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J. Brotzge
,
S. Erickson
, and
H. Brooks

caused by tornadoes. Thus, a reduction in the FAR is accompanied by a reduction in the number of tornado fatalities and injuries and is subsequently an important measure to understand. One of the National Oceanic and Atmospheric Administration’s (NOAA’s) goals for 2025 is to provide an average 60-min lead time for tornadoes ( Berchoff 2009 ). This goal of providing advance warning prior to tornadogenesis (i.e., “warn-on forecast”) requires that warnings be issued based upon the anticipation of

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J. Brotzge
,
K. Hondl
,
B. Philips
,
L. Lemon
,
E. J. Bass
,
D. Rude
, and
D. L. Andra Jr.

, just prior to tornadogenesis, which occurred a short time later at approximately 0355 UTC from the same storm cell ( Fig. 7 ). The shear estimate differences between CASA and NEXRAD cannot be readily explained. The CASA wind estimates represent a much smaller pixel volume compared with that of NEXRAD, and so estimates from CASA tend to vary more widely due to the smaller averaging volume. In addition, the radial velocity estimates from CASA also had some moderate amount of uncertainty associated

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J. Brotzge
and
S. Erickson

radar coverage. However, only mesoscale numerical weather prediction and “warn on forecast” ( Stensrud et al. 2009 ) ultimately can predict tornadogenesis prior to development, a critical step in providing the necessary positive lead time required for public response. Fortunately, some recent modeling efforts are starting to demonstrate such tornado prediction is possible (e.g., Hu and Xue 2007 ). Acknowledgments We thank Brent Macaloney at NWS Headquarters for supplying us with the tornado record

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Richard P. James
and
John H. E. Clark

. , 1999 : Mesoscale analysis of arc rainbands in a dry slot. Quart. J. Roy. Meteor. Soc. , 125 , 3495 – 3511 . 10.1002/qj.49712556118 Carr, F. H. , and Millard J. P. , 1985 : A composite study of comma clouds and their association with severe weather over the Great Plains. Mon. Wea. Rev. , 113 , 370 – 387 . 10.1175/1520-0493(1985)113<0370:ACSOCC>2.0.CO;2 Curtis, L. , 2001 : Mid-level dry intrusions as a factor in tornadogenesis associated with landfalling tropical cyclones in the

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Vivek N. Mahale
,
Jerald A. Brotzge
, and
Howard B. Bluestein

://ams.confex.com/ams/pdfpapers/175727.pdf .] Snook, N. , and Xue M. , 2008 : Effects of microphysical drop size distribution on tornadogenesis in supercell thunderstorms . Geophys. Res. Lett. , 35 , L24803 , doi:10.1029/2008GL035866 . Snyder, J. C. , Bluestein H. B. , Zhang G. , and Frasier S. J. , 2010 : Attenuation correction and hydrometeor classification of high-resolution, X-band, dual-polarized mobile radar measurements in severe convective storms . J. Atmos. Oceanic Technol. , 27 , 1979 – 2001 . Trabal

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Thea N. Sandmæl
,
Brandon R. Smith
,
Anthony E. Reinhart
,
Isaiah M. Schick
,
Marcus C. Ake
,
Jonathan G. Madden
,
Rebecca B. Steeves
,
Skylar S. Williams
,
Kimberly L. Elmore
, and
Tiffany C. Meyer

purpose of this evaluation. Due to the TDA’s binary nature, a threshold of 50% is used to indicate a predicted tornado by TORP in order to compare algorithm performance. Both the operational TDA and TORP were tested on a subset of the 2017–18 severe storm report dataset, consisting of surveyed tornadoes only and no nontornadic reports within 1 h of tornadogenesis. Additionally, only reports within 100 km of a radar were considered to achieve a fair comparison due to the TDA’s range limitation. This

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G. Eli Jergensen
,
Amy McGovern
,
Ryan Lagerquist
, and
Travis Smith

, GBFs are more computationally expensive, because the trees must be trained in series, whereas those in a random forest can be trained in parallel. Random forests and GBFs have been applied successfully to predict convectively induced turbulence ( Williams 2014 ), tornadogenesis ( McGovern et al. 2014 ), solar radiation ( McGovern et al. 2015 ), and damaging straight-line wind ( Lagerquist et al. 2017 ); and to identify features such as drylines ( Clark et al. 2015 ); and mesoscale convective

Open access
Matthew J. Bunkers
,
Brian A. Klimowski
,
Jon W. Zeitler
,
Richard L. Thompson
, and
Morris L. Weisman

. H. Jain, 1985: Formation of mesoscale lines of precipitation: Severe squall lines in Oklahoma during the spring. J. Atmos. Sci., 42, 1711–1732. 10.1175/1520-0469(1985)042<1711:FOMLOP>2.0.CO;2 Bracken, W. E., L. F. Bosart, A. Seimon, K. D. Lapenta, J. S. Quinlan, and J. W. Cannon, 1998: Supercells and tornadogenesis over complex terrain: The Great Barrington (Massachusetts) Memorial Day (1995) tornado. Preprints, 19th Conf. on Severe Local Storms, Minneapolis, MN, Amer. Meteor. Soc., 18

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Corey K. Potvin
and
Louis J. Wicker

1. Introduction National Weather Service forecasters' ability to provide advanced warning of supercell tornadoes currently relies heavily upon the detection (by radar or human observers) of strong low-level rotation (LLR) in storms. This paradigm hinders the tornado-warning process in three important ways. First, tornado-warning lead times are significantly limited in cases where the onset of strong LLR precedes tornadogenesis by only several minutes. It is therefore not surprising that the

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Erik R. Nielsen
,
Gregory R. Herman
,
Robert C. Tournay
,
John M. Peters
, and
Russ S. Schumacher

mean LSAs of −0.44 and −0.31 for the zonal component of 10- and 80-m winds, respectively. In the mid- to upper levels, an anomalous westerly component of the wind is typically present, which likely corresponds to a stronger than normal upper-level jet. Further, verified TORFF events also occur with anomalously strong meridional wind shear, which is unsurprising considering shear is a necessary ingredient for tornadogenesis (e.g., Markowski and Richardson 2010 ). A statistically significant warm

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