Global Ensemble Forecast System (GEFS) Predictions of Days 1–15 U.S. Tornado and Hail Frequencies

Gensini, Vittorio A.; Tippett, Michael K.

doi:10.1029/2018gl081724

Cited by 17 publications

(17 citation statements)

References 21 publications

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“…ERTAF began in spring 2015 motivated by the realization that patterns favorable for severe weather can sometimes be predicted at extended lead times (7+ days), beyond the typical range at which numerical weather prediction (NWP) models have useful skill at predicting atmospheric ingredients favorable for tornadoes (Gensini & Tippett, ; Zhang et al, ). These occasional forecasts of opportunity are made possible by catching the emergence of coherent subseasonal signals within the GSDM framework and using the time scales typical of these processes to anticipate the development of regional circulation anomalies favorable for tornadoes, such as those that developed in May 2019.…”

Section: Resultsmentioning

confidence: 99%

Extended U.S. Tornado Outbreak During Late May 2019: A Forecast of Opportunity

Gensini

Gold²,

Allen

et al. 2019

Geophysical Research Letters

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The second half of May 2019 was an unusually active period for tornadic thunderstorms across the U.S. Great Plains, Midwest, and lower Great Lakes. While this period typically coincides with the peak climatological frequency of tornadoes, preliminary reports of tornadoes were over triple the expected 30‐year average. Multiple‐day outbreaks of tornadoes are not unprecedented in the United States; however, this event was perhaps the first to be forecast at subseasonal lead times (3–4 weeks) by the Extended Range Tornado Activity Forecast team. This forecast of opportunity was driven, in part, by anomalous convective forcing in portions of the tropical Indian and Pacific Oceans, causing subsequent changes in Northern Hemisphere atmospheric angular momentum. This manuscript analyzes the evolution of hemispheric‐scale circulation features leading up to the event, examines teleconnection processes known to influence U.S. tornadoes, and provides insights into the forecast process at subseasonal lead times.

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Section: Resultsmentioning

confidence: 99%

Extended U.S. Tornado Outbreak During Late May 2019: A Forecast of Opportunity

Gensini

Gold²,

Allen

et al. 2019

Geophysical Research Letters

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“…This is particularly true for severe convective storms (SCSs; defined as thunderstorms that produce tornadoes, large hail, and/or damaging convective wind gusts) given the significant impacts on various economic and societal sectors (Simmons and Sutter 2013;Smith and Matthews 2015;NCEI 2019). Recent research has shown skill in forecasting U.S. tornado and hail frequency at various lead times in the subseasonal period (Allen et al 2015;Lepore et al 2017;Baggett et al 2018;Lepore et al 2018;Gensini and Tippett 2019), including a recently documented operational forecast of an anomalously high period of tornado frequency in late May 2019 issued more than three weeks in advance (Gensini et al 2019).…”

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confidence: 99%

“…The Madden-Julian oscillation (MJO) and the global wind oscillation (GWO) are two such modes of atmospheric variability with documented periodicity on the subseasonal time scale (Weickmann and Berry 2009;Zhang 2013). While not mutually exclusive (the GWO encompasses the MJO through incorporation of the tropical zonal wind fields), both processes have been shown to modulate tornado and hail frequency across the United States (Barrett and Gensini 2013;Thompson and Roundy 2013;Barrett and Henley 2015;Gensini and Marinaro 2016;Baggett et al 2018;Gensini and Allen 2018;Tippett 2018;Moore 2018;Gensini et al 2019;Moore and McGuire 2019). A known physical pathway by which the MJO and GWO influence CONUS severe weather is by generating positive mountain and frictional torques, particularly as convection associated with the MJO increases across the Maritime Continent and moves toward the international date line.…”

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confidence: 99%

“…This gives rise to positive atmospheric angular momentum anomalies, characteristic of GWO phases 5 and 6, with potential for jet extension that eventually leads to wave breaking and a reduction of atmospheric angular momentum. It is this decreasing tendency of atmospheric angular momentum that favors synoptic weather patterns supportive of tornadoes east of the U.S. Rocky Mountains (Weickmann and Berry 2009;Gensini and Marinaro 2016). These synoptic weather patterns often include a midtropospheric trough in the western United States and a poleward flux in surface moisture across the Great Plains.…”

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confidence: 99%

“…These synoptic weather patterns often include a midtropospheric trough in the western United States and a poleward flux in surface moisture across the Great Plains. More simply, GWO and MJO have been shown to alter the 300-hPa height fields, with E702 positive severe weather frequency anomalies generally located southeast of negative height anomalies, in regions favorable for ascent and for greater vertical wind shear (Barrett and Gensini 2013;Barrett and Henley 2015;Gensini and Marinaro 2016).…”

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The Extended-Range Tornado Activity Forecast (ERTAF) Project

Gensini

Barrett

Allen

et al. 2020

Bulletin of the American Meteorological Society

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Large-scale weather patterns favorable for tornado occurrence have been understood for many decades. Yet prediction of tornadoes, especially at extended lead periods of more than a few days, remains an arduous task, partly due to the space and time scales involved. Recent research has shown that tropical convection, sea surface temperatures, and the Earth-relative atmospheric angular momentum can induce jet stream configurations that may increase or decrease the probability of tornado frequency across the United States. Applying this recent theoretical work in practice, on 1 March 2015, the authors began the Extended-Range Tornado Activity Forecast (ERTAF) project, with the following goals: 1) to have a map room–style discussion of the anticipated atmospheric state in the 2–3-week lead window; 2) to predict categorical level of tornado activity in that lead window; and 3) to learn from the forecasts through experience by identifying strengths and weaknesses in the methods, as well as identifying any potential scientific knowledge gaps. Over the last five years, the authors have shown skill in predicting U.S. tornado activity two to three weeks in advance during boreal spring. Unsurprisingly, skill is shown to be greater for forecasts spanning week 2 versus week 3. This manuscript documents these forecasting efforts, provides verification statistics, and shares the challenges and lessons learned from predicting tornado activity on the subseasonal time scale.

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Using the daily change in the Southern Oscillation Index to develop analogues and the relationship to severe weather outbreaks

Renken

Brown

Kennedy

et al. 2022

Intl Journal of Climatology

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The occurrence of severe weather is an annual problem for much of the United States and North America and maximizes from March through June.With the increased interest in subseasonal weather forecasting, there have been attempts to anticipate the occurrence of anomalous weather on the timescale of one to 4 weeks including the occurrence of severe weather. Previous research has shown that teleconnection indices, associated with long period Rossby wave activity, or persistent large-scale flow regimes have been useful tools in this endeavour. Here, abrupt changes over a 24-72-hr period (10 or more units per day or 20 or more units over 3 days) in the Southern Oscillation Index (SOI) time series will be used to demonstrate that these changes can be associated with the possible occurrence of major severe weather event-days defined as; 20 or more tornado, 155 or more wind speed events >25.9 mÁs −1 , or 135 or more hail diameter larger than 25.4 mm, reports over the United States one to 3 weeks in advance, especially during the March through June period.The severe weather events obtained from the archive at the Storm Prediction Center (SPC) from 1991 through 2020 were used. The results here demonstrate that more than 7 in 10 major severe weather occurrences were associated with abrupt positive and negative changes in the daily SOI when using signal detection methods.

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Global Ensemble Forecast System (GEFS) Predictions of Days 1–15 U.S. Tornado and Hail Frequencies

Cited by 17 publications

References 21 publications

Extended U.S. Tornado Outbreak During Late May 2019: A Forecast of Opportunity

Extended U.S. Tornado Outbreak During Late May 2019: A Forecast of Opportunity

The Extended-Range Tornado Activity Forecast (ERTAF) Project

Using the daily change in the Southern Oscillation Index to develop analogues and the relationship to severe weather outbreaks

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