Showing papers in "Weather and Forecasting in 1989"
TL;DR: The National Meteorological Center's (NMC) Global Data Assimilation and Forecast System is described in some detail.
Abstract: The National Meteorological Center's (NMC) Global Data Assimilation and Forecast System is described in some detail. The system consists of 1) preprocessing of the initial guess, 2) optimum interpolation objective analysis, 3) update of the initial guess, 4) initialization, 5) forecast, and 6) postprocessing of the forecast. The assimilation and forecast system are continually evolving; the version described here was implemented on 30 November 1988.
621 citations
TL;DR: A review of recent advances in our understanding of cyclogenesis in polar air masses can be found in this article, where a survey of the observed features of polar lows as documented in a number of case studies presented in the recent literature is presented.
Abstract: The small-scale and rapid development of polar lows over relatively data-sparse areas results in a special forecast challenge for the operational forecasting community. This paper constitutes a review of recent advances in our understanding of cyclogenesis in polar air masses. The review is primarily comprised of a survey of the observed features of polar lows as documented in a number of case studies presented in the recent literature. The review is organized on the basis of a combination of observational and physical considerations and is aimed at diagnosing common types of developments. Theoretical ideas concerning the origins of polar lows and results of numerical modeling experiments aimed at simulating their development are also summarized. Finally, a discussion of approaches to the operational problem of forecasting polar lows is given.
136 citations
TL;DR: In this paper, two principal formulation methods that have been employed are the model output statistics (MOS) and the perfect prog (Probability Estimation) approaches for forecasting weather elements.
Abstract: The production of interpretive weather element forecasts from dynamical model output variables is now an integral part of the centralized guidance systems of weather services throughout the world. The statistical forecasting system in the United States probably generates the most extensive suite of operational products, although other nations including Australia, Canada, France, Italy, The Netherlands, and the United Kingdom also routinely provide guidance for many weather elements and locations. The United States' statistical guidance system has evolved throughout the past 20 yr. The two principal formulation methods that have been employed are the model output statistics (MOS) and “perfect prog” approaches. These techniques have advantages and disadvantages that influence both aggregate and specific day-to-day performance characteristics of the associated weather element forecasts. Verification results indicate that forecasts from both statistical approaches provide useful guidance for most wea...
129 citations
TL;DR: The first modern numerical weather prediction (NWP) models were developed for the computer that was announced in 1932 at the Institute for Advanced Study, in Princeton, New Jersey as mentioned in this paper, but it was quickly discovered that current models had very serious defects.
Abstract: The first modern numerical weather prediction (NWP) models were developed for the computer that was announced in 1932 at the Institute for Advanced Study, in Princeton, New Jersey. Within 3 yr three agencies of the United States Government jointly created a numerical weather prediction service, but it was quickly discovered that current models had very serious defects. After considerable research, the first operationally effective model was achieved in 1958—a barotropic model covering most of the Northern Hemisphere. Over the years, models have evolved through multilevel filtered equation models and several primitive equation models. Analysis and data assimilation systems necessary for timeliness were also developed, and have likewise evolved. The result has been a revolution in weather forecasting.
113 citations
TL;DR: The Regional Analysis and Forecast System (RAFS) of the National Meteorological Center (NMC) is described in this article, where three components of the RAFS are the regional optimum interpolation analysis, the Baer-Tribbia nonlinear normal mode initialization, and the nested grid model.
Abstract: The three components of the Regional Analysis and Forecast System (RAFS) of the National Meteorological Center (NMC) are described. This system was implemented in March 1985 to supplement guidance from NMC's limited-area fine-mesh model (LFM), especially for precipitation forecasting. The three components of the RAFS are the regional optimum interpolation analysis, the Baer–Tribbia nonlinear normal mode initialization, and the nested grid model—a grid point, primitive-equation model in sigma coordinates. Postprocessing of model forecasts and plans for system improvement are also discussed.
100 citations
TL;DR: A diagnostic approach to forecast verification is described and illustrated based on a general framework for forecast verification that focuses on the fundamental characteristics of the forecasts, the corresponding observations, and their relationship.
Abstract: A diagnostic approach to forecast verification is described and illustrated. This approach is based on a general framework for forecast verification. It is “diagnostic” in the sense that it focuses on the fundamental characteristics of the forecasts, the corresponding observations, and their relationship. Three classes of diagnostic verification methods are identified: 1) the joint distribution of forecasts and observations and conditional and marginal distributions associated with factorizations of this joint distribution; 2) summary measures of these joint, conditional, and marginal distributions; and 3) performance measures and their decompositions. Linear regression models that can be used to describe the relationship between forecasts and observations are also presented. Graphical displays are advanced as a means of enhancing the utility of this body of diagnostic verification methodology. A sample of National Weather Service maximum temperature forecasts (and observations) for Minneapolis, ...
79 citations
TL;DR: In this article, seven familiar stability indices were computed from sounding data for each of 83 days of a convection forecasting experiment conducted during the summer of 1985 in northeast Colorado and compared against this dataset to examine their performance as predictors of severe weather (large hail, tornadoes, high wind) and significant weather (nonsevere but important from an economic or public safety standpoint).
Abstract: Seven familiar stability indices were computed from sounding data for each of 83 days of a convection forecasting experiment conducted during the summer of 1985 in northeast Colorado. Observations of convectively driven weather events were collected; the values of the indices were compared against this dataset to examine their performance as predictors of severe weather (large hail, tornadoes, high wind) and significant weather (nonsevere but important from an economic or public safety standpoint). The results of the analysis are Benchmark values of the indices that give their typical magnitudes on active days versus quiescent days. These values, compared with those computed in other regions, illustrate the potential fallacy of interpreting the indices in the absence of analogous region-specific reference statistics. Rankings that determine which indices worked best in this experiment. The highest ranked indices were the SWEAT index for severe weather and buoyancy for significant weather. Interes...
69 citations
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TL;DR: In the period 1680-1988, 107 significant tornadoes in the Fujita scale categories F2-F5 have occurred in France as discussed by the authors, including 49 such events from 1680 to 1959 and 58 from 1960 to 1988.
Abstract: In the period 1680–1988, 107 significant tornadoes in the Fujita scale categories F2–F5 have occurred in France. These include 49 such events in the historical period 1680–1959, and 58 events in the modem period 1960–1988. Estimates of the temporal and spatial climatological distributions of significant tornadoes in France have been developed that suggest June and August are the months with the greatest number of such tornadoes; 1600–1700 UTC is the interval in which occurrence is most likely, with a secondary maximum in likelihood between 1800 and 1900 UTC; the northwestern quarter of the country is the region where a significant tornado is most likely to occur. A second, much smaller area with several observations is evident in the far south-center portion of France, near the Mediterranean coast; two significant tornadoes can be expected in France each year; the mean area stricken by such a tornado is about 4 km2; France has a mean risk probability of a significant tornado occurring at a point ...
48 citations
TL;DR: It was found that forecasts made by meteorologists were closely approximated by an additive model, and that the model captured most of their forecasting skill.
Abstract: This study compared meteorologists, an expert system, and simple weighted-sum models in a limited-information hail forecasting experiment. It was found that forecasts made by meteorologists were closely approximated by an additive model, and that the model captured most of their forecasting skill. Furthermore, the additive model approximated the meteorologists’ forecasts better than the expert system did. Results of this study am consistent with the results of extensive psychological research on judgment and decision making processes. Potential implications are discussed.
39 citations
TL;DR: In this article, a method of improving the accuracy of model output statistics (MOS) probability of precipitation (POP) forecasts was investigated by using a perfect prog (PP) forecast as a potential predictor in a MOS equation.
Abstract: A method of improving the accuracy of model output statistics (MOS) probability of precipitation (POP) forecasts was investigated. The method uses a perfect prog (PP) forecast as a potential predictor in a MOS equation. The PP method, with its larger developmental databases has the potential of incorporating additional information about local climatology, seasonality, and synoptic pattern type, which might be otherwise lacking in the MOS predictor dataset. Three PP models were developed: an analog model, a 1ogistic regression model and an analog/regression hybrid model. The POP forecasts were generated by the three PP models and the MOS model at four Pennsylvania stations by using 6 months of independent limited-area fine mesh (LFM) forecasts. Three MOS/PP combination models were derived by linearly combining MOS with each of the three PP models. The MOS/PP combination model forecasts were generated with the independent MOS and PP forecasts by using a cross-validation technique. The three MOS/PP ...
38 citations
TL;DR: In this paper, the authors describe some basic research techniques and algorithms developed to diagnose fronts in cyclonic storms over the ocean with data from satellite-borne microwave radiometers (SSMR) on board the polar orbiting Seasat and Nimbus-7 satellites.
Abstract: This paper describes some basic research techniques and algorithms developed to diagnose fronts in cyclonic storms over the ocean with data from satellite-borne microwave radiometers. Methods are developed for flagging strong gradients in integrated atmospheric water vapor and the presence of rain by using data from the SSMR on board the polar orbiting Seasat and Nimbus-7 satellites. Examination of 65 frontal systems showed that the water vapor gradient flag correctly identified 86 percent of the fronts, while the precipitation flagged 91 percent. The two types of flags emphasize different portions of the cyclone and are therefore complementary. Ultimately, these techniques are intended for operational use with data from the Special Sensor Microwave Imager which was launched in June 1987 on a satellite in the Defense Meteorological Satellite Program (DMSP).
TL;DR: In this paper, the impact of various types of weather on aircraft operations for one airline for 3 years at Atlanta Hartsfield International Airport is investigated, defined as delays defined in terms of the difference between the actual flight time and that projected by the air traffic control system assuming an accurate weather forecast.
Abstract: The impact of various types of weather on aircraft operations for one airline for 3 yr at Atlanta Hartsfield International Airport is investigated. Impacts are expressed as delays defined in terms of the difference between the actual flight time and that projected by the air traffic control system assuming an accurate weather forecast. The impacts of weather events were measured as the difference between these delays in clear conditions and in various types of inclement weather. Fog and thunderstorms create delays in various phases of each flight. The resultant delays at Atlanta alone create costs amounting to over $6 million annually for the airline. More accurate forecasts have the potential to reduce these costs by allowing more accurate flight planning. Decreases in the number and length of delay over time suggest that improvements in forecasts have already had an economic benefit to the airline. Delays associated with three snowstorms were also investigated. Early morning storms, even when f...
TL;DR: The evolution of criteria for nontornadic severe thunderstorms from undefined categories and general terms to the present day definition for this class of thunderstorm is presented in this article, where major historical events in the development of the Severe Local Storms Unit (SELS) which directly or indirectly influenced changes in the criteria are included.
Abstract: The evolution of criteria for nontornadic severe thunderstorms from undefined categories and general terms to the present day definition for this class of thunderstorm is presented. Major historical events in the development of the Severe Local Storms Unit (SELS) which directly or indirectly influenced changes in the criteria are included.
TL;DR: Verification of forecasts during research field experiments is discussed and exemplified using the DOPLIGHT '87 experiment, stressing the importance of forecast verification if forecasting is to be a serious component of the research.
Abstract: Verification of forecasts during research field experiments is discussed and exemplified using the DOPLIGHT '87 experiment. We stress the importance of forecast verification if forecasting is to be a serious component of the research. A direct comparison and contrast is done between forecasting for field research and forecasting in the operational sense, highlighting the differences between them. Ale verification of field research program forecasting is also different from that done in operations, as a result of those forecasting differences. DOPLIGHT '87 was a field project conducted jointly by the National Severe Storms Laboratory and the Oklahoma City National Weather Service Forecast Office, and is described in detail. During the experimental design, special attention was given to forecast design, to ensure that verification would be unambiguous and that the data collected would be appropriate for validating the forecasts. This a priori design of the forecasts to consider proper objective ver...
TL;DR: The operational model used to generate medium-range forecasts at the National Meteorological Center (NMC) has undergone significant changes in the last few years, resulting in considerable improvement in the skill of its forecasts as mentioned in this paper.
Abstract: The operational model used to generate medium-range forecasts at the National Meteorological Center (NMC) has undergone significant changes in the last few years, resulting in considerable improvement in the skill of its forecasts. The introduction of interactive clouds in late 1988 significantly reduced a cold bias present in model forecasts since April 1985. Model errors during recent Northern Hemisphere summers appear linked to thermal forcing, causing temperatures and upper tropospheric heights over cooler ocean areas to be too low, and heights over the western United States to be too high.
TL;DR: An overview of the regularly scheduled sequence of computer analyses and forecasts produced at the National Meteorological Center (NMC) is presented.
Abstract: An overview of the regularly scheduled sequence of computer analyses and forecasts produced at the National Meteorological Center (NMC) is presented. The available computer resources and time schedule constraints are discussed, the sources and treatment of incoming data are described, the purposes and configurations of the operational analysis/forecasting systems are outlined, and the mechanisms for product distribution are presented.
TL;DR: In this article, the performance characteristics of the two regional dynamical models used at the National Meteorological Center to forecast for North America were analyzed and the strengths and weaknesses of these models were presented in terms of their ability to predict such fields and features as 500-mb heights, surface lows and highs, precipitation events, and the diurnal cycle.
Abstract: This paper details the performance characteristics of the two regional dynamical models used at the National Meteorological Center to forecast for North America. Strengths and weaknesses of these models—the limited-area fine-mesh (LFM) model and the nested grid model (NGM) of the Regional Analysis and Forecast System (RAFS)—are presented in terms of their ability to predict such fields and features as 500-mb heights, surface lows and highs, precipitation events, and the diurnal cycle. The systematic characteristics of the models are emphasized. Overall, the NGM was found to be more accurate than the LFM. Nevertheless, the LFM is a valuable forecast model because of its accuracy and longevity in providing operational guidance.
TL;DR: In this paper, vertical wind shears measured by the Plattevilie, Colorado wind profiler were used in conjunction with the geostrophic thermal wind equation to retrieve the horizontal thermal gradients and associated advections for a case involving an upper-tropospheric jet stream/frontal zone on 23-24 November 1986.
Abstract: Vertical wind shears measured by the Plattevilie, Colorado wind profiler were used in conjunction with the geostrophic thermal wind equation to retrieve the horizontal thermal gradients and associated advections for a case involving an upper-tropospheric jet stream/frontal zone on 23–24 November 1986. The profiler-retrieved thermal gradients and advections and their evolutions compared favorably with those observed by the operational rawinsonde network. The retrieval of horizontal temperature gradients by a single wind profiler is generally effective in quasi-balanced flow regimes, but becomes less reliable in flow regimes dominated by nonbalanced gravity wave activity. In quasi-balanced flow regimes this simple thermal retrieval technique can aid the operational community by monitoring baroclinic features and associated temperature advections on an hourly basis, rather than on a 12-hourly basis currently available through the operational rawinsonde network.
TL;DR: The thermodynamic structure of the troposphere in the vicinity of the microburst storm at Dallas-Ft. Worth Airport (DFW), Texas on 2 August 1985 is described in this article.
Abstract: The thermodynamic structure of the troposphere in the vicinity of the microburst storm at Dallas-Ft. Worth Airport (DFW), Texas on 2 August 1985 is described. The analysis was based principally on a set of vertical soundings from the Visible and Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) onboard the Geostationary Operational Environmental Satellite (GOES), valid about 1 h before the occurrence of peak surface winds. Convection in the DFW area developed in a gradient of stability on the west side of a tongue of low lifted index and high precipitable water. The lapse rates in the 850 mb-700 mb layer were large (8°–9°C km−1). Vertical profiles of VAS data showed that DFW was in a transition zone in which conditions became drier at all levels and slightly warmer near 500 mb to the south and southwest. The midlevel warming reduced the buoyant energy available above cloud base, thus acting as a capping mechanism for the unstable, northward- moving low-level air. The potential insta...
TL;DR: In this paper, the most violent storm to hit France in recent history, with wind gusts of 50 m s−1 and waves of 15 m, was described, but there were very few human casualties.
Abstract: The most violent storm to hit France in recent history–with wind gusts of 50 m s−1 and waves of 15 m– is described. The structural and economic damage in France was considerable, but there were very few human casualties. Forecasts issued by the French weather service (Direction de la Meteorologie Nationale or DMN) were successful in predicting the intensity of the storm, and an analysis is presented of how and why such forecasts were possible. In particular, the observations and numerical guidance from the fine mesh PERIDOT and the large-scale EMERAUDE DMN numerical systems and from the European Centre for Medium Range Weather Forecasts (ECMWF) available to operational forecasters are reviewed and the crucial role of proper use of numerical forecasts and human experience is examined.
TL;DR: In contrast to short and extended range forecasts, predictions for periods beyond 5-day use time-averaged, mid-tropospheric height fields as their primary guidance.
Abstract: In contrast to short and extended range forecasts, predictions for periods beyond 5 days use time-averaged, midtropospheric height fields as their primary guidance. As time ranges are increased to 3O- and 90-day outlooks, guidance increasingly relies on statistical techniques using autocorrelation fields rather than numerical weather prediction (NWP) products as the primary prediction tool. The basis for the medium-range 6- to 10-day forecast is a mean 500 mb height and anomaly field for the forecast period, derived from a mix of output from two different numerical models, with some statistical and subjective modification added if desired. The monthly or 30-day outlook is based on a subjectively constructed mean 700 mb prognostic map based on available NWP mean height and anomaly fields out to 10 days, the appropriate 700 mb 1-month lag auto-correlation field, and subjective use of teleconnection and empirical orthogonal function patterns for consistency. A quantitative midtropospheric height and...
TL;DR: In this article, an analysis and prediction of explosive cyclogenesis over the western North Atlantic Ocean during the 1987/88 cold season were compared using both manual and automated series produced at the National Meteorological Center (NMC).
Abstract: Analyses and predictions of explosive cyclogenesis over the western North Atlantic Ocean during the 1987/88 cold season were compared. The analyses were the manual and automated series produced at the National Meteorological Center (NMC). The forecasts were those produced by the nested grid model (NGM) and the “aviation run” of the global spectral model (AVN) at NMC, and also by a simple checklist employed by the National Weather Service (NWS) Forecast Office, Boston. Skill of the forecast has evidently improved since the preceding year. Probability of detection of an event in a specified 24-h period, with the manual analyses used as verification, approached 72% for the NGM in the range of 0–24 h with a false alarm rate of 17%. In the range of 36–60 h, the values for the AVN forecasts were 42% and 30%. When the automated analyses were used for verification, forecast performance was somewhat better. The accuracy of the checklist forecasts was comparable to that of the AVN forecasts but not as good...
TL;DR: The objective analysis of meteorological variables has been routinely performed at the National Meteorological Center (NMC) since October 1955 as mentioned in this paper, and much attention was devoted to incorporating subjective meteorological analysis into the automated procedures: spatial coherence, temporal continuity and adherence to dynamic constraints.
Abstract: The objective analysis of meteorological variables has been routinely performed at the National Meteorological Center (NMC) since October 1955. In the first few years, much attention was devoted to incorporating three principles of subjective meteorological analysis into the automated procedures: spatial coherence, temporal continuity, and adherence to dynamic constraints. Consideration of these principles has continued in subsequent years as objective analysis methodology has evolved. That evolution has been driven by three interrelated developments: advances in observing technology, progress in prediction modeling, and a marked increase in computer capability. In light of these factors, this paper surveys the evolution of analysis methodology at NMC from 1955 to the end of 1988.
TL;DR: In this article, the authors describe an operational system for specifying monthly precipitation amounts in the contiguous United States from the concurrent 700-mb monthly mean height field over North America and adjacent oceans.
Abstract: This paper describes an operational system for specifying monthly precipitation amounts in the contiguous United States from the concurrent 700-mb monthly mean height field over North America and adjacent oceans. Multiple regression equations are derived for each month of the year at 60 climate divisions by applying a quasi-objective, forward selection procedure to 30 yr of data for 1951–80. The resulting specification equations explain an average of 37% of the precipitation variance, but values range from 70% along the Pacific Coast in January to 10% in southern New England in July. When applied to prognostic 700-mb charts for 1987 and 1988, the equations have shown more skill than persistence but less skill than official monthly outlooks. Four attempts to improve the specifications are discussed. Best results were obtained by screening the mean precipitation amounts within 10–12 coherent regions, selected by factor analysis, instead of 60 smaller climate divisions. This procedure raised the exp...
TL;DR: In this article, the response of the Regional Analysis and Forecast System (RAFS) low-level forecast fields to the geographical distribution of snow cover is discussed, and the use of the snow-cover data in the forecast model and its effect on forecast guidance are described.
Abstract: The response of the Regional Analysis and Forecast System (RAFS) low-level forecast fields to the geographical distribution of snow cover is discussed. The errors produced by an improper specification of this field in the forecast model can have a wide variety of local forecasting implications, ranging from poor forecasts of lee-side Great Lakes snowfalls, to errors in forecasts of the earth's surface temperature in areas where the snow cover is changing rapidly. The use of the snow-cover data in the forecast model and its effect on forecast guidance are described.
TL;DR: The mission and organization of the National Meteorological Center (NMC) is described in this article. But the NMC is not the only one that uses the CYBER 205 computers.
Abstract: This article describes the mission and organization of the National Meteorological Center (NMC), summarizes progress since the introduction of the CYBER 205 computers in 1983, and describes plans for NMC numerical prediction systems in the 1990s. Plans include the introduction of a new mewsoscale “storm” model on next generation computers, continued improvements in the resolution and physics of the NMC global model, and extension of daily forecasts from 5 to 7 days with a “week-two” forecast of average weather conditions.
TL;DR: In this paper, a study of more than 200 tornado events was conducted and it was shown that Tornado intensity is best related to the magnitude of the vertical wind shear in the layer between the ground and 600 hPa.
Abstract: Although violent tornadoes comprise only 2.3% of tornado occurrences in the United States, they cause 68% of the fatalities attributed to tornadoes and severe thunderstorms. Despite these statistics, no attempt is made to forecast or warn of tornado intensity. A basis for this is provided in a study of more than 200 tornado events. Tornado intensity is best related to the magnitude of the vertical wind shear in the layer between the ground and 600 hPa. The results for this and other shear parameters are statistically highly significant when the data are grouped into two or three intensity classifications. Stability, as indicated by the “lifted index,” and midtropospheric relative humidity, correlate poorly with tornado intensity. The relationships established have application to tornado forecasting and nowcasting.
TL;DR: The Meteorological Operations Division of the National Meteorological Center (NOMC) is the primary analysis and forecast facility of the US National Weather Service as discussed by the authors, which provides guidance to the meteorological community throughout the United States and around the world.
Abstract: The Meteorological Operations Division of the National Meteorological Center is the primary analysis and forecast facility of the National Weather Service. The division's many products provide guidance to the meteorological community throughout the United States and around the world. This paper describes the various analyses and forecast functions of the division, with special emphasis on how manual and objective techniques are combined to produce the best possible products.
TL;DR: In this paper, a strongly developing cyclone east of the Rockies moved northward along the Montana/North Dakota border between 24-26 September 1986 and deposited over 1 in. of rain throughout much of eastern Montana.
Abstract: A strongly developing cyclone east of the Rockies moved northward along the Montana/North Dakota border between 24–26 September 1986 and deposited over 1 in. of rain throughout much of eastern Montana. Included in this area of precipitation was an embedded heavy band, with rainfall amounts exceeding 7 in. over a 36-hour period. Often when significant banding exists across a relatively homogeneous precipitation area, symmetric instability may exist. Slantwise convection associated with this area of instability may be the source of the precipitation banding. Conceptual models are described, based on available synoptic data and computer derived fields, which suggest the frontogenetic dynamics necessary to utilize the symmetric instability in the form of banded convection. The potential for operational use of symmetric instability concepts are discussed with respect to today's and the future operational environment.
TL;DR: The Ocean Products Center (OPC) represents a consolidation of personnel from different parts of the National Oceanic and Atmospheric Administration (NOAA) and is used to generate and disseminate various marine meteorological, and oceanographic analyses and forecasts as discussed by the authors.
Abstract: The Ocean Products Center (OPC) represents a consolidation of personnel from different parts of the National Oceanic and Atmospheric Administration (NOAA). The purpose of OPC is to generate and disseminate various marine meteorological, and oceanographic analyses and forecasts. Emphasis is placed on using real-time data, analysis, and forecast fields from operational numerical weather prediction models to produce relevant products for marine applications. This article describes some of the operational products that are routinely disseminated to various users, and research activities for improving the quality of the operational products and the generation of new ones.