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Russell S. Schneider

Abstract

On 15 December 1987 several long-lived, large-amplitude mesoscale wave disturbances embedded within a rapidly intensifying extratropical cyclone traversed the Midwest and created life-threatening blizzard conditions. Within the wave disturbances, which likely were atmospheric gravity waves, pressure fails of up to 11 mb in 15 min were accompanied by winds in excess of 30 m s−1 (60 kt), cloud-to-ground lightning and heavy snowfall. One of the large-amplitude mesoscale wave disturbances, characterized by a surface pressure minimum lower than the cyclone's central pressure, propagated through the cyclone center during the rapid intensification stage of the storm system. The rapid changes in weather conditions associated with these wave disturbances played havoc with attempts to make short-range forecasts at the height of the 15 December 1987 snowstorm. To help forecasters anticipate and identify mesoscale wave disturbances, basic forecast guidelines based on gravity wave principles and recent research results are discussed.

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Norman W. Junker, Russell S. Schneider, and Stephanie L. Fauver

Abstract

A synoptic–dynamic climatology was constructed using all 24-h 2-in. (50.8 mm) or greater rainfall events in nine states affected by heavy rains and flooding from June through September 1993 using 6- or 12-h gridded analyses from the Regional Data Assimilation System and geostationary satellite imagery. Each of the 85 events was assigned a category (0–4) based on the areal coverage of the 3-in. (76.2 mm) or greater observed precipitation isohyet. A variety of meteorological fields and rules of thumb used by forecasters at the Hydrometeorological Prediction Center are investigated that may help identify the most likely location and scale of a convective precipitation event.

The heaviest rain usually fell to the north (downwind) of the axis of highest 850-mb winds and moisture flux in an area of 850-mb warm temperature and equivalent potential temperature advection. The rainfall maximum also usually occurred to the north or northeast of the axis of highest 850-mb equivalent potential temperature. The scale and intensity of the rainfall appeared to be related to 1) the magnitude of the warm advection, 2) the 1000–500-mb mean relative humidity, 3) the breadth of the axis of stronger values of moisture transport feeding northward into a surface boundary, 4) the strength of low-level moisture flux convergence, and 5) the length of the low-level moisture flux convergence that was aligned along the mean flow upstream from the location of the rainfall maximum. The latter finding suggests that propagation plays an important role in modulating the scale and intensity of rainfall events.

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Louis W. Uccellini, Paul J. Kocin, Russell S. Schneider, Paul M. Stokols, and Russell A. Dorr

This paper describes the decision-making process used by the forecasters in the National Meteorological Center's Meteorological Operations Division and in Weather Forecast Offices of the National Weather Service to provide the successful forecasts of the superstorm of 12–14 March 1993. This review illustrates 1) the difficult decisions forecasters faced when using sometimes conflicting model guidance, 2) the forecasters' success in recognizing the mesoscale aspects of the storm as it began to develop and move along the Gulf and East Coasts of the United States, and 3) their ability to produce one of the most successful heavy snow and blizzard forecasts ever for a major winter storm that affected the eastern third of the United States.

The successful aspects of the forecasts include the following. 1) Cyclogenesis was predicted up to 5 days prior to its onset. 2) The unusual intensity of the storm was predicted three days in advance, allowing forecasters, government officials, and the media ample time to prepare the public, marine, and aviation interests to take precautions for the protection of life and property. 3) The excessive amounts and areal distribution of snowfall were predicted two days in advance of its onset. 4) An extensive number of blizzard watches and warnings were issued throughout the eastern United States with unprecedented lead times. 5) The coordination of forecasts within the National Weather Service and between the National Weather Service, private forecasters, and media meteorologists was perhaps the most extensive in recent history.

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John S. Kain, Paul R. Janish, Steven J. Weiss, Michael E. Baldwin, Russell S. Schneider, and Harold E. Brooks

Collaborative activities between operational forecasters and meteorological research scientists have the potential to provide significant benefits to both groups and to society as a whole, yet such collaboration is rare. An exception to this state of affairs is occurring at the National Severe Storms Laboratory (NSSL) and Storm Prediction Center (SPC). Since the SPC moved from Kansas City to the NSSL facility in Norman, Oklahoma in 1997, collaborative efforts between researchers and forecasters at this facility have begun to flourish. This article presents a historical background for this interaction and discusses some of the factors that have helped this collaboration gain momentum. It focuses on the 2001 Spring Program, a collaborative effort focusing on experimental forecasting techniques and numerical model evaluation, as a prototype for organized interactions between researchers and forecasters. In addition, the many tangible and intangible benefits of this unusual working relationship are discussed.

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Alicia C. Wasula, Lance F. Bosart, Russell Schneider, Steven J. Weiss, Robert H. Johns, Geoffrey S. Manikin, and Patrick Welsh

Abstract

The 22–23 February 1998 central Florida tornado outbreak was one of the deadliest and costliest in Florida’s history; a number of long-track tornadoes moved across the Florida peninsula after 0000 UTC 23 February 1998. In the 12–24 h prior to 0000 UTC 23 February, a vigorous upper-level synoptic system was tracking across the southeast United States, and a north–south-oriented convective band located ahead of the cold front was moving eastward across the Gulf of Mexico. Strong vertical wind shear was present in the lowest 1 km, due to a ∼25 m s−1 low-level jet at 925 hPa and south-southeasterly surface flow over the Florida peninsula. Further, CAPE values across the central Florida peninsula exceeded 2500 J kg−1. Upon making landfall on the Florida peninsula, the convective band rapidly intensified and developed into a line of tornadic supercells. This paper examines the relationship between a diabatically induced front across the central Florida peninsula and the rapid development of tornadic supercells in the convective band after 0000 UTC 23 February. Results suggest that persistent strong frontogenesis helped to maintain the front and enhanced ascent in the warm, moist unstable air to the south of the east–west-oriented front on the Florida peninsula, thus allowing the updrafts to rapidly intensify as they made landfall. Further, surface observations from three key locations along the surface front suggest that a mesolow moved eastward along the front just prior to the time when supercells developed. It is hypothesized that the eastward-moving mesolow may have caused the winds in the warm air to the south of the surface front to back to southeasterly and create a favorable low-level wind profile in which supercells could rapidly develop.

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Thomas M. Hamill, Russell S. Schneider, Harold E. Brooks, Gregory S. Forbes, Howard B. Bluestein, Michael Steinberg, Daniel Meléndez, and Randall M. Dole
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Thomas M. Hamill, Russell S. Schneider, Harold E. Brooks, Gregory S. Forbes, Howard B. Bluestein, Michael Steinberg, Daniel Meléndez, and Randall M. Dole
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Thomas M. Hamill, Russell S. Schneider, Harold E. Brooks, Gregory S. Forbes, Howard B. Bluestein, Michael Steinberg, Daniel Meléndez, and Randall M. Dole

In May 2003 there was a very destructive extended outbreak of tornadoes across the central and eastern United States. More than a dozen tornadoes struck each day from 3 May to 11 May 2003. This outbreak caused 41 fatalities, 642 injuries, and approximately $829 million dollars of property damage. The outbreak set a record for most tornadoes ever reported in a week (334 between 4–10 May), and strong tornadoes (F2 or greater) occurred in an unbroken sequence of nine straight days. Fortunately, despite this being one of the largest extended outbreaks of tornadoes on record, it did not cause as many fatalities as in the few comparable past outbreaks, due in large measure to the warning efforts of National Weather Service, television, and private-company forecasters and the smaller number of violent (F4–F5) tornadoes. This event was also relatively predictable; the onset of the outbreak was forecast skillfully many days in advance.

An unusually persistent upper-level trough in the intermountain west and sustained low-level southerly winds through the southern Great Plains produced the extended period of tornado-favorable conditions. Three other extended outbreaks in the past 88 years were statistically comparable to this outbreak, and two short-duration events (Palm Sunday 1965 and the 1974 Superoutbreak) were comparable in the overall number of strong tornadoes. An analysis of tornado statistics and environmental conditions indicates that extended outbreaks of this character occur roughly every 10 to 100 years.

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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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