Showing papers in "Weather and Forecasting in 1998"

The WSR-88D Rainfall Algorithm

Abstract: A detailed description of the operational WSR-88D rainfall estimation algorithm is presented. This algorithm, called the Precipitation Processing System, produces radar-derived rainfall products in real time for forecasters in support of the National Weather Service’s warning and forecast missions. It transforms reflectivity factor measurements into rainfall accumulations and incorporates rain gauge data to improve the radar estimates. The products are used as guidance to issue flood watches and warnings to the public and as input into numerical hydrologic and atmospheric models. The processing steps to quality control and compute the rainfall estimates are described, and the current deficiencies and future plans for improvement are discussed.

A Baseline Climatology of Sounding-Derived Supercell and Tornado Forecast Parameters

Abstract: All of the 0000 UTC soundings from the United States made during the year 1992 that have nonzero convective available potential energy (CAPE) are examined. Soundings are classified as being associated with nonsupercell thunderstorms, supercells without significant tornadoes, and supercells with significant tornadoes. This classification is made by attempting to pair, based on the low-level sounding winds, an upstream sounding with each occurrence of a significant tornado, large hail, and/or 10 or more cloud-to-ground lightning flashes. Severe weather wind parameters (mean shear, 0–6-km shear, storm-relative helicity, and storm-relative anvil-level flow) and CAPE parameters (total CAPE and CAPE in the lowest 3000 m with buoyancy) are shown to discriminate weakly between the environments of the three classified types of storms. Combined parameters (energy–helicity index and vorticity generation parameter) discriminate strongly between the environments. The height of the lifting condensation level a...

Normalized Hurricane Damages in the United States: 1925-95

Abstract: Hurricanes are the costliest natural disasters in the United States. Understanding how both hurricane frequencies and intensities vary from year to year as well as how this is manifested in changes in damages that occur is a topic of great interest to meteorologists, public and private decision makers, and the general public alike. Previous research into long-term trends in hurricane-caused damage along the U.S. coast has suggested that damage has been quickly increasing within the last two decades, even after considering inflation. However, to best capture the year-to-year variability in tropical cyclone damage, consideration must also be given toward two additional factors: coastal population changes and changes in wealth. Both population and wealth have increased dramatically over the last several decades and act to enhance the recent hurricane damages preferentially over those occurring previously. More appropriate trends in the United States hurricane damages can be calculated when a normalization of the damages are done to take into account inflation and changes in coastal population and wealth. With this normalization, the trend of increasing damage amounts in recent decades disappears. Instead, substantial multidecadal variations in normalized damages are observed: the 1970s and 1980s actually incurred less damages than in the preceding few decades. Only during the early 1990s does damage approach the high level of impact seen back in the 1940s through the 1960s, showing that what has been observed recently is not unprecedented. Over the long term, the average annual impact of damages in the continental United States is about $4.8 billion (1995 $), substantially more than previous estimates. Of these damages, over 83% are accounted for by the intense hurricanes (Saffir‐Simpson categories 3, 4, and 5), yet these make up only 21% of the U.S.landfalling tropical cyclones.

The Storm Cell Identification and Tracking Algorithm: An Enhanced WSR-88D Algorithm

Abstract: Accurate storm identification and tracking are basic and essential parts of radar and severe weather warning operations in today’s operational meteorological community. Improvements over the original WSR-88D storm series algorithm have been made with the Storm Cell Identification and Tracking algorithm (SCIT). This paper discusses the SCIT algorithm, a centroid tracking algorithm with improved methods of identifying storms (both isolated and clustered or line storms). In an analysis of 6561 storm cells, the SCIT algorithm correctly identified 68% of all cells with maximum reflectivities over 40 dB Z and 96% of all cells with maximum reflectivities of 50 dBZ or greater. The WSR-88D storm series algorithm performed at 24% and 41%, respectively, for the same dataset. With better identification performance, the potential exists for better and more accurate tracking information. The SCIT algorithm tracked greater than 90% of all storm cells correctly. The algorithm techniques and results of a detailed performance evaluation are presented. This algorithm was included in the WSR-88D Build 9.0 of the Radar Products Generator software during late 1996 and early 1997. It is hoped that this paper will give new users of the algorithm sufficient background information to use the algorithm with confidence.

An Enhanced Hail Detection Algorithm for the WSR-88D

Abstract: An enhanced hail detection algorithm (HDA) has been developed for the WSR-88D to replace the original hail algorithm. While the original hail algorithm simply indicated whether or not a detected storm cell was producing hail, the new HDA estimates the probability of hail (any size), probability of severe-size hail (diameter ≥19 mm), and maximum expected hail size for each detected storm cell. A new parameter, called the severe hail index (SHI), was developed as the primary predictor variable for severe-size hail. The SHI is a thermally weighted vertical integration of a storm cell’s reflectivity profile. Initial testing on 10 storm days showed that the new HDA performed considerably better at predicting severe hail than the original hail algorithm. Additional testing of the new HDA on 31 storm days showed substantial regional variations in performance, with best results across the southern plains and weaker performance for regions farther east.

The National Severe Storms Laboratory Mesocyclone Detection Algorithm for the WSR-88D*

Abstract: The National Severe Storms Laboratory (NSSL) has developed a mesocyclone detection algorithm (NSSL MDA) for the Weather Surveillance Radar-1988 Doppler (WSR-88D) system designed to automatically detect and diagnose the Doppler radar radial velocity patterns associated with storm-scale (1–10-km diameter) vortices in thunderstorms. The NSSL MDA is an enhancement to the current WSR-88D Build 9.0 Mesocyclone Algorithm (88D B9MA). The recent abundance of WSR-88D observations indicates that a variety of storm-scale vortices are associated with severe weather and tornadoes, and not just those vortices meeting previously established criteria for mesocyclones observed during early Doppler radar studies in the 1970s and 1980s in the Great Plains region of the United States. The NSSL MDA’s automated vortex detection techniques differ from the 88D B9MA, such that instead of immediately thresholding one-dimensional shear segments for strengths comparable to predefined mesocyclone parameters, the initial stren...

The Occurrence of Tornadoes in Supercells Interacting with Boundaries during VORTEX-95

Abstract: During the Verifications of the Origins of Rotation in Tornadoes Experiment, nearly 70% of the significant tornadoes occurred near low-level boundaries not associated with the forward or rear flank downdrafts of supercells. In general, these were preexisting boundaries readily identified using conventional data sources. Most of the tornadoes occurred on the cool side of these low-level boundaries and generally within 30 km of the boundaries. It is likely that the low-level boundaries augmented the “ambient” horizontal vorticity, which, upon further generation in the forward-flank region, became sufficient to be associated with tornadic low-level mesocyclones. Some implications for forecasting and further research are discussed.

A Diagnostic Study of Three Heavy Precipitation Episodes in the Western Mediterranean Region

Abstract: A diagnostic evaluation of three project ANOMALIA case studies involving heavy precipitation in the western Mediterranean region has been carried out. The evaluation shows the unique characteristics of each event, as well as some limited similarities. Heavy precipitation events in the western Mediterranean region typically occur downstream of a significant cyclone aloft (often, but not always, exhibiting “cutoff” cyclone characteristics), but important structural and evolutionary differences are found among these cases. At low levels, a long fetch of flow over the Mediterranean Sea frequently interacts with terrain features to produce persistent heavy precipitation. Although most heavy precipitation events occur during the fall season, they can develop at other times. In the first case, the synoptic-scale environment produced low static stability and substantial storm-relative environmental helicity, thereby supporting both heavy rain in the vicinity of Valencia on mainland Spain and on Ibiza in ...

The Initiation of Moist Convection at the Dryline: Forecasting Issues from aCase Study Perspective

Abstract: The processes that force the initiation of deep convection along the dryline are inferred from special mesoscale observations obtained during the 1991 Central Oklahoma Profiler Studies project, the Verification of the Origins of Rotation in Tornadoes Experiment 1994 (VORTEX-94), and the VORTEX-95 field projects. Observations from aircraft, mobile CLASS soundings, and mobile mesonets define the fields of airflow, absolute humidity, and virtual temperature in the boundary layer across the dryline on the 15 May 1991, 7 June 1994, and 6 May 1995 case days. Film and video cloud images obtained by time-lapse cameras on the NOAA P-3 are used to reconstruct the mesoscale distribution of cumulus clouds by photogrammetric methods, permitting inferences concerning the environmental conditions accompanying cloud formation or suppression. The results of the present study confirm the classical notion that the dryline is a favored zone for cumulus cloud formation. The combined cloud distributions for the three ...

Development of an Objective Scheme to Estimate Tropical Cyclone Intensity from Digital Geostationary Satellite Infrared Imagery

Abstract: The standard method for estimating the intensity of tropical cyclones is based on satellite observations (Dvorak technique) and is utilized operationally by tropical analysis centers around the world. The technique relies on image pattern recognition along with analyst interpretation of empirically based rules regarding the vigor and organization of convection surrounding the storm center. While this method performs well enough in most cases to be employed operationally, there are situations when analyst judgment can lead to discrepancies between different analysis centers estimating the same storm. In an attempt to eliminate this subjectivity, a computer-based algorithm that operates objectively on digital infrared information has been developed. An original version of this algorithm (engineered primarily by the third author) has been significantly modified and advanced to include selected ‘‘Dvorak rules,’’ additional constraints, and a time-averaging scheme. This modified version, the Objective Dvorak Technique (ODT), is applicable to tropical cyclones that have attained tropical storm or hurricane strength. The performance of the ODT is evaluated on cases from the 1995 and 1996 Atlantic hurricane seasons. Reconnaissance aircraft measurements of minimum surface pressure are used to validate the satellite-based estimates. Statistical analysis indicates the technique to be competitive with, and in some cases superior to, the Dvorak-based intensity estimates produced operationally by satellite analysts from tropical analysis centers. Further analysis reveals situations where the algorithm needs improvement, and directions for future research and modifications are suggested.

Localized Precipitation Forecasts from a Numerical Weather Prediction Model Using Artificial Neural Networks

Abstract: Although the resolution of numerical weather prediction models continues to improve, many of the processes that influence precipitation are still not captured adequately by the scales of present operational models, and consequently precipitation forecasts have not yet reached the level of accuracy needed for hydrologic forecasting. Postprocessing of model output to account for local differences can enhance the accuracy and usefulness of these forecasts. Model Output Statistics have performed this important function for a number of years via regression techniques; this paper presents an alternate approach that uses artificial neural networks to produce 6-h precipitation forecasts for specific locations. Tests performed on four locations in the middle Atlantic region of the United States show that the accuracy of the forecasts produced using neural networks compares favorably with those generated using linear regression, especially for heavier precipitation amounts.

Rainfall Estimation by the WSR-88D for Heavy Rainfall Events

Abstract: Storms that produce extreme flooding present a special challenge for the WSR-88D rainfall algorithms. The authors assess the utility of weather radar in the investigation of extreme rain-producing storms through both climatological analyses of long-term radar datasets and case studies of storm events. Climatological analyses are presented for long records of WSR-88D volume scan reflectivity observations, for hourly radar rainfall accumulations products (WSR-88D and WSR-57D), and for radar–rain gauge intercomparisons. These analyses provide a context for interpreting case study assessments of WSR-88D rainfall estimates. Case studies are presented of five storms that produced extreme floods in the United States. Events include 1) the orographically enhanced Rapidan storm in the Blue Ridge region of Virginia, which resulted in more than 600 mm of rain during a 6-h period on 27 June 1995; 2) the southeast Texas storms of 16–17 October 1994 in which approximately 750 mm of rain fell during a 6-h time ...

Displays of Bird Movements on the WSR-88D: Patterns and Quantification*

Abstract: The WSR-88D can readily detect birds in the atmosphere in both clear air and precipitation mode, and echo reflectivities of 30–35 dBZ may be realized during heavy migration events or when birds are departing a roosting site. This paper describes the appearance of birds on base reflectivity, base velocity, and velocity azimuth display wind profile products, and presents a calibration curve that relates decibel values of reflectivity to bird migration traffic rates. The recognition of bird displays in WSR-88D products is essential for the accurate interpretation of data gathered by the radar and its use in the development of forecasts. The findings also document the importance of the WSR-88D as a remote sensing tool for biological studies of birds and insects in the atmosphere and the application of such information in the avoidance of bird–aircraft collisions.

Seasonal Forecasting of Tropical Cyclone Activity over theWestern North Pacific and the South China Sea

Abstract: This paper presents the development of operational statistical forecasts of seasonal tropical cyclone (TC) activity over the western North Pacific (WNP) and the South China Sea (SCS) based on 30 yr of data (1965–94). Predictors include monthly values of indices representing (a) the El Nino–Southern Oscillation phenomenon, and (b) the environmental conditions over East Asia and the WNP for the months from April of the previous year to March of the current year. Trends and short-term oscillations of the TC activity are also incorporated. The prediction equations are derived from the predictors of individual parameters using the Projection Pursuit Regression technique, which is a statistical method that reduces high-dimensional data to a lower-dimensional subspace before the regression is performed. This technique is found to provide explanations of certain nonlinear variations of the predictands. The predictions from individual parameters are then tested using the jackknife technique. Those predict...

Assessing the Vertical Distribution of Convective Available Potential Energy

Abstract: Comparisons of convective available potential energy (CAPE) with standard instability indices for evaluating the convective potential of the atmosphere such as the lifted index (LI) reveal only moderate correlations. This is because the LI is a measure of single-level buoyancy while CAPE is a measure of both integration depth and the buoyancy. Normalizing the CAPE values by the depth over which the integration takes place provides an index (NCAPE) that is independent of the depth and is a convenient measure of the mean parcel buoyancy. This normalization effectively distinguishes between environments with similar CAPE but exhibiting different buoyancy and integration depth. Also, because the vertical distribution of CAPE can have an important effect on convective updraft strength, it is advantageous to vertically partition CAPE and NCAPE into multiple layers. NCAPE may provide a more useful indicator of buoyancy in environments in which the depth of free convection is shallow and total CAPE is sm...

The National Severe Storms Laboratory Tornado Detection Algorithm

Abstract: The National Severe Storms Laboratory (NSSL) has developed and tested a tornado detection algorithm (NSSL TDA) that has been designed to identify the locally intense vortices associated with tornadoes using the WSR-88D base velocity data. The NSSL TDA is an improvement over the current Weather Surveillance Radar-1988 Doppler (WSR-88D) Tornadic Vortex Signature Algorithm (88D TVS). The NSSL TDA has been designed to address the relatively low probability of detection (POD) of the 88D TVS algorithm without a high false alarm rate (FAR). Using an independent dataset consisting of 31 tornadoes, the NSSL TDA has a POD of 43%, FAR of 48%, critical success index (CSI) = 31%, and a Heidke skill score (HSS) of 46% compared to the 88D TVS, which has a POD of 3%, FAR of 0%, CSI of 3%, and HSS of 0%. In contrast to the 88D TVS, the NSSL TDA identifies tornadic vortices by 1) searching for strong shear between velocity gates that are azimuthally adjacent and constant in range, and 2) not requiring the presence...

Estimation of Rainfall for Flood Prediction from WSR-88D Reflectivity: A Case Study, 17–18 October 1994*

Abstract: Flood forecasting requires accurate estimates of the spatial and temporal rainfall rates over a catchment. Depending on the Z–R relationship and threshold values, processing of WSR-88D reflectivity data affects the rainfall estimates used in flood prediction. How much rainfall the catchment receives during an extreme event and the resulting hydrograph response depends on catchment characteristics that transform rainfall into runoff. A case study of an extreme meteorological and hydrologic event occurring 17–18 October 1994 in south Texas is examined. After the event, a review of the National Oceanic and Atmospheric Administration, National Weather Service (NWS) operations raised concerns over low estimates of accumulated rainfall by the WSR-88D radar compared to gauge accumulations. At the time of the review, the Z–R relationship in use during the event, Z = 300R1.4, and a 53-dBZ reflectivity threshold were suspected of having caused poor performance of the radar accumulation estimates. Because o...

The Utilization of Statistical Properties of Satellite-Derived Atmospheric Motion Vectors to Derive Quality Indicators

Abstract: The extraction of atmospheric motion vectors (AMVs) from cloud and moisture features from successive geostationary satellite images is an established and important data source for numerical weather prediction (NWP). So far the extraction of AMVs has been confined to the main synoptic times only, which grossly underutilizes the potential of these satellite-derived data. The advent of four-dimensional variational assimilation techniques provides the opportunity to utilize data derived at asynoptic times. This will enhance the capabilities of geostationary satellite systems that can provide continuous and near–real time observations. The new assimilation schemes are able to digest data representing various scales and with variable quality, which further enhances the usefulness of the satellite data. In order to fully exploit the AMVs derived with satellite data, it is imperative to accurately assess the quality and representativeness of individual wind vectors and to provide this information to the ...

Five-Day Tropical Cyclone Track Forecasts in the North Atlantic Basin

Abstract: Statistical analyses of the most recent 40 yr of hurricane tracks (1956–95) are presented, leading to a version of the North Atlantic climatology and persistence (CLIPER) model that exhibits much smaller forecast biases but similar forecast errors compared to the previously used version. Changes to the model involve the inclusion of more accurate historical tropical cyclone track data and a simpler derivation of the regression equations. Nonlinear systems analysis shows that the predictability timescale in which the average errors increase by a factor e is approximately 2.5 days in the Atlantic basin, which is larger than that found by similar methods near Australia. This suggests that 5-day tropical cyclone track forecasts may have some benefit, and therefore a version of CLIPER extended to 5 days to be used as a baseline to measure this skill is needed.

An Update on the NEXRAD Program and Future WSR-88D Support to Operations

Abstract: The operational network of WSR-88D systems is in place. These radars provide a large increase in performance and coverage over the radars they replaced—and in some locations are the first operational weather radars. The early years of experience using these radars have shown that they have contributed to increased weather warning and forecast performance. These systems must be regularly upgraded, however, to maintain a viable network, meet new requirements, and take advantage of new science and technology. In addition to the NEXRAD program’s standard modification and retrofit process, the NEXRAD agencies (Department of Commerce/National Weather Service, Department of Defense, and Department of Transportation/Federal Aviation Administration) have established a NEXRAD product improvement program to initiate major hardware upgrades to the WSR-88D. This paper describes the status of the NEXRAD program, improvements to the WSR-88D that have taken place, improvements that are planned, and a discussion ...

Scalar measures of performance in rare-event situations

Abstract: A set of 14 scalar, nonprobabilistic measures—some old, some new—is examined in the rare-event situation. The set includes measures of accuracy, association, discrimination, bias, and skill. It is found that all measures considered herein are inequitable in that they induce under- or overforecasting. One condition under which such bias is not induced (for some of the measures) is when the underlying class-conditional distributions are Gaussian (normal) and equivariant.

Evaluating the Performance of WSR-88D Severe Storm Detection Algorithms

Abstract: This paper discusses some important issues and problems associated with evaluating the performance of radarbased severe storm detection algorithms. The deficiencies of using Storm Data as a source of verification are examined. Options for equalizing the time- and space scales of the algorithm predictions and the corresponding verification data are presented. Finally, recommendations are given concerning the different evaluation procedures that are available.

Nationwide Comparisons of Hail Size with WSR-88D Vertically Integrated Liquid Water and Derived Thermodynamic Sounding Data

Abstract: This study tests hypothetical correspondences between size of severe hail, WSR-88D derived vertically integrated liquid water (VIL), and an array of thermodynamic variables derived from computationally modified sounding analyses. In addition, these associations are documented for normalized VIL using various sounding parameters, and statistical predictive value is assigned to the various VIL-based and sounding variables. The database was gathered from Weather Service Radar-1988 Doppler (WSR-88D) units nationwide from cases identified during real-time operations and consists of over 400 hail events, each associated with a radar-observed VIL value and a modified observational sounding. Some parameters are found to increase in the mean with larger hail-size categories. Specific hail size, however, varies widely across the spectra of VIL, thermodynamic sounding variables, and combinations thereof, with only a few exceptions. No operationally useful parameters of value in hail-size prediction were discovered in the database of VIL and thermodynamic sounding data. These largely antihypothetical findings are compared with hail forecasting and warning techniques developed in the WSR-88D era—few in number and mostly regionalized and informal in nature—and with more widespread and empirical forecasting assumptions involving many of the same variables.

Observations of Widespread Lake-Effect Cloudiness: Influences of Lake Surface Temperature and Upwind Conditions

Abstract: Large spatial and temporal variations were observed in the location of the upwind cloud edge over Lake Michigan during five westerly wind lake-effect events in November 1995 through January 1996 This study examines the impacts of variations of Lake Michigan surface water temperatures (and corresponding surface fluxes) and upwind static stability on the location of the upwind edge of lake-effect clouds, which develop as cold air crosses the lake during the winter Data used in this study were collected during the 1995/96 National Weather Service Lake-Effect Snow study Spatial variations in the location of the upwind lake-effect cloud edge are shown to be related to spatial variations in surface heat and moisture fluxes between the lake surface and overlying air Surface fluxes are influenced by both the distribution of lake surface water temperatures and variations of surface wind speed, air temperature, and relative humidity Temporal variations of heat and moisture fluxes from the lake surface

The Radar “Three-Body Scatter Spike”: An Operational Large-Hail Signature

Abstract: Recently, a rare radar artifact called the “flare echo” or “three-body scatter signature” has been examined by several researchers. Here, this midlevel storm signature is called the “three-body scatter spike” (TBSS) and is examined in detail for some severe storms scanned by operational WSR-88Ds. The TBSS is a generally 10–30-km long region of echo aligned radially downrange from a highly reflective (>63 dBZ) echo core. It is found almost exclusively aloft and is characterized by low reflectivity and is usually characterized by near-zero or weak inbound velocities. Spectrum widths are very broad and often noise like. The aforementioned research concluded that it is caused by non-Rayleigh radar microwave scattering (Mie scattering) from a region of large hydrometeors; most likely large, wet hail. This conclusion is supported and expanded upon. WSR-88D data are presented concerning a storm attended by a TBSS that produced giant (>5 cm) hail and violent surface winds. In this case, the three-body si...

Mesoscale Convective Systems in the Southeast United States during 1994–95: A Survey

Abstract: A preliminary survey of mesoscale convective systems (MCSs) in the southeastern United States is presented. MCSs are identified and characterized by means of high-resolution, digital, composite radar reflectivity data. Surveys of this kind are needed to give forecasters better guidance in their real-time assessment of MCS evolution, severe weather potential, and quantitative precipitation. The average lifetime and maximum length of the nearly 400 MCSs included in this survey are 9 h and 350 km, respectively. MCSs are more common in the summer months, when small and short-lived MCSs dominate. In winter larger and longer-lived systems occur more frequently. Because cold-season MCSs, which are about half as numerous as warm-season MCSs, are larger in size and duration, the MCS probability at any location is about constant throughout the year. In summer MCSs occur more commonly in the afternoon, approximately in phase with thunderstorm activity, but the amplitude of the diurnal cycle is small compared to that of observed thunderstorms. Some characteristic echo patterns are discussed.

Mesoscale Model Simulation of the 4–5 January 1995 Lake-Effect Snowstorm

Abstract: The Pennsylvania State University–NCAR Mesoscale Model version 5 (MM5), running on a triply nested grid, was used to simulate the intense lake-effect snowstorm of 4–5 January 1995. On the finest grid (5-km resolution) centered over Lake Ontario, MM5 produced a snowband in the correct location having a size and orientation similar to the band observed by the WSR-88D radar at Binghamton, New York. The simulated precipitation distribution agreed well with the observed snowfall during the first 18 h during the time when the snowband was in its midlake position extending into the Tug Hill plateau. During the last 12 h of the simulation, when both the observed and simulated snowbands lay along the south shore of Lake Ontario, the simulated snowfall at inland locations of Oswego County was less than observed. During this period, the simulated precipitation over Lake Ontario appeared to be excessive, although no radar data or ground truth was available to confirm this. Two short-wave troughs interacted w...

A Neural Network for Damaging Wind Prediction

Abstract: A neural network is developed to diagnose which circulations detected by the National Severe Storms Laboratory’s Mesocyclone Detection Algorithm yield damaging wind. In particular, 23 variables characterizing the circulations are selected to be used as the input nodes of a feed-forward, supervised neural network. The outputs of the network represent the existence/nonexistence of damaging wind, based on ground observations. A set of 14 scalar, nonprobabilistic measures and a set of two multidimensional, probabilistic measures are employed to assess the performance of the network. The former set includes measures of accuracy, association, discrimination, skill, and the latter consists of reliability and refinement diagrams. Two classification schemes are also examined. It is found that a neural network with two hidden nodes outperforms a neural network with no hidden nodes when performance is gauged with any of the 14 scalar measures, except for a measure of discrimination where the results are opp...

Improving WSR-88D Hourly Rainfall Estimates

Abstract: A statistical objective analysis (SOA) scheme is used to reanalyze the stage III estimate of rainfall, an hourly mosaic of digital precipitation arrays produced by a network of WSR-88Ds. The technique also uses rainfall measurements from the Oklahoma Mesonetwork that are taken over the Lake Altus area in southwest Oklahoma. The Lake Altus area is monitored by four WSR-88D radars: Frederick, Oklahoma; Twin Lakes, Oklahoma; Amarillo, Texas; and Lubbock, Texas. A total of 185 hourly maps of precipitation accumulation between June 1995 and July 1996 are used in the reanalysis. The results indicate that the stage III analysis underestimates total rainfall accumulations by as much as 40% when compared to the SOA reanalysis. Furthermore, the largest discrepancies between the stage III analysis and the SOA reanalysis coincide with overlapping areas of coverage between WSR-88D umbrellas. Some stage III precipitation fields used in this study clearly show fictitious high gradients of rainfall that exactly ...

The Early History of Probability Forecasts: Some Extensions and Clarifications

Abstract: Heretofore it has been widely accepted that the contributions of W. E. Cooke in 1906 represented the first works related to the explicit treatment of uncertainty in weather forecasts. Recently, however, it has come to light that at least some aspects of the rationale for quantifying the uncertainty in forecasts were discussed prior to 1900 and that probabilities and odds were included in some weather forecasts formulated more than 200 years ago. An effort to summarize these new historical insights, as well as to clarify the precise nature of the contributions made by various individuals to early developments is this area, appears warranted. The overall purpose of this paper is to extend and clarify the early history of probability forecasts. Highlights of the historical review include 1) various examples of the use of qualitative and quantitative probabilities or odds in forecasts during the eighteenth and nineteenth centuries, 2) a brief discussion in 1890 of the economic component of the ration...