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Frederick P. Ostby

Abstract

The purpose of this paper is to review the large strides made in tornado and severe thunderstorm forecasting by the Severe Local Storms Unit (SELS) of the National Severe Storms Forecast Center during the last 25 years or so of its existence. The author compares and illustrates the tools available to the SELS forecasters in the early 1970s versus those of the 1990s. Also discussed is the transition over the years from a largely empirical forecast approach to an approach based strongly on physical reasoning. The evolution of the computer systems employed at SELS and their impact on the forecast operation are traced. With the advent of interactive computer processing capability, SELS forecasters were able to assess the potential for severe convection with much greater precision than ever before. Noteworthy was the improvement brought about by the automation of largely clerical tasks, allowing the forecasters more time to focus on the forecast problem at hand. In addition, the forecast staff was able to devote more time to relevant research projects and benefit from the significant advances taking place in improved understanding of mesoscale processes. Verification results are shown to validate the notion that these advances led to better predictions. For example, the watch accuracy in terms of percent of severe weather watches verified rose from 63% in 1975 to 90% in 1996. Finally, information is given showing important milestones in the history of SELS and a list of the lead forecasters whose experience, judgment, and forecast skill brought about these improvements.

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Frederick P. Ostby

Abstract

The National Severe Storms Forecast Center in Kansas City, Missouri, is composed of several operational forecasting units, all national in scope. It includes the Severe Local Storms Unit (SELS), the National Aviation Weather Advisory Unit (NAWAU), and a Techniques Development Unit (TDU). Within SELS there is a synoptic interpretation message (SIM) section and a mesoscale discussion (MD) section.

The SELS Unit has been in Kansas City since 1954 and is responsible for providing a wide array of products related to severe weather: convective outlooks, public weather statements, mesoscale discussions, status reports, and tornado and severe thunderstorm watches for the 48 conterminous states. SELS is also responsible for preparing a national weather summary. NAWAU provides alerts, nationally, of hazardous weather, known as AIRMETs and SIGMETs, and convective SIGMETs to aviation interests. NAWAU also issues aviation area forecasts. The SIM section prepares a diagnostic interpretative message that incorporates satellite and other information and relates them to model trends. The MD section supports the SELS program by providing short-range updates on developing mesoscale systems.

The Techniques Development Unit has been responsible for working hand in hand with SELS to reap the benefits of applying interactive computer-processing technology, progressively giving the forecaster more effective means to provide improved services. Illustrating these improvements is the fact that severe weather watches have significantly increased in accuracy, especially in handling violent death-dealing tornado situations.

An illustrative example of SELS products is shown for the severe weather outbreak of 15–17 June 1992. The example shows how skillfully this episode, producing 172 tornadoes and 462 other reported severe weather events, was forecast. Emphasis is made of the need for consistent and well-coordinated watches and other advisories when dealing with widespread, rapidly moving, severe weather-producing systems.

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Keith W. Veigas
and
Frederick P. Ostby Jr.

Abstract

A statistically derived procedure for forecasting the 24-hr displacement. change in central pressure, and change in intensity of east coast cyclones is presented. The analysis is based on a moving coordinate system—i.e., predictor information is measured at points fixed with respect to the moving cyclone center rather than at points fixed with respect to the earth.

Two sets of multiple linear regression prediction equations are derived from a sample of 352 cyclone cases. The first set is based solely on point values of sea-level pressure, 500-mb height, 1000–500-mb thickness, and 12-hr changes of these variables. The second set is based on point values plus a series of quantities derived from point values such as steering components, gradients, vorticity and thickness advection, and thermal wind.

When applied to 106 independent cases, the point value equation yield a vector position root-mean-square (rms) error of 4.01 deg of latitude and a central pressure rms error of 8.70 mb. The complex equations fail to improve these scores significantly.

Operational 24-hr forecasts made for 31 cases during the winter of 1959–1960 are compared with corresponding 18-hr forecasts prepared by the National Weather Analysis Center (NWAC). The statistical forecasts incur a vector rms error of 2.25 deg of latitude for position and a rms error of 8.14 mb for deepening; NWAC forecasts incur a rms error of 3.87 deg of latitude and a rms error of 7.25 mb for deepening.

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Steven J. Weiss
,
Charles A. Doswell III
, and
Frederick P. Ostby

Abstract

No abstract available.

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Edward W. Ferguson
,
Frederick P. Ostby
, and
Preston W. Leftwich Jr.

Abstract

A review of tornado activity in the United States during 1986 is presented. Annual statistics are compared with both recent and long-term values. Month-by-month highlights of tornado events are summarized. Meteorological patterns associated with four noteworthy tornado outbreaks are examined.

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Edward W. Ferguson
,
Frederick P. Ostby
, and
Preston W. Leftwich Jr.

Abstract

A review of tornado activity in the United States during 1985 is presented. Annual statistics are compared with both recent and long-term values. Month-by-month highlights of tornado events are summarized. Meteorology patterns associated with three noteworthy tornado outbreaks are examined.

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Edward W. Ferguson
,
Joseph T. Schaefer
,
Steven J. Weiss
,
Larry F. Wilson
, and
Frederick P. Ostby

Abstract

The tornado events of 1982 are reviewed. Significant and interesting aspects of the 1047 reported storms are noted. The synoptic patterns associated with four major tornado days are examined.

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Edward W. Ferguson
,
Frederick P. Ostby
,
Preston W. Leftwich Jr.
, and
John E. Hales Jr.

Abstract

Tornado events of 1984 are reviewed. Significant and interesting aspects of the 907 reported tornadoes are noted. Synoptic patterns associated with four noteworthy tornado days are examined.

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Edward W. Ferguson
,
Frederick P. Ostby
,
Preston W. Leftwich Jr.
,
William E. Carle
,
Steven F. Corfidi
,
Richard G. Cundy
, and
William D. Hirt

Abstract

Tornado events of 1983 are reviewed. Significant and interesting aspects of the 931 reported tornadoes are noted. Synoptic patterns associated with four noteworthy tornado days are examined.

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