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Showing papers in "Monthly Weather Review in 2016"


Journal ArticleDOI
TL;DR: The Rapid Refresh (RAP) as mentioned in this paper is an hourly updated assimilation and model forecast system, which replaced the Rapid Update Cycle (RUC) as an operational regional analysis and forecast system among the suite of models at the NOAA/National Centers for Environmental Prediction (NCEP).
Abstract: The Rapid Refresh (RAP), an hourly updated assimilation and model forecast system, replaced the Rapid Update Cycle (RUC) as an operational regional analysis and forecast system among the suite of models at the NOAA/National Centers for Environmental Prediction (NCEP) in 2012. The need for an effective hourly updated assimilation and modeling system for the United States for situational awareness and related decision-making has continued to increase for various applications including aviation (and transportation in general), severe weather, and energy. The RAP is distinct from the previous RUC in three primary aspects: a larger geographical domain (covering North America), use of the community-based Advanced Research version of the Weather Research and Forecasting (WRF) Model (ARW) replacing the RUC forecast model, and use of the Gridpoint Statistical Interpolation analysis system (GSI) instead of the RUC three-dimensional variational data assimilation (3DVar). As part of the RAP development, modif...

762 citations


Journal ArticleDOI
TL;DR: For the EnKF in general, but higher-resolution applications in particular, it is desirable to use a short assimilation window, and a focus on approaches for maintaining balance during the EnkF update is focused on.
Abstract: This paper reviews the development of the ensemble Kalman filter (EnKF) for atmospheric data assimilation. Particular attention is devoted to recent advances and current challenges. The distinguishing properties of three well-established variations of the EnKF algorithm are first discussed. Given the limited size of the ensemble and the unavoidable existence of errors whose origin is unknown (i.e., system error), various approaches to localizing the impact of observations and to accounting for these errors have been proposed. However, challenges remain; for example, with regard to localization of multiscale phenomena (both in time and space). For the EnKF in general, but higher-resolution applications in particular, it is desirable to use a short assimilation window. This motivates a focus on approaches for maintaining balance during the EnKF update. Also discussed are limited-area EnKF systems, in particular with regard to the assimilation of radar data and applications to tracking severe storms ...

453 citations


Journal ArticleDOI
TL;DR: In this article, a new data assimilation approach based on the particle filter (PF) was proposed for nonlinear/non-Gaussian applications in geoscience, denoted the local PF, which extends the particle weights into vector quantities to reduce the influence of distant observations on the weight calculations via a localization function.
Abstract: This paper presents a new data assimilation approach based on the particle filter (PF) that has potential for nonlinear/non-Gaussian applications in geoscience. Particle filters provide a Monte Carlo approximation of a system’s probability density, while making no assumptions regarding the underlying error distribution. The proposed method is similar to the PF in that particles—also referred to as ensemble members—are weighted based on the likelihood of observations in order to approximate posterior probabilities of the system state. The new approach, denoted the local PF, extends the particle weights into vector quantities to reduce the influence of distant observations on the weight calculations via a localization function. While the number of particles required for standard PFs scales exponentially with the dimension of the system, the local PF provides accurate results using relatively few particles. In sensitivity experiments performed with a 40-variable dynamical system, the local PF require...

159 citations


Journal ArticleDOI
TL;DR: In this article, the authors introduced scale-aware parameterized cloud dynamics for high-resolution forecasts by making several changes to the Kain-Fritsch (KF) convective parameterization scheme in the WRF Model, including subgrid-scale cloud-radiation interactions, a dynamic adjustment time scale, impacts of cloud updraft mass fluxes on grid-scale vertical velocity, and lift lift.
Abstract: Efforts to improve the prediction accuracy of high-resolution (1–10 km) surface precipitation distribution and variability are of vital importance to local aspects of air pollution, wet deposition, and regional climate. However, precipitation biases and errors can occur at these spatial scales due to uncertainties in initial meteorological conditions and/or grid-scale cloud microphysics schemes. In particular, it is still unclear to what extent a subgrid-scale convection scheme could be modified to bring in scale awareness for improving high-resolution short-term precipitation forecasts in the WRF Model. To address these issues, the authors introduced scale-aware parameterized cloud dynamics for high-resolution forecasts by making several changes to the Kain–Fritsch (KF) convective parameterization scheme in the WRF Model. These changes include subgrid-scale cloud–radiation interactions, a dynamic adjustment time scale, impacts of cloud updraft mass fluxes on grid-scale vertical velocity, and lift...

148 citations


Journal ArticleDOI
TL;DR: In this paper, a statistical method for postprocessing ensembles based on quantile regression forests (QRF), a generalization of random forests for quantile regressions, is proposed.
Abstract: Ensembles used for probabilistic weather forecasting tend to be biased and underdispersive. This paper proposes a statistical method for postprocessing ensembles based on quantile regression forests (QRF), a generalization of random forests for quantile regression. This method does not fit a parametric probability density function (PDF) like in ensemble model output statistics (EMOS) but provides an estimation of desired quantiles. This is a nonparametric approach that eliminates any assumption on the variable subject to calibration. This method can estimate quantiles using not only members of the ensemble but any predictor available including statistics on other variables.The method is applied to the Meteo-France 35-member ensemble forecast (PEARP) for surface temperature and wind speed for available lead times from 3 up to 54 h and compared to EMOS. All postprocessed ensembles are much better calibrated than the PEARP raw ensemble and experiments on real data also show that QRF performs better t...

120 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the full 15-yr TRMM Precipitation Radar dataset in conjunction with high-resolution simulations from the Weather Research and Forecasting Model to better understand the physical factors that control the climatology of high-impact weather in subtropical South America.
Abstract: Satellite radar and radiometer data indicate that subtropical South America has some of the deepest and most extreme convective storms on Earth. This study uses the full 15-yr TRMM Precipitation Radar dataset in conjunction with high-resolution simulations from the Weather Research and Forecasting Model to better understand the physical factors that control the climatology of high-impact weather in subtropical South America. The occurrence of intense storms with an extreme horizontal dimension is generally associated with lee cyclogenesis and a strengthening South American low-level jet (SALLJ) in the La Plata basin. The orography of the Andes is critical, and model sensitivity calculations removing and/or reducing various topographic features indicate the orographic control on the initiation of convection and its upscale growth into mesoscale convective systems (MCSs). Reduced Andes experiments show more widespread convective initiation, weaker average storm intensity, and more rapid propagation ...

117 citations


Journal ArticleDOI
TL;DR: In this paper, an analysis of atmospheric rivers (ARs) as defined by an automated AR detection tool based on integrated water vapor transport (IVT) and the connection to heavy precipitation in the southeast United States (SEUS) is performed.
Abstract: An analysis of atmospheric rivers (ARs) as defined by an automated AR detection tool based on integrated water vapor transport (IVT) and the connection to heavy precipitation in the southeast United States (SEUS) is performed. Climatological water vapor and water vapor transport fields are compared between the U.S. West Coast (WCUS) and the SEUS, highlighting stronger seasonal variation in integrated water vapor in the SEUS and stronger seasonal variation in IVT in the WCUS. The climatological analysis suggests that IVT values above ~500 kg m−1 s−1 (as incorporated into an objective identification tool such as the AR detection tool used here) may serve as a sensible threshold for defining ARs in the SEUS.Atmospheric river impacts on heavy precipitation in the SEUS are shown to vary on an annual cycle, and a connection between ARs and heavy precipitation during the nonsummer months is demonstrated. When identified ARs are matched to heavy precipitation days (>100 mm day−1), an average match rate of...

115 citations


Journal ArticleDOI
TL;DR: The structural evolution of the inner core and near-environment throughout the life cycle of Hurricane Edouard (2014) was examined using a synthesis of airborne and satellite measurements as discussed by the authors.
Abstract: The structural evolution of the inner core and near-environment throughout the life cycle of Hurricane Edouard (2014) is examined using a synthesis of airborne and satellite measurements. This study specifically focuses on differences in the distribution of deep convection during two periods: when Edouard intensified toward hurricane status, and when Edouard peaked in intensity and began to weaken. While both periods saw precipitation maximized in the downshear-left and upshear-left quadrants, deep convection was only seen from the aircraft during the intensifying period.Deep convection was located farther inside the radius of maximum winds (RMW) during the intensifying period than the weakening period. This convection is traced to strong updrafts inside the RMW in the downshear-right quadrant, tied to strong low-level convergence and high convective available potential energy (CAPE) as the storm remained over warm water in a moist environment. Strong updrafts persisted upshear left and were collo...

112 citations


Journal ArticleDOI
TL;DR: The land surface model (LSM) described in this manuscript was originally developed as part of the NOAA Rapid Update Cycle (RUC) model development effort; with ongoing modifications, it is now used as an option for the WRF community model.
Abstract: The land surface model (LSM) described in this manuscript was originally developed as part of the NOAA Rapid Update Cycle (RUC) model development effort; with ongoing modifications, it is now used as an option for the WRF community model. The RUC model and its WRF-based NOAA successor, the Rapid Refresh (RAP), are hourly updated and have an emphasis on short-range, near-surface forecasts including aviation-impact variables and preconvective environment. Therefore, coupling to this LSM (hereafter the RUC LSM) has been critical to provide more accurate lower boundary conditions. This paper describes changes made to the RUC LSM since earlier descriptions, including extension from six to nine levels, improved snow treatment, and new land-use data from MODIS.The RUC LSM became operational at the NOAA/National Centers for Environmental Prediction (NCEP) as part of the RUC from 1998–2012 and as part of the RAP from 2012 through the present. The simple treatments of basic land surface processes in the RUC...

110 citations


Journal ArticleDOI
TL;DR: In this article, the structural evolution of the inner core and near environment throughout the life cycle of Hurricane Edouard (2014) was examined using a synthesis of airborne and satellite measurements.
Abstract: The structural evolution of the inner core and near environment throughout the life cycle of Hurricane Edouard (2014) is examined using a synthesis of airborne and satellite measurements. This study specifically focuses on the precipitation evolution and thermodynamic changes that occur on the vortex scale during four periods: when Edouard was a slowly intensifying tropical storm, another while a rapidly intensifying hurricane, during the initial stages of weakening after reaching peak intensity, and later while experiencing moderate weakening in the midlatitudes. Results suggest that, in a shear-relative framework, a wavenumber-1 asymmetry exists whereby the downshear quadrants consistently exhibit the greatest precipitation coverage and highest relative humidity, while the upshear quadrants (especially upshear right) exhibit relatively less precipitation coverage and lower humidity, particularly in the midtroposphere. Whether dynamically or precipitation driven, the relatively dry layers upshear...

109 citations


Journal ArticleDOI
TL;DR: In this article, the authors used Atmospheric Infrared Sounder (AIRS) data to study an extreme warm and humid air mass transported over the Barents-Kara Seas region by an Arctic cyclone at the end of December 2015.
Abstract: Atmospheric data from the Atmospheric Infrared Sounder (AIRS) were used to study an extreme warm and humid air mass transported over the Barents–Kara Seas region by an Arctic cyclone at the end of December 2015. Temperature and humidity in the region was ~10°C (>3σ above the 2003–14 mean) warmer and ~1.4 g kg−1 (>4σ above the 2003–14 mean) wetter than normal during the peak of this event. This anomalous air mass resulted in a large and positive flux of energy into the surface via the residual of the surface energy balance (SEB), compared to the weakly negative SEB from the surface to the atmosphere expected for that time of year. The magnitude of the downwelling longwave radiation during the event was unprecedented compared to all other events detected by AIRS in December/January since 2003. An approximate budget scaling suggests that this anomalous SEB could have resulted in up to 10 cm of ice melt. Thinning of the ice pack in the region was supported by remotely sensed and modeled estimates of ...

Journal ArticleDOI
TL;DR: In this paper, an extreme precipitation event affected the region on 24-26 March 2015 with 1-day accumulated precipitation exceeding 40 mm in several locations and hourly mean rainfall rates higher than 10 mm h−1, producing floods and resulting in casualties and significant damage.
Abstract: Northern Chile hosts the driest place on Earth in the Atacama Desert. Nonetheless, an extreme precipitation event affected the region on 24–26 March 2015 with 1-day accumulated precipitation exceeding 40 mm in several locations and hourly mean rainfall rates higher than 10 mm h−1, producing floods and resulting in casualties and significant damage. The event is analyzed using ERA-Interim, surface station data, sounding observations, and satellite-based radar. Two main conditions favorable for precipitation were present at the time of the event: (i) a cutoff low (COL) off the coast of northern Chile and (ii) positive sea surface temperature (SST) anomalies over the eastern tropical Pacific. The circulation driven by the COL was strong but not extraordinary. Regional Climate Model, version 4 (RegCM4), is used to test the sensitivity of precipitation to SST anomalies by removing the warm SST anomaly in the eastern tropical Pacific. The cooler simulation produced very similar COL dry dynamics to that ...

Journal ArticleDOI
TL;DR: In this paper, the authors used a newly developed feature tracking algorithm to identify Indian monsoon depressions originating in or near the Bay of Bengal and then rotated, centralized, and combined to give a fully three-dimensional 106-depression composite structure.
Abstract: ERA-Interim reanalysis data from the past 35 years have been used with a newly developed feature tracking algorithm to identify Indian monsoon depressions originating in or near the Bay of Bengal. These were then rotated, centralized, and combined to give a fully three-dimensional 106-depression composite structure—a considerably larger sample than any previous detailed study on monsoon depressions and their structure. Many known features of depression structure are confirmed, particularly the existence of a maximum to the southwest of the center in rainfall and other fields and a westward axial tilt in others. Additionally, the depressions are found to have significant asymmetry owing to the presence of the Himalayas, a bimodal midtropospheric potential vorticity core, a separation into thermally cold (~−1.5 K) and neutral (~0 K) cores near the surface with distinct properties, and the center has very large CAPE and very small CIN. Variability as a function of background state has also been explo...

Journal ArticleDOI
TL;DR: The capability of all-sky microwave radiance assimilation in the Gridpoint Statistical Interpolation (GSI) analysis system has been developed at the National Centers for Environmental Prediction (NCEP) as discussed by the authors.
Abstract: The capability of all-sky microwave radiance assimilation in the Gridpoint Statistical Interpolation (GSI) analysis system has been developed at the National Centers for Environmental Prediction (NCEP). This development effort required the adaptation of quality control, observation error assignment, bias correction, and background error covariance to all-sky conditions within the ensemble–variational (EnVar) framework. The assimilation of cloudy radiances from the Advanced Microwave Sounding Unit-A (AMSU-A) microwave radiometer for ocean fields of view (FOVs) is the primary emphasis of this study.In the original operational hybrid 3D EnVar Global Forecast System (GFS), the clear-sky approach for radiance data assimilation is applied. Changes to data thinning and quality control have allowed all-sky satellite radiances to be assimilated in the GSI. Along with the symmetric observation error assignment, additional situation-dependent observation error inflation is employed for all-sky conditions. Mo...

Journal ArticleDOI
TL;DR: In this article, the authors compared the performance of the momentum control variables ψ and χ (ψχ) for high-resolution data assimilation and forecast experiments for seven convective events in a domain that encompasses the Rocky Mountain Front Range using the 3DVar system of the Weather Research and Forecasting (WRF) Model.
Abstract: The momentum variables of streamfunction and velocity potential are used as control variables in a number of operational variational data assimilation systems. However, in this study it is shown that, for limited-area high-resolution data assimilation, the momentum control variables ψ and χ (ψχ) pose potential difficulties in background error modeling and, hence, may result in degraded analysis and forecast when compared with the direct use of x and y components of wind (UV). In this study, the characteristics of the modeled background error statistics, derived from an ensemble generated from Weather Research and Forecasting (WRF) Model real-time forecasts of two summer months, are first compared between the two control variable options. Assimilation and forecast experiments are then conducted with both options for seven convective events in a domain that encompasses the Rocky Mountain Front Range using the three-dimensional variational data assimilation (3DVar) system of the WRF Model. The impact...

Journal ArticleDOI
TL;DR: In this article, the role of diabatic outflow in midlatitude flow amplification was highlighted in the context of a review of the physical and dynamical processes involved in extratropical transition.
Abstract: Recurving tropical cyclones (TCs) undergoing extratropical transition (ET) may substantially modify the large-scale midlatitude flow pattern. This study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in ET. Composite fields of 12 western North Pacific ET cases are used as initial and boundary conditions for high-resolution numerical simulations of the North Pacific–North American sector with and without the TC present. It is demonstrated that a three-stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern: 1) preconditioning by a predecessor rain event (PRE), 2) TC–extratropical flow interaction, and 3) downstream flow amplification by a downstream warm conveyor belt (WCB). An ensemble of perturbed simulations demonstrates the robustness of these stages. Beyond earlier studies investigating PREs, recurv...

Journal ArticleDOI
TL;DR: In this paper, the temporal clustering of regional-scale extreme precipitation events in southern Switzerland is studied and the dynamics that are responsible for the clustering are identified. But the results of the study were limited to the fall season.
Abstract: Temporal clustering of extreme precipitation events on subseasonal time scales is of crucial importance for the formation of large-scale flood events. Here, the temporal clustering of regional-scale extreme precipitation events in southern Switzerland is studied. These precipitation events are relevant for the flooding of lakes in southern Switzerland and northern Italy. This research determines whether temporal clustering is present and then identifies the dynamics that are responsible for the clustering.An observation-based gridded precipitation dataset of Swiss daily rainfall sums and ECMWF reanalysis datasets are used. Also used is a modified version of Ripley’s K function, which determines the average number of extreme events in a time period, to characterize temporal clustering on subseasonal time scales and to determine the statistical significance of the clustering. Significant clustering of regional-scale precipitation extremes is found on subseasonal time scales during the fall season.Fo...

Journal ArticleDOI
TL;DR: In this article, three sets of idealized, cloud-resolving simulations are performed to investigate the sensitivity of tropical cyclone (TC) structure and intensity to the height and depth of environmental vertical wind shear.
Abstract: Three sets of idealized, cloud-resolving simulations are performed to investigate the sensitivity of tropical cyclone (TC) structure and intensity to the height and depth of environmental vertical wind shear. In the first two sets of simulations, shear height and depth are varied independently; in the third set, orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis. Despite all simulations having the same westerly deep-layer (200–850 hPa) shear of 10 m s−1, different intensity and structural evolutions are observed, suggesting the deep-layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on TCs. In general, vertical wind shear that is shallower and lower in the troposphere is more destructive to model TCs because it tilts the TC vortex farther into the downshear-left quadrant. The vortices that tilt the most are unable to precess upshear and realign, resulting in their failure to intensify. Shear height appears to ...

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the performance of convective PBL parameterizations in the Weather Research and Forecasting (WRF) Model at subkilometer grid spacings, considering expectations for improvement in the resolved fields by using the fine meshes.
Abstract: Planetary boundary layer (PBL) parameterizations in mesoscale models have been developed for horizontal resolutions that cannot resolve any turbulence in the PBL, and evaluation of these parameterizations has been focused on profiles of mean and parameterized flux. Meanwhile, the recent increase in computing power has been allowing numerical weather prediction (NWP) at horizontal grid spacings finer than 1 km, at which kilometer-scale large eddies in the convective PBL are partly resolvable. This study evaluates the performance of convective PBL parameterizations in the Weather Research and Forecasting (WRF) Model at subkilometer grid spacings. The evaluation focuses on resolved turbulence statistics, considering expectations for improvement in the resolved fields by using the fine meshes. The parameterizations include four nonlocal schemes—Yonsei University (YSU), asymmetric convective model 2 (ACM2), eddy diffusivity mass flux (EDMF), and total energy mass flux (TEMF)—and one local scheme, the M...

Journal ArticleDOI
TL;DR: In this paper, the authors examined the meteorological background of this fatal flood and found that considerable filamentary transport of water vapor from the Indochina Peninsula to the Japanese islands occurred, forming a so-called atmospheric river (AR).
Abstract: Precipitation in excess of 100 mm h−1 in Hiroshima, Japan, on 19 August 2014, caused a flash flood that resulted in 75 deaths and destroyed 330 houses. This study examined the meteorological background of this fatal flood. During this event, considerable filamentary transport of water vapor from the Indochina Peninsula to the Japanese islands occurred, forming a so-called atmospheric river (AR). This AR had a deep structure with an amount of free tropospheric moisture comparable with that of the boundary layer. Furthermore, a cutoff low (COL), detached from the subtropical jet over the central Pacific, moved northwestward to the Japanese islands. Instability associated with the cold core of the COL and dynamical ascent induced in front of it, interacted with the free tropospheric moisture of the AR, which caused the considerable precipitation in Hiroshima. Moreover, the mountains of the Japanese islands played a role in localizing the precipitation in Hiroshima. These roles were separately evaluat...

Journal ArticleDOI
TL;DR: In this article, the authors calculated the observation error statistics for the Doppler radar radial winds (DRWs) that are assimilated into the Met Office high-resolution U.K. model (UKV) using a diagnostic that makes use of statistical averages of observation-minus-background and observationminus-analysis residuals.
Abstract: With the development of convection-permitting numerical weather prediction the efficient use of high-resolution observations in data assimilation is becoming increasingly important. The operational assimilation of these observations, such as Doppler radar radial winds (DRWs), is now common, although to avoid violating the assumption of uncorrelated observation errors the observation density is severely reduced. To improve the quantity of observations used and the impact that they have on the forecast requires the introduction of the full, potentially correlated, error statistics. In this work, observation error statistics are calculated for the DRWs that are assimilated into the Met Office high-resolution U.K. model (UKV) using a diagnostic that makes use of statistical averages of observation-minus-background and observation-minus-analysis residuals. This is the first in-depth study using the diagnostic to estimate both horizontal and along-beam observation error statistics. The new results obtai...

Journal ArticleDOI
TL;DR: In this article, the first multimodel study to estimate the predictability of a boreal sudden stratospheric warming (SSW) is performed using five NWP systems.
Abstract: The first multimodel study to estimate the predictability of a boreal sudden stratospheric warming (SSW) is performed using five NWP systems. During the 2012/13 boreal winter, anomalous upward propagating planetary wave activity was observed toward the end of December, which was followed by a rapid deceleration of the westerly circulation around 2 January 2013, and on 7 January 2013 the zonal-mean zonal wind at 60°N and 10 hPa reversed to easterly. This stratospheric dynamical activity was followed by an equatorward shift of the tropospheric jet stream and by a high pressure anomaly over the North Atlantic, which resulted in severe cold conditions in the United Kingdom and northern Europe. In most of the five models, the SSW event was predicted 10 days in advance. However, only some ensemble members in most of the models predicted weakening of westerly wind when the models were initialized 15 days in advance of the SSW. Further dynamical analysis of the SSW shows that this event was characterized ...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the role of sea-breeze passage in the collapse of urban heat island intensity during the nighttime. And they found that during the night time, the urban heat islands experienced frequent "collapses" (sudden decreases) around midnight during August 2011, while the region was experiencing an intense heat wave.
Abstract: When assessed using the difference between urban and rural air temperatures, the urban heat island (UHI) is most prominent during the nighttime. Typically, nocturnal UHI intensity is maintained throughout the night. The UHI intensity over Dallas–Fort Worth (DFW), Texas, however, experienced frequent “collapses” (sudden decreases) around midnight during August 2011, while the region was experiencing an intense heat wave. Observational and modeling studies were conducted to understand this unique phenomenon. Sea-breeze passage was found to be ultimately responsible for the collapses of the nocturnal UHI. Sea-breeze circulation developed along the coast of the Gulf of Mexico during the daytime. During the nighttime, the sea-breeze circulation was advected inland (as far as ~400 km) by the low-level jet-enhanced southerly flow, maintaining the characteristics of sea-breeze fronts, including the enhanced wind shear and vertical mixing. Ahead of the front, surface radiative cooling enhanced the near-sur...

Journal ArticleDOI
TL;DR: In this article, changes in the diurnal precipitation cycle as the Madden-Julian oscillation propagates through the Maritime Continent are investigated to explore the processes behind seaward-propagating precipitation northeast of New Guinea.
Abstract: Changes in the diurnal precipitation cycle as the Madden–Julian oscillation (MJO) propagates through the Maritime Continent are investigated to explore the processes behind seaward-propagating precipitation northeast of New Guinea. Satellite rainfall estimates from TRMM 3B42 and the Climate Prediction Center morphing technique (CMORPH) are combined with simulations from the Weather Research and Forecasting (WRF) Model with a horizontal resolution of 4 km.Comparison with 24-h rain gauge measurements indicates that both satellite estimates and the WRF Model exhibit systematic biases. Despite these biases, the changing patterns of offshore precipitation with the passage of the MJO show good consistency between satellite estimates and the WRF Model. In the few days prior to the main MJO envelope, light background wind, relatively clear skies, and an increasingly moist environment promote favorable conditions for the diurnal precipitation cycle.Two distinct processes are identified: 100–200 km from the...

Journal ArticleDOI
TL;DR: In this article, a synthesis of tornado observations across Europe between 1800 and 2014 is used to produce a pan-European climatology based on regional tornado-occurrence datasets and articles published in peer-reviewed journals, the evolution and major contributions to tornado databases for 30 European countries were analyzed.
Abstract: A synthesis of tornado observations across Europe between 1800 and 2014 is used to produce a pan-European climatology. Based on regional tornado-occurrence datasets and articles published in peer-reviewed journals, the evolution and the major contributions to tornado databases for 30 European countries were analyzed. Between 1800 and 2014, 9563 tornadoes were reported in Europe with an increase from 8 tornadoes per year between 1800 and 1850 to 242 tornadoes per year between 2000 and 2014. The majority of the reports came from northern, western, and southern Europe, and to a lesser extent from eastern Europe where tornado databases were developed after the 1990s. Tornadoes occur throughout the year with a maximum in June–August for most of Europe and in August–November for southern Europe. Tornadoes occur more frequently between 1300 and 1500 UTC over most of Europe and between 0900 and 1100 UTC over southern Europe. Where intensity was known, 74.7% of tornadoes were classified as F0 and F1, 24.5%...

Journal ArticleDOI
TL;DR: The HAILCAST hail growth model has been integrated into the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) Model to predict hail size at the ground as mentioned in this paper.
Abstract: The HAILCAST hail growth model has been integrated into the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) Model to predict hail size at the ground. Significant updates to the physics of the hail growth model are added, including variable hail density for both wet and dry growth regimes, an updraft multiplier that parameterizes advection of the hail embryo across an updraft, temperature-dependent ice collection efficiency, mass growth by vapor deposition or condensation, and an improved liquid water shedding threshold. Sample hail trajectories from three different updrafts are presented showing the effects of these physical updates. The updraft multiplier in particular improves the representation of the hail growth by not requiring a hail embryo to be locked in the center of an updraft until it grows large enough to fall. Five weeks of hail diameter forecasts are verified using a maximum expected size of hail (MESH) product. At points where WRF successfully forecasts c...

Journal ArticleDOI
TL;DR: In this paper, a relatively simple method to estimate tropical cyclone (TC) wind radii from routinely available information including storm data (location, motion, and intensity) and TC size is introduced.
Abstract: A relatively simple method to estimate tropical cyclone (TC) wind radii from routinely available information including storm data (location, motion, and intensity) and TC size is introduced. The method is based on a combination of techniques presented in previous works and makes an assumption that TCs are largely symmetric and that asymmetries are based solely on storm motion and location. The method was applied to TC size estimates from two sources: infrared satellite imagery and global model analyses. The validation shows that the methodology is comparable with other objective methods based on the error statistics. The technique has a variety of practical research and operational applications, some of which are also discussed.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the performance of the assimilation of total lightning data within a 3DVAR framework for the analysis and short-term forecast of the 24 May 2011 tornado outbreak using the Weather Research and Forecasting (WRF) Model at convection-allowing scales.
Abstract: This work evaluates the performance of the assimilation of total lightning data within a three-dimensional variational (3DVAR) framework for the analysis and short-term forecast of the 24 May 2011 tornado outbreak using the Weather Research and Forecasting (WRF) Model at convection-allowing scales. Between the lifted condensation level and a fixed upper height, pseudo-observations for water vapor mass first are created based on either the flash extent densities derived from Oklahoma Lightning Mapping Array data or the lightning source densities derived from the Earth Networks pulse data, and then assimilated by the 3DVAR system. Assimilation of radar data with 3DVAR and a cloud analysis algorithm (RAD) also are performed as a baseline for comparison and in tandem with lightning to evaluate the added value of this lightning data assimilation (LDA) method.Given a scenario wherein the control experiment without radar or lightning data assimilation fails to accurately initiate and forecast the observe...

Journal ArticleDOI
TL;DR: In this article, Lien et al. proposed to assimilate precipitation using the local ensemble transform Kalman filter (LETKF) with a Gaussian transformation technique and succeeded in improving the model forecasts in perfect-model observing system simulation experiments.
Abstract: Current methods of assimilation of precipitation into numerical weather prediction models are able to make the model precipitation become similar to the observed precipitation during the assimilation, but the model forecasts tend to return to their original solution after a few hours. To facilitate the precipitation assimilation, a logarithm transformation has been used in several past studies. Lien et al. proposed instead to assimilate precipitation using the local ensemble transform Kalman filter (LETKF) with a Gaussian transformation technique and succeeded in improving the model forecasts in perfect-model observing system simulation experiments (OSSEs).In this study, the method of Lien et al. is tested within a more realistic configuration: the TRMM Multisatellite Precipitation Analysis (TMPA) data are assimilated into a low-resolution version of the NCEP Global Forecast System (GFS). With guidance from a statistical study comparing the GFS model background precipitation and the TMPA data, som...

Journal ArticleDOI
TL;DR: Results from a 1-week impact test demonstrate that DFI is effective at reducing high-frequency noise in short-term operational forecasts as well as providing evidence of reduced errors in the 1-h mass and momentum fields.
Abstract: Because of limitations of variational and ensemble data assimilation schemes, resulting analysis fields exhibit some noise from imbalance in subsequent model forecasts. Controlling finescale noise is desirable in the NOAA’s Rapid Refresh (RAP) assimilation/forecast system, which uses an hourly data assimilation cycle. Hence, a digital filter initialization (DFI) capability has been introduced into the Weather Research and Forecasting Model and applied operationally in the RAP, for which hourly intermittent assimilation makes DFI essential. A brief overview of the DFI approach, its implementation, and some of its advantages are discussed. Results from a 1-week impact test with and without DFI demonstrate that DFI is effective at reducing high-frequency noise in short-term operational forecasts as well as providing evidence of reduced errors in the 1-h mass and momentum fields. However, DFI is also shown to reduce the strength of parameterized deep moist convection during the first hour of the forecast.