severe weather. Just this week the Storm Prediction Center released a simulation of what today’s storm-scale models may have forecast for this event. While warning lead-times have more than doubled since the 1970s, forecasting where and when tornadoes will form remains a critical challenge still today.

spc-1974-storm-scale

Storm-scale simulation of April 3-4, 1974 Super Outbreak

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It’s 2014, and we have a couple of changes to the format of the Tornado Threat Forecasts. There may be some additional tweaks as we get settled into the 2014 tornado season. Firstly, the Tornado Potential, which was just a gauge of how many tornadoes to expect, will be replaced with an actual tornado range, since that’s just basically what the Tornado Potential was, anyway. Forecasting an actual range once you get above several tornadoes can be pretty difficult, so the Forecast Confidence and the text discussion will balance how likely I think that the actual tornado count will fit within the given range. A wider range may also hint at the amount of uncertainty in the forecast.

Sometimes there will be a large risk area, but most tornadoes will be concentrated in a certain part of it. To help give more detail to the forecast, we have added the Expected Tornado Hotspot for where tornadoes will be most likely and/or most numerous.

(Note: This is not an April Fool’s joke… I blame the bad timing of the more active weather pattern.)

20140401_update
Tuesday

North-central Texas, southern Oklahoma — TORNADO RANGE: 0-3 — CONFIDENCE: Normal
Expected Tornado Hotspot: None
Pros: Moderate instability, strong directional shear, good speed shear
Cons: Strong capping inversion leading to questionable storm coverage

California — TORNADO RANGE: 0-2 — CONFIDENCE: High
Expected Tornado Hotspot: None
Pros: Good upper-level forcing, strong directional shear
Cons: Low instability, weak speed shear in the low to mid levels

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Tornadoes can be very scary, but they’re also incredible. Photographing one in person is a tricky ordeal for many reasons, most importantly the question of safety. When adrenaline is pumping, getting the shot can be even more difficult.

Over the two years since we started this site, we’ve been fortunate enough to have a number of excellent photographers join up with the U.S. Tornadoes photo group over on flickr and share photos there.

In the spirit of kicking off peak tornado season (April, May, and June), below are my current top 10 from the group. Truly stunning.

Fall River County, SD
Blake Knapp

fall-river-sd-blake-knapp

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March 29, 2014 in northern California. (NWS Sacramento)

March 29, 2014 in northern California. (NWS Sacramento)

It’s “tornado season” again, maybe. March has been extremely quiet any way you cut it when it comes to severe weather — winter just keeps on coming. However, as we got through the last week of March, spring storms became more commonplace. With that, we rev Tornado Digest back up. Never heard of it? It used to be called Tornado Weekly.

While we’ll probably mainly focus on peak season again this year, the name change will allow for Tornado Digests to show up for reasons other than just a weekly recap.

Anyway, on to this past week’s show, and a brief look to the future.

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On March 18, 1925 a dark “smokey fog” touched down approximately three miles northwest of Ellington, Missouri. It would become known as the Tri-State Tornado. By all accounts the Tri-State Tornado was one for the record books.

The Tri-State Tornado is currently the U.S. record holder for longest tornado track (219 miles), most deaths in a single tornado (695), and most injuries in a single tornado (2027). While it occurred before the modern record, it is considered by all accounts to be a F5/EF5 Tornado. It crossed the three states, thus it’s namesake “Tri-State,” tearing through thirteen counties of Missouri, Illinois, Indiana. It crossed over and destroyed or significantly damaged nine towns and numerous smaller villages.

The track of this tornado has been lost to the 89 years of growth of vegetation and development by humans. One map, done by Wilson and Changnon in 1971, seems to provide the most accurate path of this tornado. However, in searching for an electronic or digitized copy of this map I could not find one. I decided to re-create their map in geographic software as seen below.

Re-Creation of the Wilson, 1971 Tri-State tornado path and resulting deaths in hardest hit towns.

Re-Creation of the Wilson, 1971 Tri-State tornado path and resulting deaths in hardest hit towns.

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