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Showing papers in "Weather and Forecasting in 1997"


Journal ArticleDOI
TL;DR: In this paper, an updated procedure for objective identification and tracking of surface cyclones from gridded analyses is described, where prior smoothing of the raw data with a constant radius spatial filter is used to remove distortions related to the particular grid configuration used and to consistently admit a known scale of disturbance over the domain.
Abstract: An updated procedure for objective identification and tracking of surface cyclones from gridded analyses is described. Prior smoothing of the raw data with a constant radius spatial filter is used to remove distortions related to the particular grid configuration used and to consistently admit a known scale of disturbance over the domain. Pitfalls of using central pressure or vorticity to infer cyclone intensity are illustrated, and a procedure for obtaining a more realistic areal measure of circulation is described. An automated selection procedure for storms having specific properties is outlined. Case selection is by computer search of a database of cyclone tracks, obtained from an application of the cyclone finding and tracking procedure to an extended series of gridded mean sea level pressure analyses. A selection of winter season cyclone statistics for both hemispheres is obtained from European Centre for Medium-Range Weather Forecasts analyses. Discrepancies with and between earlier studie...

221 citations


Journal ArticleDOI
TL;DR: In this article, the vertically integrated liquid water content (VIL) product from the WSR-88D was used to estimate storm severity and particularly the size of the storm.
Abstract: In current severe thunderstorm warning operations, forecasters frequently use the vertically integrated liquid water content (VIL) product from the WSR-88D to estimate thunderstorm severity and, particularly, hail size. Since VIL varies greatly based on airmass characteristics, forecasters have typically determined a threshold VIL to be used for each new thunderstorm event. A product that is independent of airmass characteristics, and thus independent of season and geographic location, would be more desirable in an operational warning environment. It has been observed that high-topped thunderstorms with high VILs do not always produce large hail. It has also been observed that low-topped thunderstorms with low VILs occasionally do produce large hail. However, the maximum reflectivity in both high-topped and low-topped thunderstorms is similar when both produce similar-sized hail. From this, it was hypothesized that dividing the VIL by the echo top would “normalize” the VIL and produce a common va...

147 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss the potential for consistent, around-the-clock image products that can trace the movement and evolution of low, stratiform clouds using data from the GOES-8-9 imager.
Abstract: Using data from the GOES-8–9 imager, this paper discusses the potential for consistent, around-the-clock image products that can trace the movement and evolution of low, stratiform clouds. In particular, the paper discusses how bispectral image sequences based on the shortwave (3.9 μm) and longwave (10.7 μm) infrared channels can be developed for this purpose. These sequences can be animated to produce useful loops. The techniques address several problems faced by operational forecasters in the tracking of low clouds. Low clouds are often difficult or impossible to detect at night because of the poor thermal contrast with the background on infrared images. During the day, although solar reflection makes low, stratiform clouds bright on GOES visible images, it is difficult to distinguish low clouds from adjacent ground snowcover or dense cirrus overcasts. The shortwave infrared channel often gives a superior delineation of low clouds on images because water droplets produce much higher reflectance...

132 citations


Journal ArticleDOI
TL;DR: In this article, the preconvective environment on thunderstorm days in Switzerland north of the Alps has been investigated during a 5-yr period (1985-89) using thermodynamic and kinematic parameters calculated from the radiosounding in Payerne (started at 0000 and 1200 UTC) were used to characterize the initiation of convection.
Abstract: The preconvective environment on thunderstorm days in Switzerland north of the Alps has been investigated during a 5-yr period (1985–89). Thermodynamic and kinematic parameters calculated from the radiosounding in Payerne (started at 0000 and 1200 UTC) were used to characterize the initiation of convection. The best parameters were evaluated by using three methods: 1) skill scores, 2) probability distributions, and 3) mean temperature soundings and hodographs. For the decision whether a thunderstorm day was expected or not, the best results were obtained at 0000 UTC with the original Showalter index and at 1200 UTC with the SWEAT index. In addition, to decide whether an isolated or widespread thunderstorm day was expected, the most successful parameter was the modified CAPECCL. Furthermore, the best thermodynamic and kinematic parameters were combined to create new thunderstorm indices, similar to the calculations of the SWEAT index in the United States. The new thunderstorm indices especially de...

130 citations


Journal ArticleDOI
TL;DR: In this article, the National Centers for Environmental Prediction (formerly the National Meteorological Center) global analysis-forecast system is described, and the most significant analysis change was the direct use of satellite-measured radiances as input to the analysis system.
Abstract: Recent changes in the operational National Centers for Environmental Prediction (formerly the National Meteorological Center) global analysis–forecast system are described. The most significant analysis change was the direct use of satellite-measured radiances as input to the analysis system. Other analysis system changes involved the inclusion of near-surface winds from the ERS-1 satellite system and the addition of a constraint on the divergence increment. In the forecast model, the parameterization of deep convection and the boundary layer scheme were modified. During two months of tests (June and July 1995), the new system produced substantially better forecasts of geopotential height and wind throughout the troposphere, especially in the Southern Hemisphere. Precipitation forecasts over the United States were slightly more skillful in the new system. Subjective evaluations over the Tropics revealed that the new model is more active at small scales, producing more clearly defined convective r...

126 citations


Journal ArticleDOI
TL;DR: In this paper, an explicit cloud prediction scheme has been developed and incorporated into the Eta Model at the National Centers for Environmental Prediction (NCEP) to improve the cloud and precipitation forecasts.
Abstract: An explicit cloud prediction scheme has been developed and incorporated into the Eta Model at the National Centers for Environmental Prediction (NCEP) to improve the cloud and precipitation forecasts. In this scheme, the cloud liquid water and cloud ice are explicitly predicted by adding only one prognostic equation of cloud mixing ratio to the model. Precipitation of rain and snow in this scheme is diagnostically calculated from the predicted cloud fields. The model-predicted clouds are also used in the model’s radiation calculations. Results from the parallel tests performed at NCEP show improvements in precipitation forecasts when prognostic cloud water is included. Compared with the diagnostic clouds, the model-predicted clouds are more accurate in both amount and position. Improvements in specific humidity forecasts have also been found, especially near the surface and above the freezing level.

117 citations


Journal ArticleDOI
TL;DR: The authors address challenges associated with ensemble forecasting such as 1) formulating an ensemble, 2) choosing the number of forecasts in a ensemble, 3) extracting information from an ensemble of forecasts, 4) displaying information from a ensemble of forecast, and 5) interpreting ensemble forecasts.
Abstract: An ensemble forecast is a collection (an ensemble) of forecasts that all verify at the same time. These forecasts are regarded as possible scenarios given the uncertainty associated with forecasting. With such an ensemble, one can address issues that go beyond simply estimating the best forecast. These include estimation of the probability of various events and estimation of the confidence that can be associated with a forecast. Global ensemble forecasts out to 10 days have been computed at both the U.S. and European central forecasting centers since December 1992. Since 1995, the United States has computed experimental regional ensemble forecasts focusing on smaller-scale forecast uncertainties out to 2 days. The authors address challenges associated with ensemble forecasting such as 1) formulating an ensemble, 2) choosing the number of forecasts in an ensemble, 3) extracting information from an ensemble of forecasts, 4) displaying information from an ensemble of forecasts, and 5) interpreting ensemble forecasts. Two synopticscale examples of ensemble forecasting from the winter of 1995/96 are also shown.

113 citations


Journal ArticleDOI
TL;DR: The NCEP ensemble forecasting has been operational at the National Meteorological Center (NCEP) since December 1992 and has been used to forecast the global forecast of the US weather system as mentioned in this paper.
Abstract: Ensemble forecasting has been operational at NCEP (formerly the National Meteorological Center) since December 1992. In March 1994, more ensemble forecast members were added. In the new configuration, 17 forecasts with the NCEP global model are run every day, out to 16-day lead time. Beyond the 3 control forecasts (a T126 and a T62 resolution control at 0000 UTC and a T126 control at 1200 UTC), 14 perturbed forecasts are made at the reduced T62 resolution. Global products from the ensemble forecasts are available from NCEP via anonymous FTP. The initial perturbation vectors are derived from seven independent breeding cycles, where the fast-growing nonlinear perturbations grow freely, apart from the periodic rescaling that keeps their magnitude compatible with the estimated uncertainty within the control analysis. The breeding process is an integral part of the extended-range forecasts, and the generation of the initial perturbations for the ensemble is done at no computational cost beyond that of...

108 citations


Journal ArticleDOI
TL;DR: In this article, the present status of ocean wave modeling at the European Centre for Medium-Range Weather Forecasts (ECMWF) is reviewed, and the analyzed wave height and peak period field are verified against buoy data and show a considerable improvement compared to verification results of a decade ago.
Abstract: The present status of ocean wave modeling at the European Centre for Medium-Range Weather Forecasts (ECMWF) is reviewed. Ocean waves are forecasted globally up to 10 days by means of the Wave Model (WAM), which is driven by 10-m winds from the ECMWF atmospheric model. Initial conditions are provided by assimilation of ERS-1 data into the first-guess wave field. The analyzed wave height and peak period field are verified against buoy data and show a considerable improvement compared to verification results of a decade ago. This is confirmed by a comparison of first-guess wave height against ERS-1 altimeter data. The main reasons for this improvement are (i) the higher quality of ECMWF winds compared to a decade ago, (ii) the improved physics of the WAM model, and (iii) the assimilation of ERS-1 data. The forecast skill of the ECMWF wave forecasting system is also studied by comparing forecasts with buoy data and verifying analysis. Error growth in forecast wave height is less rapid than in forecas...

108 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of discrete azimuthal sampling on Doppler velocity signatures of modeled mesocyclones and tornadoes at various ranges from the radar and for various random positions of the radar beam with respect to the vortices were investigated.
Abstract: Simulated WSR-88D (Weather Surveillance Radar-1988 Doppler) radar data were used to investigate the effects of discrete azimuthal sampling on Doppler velocity signatures of modeled mesocyclones and tornadoes at various ranges from the radar and for various random positions of the radar beam with respect to the vortices. Results show that the random position of the beam can change the magnitudes and locations of peak Doppler velocity values. The important implication presented in this study is that short-term variations in tornado and far-range mesocyclone intensity observed by a WSR-88D radar may be due to evolution or due to the chance positions of the radar beam relative to the vortex’s maximum rotational velocities or due to some combination of both.

107 citations


Journal ArticleDOI
TL;DR: A new type of reliability diagram is developed here and applied to probabilistic quantitative precipitation forecasts from a university contest and shown to potentially be useful in helping the forecaster to correct some errors in assigning the categorical probabilities.
Abstract: The most common method of verifying multicategory probabilistic forecasts such as are used in probabilistic quantitative precipitation forecasting is through the use of the ranked probability score. This single number description of forecast accuracy can never capture the multidimensional nature of forecast quality and does not inform the forecaster about the sources of forecast deficiencies. A new type of reliability diagram is developed here and applied to probabilistic quantitative precipitation forecasts from a university contest. This diagram is shown to potentially be useful in helping the forecaster to correct some errors in assigning the categorical probabilities.

Journal ArticleDOI
TL;DR: In this article, an automated gravity wave detection system is proposed for real-time prediction, detection, and nowcasting of mesoscale gravity wave events based on the synoptic flow pattern in which such waves are consistently found to occur.
Abstract: Mesoscale gravity waves display periods of 1–4 h, have wavelengths of 50–500 km, and can have important effects upon the sensible weather. Real-time prediction, detection, and nowcasting of these mesoscale phenomena is shown to be feasible, due to recent major advances in operational observing and modeling systems. The ability to predict the likelihood of a gravity wave event rests upon recognizing the synoptic flow pattern in which such waves are consistently found to occur. The delineation of the most likely region for wave activity can be further refined by computing simple indicators of unbalanced flow and conducting a cursory search for a suitable wave “duct” with meso-Eta Model data. Particular emphasis should be placed on propagating unbalanced fields. Whenever and wherever a suitable gravity wave environment is found, the Automated Surface Observing System pressure data should be carefully monitored for evidence of gravity wave activity. An automated gravity wave detection system is devel...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the environmental characteristics associated with 313 significant convective events in the western Mediterranean using radiosonde ascents made in Mallorca (Spain) and separated them into five groups, based on the observed event (hail, heavy rain, dry, storms with heavy rain and tornadoes). Classic stability indices, as well as values of convective available potential energy and helicity, are considered for each group.
Abstract: The environmental characteristics associated with 313 significant convective events in the western Mediterranean are investigated using radiosonde ascents made in Mallorca (Spain). The events are separated into five groups, based on the observed event (hail, heavy rain, “dry” storms, storms with heavy rain, and tornadoes). Classic stability indices, as well as values of convective available potential energy and helicity, are considered for each group. These traditional convective indices appear not to provide good guidance for discriminating environments associated with each group of events. In order to classify the environments, each sounding is defined by means of 34 variables that describe the thermal and humidity vertical structure, instability, precipitable water, and helicity. A cluster analysis shows that four different vertical structures appear. Each kind of event shows preference for the environments defined by a cluster. A simple method is presented for sounding classification using th...

Journal ArticleDOI
TL;DR: In this paper, the authors used synoptic features and parameters to identify 312 heavy rainfall events over the southeastern United States and used them to construct a Synoptic Climatology.
Abstract: Previous research has established links between heavy rainfall and a wide variety of synoptic features and parameters. In this study, 312 heavy rainfall events are identified over the southeastern United States and used to construct a synoptic climatology that relates 14 synoptic features and parameters to the occurrence and amounts of heavy rainfall. To carry this out, an automated synoptic typing scheme is employed to classify the heavy rainfall sample according to several characteristics of the synoptic regime. This classification provides five distinct synoptic patterns that can be associated with heavy rainfall over the southeastern United States. Commonly occurring synoptic features in each synoptic pattern are highlighted and discussed. Correlation analysis is then used to relate the occurrence and strength of these features to the heavy precipitation totals. Heavy rainfall in four out of the five identified synoptic patterns is most frequently associated with high levels of moisture at the 700-mb level. Ridging in the 850-mb warm air advection field is common over the heavy rain area as well. Numerous relationships are identified between the heavy rainfall amounts and the character of synoptic features; however, the nature of these relationships is found to vary strongly according to the synoptic pattern.

Journal ArticleDOI
TL;DR: In this paper, the average cloud-to-ground lightning flash density values for Florida have been calculated for the 10-yr period 1986-95 and the locations of relative areas of lightning maxima and minima are strongly affected by the various combinations of synoptic and mesoscale contributions.
Abstract: Average cloud-to-ground lightning flash density values for Florida have been calculated for the 10-yr period 1986–95. An annual mean map and monthly mean maps were constructed from a database exceeding 25 million flashes. These maps represent a 10-yr climatology of the geographic distribution of detected cloud-to-ground lightning flashes and provide an insight into the thunderstorm distribution in Florida. The locations of relative areas of lightning maxima and minima are strongly affected by the various combinations of synoptic and mesoscale contributions and are discussed. During the cool season, November–February, the greatest flash densities occur over the panhandle from storms mostly associated with midlatitude synoptic-scale systems. During the spring transitional period of March–May, flash densities increase over the entire state as synoptic contributions transition to mesoscale. Flash density totals in the warm season, June–August, exceed 10 flashes km−2 in the central part of Florida. Fl...

Journal ArticleDOI
TL;DR: In this article, a radar-based analysis of known tornadic mesocyclones associated with two mature tropical cyclones that were not landfalling in the vicinity of the tornado occurrence, namely, Tropical Storm Gordon (1994) and Hurricane Allison (1995), is presented.
Abstract: As part of the National Weather Service (NWS) Modernization and Restructuring Program, WSR-88D (NEXRAD) Doppler radar installation has been completed at each Weather Service Office in Florida. Recently, this powerful new tool provided unique opportunities for Jacksonville, Tampa Bay, and Melbourne NEXRAD Weather Service Office personnel to investigate tropical cyclone (TC) rainbands for evidence of tornadogenesis. This study provides a radar-based analysis of known tornadic mesocyclones associated with two mature tropical cyclones that were not landfalling in the vicinity of the tornado occurrence, namely, Tropical Storm Gordon (1994) and Hurricane Allison (1995). Based on successful NEXRAD sampling strategies, detailed analyses of storm-scale reflectivity and velocity signatures are conducted in the context of establishing preliminary critical criteria for use in the tornado detection and warning process. Important characteristics were found to include detection of discrete, small diameter .50 dBZ echos collocated with storm-relative rotational velocities of 6.5‐ 15 ms 2 1. Rotational features, although often subtle, were identifiable for an average of 30 min prior to tornado production, with total durations of 1‐2 h. Near the time of tornado touchdown, the core diameter of the lowlevel circulation couplets contracted to approximately 1.85 km (1 n mi), leading to an associated increase of shear across the circulation to 0.010 s 21 or greater. A comparison between the well-studied Great Plains tornadic supercell and the observed TC-tornado cells revealed a common trait of persistence. While the average depth of rotation associated with the TC-tornado cells (3.5 km) was much more shallow than their midwest counterparts, the ratio of depth of rotation to storm top were comparable. However, the shallow depth and weaker detectable rotation of the TC (tornadic) mesocyclones greatly reduced the detection capability of the current WSR-88D mesocyclone algorithm when compared to identification of traditional supercells. Based upon the analyzed data, the authors offer several recommendations to assist operational radar meteorologists with the challenging task of detecting outer rainband tornadoes. Additionally, the authors propose a new WSR-88D scan strategy (volume coverage pattern, VCP) that would provide additional low-level slices in lieu of several current upper-elevation angles. This new VCP would facilitate improved vertical sampling at lower heights where TC mesoscale circulations are most likely to be detected.

Journal ArticleDOI
TL;DR: In this paper, cloud-to-ground (CG) lightning patterns were analyzed in 42 violent tornado-producing (F4, F5) supercells that occurred between January 1989 and November 1992.
Abstract: Cloud-to-ground (CG) lightning patterns were analyzed in 42 violent tornado-producing (F4, F5) supercells that occurred between January 1989 and November 1992. The purpose of this analysis was to identify potential correlations between CG lightning patterns and tornadogenesis. Lightning characteristics were analyzed for a 30-min period before, during, and 30 min after each tornado’s lifetime. Thirty-one of the storms were characterized by a peak in CG flash rate preceding tornado formation; 20 storms displayed a decrease in CG flash activity coincident with tornado touchdown. Six of the 42 storms exhibited a polarity reversal, from positive to negative, in the sign of the charge lowered to ground. Storms exhibiting a majority of positive flashes were generally associated with long-track tornadoes, F5 damage ratings, or severe weather outbreak conditions. The total number of flashes associated with each storm had no correlation with tornadogenesis (total number of flashes ranged from 16 to 3394). ...

Journal ArticleDOI
TL;DR: In this article, a preliminary attempt at such a model is presented for the southern region of the United States (gulf coastal states) and requires information regarding cloud condensation nuclei, moisture availability (or saturation), and dynamic forcing.
Abstract: The prediction of fog occurrence, extent, duration, and intensity remains difficult despite improvements in numerical guidance and modeling of the fog phenomenon. This is because of the dependency of fog on microphysical and mesoscale processes that act within the boundary layer and that, in turn, are forced by the prevailing synoptic regime. Given existing and new technologies and techniques already available to the operational forecaster, fog prediction may be improved by the development and application of a simple conceptual model. A preliminary attempt at such a model is presented for the southern region of the United States (gulf coastal states) and requires information regarding cloud condensation nuclei, moisture availability (or saturation), and dynamic forcing. Each of these factors are assessed with regard to their extent and evolution with time. An illustration, and potential application, of how the model could be used is detailed as no extensive operational testing has yet been completed. Instead, the model is applied in hindcast to verify its application. Successful use of the model will require an operational forecaster to assimilate all available tools including climatology, numerical guidance, sounding analysis, model diagnostic software, and satellite imagery. These must be used to characterize and quantify the nature of the local and regional boundary layer in the forecast region according to macroscale forcing and moisture availability, the initial local settings and boundary layer, qualitative assessment of cloud condensation nuclei, and the interaction of these in time and space. Once identified, the evolution of the boundary layer may be forecast with regard to the overall environment for fog occurrence, its likely extent, intensity, and duration.

Journal ArticleDOI
TL;DR: In this paper, the abilities of several algorithms to predict in-flight icing conditions, as verified by pilot reports (PIREPs), are compared for two numerical weather prediction models (Eta and the Mesoscale Analysis and Prediction System) for the Winter Icing and Storms Program 1994 (WISP94) time period (25 January-25 March 1994).
Abstract: Recent research to improve forecasts of in-flight icing conditions has involved the development of algorithms to apply to the output of numerical weather prediction models. The abilities of several of these algorithms to predict icing conditions, as verified by pilot reports (PIREPs), are compared for two numerical weather prediction models (Eta and the Mesoscale Analysis and Prediction System) for the Winter Icing and Storms Program 1994 (WISP94) time period (25 January–25 March 1994). Algorithms included in the comparison were developed by the National Aviation Weather Advisory Unit [NAWAU, now the Aviation Weather Center (AWC)], the National Center for Atmospheric Research’s Research Applications Program (RAP), and the U.S. Air Force. Operational icing forecasts (AIRMETs) issued by NAWAU for the same time period are evaluated to provide a standard of comparison. The capabilities of the Eta Model’s explicit cloud liquid water estimates for identifying icing regions are also evaluated and compar...

Journal ArticleDOI
TL;DR: In this article, the ability to discriminate between tornadic and nontornadic thunderstorms using a mesoscale model was investigated using a simulation of nine severe weather events: four events are tornadic supercell thunderstorm outbreaks that occur in conjunction with strong large-scale forcing for upward motion, three events are bow-echo outbreaks that also occur in conjunctious conditions, and two are isolated supercell storms that occur under much weaker large scale forcing.
Abstract: The ability to discriminate between tornadic and nontornadic thunderstorms is investigated using a mesoscale model. Nine severe weather events are simulated: four events are tornadic supercell thunderstorm outbreaks that occur in conjunction with strong large-scale forcing for upward motion, three events are bow-echo outbreaks that also occur in conjunction with strong large-scale forcing for upward motion, and two are isolated tornadic supercell thunderstorms that occur under much weaker large-scale forcing. Examination of the mesoscale model simulations suggests that it is possible to discriminate between tornadic and nontornadic thunderstorms by using the locations of model-produced convective activity and values of convective available potential energy to highlight regions of likely thunderstorm development, and then using the values of storm-relative environmental helicity (SREH) and bulk Richardson number shear (BRNSHR) to indicate whether or not tornadic supercell thunderstorms are likely....

Journal ArticleDOI
TL;DR: In this paper, a multiple regression scheme with tropical cyclone intensity change as the dependent variable has been developed for the western North Pacific Ocean, and utilizes digitized satellite data; the first time such satellite information has been combined with other predictors in a tropicalcyclone multiple regression schemes.
Abstract: A multiple regression scheme with tropical cyclone intensity change as the dependent variable has been developed. The new scheme is titled the Typhoon Intensity Prediction Scheme (TIPS) and is similar to one used operationally at the National Hurricane Center. However, TIPS contains two major differences: it is developed for the western North Pacific Ocean, and utilizes digitized satellite data; the first time such satellite information has been combined with other predictors in a tropical cyclone multiple regression scheme. It is shown that the satellite data contains vital information that distinguishes between fast and slow developing tropical cyclones. The importance of other predictors (such as wind shear, persistence, climatology, and an empirical formula dependent on sea surface temperature) to intensity change are also clarified in the statistical analysis. A normalization technique reveals threshold values useful to forecasters. It is shown that TIPS may be competitive with the Joint Typhoon Warning Center in forecasting tropical cyclone intensity change.

Journal ArticleDOI
TL;DR: In this article, the authors examined heavy rain events over the southeast flank of Mauna Loa volcano on the island of Hawaii using surface, rawinsonde, rain gauge, and satellite data.
Abstract: Heavy rain events (>100 mm day−1) over the southeast flank of Mauna Loa volcano on the island of Hawaii are examined using surface, rawinsonde, rain gauge, and satellite data. The events occur in the presence of four types of synoptic-scale disturbances that include Kona storms, cold fronts, upper-tropospheric troughs, and tropical systems. The heaviest rainfall occurs at elevations above 0.5 km over the volcano slopes facing the prevailing low-level flow with the leeside slopes experiencing considerably smaller amounts. Rainfall duration and patterns demonstrate that the rains and flash floods are the result of more than one convective cell. Soundings prior to the heavy rain events show only modest instability, with only the K index serving as a useful predictor for heavy rain among the standard stability indices. There is an increase in both the moisture content of the midlevels (750–450 mb) and the onshore flow normal to the terrain gradient prior to the heavy rain. The lack of the trade winds...

Journal ArticleDOI
TL;DR: A dataset of all significant winter-type weather events reported in Storm Data within the contiguous United States from 1982 through 1994 has been compiled as discussed by the authors, which is intended to assist in development of operational forecasting issues such as staffing requirements, forecast formats and lead times, and local and regional winter weather preparedness activities.
Abstract: A dataset of all significant winter-type weather events reported in Storm Data within the contiguous United States from 1982 through 1994 has been compiled. Statistical analysis of this dataset is used to determine climatological frequencies of winter weather, including seasonal fluctuations, relative frequencies of different hazards (e.g., heavy snow vs freezing precipitation), duration variations, and size (areal coverage) distributions. Findings are intended to assist in development of operational forecasting issues such as staffing requirements, forecast formats and lead times, and local and regional winter weather preparedness activities. In particular, the database is intended to assist in these issues as they apply to the Storm Prediction Center (SPC), which will begin operational short-term forecasting of hazardous winter weather in fall 1997. From the 13-yr database of 1663 events and 2075 event days, significant winter weather is shown to occur somewhere within the contiguous United Sta...

Journal ArticleDOI
TL;DR: In this paper, a mesoanalysis of summertime convergence boundaries in the southeastern United States by combining capabilities of the new WSR-88D Doppler radar with Geostationary Operational Environmental Satellite imagery and conventional surface data is demonstrated.
Abstract: It is demonstrated that it is possible to perform informative mesoanalysis of summertime convergence boundaries in the southeastern United States by combining capabilities of the new WSR-88D Doppler radar with Geostationary Operational Environmental Satellite imagery and conventional surface data. Observed phenomena are identified as thunderstorm outflow boundaries, sea-breeze fronts, horizontal convective rolls, deep synoptic-scale fronts, prefrontal troughs, shallow fronts (airmass boundaries lacking upper-level support), stationary and propagating boundaries of unknown origin, and the “Piedmont trough,” which is apparently a new feature discovered in the course of this research. The transition zone between the Piedmont and the Coastal Plain was found to be a preferred location for convergence boundaries. An unexpectedly far inland advance of the sea breeze to central North Carolina occurred in some instances. The very sensitive “clear air mode” of the WSR-88D radar, when used in combination wi...

Journal ArticleDOI
TL;DR: In this paper, several methods of generating very short-term (0-6h) probabilistic forecasts of ceiling and visibility are investigated: 1) an observations-based (OBS-based) system in which potential predictors consist of weather observations from a network of surface stations along with several climatic terms; 2) the traditional model output statistics (MOS)-based approach in which possible predictors consisting of nested grid model (NGM) output, the latest observation from the forecast site, and climatic variables; and 3) persistence climatology in which
Abstract: Several methods of generating very short term (0–6 h) probabilistic forecasts of ceiling and visibility are investigated: 1) an observations-based (OBS-based) system in which potential predictors consist of weather observations from a network of surface stations along with several climatic terms; 2) the traditional model output statistics (MOS)-based approach in which potential predictors consist of nested grid model (NGM) output, the latest observation from the forecast site, and climatic variables; and 3) persistence climatology in which potential predictors consist of the latest observation of the predictand variable from the forecast site and several climatic terms. Forecasts are generated for each technique on 2 yr (1993–94) of independent data for 25 stations in the eastern United States. Two variables (ceiling and visibility) are forecasted for eight thresholds, two initial times (0300 and 1500 UTC), and three lead times (1, 3, and 6 h). Results show that the OBS-based method is superior t...

Journal ArticleDOI
TL;DR: In this paper, a statistical prediction method based entirely on the optimal combination of persistence, month-to-month trend of initial conditions, and climatology is developed for the El Nino-Southern Oscillation (ENSO) phenomena.
Abstract: A statistical prediction method, which is based entirely on the optimal combination of persistence, month-to-month trend of initial conditions, and climatology, is developed for the El Nino–Southern Oscillation (ENSO) phenomena. The selection of predictors is by design intended to avoid any pretense of predictive ability based on “model physics” and the like, but rather is to specify the optimal “no-skill” forecast as a baseline comparison for more sophisticated forecast methods. Multiple least squares regression using the method of leaps and bounds is employed to test a total of 14 possible predictors for the selection of the best predictors, based upon 1950–94 developmental data. A range of zero to four predictors were chosen in developing 12 separate regression models, developed separately for each initial calendar month. The predictands to be forecast include the Southern Oscillation (pressure) index (SOI) and the Nino 1+2, Nino 3, Nino 4, and Nino 3.4 SST indices for the equatorial eastern a...

Journal ArticleDOI
TL;DR: In this article, multiple regression and logistic regression equations were derived for the prediction of hail size based on data from 1992 through 1994, and the multiple regression equation was formulated to predict hail diameter.
Abstract: Multiple regression and logistic regression equations were derived for the prediction of hail size based on data from 1992 through 1994. The multiple regression equation was formulated to predict hail diameter. The logistic regression equation was developed to predict the probability of hail size greater than or equal to 1.9 cm in diameter. Variables used for this study consisted of vertically integrated liquid (VIL) computed from the Weather Surveillance Radar-1988 Doppler (WSR-88D) radar and convective parameters derived from the skew-T/Hodograph analysis and research program. Data were obtained from the Baltimore, Maryland/Washington D.C., WSR-88D radar and Dulles, Virginia, upper-air soundings. Numerous parameters were tested; however, only VIL, 85-kPa temperature, freezing level, and mean storm-relative inflow in the lowest 2-km were retained for the multiple regression equation. These four parameters were used as a base to derive the logistic regression equation, and this derivation process...

Journal ArticleDOI
TL;DR: The second-generation GFS as discussed by the authors uses multivariate optimum interpolation analysis and incremental nonlinear normal-mode initialization to initialize the forecast model, which is a global primitive equation model with a resolution of 18 sigma levels in the vertical and 79 waves of triangular truncation in the horizontal.
Abstract: The global forecast system (GFS), which started its operation in 1988 at the Central Weather Bureau in Taiwan, has been upgraded to incorporate better numerical methods and more complete parameterization schemes. The second-generation GFS uses multivariate optimum interpolation analysis and incremental nonlinear normal-mode initialization to initialize the forecast model. The forecast model is a global primitive equation model with a resolution of 18 sigma levels in the vertical and 79 waves of triangular truncation in the horizontal. The forecast model includes a 1.5-order eddy mixing parameterization, a gravity wave drag parameterization, a shallow convection parameterization, a relaxed version of Arakawa–Schubert cumulus parameterization, grid-scale condensation calculation, and longwave and shortwave radiative transfer calculations with consideration of fractional clouds. The performance of the second-generation GFS is significantly better than the first-generation GFS. For two 3-month period...

Journal ArticleDOI
TL;DR: This paper examined the relationship between cloud-to-ground (CG) lightning and surface precipitation using observations from six regions (each on the order of 10000 km2), April through October (1989-93), in the south-central United States.
Abstract: This study examines the relationship between cloud-to-ground (CG) lightning and surface precipitation using observations from six regions (each on the order of 10000 km2), April through October (1989–93), in the south-central United States. The relationship is evaluated using two different methods. First, regression equations are fit to the data, initially for only the CG lightning flash density and precipitation, and then with additional atmospheric and lightning parameters. Second, days are categorized according to differences in the precipitation-to-CG lightning ratio; the same additional parameters are then examined for differences occurring within each category. Results show that the relationship between CG lightning and surface precipitation is highly variable; r2 coefficients range from 0.121 in Baton Rouge to 0.601 in Dallas. A measure of the positive CG lightning flash density is the best addition to the model, statistically significant in all regions. When days are categorized, the perc...

Journal ArticleDOI
TL;DR: In this paper, the authors describe a portion of the in-flight aircraft icing prediction effort through a comprehensive icing prediction and evaluation project conducted by the Research Applications Program at the National Center for Atmospheric Research.
Abstract: The purpose of the Federal Aviation Administration’s Icing Forecasting Improvement Program is to conduct research on icing conditions both in flight and on the ground. This paper describes a portion of the in-flight aircraft icing prediction effort through a comprehensive icing prediction and evaluation project conducted by the Research Applications Program at the National Center for Atmospheric Research. During this project, in- flight icing potential was forecast using algorithms developed by RAP, the National Weather Service’s National Aviation Weather Advisory Unit, and the Air Force Global Weather Center in conjunction with numerical model data from the Eta, MAPS, and MM5 models. Furthermore, explicit predictions of cloud liquid water were available from the Eta and MM5 models and were also used to forecast icing potential. To compare subjectively the different algorithms, predicted icing regions and observed pilot reports were viewed simultaneously on an interactive, real-time display. To m...