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James W. Wilson
,
Elizabeth E. Ebert
,
Thomas R. Saxen
,
Rita D. Roberts
,
Cynthia K. Mueller
,
Michael Sleigh
,
Clive E. Pierce
, and
Alan Seed

Abstract

Five of the nowcasting systems that were available during the Sydney 2000 Forecast Demonstration Project (FDP) were selected for evaluation. These systems, from the United States, the United Kingdom, and Australia, had the capability to nowcast the location and, with one exception, the intensity of convective storms. Six of the most significant convective storm cases from the 3-month FDP were selected for evaluating the performance of these state-of-the-art nowcasting systems, which extrapolated storms using a variety of methods, including cell and area tracking, model winds, and sounding winds. Three of the systems had the ability to forecast the initiation and growth of storms. Nowcasts for 30 and 60 min were evaluated, and it was found that even for such short time periods the skill of the extrapolation-only systems was often very low. Extrapolation techniques that allowed for differential motion performed slightly better, since high-impact storms often have motions different than surrounding storms. The ability to forecast initiation, growth, and dissipation is in its infancy. However, it was demonstrated that significant improvement in forecast accuracy was obtained for several of these cases when the locations of boundary layer convergence lines (sea breeze and gust fronts) were used in the nowcasts.

Based on the experiences during the FDP, and in forecast offices in the United States, a discussion is provided of the overall status of nowcasting convective storms. In addition, proposed future directions are discussed concerning the specificity of nowcast products, experimental test beds, and additional observations and research required.

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Neil I. Fox
,
Rob Webb
,
John Bally
,
Michael W. Sleigh
,
Clive E. Pierce
,
David M. L. Sills
,
Paul I. Joe
,
James Wilson
, and
Chris G. Collier

Abstract

One of the principal aims of the Sydney 2000 Forecast Demonstration Project was to assess the utility of advanced nowcasting systems to operational severe weather forecasters. This paper describes the application of the products of a variety of systems by forecasters during a severe weather event in Sydney, Australia, on 3 November 2000. During this day a severe storm developed to the south of the metropolitan area and tracked north producing large, damaging hail, heavy rainfall, and at least three tornadoes. A number of severe weather warnings were issued by the Australian Bureau of Meteorology to a variety of customers throughout the day.

This paper investigates how the novel nowcast products were used by the forecasters and the impact they had on the forecast and warning dissemination procedure. The products used are contrasted with those that were available or could have been made available at various stages of the storm development and the efficiency of use of these products is discussed. The severe weather forecasters expressed their satisfaction with the systems and believed that the additional information enhanced the quality and timeliness of the warnings issued during the event.

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John R. Gyakum
,
Marco Carrera
,
Da-Lin Zhang
,
Steve Miller
,
James Caveen
,
Robert Benoit
,
Thomas Black
,
Andrea Buzzi
,
Cliément Chouinard
,
M. Fantini
,
C. Folloni
,
Jack J. Katzfey
,
Ying-Hwa Kuo
,
François Lalaurette
,
Simon Low-Nam
,
Jocelyn Mailhot
,
P. Malguzzi
,
John L. McGregor
,
Masaomi Nakamura
,
Greg Tripoli
, and
Clive Wilson

Abstract

The authors evaluate the performance of current regional models in an intercomparison project for a case of explosive secondary marine cyclogenesis occurring during the Canadian Atlantic Storms Project and the Genesis of Atlantic Lows Experiment of 1986. Several systematic errors are found that have been identified in the refereed literature in prior years. There is a high (low) sea level pressure bias and a cold (warm) tropospheric temperature error in the oceanic (continental) regions. Though individual model participants produce central pressures of the secondary cyclone close to the observed during the final stages of its life cycle, systematically weak systems are simulated during the critical early stages of the cyclogenesis. Additionally, the simulations produce an excessively weak (strong) continental anticyclone (cyclone); implications of these errors are discussed in terms of the secondary cyclogenesis. Little relationship between strong performance in predicting the mass field and skill in predicting a measurable amount of precipitation is found. The bias scores in the precipitation study indicate a tendency for all models to overforecast precipitation. Results for the measurable threshold (0.2 mm) indicate the largest gain in precipitation scores results from increasing the horizontal resolution from 100 to 50 km, with a negligible benefit occurring as a consequence of increasing the resolution from 50 to 25 km. The importance of a horizontal resolution increase from 100 to 50 km is also generally shown for the errors in the mass field. However, little improvement in the prediction of the cyclogenesis is found by increasing the horizontal resolution from 50 to 25 km.

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Masashi Nagata
,
Lance Leslie
,
Yoshio Kurihara
,
Russell L. Elsberry
,
Masanori Yamasaki
,
Hirotaka Kamahori
,
Robert Abbey Jr.
,
Kotaro Bessho
,
Javier Calvo
,
Johnny C. L. Chan
,
Peter Clark
,
Michel Desgagne
,
Song-You Hong
,
Detlev Majewski
,
Piero Malguzzi
,
John McGregor
,
Hiroshi Mino
,
Akihiko Murata
,
Jason Nachamkin
,
Michel Roch
, and
Clive Wilson

The Third Comparison of Mesoscale Prediction and Research Experiment (COMPARE) workshop was held in Tokyo, Japan, on 13–15 December 1999, cosponsored by the Japan Meteorological Agency (JMA), Japan Science and Technology Agency, and the World Meteorological Organization. The third case of COMPARE focuses on an event of explosive tropical cyclone [Typhoon Flo (9019)] development that occurred during the cooperative three field experiments, the Tropical Cyclone Motion experiment 1990, Special Experiment Concerning Recurvature and Unusual Motion, and TYPHOON-90, conducted in the western North Pacific in August and September 1990. Fourteen models from nine countries have participated in at least a part of a set of experiments using a combination of four initial conditions provided and three horizontal resolutions. The resultant forecasts were collected, processed, and verified with analyses and observational data at JMA. Archived datasets have been prepared to be distributed to participating members for use in further evaluation studies.

In the workshop, preliminary conclusions from the evaluation study were presented and discussed in the light of initiatives of the experiment and from the viewpoints of tropical cyclone experts. Initial conditions, depending on both large-scale analyses and vortex bogusing, have a large impact on tropical cyclone intensity predictions. Some models succeeded in predicting the explosive deepening of the target typhoon at least qualitatively in terms of the time evolution of central pressure. Horizontal grid spacing has a very large impact on tropical cyclone intensity prediction, while the impact of vertical resolution is less clear, with some models being very sensitive and others less so. The structure of and processes in the eyewall clouds with subsidence inside as well as boundary layer and moist physical processes are considered important in the explosive development of tropical cyclones. Follow-up research activities in this case were proposed to examine possible working hypotheses related to the explosive development.

New strategies for selection of future COMPARE cases were worked out, including seven suitability requirements to be met by candidate cases. The VORTEX95 case was withdrawn as a candidate, and two other possible cases were presented and discussed.

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