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J. T. Schaefer and C. A. Doswell III

Abstract

A flow where the pressure gradient, Coriolis and viscous forces are balanced is examined. It is found that such a flow is a reasonable approximation to the “steady state” flow in the vicinity of the contact layer. Kinematic effects implicit in the adjustment of an arbitrary flow to this balanced state are examined and can be used to explain several features of the nocturnal low-level jet. A method to use this balanced flow operationally to infer Ekman layer features is developed and several cases are examined.

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A. R. Cook and J. T. Schaefer

Abstract

Winter tornado activity (January–March) between 1950 and 2003 was analyzed to determine the possible effect of seasonally averaged sea surface temperatures in the equatorial Pacific Ocean, the ENSO phase, on the location and strength of tornado outbreaks in the United States. Tornado activity was gauged through analyses of tornadoes occurring on tornado days (a calendar day featuring six or more tornadoes within the contiguous United States) and strong and violent tornado days (a calendar day featuring five or more tornadoes rated F2 and greater within the contiguous United States). The tornado days were then stratified according to warm (37 tornado days, 14 violent days), cold (51 tornado days, 28 violent days), and neutral (74 tornado days, 44 violent days) winter ENSO phase. It is seen that during winter periods of neutral tropical Pacific sea surface temperatures, there is a tendency for U.S. tornado outbreaks to be stronger and more frequent than they are during winter periods of anomalously warm tropical Pacific sea surface temperatures (El Niño). During winter periods with anomalously cool Pacific sea surface temperatures (La Niña), the frequency and strength of U.S. tornado activity lies between that of the neutral and El Niño phase. ENSO-related shifts in the preferred location of tornado activity are also observed. Historically, during the neutral phase, tornado outbreaks typically occurred from central Oklahoma and Kansas eastward through the Carolinas. During cold phases, tornado outbreaks have typically occurred in a zone stretching from southeastern Texas northeastward into Illinois, Indiana, and Michigan. During anomalously warm phases activity was mainly limited to the Gulf Coast states, including central Florida. The data are statistically and synoptically analyzed to show that they are not only statistically significant, but also meteorologically reasonable.

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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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D. L. Kelly, J. T. Schaefer, R. P. McNulty, C. A. Doswell III, and R. F. Abbey Jr.

Abstract

Careful screening of the National Severe Storms Forecast Center's tornado log eliminated almost 20% of the reports as doubtful, leaving 17 659 tornadoes during 27 years, 1950–76 (654 annually). Newspaper accounts and other local information provided intensifies (Fujita wale) for all but 2346 tornadoes and path lengths for all but 2011 tornadoes. There were 14 409 tornadoes for which both intensity and path length estimates were made. Of these, 61.7% were weak (<112 mph), 36% strong (113–206 mph), and only 2.3% violent (207–318 mph). However, the 340 violent tornadoes caused 68% of the 3070 fatalities attributed to tornadoes for which force estimates could he made (113.7 annually). Most violent tornadoes came in swarms except in southeastern United States, where no day had mart than one. Some 61% of the violent tornadoes had intermediate paths (3.2–31 mi), while 73% of weak and strong tornadoes had short paths. Violent tornadoes occurred at all times of day and night, while weak and strong tornadoes showed diurnal trends. May and June accounted for 40.8% of all tornadoes. Other aspects of tornado climatology are shown in tables, diagrams and maps of average annual incidence normalized to 10 000 mi2 area per year.

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J. T. Schaefer, F. P. Ostby, C. A. Doswell III, L. R. Lemon, R. P. McNulty, S. J. Weiss, and L. F. Wilson
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L. M. Bastiaans, D. R. Smith, R. A. McPherson, P. A. Phoebus, J. M. Moran, P. J. Croft, M. J. Ceritelli, G. V. Rao, J. T. Schaefer, F. J. Gadomski, K. A. Kloesel, R. G. Quayle, and J. W. Zeitler

The American Meteorological Society held its Sixth Symposium on Education in conjunction with the 77th Annual Meeting in Long Beach, California. The theme of the symposium was “Atmospheric and Oceanographic Education: Teaching about the Global Environment.” Thirty-eight oral presentations and 37 poster presentations summarized a variety of educational programs or examined educational issues for both the precollege and university levels. There was also a joint session with the Eighth Symposium on Global Change Studies and a special session on “home pages” to promote popular meteorological education. Over 200 people representing a wide spectrum of the Society attended one or more of the sessions in this two-day conference where they increased their awareness of teaching about the global environment.

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David J. Stensrud, Ming Xue, Louis J. Wicker, Kevin E. Kelleher, Michael P. Foster, Joseph T. Schaefer, Russell S. Schneider, Stanley G. Benjamin, Stephen S. Weygandt, John T. Ferree, and Jason P. Tuell

The National Oceanic and Atmospheric Administration's (NOAA's) National Weather Service (NWS) issues warnings for severe thunderstorms, tornadoes, and flash floods because these phenomena are a threat to life and property. These warnings are presently based upon either visual confirmation of the phenomena or the observational detection of proxy signatures that are largely based upon radar observations. Convective-scale weather warnings are unique in the NWS, having little reliance on direct numerical forecast guidance. Because increasing severe thunderstorm, tornado, and flash-flood warning lead times are a key NOAA strategic mission goal designed to reduce the loss of life, injury, and economic costs of these high-impact weather phenomena, a new warning paradigm is needed in which numerical model forecasts play a larger role in convective-scale warnings. This new paradigm shifts the warning process from warn on detection to warn on forecast, and it has the potential to dramatically increase warning lead times.

A warn-on-forecast system is envisioned as a probabilistic convective-scale ensemble analysis and forecast system that assimilates in-storm observations into a high-resolution convection-resolving model ensemble. The building blocks needed for such a system are presently available, and initial research results clearly illustrate the value of radar observations to the production of accurate analyses of convective weather systems and improved forecasts. Although a number of scientific and cultural challenges still need to be overcome, the potential benefits are significant. A probabilistic convective-scale warn-on-forecast system is a vision worth pursuing.

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L.W. Larson, R.L. Ferral, E.T. Strem, A.J. Morin, B. Armstrong, T.R. Carroll, M.D. Hudlow, L.A. Wenzel, G.L. Schaefer, and D.E. Johnson

Abstract

The River and Flood Program in the National Weather Service, in its mission to save lives and property, has the responsibility to gather hydrologic data from a variety of sources and to assemble the data to make timely and reliable hydrologic forecasts. The intent of this paper, the second in a series of three, is to present an overview of the operational responsibilities of the River and Flood Program: how data are collected, what models-systems are currently in operation to process the data, and how the application of these procedures and techniques are applied in different types of hydrologic forecasting.

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