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Below normal extreme… Northern Hemisphere tornado activity in 2021 Below normal… U.S. tornadoes below normal – Did they emerge because of it?


From NoTricksZone

Via P Gosselin above November 20, 2021

By meteorologist Paul Dorian

Cyclone Cumulative Energy (ACE) is the best measure of overall tropical activity and it is below normal for the 2021 season across the Northern Hemisphere.

Data: Colorado State University, NOAA

Overview

Tropical cyclone activity across the Northern Hemisphere will be below normal in 2021 like last year. Specifically, while the Atlantic Basin experienced above-normal tropical activity this year and last year, the Pacific Ocean experienced below-normal conditions in both years resulting in below-normal levels. usually throughout the hemisphere.

Regarding tornadoes, it was another below-normal season in the United States with no EF-5 recorded. However, there has been tornado activity in some unusual places in 2021 including the Mid-Atlantic and New England.

Colder-than-normal sea surface temperatures continue to dominate the equatorial Pacific Ocean landscape. These “La Nina” conditions could play an important role in above-normal tropical activity over the Atlantic basin in 2021 and below-normal activity in the Pacific. NOAA map, Tropicaltidbits.com

Tropical activity in the Northern Hemisphere… below normal

There is currently no tropical activity in the Atlantic or Pacific Oceans, and no activity is forecast for the foreseeable future. In fact, tropical activity in both of these large bodies of water is most likely going for the 2021 season, and there has been a rather dramatic drop in activity in recent weeks. In fact, the quiet period for tropical activity begins in October, and it turns out to be quite unusual in that there are no “major” (category 3 or higher) storms anywhere in the globe.

October surprise

Based on Dr. Philip Klotzbach of Colorado State University, it was the first time since 1977 that there were no “major” October storms anywhere around the globe. Furthermore, between mid-October and mid-November, the cumulative cyclone energy (identified below) globally was the lowest in the satellite era (since 1966).

The 2021 Atlantic Basin was above normal in the number of named storms (21), making it the third most active basin on record using that particular metric.

There is another metric called cumulative cyclonic energy (ACE) that meteorologists tend to favor to gauge overall tropical activity in a given season. ACE Index – originally created by Dr. William Gray et al. at Colorado State University and subsequently adjusted by NOAA – not just factors in intensity of a tropical cyclone, it also takes into account longevity.

The average energy per storm is much lower

While the “number of storms” in the Atlantic basin this season ranks fairly high on a historic scale, the average ACE per hurricane is much lower on the chart than in previous seasons. This result demonstrates the fact that many of the tropical systems named this year are short-lived and/or relatively weak.

Last 50 years of Energy Saturation accumulated globally and Northern Hemisphere: total run for 24 months. Note that the year indicated represents the value of ACE for the previous 24 months for the Northern Hemisphere (bottom line/grey box) and global (top line/blue box). The area in the middle represents the total Southern Hemisphere ACE. Dr. Ryan Maue is polite

Increased activity in Atlantic linked to cool equatorial Pacific

Above-normal activity in the Atlantic basin this year (and all of 2020) was driven in part by La Nina conditions in the equatorial portion of the Pacific Ocean. Typically, colder-than-normal sea surface temperatures in the tropical Pacific (i.e. La Nina conditions) lead to an overall reduction in wind shear in the tropical Atlantic, and this is again weak. favorable factors for the formation and strengthening of tropical cyclones. in that part of the hemisphere.

Operations in the Pacific are curtailed

While La Nina conditions are a favorable factor for tropical activity in the Atlantic basin, it tends to inhibit activity in the equatorial portion of the Pacific Ocean. In both areas of the Pacific (i.e. east and west of the “international date line”), overall tropical activity is below normal this season in terms of cumulative cyclone energy . The Pacific outage began in September when only one storm was named (Olaf) making it the least active month since 2010.

Of all the countries in the world, the US has the highest number of tornadoes and this year has been lower than usual nationally. The annual tornado trend graph is the result of the following method applied to the SPC observed tornado data set by Harold Brooks, NSSL and Greg Carbin, NOAA/SPC.

Details: A simple linear regression equation fits the annual tornado count from 1954-2007. This equation is then used to calculate the delta, or difference, between the original/observed annual total number of tornadoes and the flattened or “modified” annual total. correction” is represented by the point on the linear trend line for that year.

US tornadic activity… below normal

2021 was a below-normal year in terms of the number of tornadoes nationwide falling below the “25th percentile. The United States had the most tornadoes of any country, as well as strong tornadoes. most and most intense. Despite some outbreaks in March and another major outbreak in early May, overall the year remains below average due largely to inactivity during the months of April and June.

Cyclone Abnormal Activity

While the entire country has experienced less tornado activity than usual, there are some areas where unusual action has occurred. For example, the Mid-Atlantic region experienced an unusual midsummer outbreak of tornadoes originating in the Upper Midwest.

On July 29, mass tornado supercells developed through the eastern Ohio Valley and the Mid-Atlantic resulting in multiple tornadoes. In fact, several powerful and damaging tornadoes including the EF-3 tornado caused severe damage in the Philly suburbs of Trevose and Bethlehem. This was the first EF-3 tornado to hit the lower Bucks ever, but the F3 tornado passed through the Central Bucks about 125 years ago in 1896, according to the National Weather Service.

Another unusual tornado caused damage in southeastern Pennsylvania late summer (September 21) when an EF-2 crashed in the Philly suburb of Fort Washington.

Also, just in the past week, there has been an unusual tornado outbreak in parts of New York and New England. On Saturday, November 13, the powerful storms that produced at least 11 tornadoes were confirmed to have hit New York state and New England with all classified as EF-0 or EF-1 .

According to NWS East Area, there have been six tornadoes on Long Island (plus a sixth in the middle of New York State’s Hudson Valley), four in Connecticut and three in Rhode Island (two of the tornado goes from CT to RI). According to the NWS, there have been no recorded tornadoes in Connecticut or Rhode Island in November since 1950.

According to NOAA’s Hurricane Prediction Center (SPC), the last recorded EF-5 tornado – the most intense classification – was in 2013.

No EF-5 tornadoes in 8 years

One of the notable findings of the 2021 U.S. tornado season is that it doesn’t have any of the strongest EF-5 tornadoes out there. In fact, it’s been more than eight years since the last EF-5 tornado hit the United States, which was in Moore County, Oklahoma in May 2013. According to NOAA, there have been a total of 36 EF-5 tornadoes in the United States since 1970 with 14 of those occurring in the 1970s.

Original article here.



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