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Robert H. Johns
and
Charles A. Doswell III

suggest thatonly about 50% (or perhaps less) of all Doppler-detected mesocyclones occurring in the southern plainsin spring produce tornadoes (Burgess and Lemon1990). One factor important for tornado generation isthe strength of the outflow from storm downdrafts (seeFig. 8). Evaporatively cooled downdrafi outflow resultsin a baroclinically generated, low-level contribution tovorticity that is critical for tornadogenesis (Rotunnoand Klemp 1985; Davies-Jones and Brooks 1993).Some recent modeling results

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Robert R. Lee
and
Anderson White

B9MA to generate false mesocyclone detections, and missing velocity values have caused circulations to be missed. The B9MA alerts forecasters to storms that need no warning and fails, at times, to detect tornadic circulations. These limitations can be mitigated, to some degree, by fine-tuning algorithm adaptable parameters; however, the B9MA will never perform perfectly because there is much more to tornadogenesis than the presence of a mesocyclone. The next section outlines how the B9MA

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Kevin M. Simmons
and
Daniel Sutter

) and meteorology’s understanding of tornadogenesis improved over the period as well ( Brooks 2004 ). And as Crum et al. (1998) explain, the NEXRAD program has undergone almost continual improvements since installation. Again our yearly dummy variables should capture components of modernization that occurred across all offices at the same time. Further research though would be required to determine the exact contribution of NEXRAD and other elements of NWS modernization to the reduction in

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J. Brotzge
and
S. Erickson

tornadogenesis during the early afternoon than during the evening. Nevertheless, the exact cause of the diurnal pattern is unknown. The number of tornadoes associated with a given tornado day may be expected to change with season. The average number of tornado warnings issued by a WFO per tornado day was calculated monthly ( Fig. 12a ). Typically, those months with more isolated, single tornado days (e.g., August) were found to have the highest proportion of zero and negative lead-time warnings ( Fig. 12b

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Vincent T. Wood
,
Rodger A. Brown
, and
Steven V. Vasiloff

Conf. on Weather Analysis and Forecasting, Norfolk, VA, Amer. Meteor. Soc., 332–335 . Doviak, R. J. , and Zrnić D. S. , 1993 : Doppler Radar and Weather Observations. 2d ed. Academic Press, 562 pp . Dunn, L. B. , and Vasiloff S. V. , 2001 : Tornadogenesis and operational considerations of the 11 August 1999 Salt Lake City tornado as seen from two different Doppler radars. Wea. Forecasting , 16 , 377 – 398 . 10.1175/1520-0434(2001)016<0377:TAOCOT>2.0.CO;2 Filiaggi, M. T. , Smith

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Harold E. Brooks
and
James Correia Jr.

, imagine the limiting scenario in which warnings are never issued prior to tornadogenesis, but some sort of system has been developed that identifies all tornadoes after they form. The POD, with case 2 defined as a hit, would be 1, even though no advanced warning on a tornado was ever issued prior to the event beginning. For later use, we will adopt the notation that denotes POD 1 as indicating only case 1 events are considered hits and POD 2 as indicating that both cases 1 and 2 are considered hits

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Melissa M. Hurlbut
and
Ariel E. Cohen

. , Seimon A. , Dickinson M. , and Galarneau T. J. Jr. , 2004 : Terrain-influenced tornadogenesis in the northeastern United States. Preprints, 11th Conf. on Mountain Meteorology and the Annual Mesoscale Alpine Program (MAP), Bartlett, NH, Amer. Meteor. Soc., 17.3. [Available online at https://ams.confex.com/ams/pdfpapers/77126.pdf .] Brooks, H. E. , and Craven J. P. , 2002 : A database of proximity soundings for significant severe thunderstorms, 1957–2003. Preprints, 21st Conf. on

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Corey K. Potvin
,
Chris Broyles
,
Patrick S. Skinner
,
Harold E. Brooks
, and
Erik Rasmussen

distribution (e.g., Anderson et al. 2007 ). This distribution describes a spatial point pattern generated by a completely spatially random process with prescribed frequency λ , which in our application is the expected actual tornado count per grid cell. Tornadogenesis locations are not completely spatially random, however; tornadic thunderstorm outbreaks and tornado families lead to considerable overdispersion, as evidenced by variance-to-mean ratios well above unity in both reported ( Elsner and Widen

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Harold E. Brooks
,
Charles A. Doswell III
, and
Louis J. Wicker

3600 5400 7200 Time (s)FIG. 8. Maximum updraft in 17 April 1991 model forecast.that there are gaps in our understanding of the physicalprocesses leading to tornadogenesis. While this notionis no more comfortable than the first one, it at leastoffers hope of a practical solution.4. Discussion STORMTIPE was a successful experiment in manyways, particularly in indicating important areas for future

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Karl A. Jungbluth

mesocyclone structure as related to tornadogenesis. Mon. Wea. Rev., 107, 1184-1197.Lilly, D. K., The structure, energetics and propagation of rotating convective storms. Part lI: Helicity and storm stabilization. J. Atmos. Sci., 43, 126-140.Maddox, R. A., and C. A. Doswell III, 1982: An examination of jet stream configurations, 500 mb vorticity advection and low level thermal advection patterns during extended periods of intense convection. Mon. Wea. Rev., 110, 184-197. , C. F. Chappell, and

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