Showing papers in "Weather and Forecasting in 2013"
TL;DR: In this article, the authors evaluate forecasts of thermodynamic variables from five convection-allowing configurations of the Weather Research and Forecasting Model with the Advanced Research core (WRF-ARW).
Abstract: This study evaluates forecasts of thermodynamic variables from five convection-allowing configurations of the Weather Research and Forecasting Model (WRF) with the Advanced Research core (WRF-ARW). The forecasts vary only in their planetary boundary layer (PBL) scheme, including three “local” schemes [Mellor–Yamada–Janjic (MYJ), quasi-normal scale elimination (QNSE), and Mellor–Yamada–Nakanishi–Niino (MYNN)] and two schemes that include “nonlocal” mixing [the asymmetric cloud model version 2 (ACM2) and the Yonei University (YSU) scheme]. The forecasts are compared to springtime radiosonde observations upstream from deep convection to gain a better understanding of the thermodynamic characteristics of these PBL schemes in this regime. The morning PBLs are all too cool and dry despite having little bias in PBL depth (except for YSU). In the evening, the local schemes produce shallower PBLs that are often too shallow and too moist compared to nonlocal schemes. However, MYNN is nearly unbiased in PBL ...
166 citations
TL;DR: In this article, the performance of an advanced research version of the Weather Research and Forecasting Model (WRF) in predicting near-surface atmospheric temperature and wind conditions under various terrain and weather regimes is examined.
Abstract: The performance of an advanced research version of the Weather Research and Forecasting Model (WRF) in predicting near-surface atmospheric temperature and wind conditions under various terrain and weather regimes is examined. Verification of 2-m temperature and 10-m wind speed and direction against surface Mesonet observations is conducted. Three individual events under strong synoptic forcings (i.e., a frontal system, a low-level jet, and a persistent inversion) are first evaluated. It is found that the WRF model is able to reproduce these weather phenomena reasonably well. Forecasts of near-surface variables in flat terrain generally agree well with observations, but errors also occur, depending on the predictability of the lower-atmospheric boundary layer. In complex terrain, forecasts not only suffer from the model's inability to reproduce accurate atmospheric conditions in the lower atmosphere but also struggle with representative issues due to mismatches between the model and the actual terr...
131 citations
TL;DR: In this article, the ability of five operational ensemble forecast systems to accurately represent and predict atmospheric rivers (ARs) is evaluated as a function of lead time out to 10 days over the northeastern Pacific Ocean and west coast of North America.
Abstract: The ability of five operational ensemble forecast systems to accurately represent and predict atmospheric rivers (ARs) is evaluated as a function of lead time out to 10 days over the northeastern Pacific Ocean and west coast of North America. The study employs the recently developed Atmospheric River Detection Tool to compare the distinctive signature of ARs in integrated water vapor (IWV) fields from model forecasts and corresponding satellite-derived observations. The model forecast characteristics evaluated include the prediction of occurrence of ARs, the width of the IWV signature of ARs, their core strength as represented by the IWV content along the AR axis, and the occurrence and location of AR landfall. Analysis of three cool seasons shows that while the overall occurrence of ARs is well forecast out to a 10-day lead, forecasts of landfall occurrence are poorer, and skill degrades with increasing lead time. Average errors in the position of landfall are significant, increasing to over 800 ...
105 citations
TL;DR: In this article, the authors used the Weather Research and Forecasting Model (WRF) with 10-km horizontal grid spacing to explore improvements in wind speed forecasts at a typical wind turbine hub height (80 m).
Abstract: The Weather Research and Forecasting Model (WRF) with 10-km horizontal grid spacing was used to explore improvements in wind speed forecasts at a typical wind turbine hub height (80 m). An ensemble consisting of WRF model simulations with different planetary boundary layer (PBL) schemes showed little spread among the individual ensemble members for forecasting wind speed. A second configuration using three random perturbations of the Global Forecast System model produced more spread in the wind speed forecasts, but the ensemble mean possessed a higher mean absolute error (MAE). A third ensemble of different initialization times showed larger model spread, but model MAE was not compromised. In addition, postprocessing techniques such as training of the model for the day 2 forecast based on day 1 results and bias correction based on observed wind direction are examined. Ramp event forecasting was also explored. An event was considered to be a ramp event if the change in wind power was 50% or more of total capacity in either 4 or 2 h or less. This was approximated using a typical wind turbine power curve such that any wind speed increase or decrease of more than 3 m s 21 within the 6‐12 m s 21 window (where power production variesgreatly)in4 horlesswouldbeconsideredaramp.ModelMAE,climatologyoframpevents,andcauses were examined. All PBL schemes examined predicted fewer ramp events compared to the observations, and model forecasts for ramps in general were poor.
82 citations
TL;DR: In this paper, a strong relationship between the cumulative pathlengths of simulated rotating storms (measured using a three-dimensional object identification algorithm applied to forecast updraft helicity) and the cumulative paths of tornadoes was found.
Abstract: Examining forecasts from the Storm Scale Ensemble Forecast (SSEF) system run by the Center for Analysis and Prediction of Storms for the 2010 NOAA/Hazardous Weather Testbed Spring Forecasting Experiment, recent research diagnosed a strong relationship between the cumulative pathlengths of simulated rotating storms (measured using a three-dimensional object identification algorithm applied to forecast updraft helicity) and the cumulative pathlengths of tornadoes. This paper updates those results by including data from the 2011 SSEF system, and illustrates forecast examples from three major 2011 tornado outbreaks—16 and 27 April, and 24 May—as well as two forecast failure cases from June 2010. Finally, analysis updraft helicity (UH) from 27 April 2011 is computed using a three-dimensional variational data assimilation system to obtain 1.25-km grid-spacing analyses at 5-min intervals and compared to forecast UH from individual SSEF members.
81 citations
TL;DR: The Storm Prediction Center’s convective outlook slight risk areas are evaluated over the period from 1973 to 2011 using practically perfect forecasts to define the maximum values of the critical success index that a forecaster could reasonably achieve given the constraints of the forecast, as well as the minimum values that are considered the baseline for skillful forecasts.
Abstract: A method for determining baselines of skill for the purpose of the verification of rare-event forecasts is described and examples are presented to illustrate the sensitivity to parameter choices. These “practically perfect” forecasts are designed to resemble a forecast that is consistent with that which a forecaster would make given perfect knowledge of the events beforehand. The Storm Prediction Center’s convective outlook slight risk areas are evaluated over the period from 1973 to 2011 using practically perfect forecasts to define the maximum values of the critical success index that a forecaster could reasonably achieve given the constraints of the forecast, as well as the minimum values of the critical success index that are considered the baseline for skillful forecasts. Based on these upper and lower bounds, the relative skill of convective outlook areas shows little to no skill until the mid-1990s, after which this value increases steadily. The annual frequency of skillful daily forecasts ...
79 citations
TL;DR: In this article, the use of tornadic debris signature (TDS) parameters to estimate tornado damage severity using KOUN, polarimetric radar data (polarimetric version of the Weather Surveillance Radar-1988 Doppler radar).
Abstract: This study investigates the use of tornadic debris signature (TDS) parameters to estimate tornado damage severity using Norman, Oklahoma (KOUN), polarimetric radar data (polarimetric version of the Weather Surveillance Radar-1988 Doppler radar). Several TDS parameters are examined, including parameters based on the 10th or 90th percentiles of polarimetric variables (lowest tilt TDS parameters) and TDS parameters based on the TDS volumetric coverage (spatial TDS parameters). Two highly detailed National Weather Service (NWS) damage surveys are compared to TDS parameters. The TDS parameters tend to be correlated with the enhanced Fujita scale (EF) rating. The 90th percentile reflectivity, TDS height, and TDS volume increase during tornado intensification and decrease during tornado dissipation. For 14 tornado cases, the maximum or minimum TDS parameter values are compared to the tornado’s EF rating. For tornadoes with a higher EF rating, higher maximum values of the 90th percentile ZHH, TDS height, ...
79 citations
TL;DR: In this article, the finescale three-dimensional structure and evolution of the near-surface boundary layer of a TBL is mapped for the first time, and a mobile mesonet anemometer measured winds at 3.5 m AGL in the core flow region.
Abstract: The finescale three-dimensional structure and evolution of the near-surface boundary layer of a tornado (TBL) is mapped for the first time. The multibeam Rapid-Scan Doppler on Wheels (RSDOW) collected data at several vertical levels, as low as 4, 6, 10, 12, 14, and 17 m above ground level (AGL), contemporaneously at 7-s intervals for several minutes in a tornado near Russell, Kansas, on 25 May 2012. Additionally, a mobile mesonet anemometer measured winds at 3.5 m AGL in the core flow region. The radar, anemometer, and ground-based velocity-track display (GBVTD) analyses reveal the peak wind intensity is very near the surface at ~5 m AGL, about 15% higher than at 10 m AGL and 25% higher than at ~40 m AGL. GBVTD analyses resolve a downdraft within the radius of maximum winds (RMW), which decreased in magnitude when varying estimates for debris centrifuging are included. Much of the inflow (from −1 to −7 m s−1) is at or below 10–14 m AGL, much shallower than reported previously. Surface outflow prec...
74 citations
TL;DR: A variety of vortex configurations observed at finescale with Doppler On Wheels (DOW) radars in and near the hook echoes of supercell thunderstorms are described in this article.
Abstract: A variety of vortex configurations observed at finescale with Doppler On Wheels (DOW) radars in and near the hook echoes of supercell thunderstorms are described. These include marginal/weak tornadoes, often with no documented condensation funnels, debris rings, or low-reflectivity eyes; multiple-vortex mesocyclones; multiple simultaneous tornadoes; satellite tornadoes; cyclonic–anticyclonic tornado pairs; multiple vortices within other multiple vortices; tornadoes with quasi-concentric multiple wind field maxima; lines of vortices outside tornadoes; and horizontal vortices. The kinematic structures of these different phenomena are documented and compared. The process of multiple vortex circulations evolving from and into tornadoes is documented. DOW observations suggest that there is no clear spatial-scale separation between multiple-vortex tornadoes and larger multiple-vortex circulations.These different vortex configurations motivate a refined definition of what constitutes a tornado, excluding...
72 citations
TL;DR: In this article, the authors analyzed TC genesis forecasts from five global models [Environment Canada's Global Environment Multiscale Model (CMC), the European Centre for Medium-Range Weather Forecasts (ECMWF), the Global Forecast System (GFS), the Navy Operational Global Atmospheric Prediction System (NOGAPS), and the Met Office global model (UKMET)] over several seasons in the North Atlantic basin.
Abstract: Tropical cyclone (TC) forecasts rely heavily on output from global numerical models. While considerable research has investigated the skill of various models with respect to track and intensity, few studies have considered how well global models forecast TC genesis in the North Atlanticbasin. This paper analyzes TC genesis forecasts from five global models [Environment Canada’s Global Environment Multiscale Model (CMC), the European Centre for Medium-Range Weather Forecasts (ECMWF) global model, the Global Forecast System (GFS), the Navy Operational Global Atmospheric Prediction System (NOGAPS), and the Met Office global model (UKMET)] over several seasons in the North Atlantic basin. Identifying TCs in the model is based on a combination of methods used previously in the literature and newly defined objective criteria. All modelindicated TCs are classified as a hit, false alarm, early genesis, or late genesis event. Missed events also are considered. Results show that the models’ ability to predict TC genesis varies in time and space. Conditional probabilities when a model predicts genesis and more traditional performance metrics (e.g., critical success index) are calculated. The models are ranked among each other, and results show that the best-performing model varies from year to year. A spatial analysis of each model identifies preferred regions for genesis, and a temporal analysis indicates that model performance expectedly decreases as forecast hour (lead time) increases. Consensus forecasts show that the probability of genesis noticeably increases when multiple models predict the same genesis event. Overall, this study provides a climatology of objectively identified TC genesis forecasts in global models. The resulting verification statistics can be used operationally to help refine deterministic and probabilistic TC genesis forecasts and potentially improve the models examined.
72 citations
TL;DR: In this paper, the authors classify mesoscale convective systems (MCSs) over central east China into seven morphologies: convective lines with no stratiform precipitation (NS), trailing stratiform rainfall (TS), leading stratiform rain (LS), parallel stratiform Rain (PS), bow echoes (BE), and embedded lines (EL).
Abstract: Composite reflectivity Doppler radar data from June to September of 2007–2010 were used to classify mesoscale convective systems (MCSs) over central east China into seven morphologies. The morphologies included one nonlinear mode (NL) and six linear modes: convective lines with no stratiform precipitation (NS), trailing stratiform precipitation (TS), leading stratiform precipitation (LS), parallel stratiform precipitation (PS), bow echoes (BE), and embedded lines (EL). Nonlinear and linear systems composed 44.7% and 55.3% of total MCSs, respectively, but there was no primary linear mode. All MCS morphologies attained their peak occurrence in July, except BE systems, which peaked in June. On average, TS and PS modes had relatively longer lifespans than did other modes.Significant differences in MCS-produced severe weather existed between dry and moist environments. High winds and hail events were mainly observed in dry environments, and in contrast, short-term intense precipitation occurred more fr...
TL;DR: In this paper, a set of mesoscale convective systems (MCSs) were simulated using the Weather Research and Forecasting model with 3-km grid spacing to investigate the skill at predicting convective initiation and upscale evolution into an MCS.
Abstract: A set of mesoscale convective systems (MCSs) was simulated using the Weather Research and Forecasting model with 3-km grid spacing to investigate the skill at predicting convective initiation and upscale evolution into an MCS. Precipitation was verified using equitable threat scores (ETSs), the neighborhood-based fractions skill score (FSS), and the Method of Object-Based Diagnostic Evaluation. An illustrative case study more closely examines the strong influence that smaller-scale forcing features had on convective initiation.Initiation errors for the 36 cases were in the south-southwest direction on average, with a mean absolute displacement error of 105 km. No systematic temporal error existed, as the errors were approximately normally distributed. Despite earlier findings that quantitative precipitation forecast skill in convection-parameterizing simulations is a function of the strength of large-scale forcing, this relationship was not present in the present study for convective initiation. H...
TL;DR: In this article, two extreme heat events impacting the New York City (NYC), New York metropolitan region during 7-10 June and 21-24 July 2011 are examined in detail using a combination of models and observations.
Abstract: Two extreme heat events impacting the New York City (NYC), New York, metropolitan region during 7–10 June and 21–24 July 2011 are examined in detail using a combination of models and observations. The U.S. Navy's Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) produces real-time forecasts across the region on a 1-km resolution grid and employs an urban canopy parameterization to account for the influence of the city on the atmosphere. Forecasts from the National Weather Service's 12-km resolution North American Mesoscale (NAM) implementation of the Weather Research and Forecasting (WRF) model are also examined. The accuracy of the forecasts is evaluated using a land- and coastline-based observation network. Observed temperatures reached 39°C or more at central urban sites over several days and remained high overnight due to urban heat island (UHI) effects, with a typical nighttime urban–rural temperature difference of 4°–5°C. Examining model performance broadly over both heat events ...
TL;DR: In this article, a real-time, weather-adaptive three-dimensional variational data assimilation (3DVAR) system has been adapted for the NOAA Warn-on-Forecast (WoF) project to incorporate all available radar observations within a moveable analysis domain.
Abstract: A real-time, weather-adaptive three-dimensional variational data assimilation (3DVAR) system has been adapted for the NOAA Warn-on-Forecast (WoF) project to incorporate all available radar observations within a moveable analysis domain. The key features of the system include 1) incorporating radar observations from multiple Weather Surveillance Radars-1988 Doppler (WSR-88Ds) with NCEP forecast products as a background state, 2) the ability to automatically detect and analyze severe local hazardous weather events at 1-km horizontal resolution every 5 min in real time based on the current weather situation, and 3) the identification of strong circulation patterns embedded in thunderstorms. Although still in the early development stage, the system performed very well within the NOAA's Hazardous Weather Testbed (HWT) Experimental Warning Program during preliminary testing in spring 2010 when many severe weather events were successfully detected and analyzed. This study represents a first step in the a...
TL;DR: The location and intensity of mesocyclone circulations can be tracked in real time by accumulating azimuthal shear values over time at every location of a uniform spatial grid as discussed by the authors.
Abstract: The location and intensity of mesocyclone circulations can be tracked in real time by accumulating azimuthal shear values over time at every location of a uniform spatial grid. Azimuthal shear at low (0–3 km AGL) and midlevels (3–6 km AGL) of the atmosphere is computed in a noise-tolerant manner by fitting the Doppler velocity observations in the neighborhood of a pulse volume to a plane and finding the slope of that plane. Rotation tracks created in this manner are contaminated by nonmeteorological signatures caused by poor velocity dealiasing, ground clutter, radar test patterns, and spurious shear values. To improve the quality of these fields for real-time use and for an accumulated multiyear climatology, new dealiasing strategies, data thresholding, and multiple hypothesis tracking (MHT) techniques have been implemented. These techniques remove nearly all nonmeteorological contaminants, resulting in much clearer rotation tracks that appear to match mesocyclone paths and intensities closely.
TL;DR: In this paper, the development of a dynamical model seasonal prediction service for island nations in the tropical South Pacific is described, where the forecast model is the Australian Bureau of Meteorology's Predictive Ocean-Atmosphere Model for Australia (POAMA), a dynamic seasonal forecast system, using a hindcast set for the period 1982-2006, POAMA is shown to provide skillful forecasts of El Nino and La Nina many months in advance and it also provides good predictions of rainfall throughout the tropical Pacific region.
Abstract: The development of a dynamical model seasonal prediction service for island nations in the tropical South Pacific is described. The forecast model is the Australian Bureau of Meteorology's Predictive Ocean–Atmosphere Model for Australia (POAMA), a dynamical seasonal forecast system. Using a hindcast set for the period 1982–2006, POAMA is shown to provide skillful forecasts of El Nino and La Nina many months in advance and, because the model faithfully simulates the spatial and temporal variability of rainfall associated with displacements of the southern Pacific convergence zone (SPCZ) and ITCZ during La Nina and El Nino, it also provides good predictions of rainfall throughout the tropical Pacific region. The availability of seasonal forecasts from POAMA should be beneficial to Pacific island countries for the production of regional climate outlooks across the region.
TL;DR: The Monte Carlo (MC) method is used to estimate the probabilities of 34-, 50-, and 64-kt (1 kt = 0.51 m s−1) winds at multiple time periods through 120 h as mentioned in this paper.
Abstract: The National Hurricane Center Hurricane Probability Program, which estimated the probability of a tropical cyclone passing within a specific distance of a selected set of coastal stations, was replaced by the more general Tropical Cyclone Surface Wind Speed Probabilities in 2006. A Monte Carlo (MC) method is used to estimate the probabilities of 34-, 50-, and 64-kt (1 kt = 0.51 m s−1) winds at multiple time periods through 120 h. Versions of the MC model are available for the Atlantic, the combined eastern and central North Pacific, and the western North Pacific. This paper presents a verification of the operational runs of the MC model for the period 2008–11 and describes model improvements since 2007. The most significant change occurred in 2010 with the inclusion of a method to take into account the uncertainty of the track forecasts on a case-by-case basis, which is estimated from the spread of a dynamical model ensemble and other parameters. The previous version represented the track uncertai...
TL;DR: In this article, three hurricane intensity models that were operational for the duration of the five hurricane seasons between 2006 and 2010, as well as the National Hurricane Center official forecast (OFCL), are evaluated for 24-, 48-, and 72-h forecasts in the Atlantic Ocean.
Abstract: Prior knowledge of the performance of a tropical cyclone intensity forecast holds the potential to increase the value of forecasts for end users. The values of certain dynamical parameters, such as storm speed, latitude, current intensity, potential intensity, wind shear magnitude, and direction of the shear vector, are shown to be related to the error of an individual model forecast. The varying success of each model in the different environmental conditions represents a source of additional information on the reliability of an individual forecast beyond average forecast error.Three hurricane intensity models that were operational for the duration of the five hurricane seasons between 2006 and 2010, as well as the National Hurricane Center official forecast (OFCL), are evaluated for 24-, 48-, and 72-h forecasts in the Atlantic Ocean. The performance of each model is assessed by computing the mean absolute error, bias, and percent skill relative to a benchmark model. The synoptic variables are bin...
TL;DR: The characteristics of tropical cyclone vertical wind profiles and their associated wind speed peaks below 1.5 km were examined through the use of a large number of GPS dropwindsondes (GPS sondes) and radar-derived velocity-azimuth display (VAD) profiles.
Abstract: The characteristics of tropical cyclone vertical wind profiles and their associated wind speed peaks below 1.5 km were examined through the use of a large number of GPS dropwindsondes (GPS sondes) and radar-derived velocity–azimuth display (VAD) profiles. Composite wind profiles were generated to document the mean structure of tropical cyclone vertical wind profiles and their changes with storm-relative position. Composite profiles were observed to change as the radius decreased inward toward the radius of maximum winds. Profiles also varied between three azimuthal sectors. At landfall, wind profiles exhibited changes with radial distance and differences were observed between those within offshore and onshore flow regimes. The observations support a general reduction in boundary layer depth with decreasing radial distance. Wind profiles with peaks at low altitudes were typically confined to radii less than 60 km, near and radially inward from the radius of maximum winds. Wind speed maxima, when sc...
TL;DR: In this article, the sensitivity of a case study bow-echo simulation to eight different microphysical schemes in the Weather Research and Forecasting model was tested, with a focus on graupel parameter characteristics.
Abstract: The sensitivity of a case study bow-echo simulation to eight different microphysical schemes in the Weather Research and Forecasting model was tested, with a focus on graupel parameter characteristics The graupel parameter in one scheme was modified to have a larger mean size and faster fall speed to represent hail (“hail like”) The goal of the study was to measure the sensitivity of five parameters that are important to operational forecasters to graupel properties: timing of bowing development, system speed, wind gusts, system areal coverage, and accumulated precipitationThe time each system initiated bowing varied by as much as 105 min Simulations containing graupel with smaller mean size and slower fall speed (“graupel like”) bowed earlier due to increased microphysical cooling and stronger cold pools These same systems had reduced precipitation efficiency, producing a peak storm-total accumulation of 36 mm, compared to a hail-like peak value of 237 mm, and observed a peak value of 53 mm
TL;DR: The authors used both traditional and newer verification methods to evaluate two 4-km grid-spacing weather Research and Forecasting Model (WRF) forecasts: a cold start forecast that uses the 12-km North American Mesoscale Model (NAM) analysis and forecast cycle to derive the initial and boundary conditions (C0) and a hot start forecast adding radar data into the initial conditions using a three-dimensional variational data assimilation (3DVAR)/cloud analysis technique (CN).
Abstract: This study uses both traditional and newer verification methods to evaluate two 4-km grid-spacing Weather Research and Forecasting Model (WRF) forecasts: a “cold start” forecast that uses the 12-km North American Mesoscale Model (NAM) analysis and forecast cycle to derive the initial and boundary conditions (C0) and a “hot start” forecast that adds radar data into the initial conditions using a three-dimensional variational data assimilation (3DVAR)/cloud analysis technique (CN). These forecasts were evaluated as part of 2009 and 2010 NOAA Hazardous Weather Test Bed (HWT) Spring Forecasting Experiments. The Spring Forecasting Experiment participants noted that the skill of CN’s explicit forecasts of convection estimated by some traditional objective metrics often seemed large compared to the subjectively determined skill. The Gilbert skill score (GSS) reveals CN scores higher than C0 at lower thresholds likely due to CN having higher-frequency biases than C0, but the difference is negligible at hi...
TL;DR: In this paper, the authors evaluated 2 years of National Weather Service (NWS) tornado warnings, verification reports, and radar-derived convective modes to appraise the ability of the NWS to warn across a variety of convective morphologies and environmental conditions.
Abstract: The ability to provide advanced warning on tornadoes can be impacted by variations in storm mode. This research evaluates 2 yr of National Weather Service (NWS) tornado warnings, verification reports, and radar-derived convective modes to appraise the ability of the NWS to warn across a variety of convective modes and environmental conditions. Several specific hypotheses are considered: (i) supercell morphologies are the easiest convective modes to warn for tornadoes and yield the greatest lead times, while tornadoes from more linear, nonsupercell convective modes, such as quasi-linear convective systems, are more difficult to warn for; (ii) parameters such as tornado distance from radar, population density, and tornado intensity (F scale) introduce significant and complex variability into warning statistics as a function of storm mode; and (iii) tornadoes from stronger storms, as measured by their mesocyclone strength (when present), convective available potential energy (CAPE), vertical wind she...
TL;DR: The authors applied ensemble sensitivity analysis to a U.S. East Coast snowstorm on 26-28 December 2010 in a way that may be beneficial for an operational forecaster to better understand the forecast uncertainties.
Abstract: This paper applies ensemble sensitivity analysis to a U.S. East Coast snowstorm on 26–28 December 2010 in a way that may be beneficial for an operational forecaster to better understand the forecast uncertainties. Sensitivity using the principal components of the leading empirical orthogonal functions (EOFs) on the 50-member European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble identifies the sensitive regions and weather systems at earlier times associated with the cyclone intensity and track uncertainty separately. The 5.5-day forecast cyclone intensity uncertainty in the ECMWF ensemble is associated with trough and ridge systems over the northeastern Pacific and central United States, respectively, while the track uncertainty is associated with a short-wave trough over the southern Great Plains. Sensitivity based on the ensemble mean sea level pressure difference between two run cycles also suggests that the track's shift between the two cycles is linked with the initial errors in...
TL;DR: In this article, a case study was selected of an intense cyclone over the North Atlantic Ocean during 7-8 December 2005 that possessed a sting jet detected from the NASA Quick Scatterometer (QuikSCAT).
Abstract: Sting jets, or surface wind maxima at the end of bent-back fronts in Shapiro–Keyser cyclones, are one cause of strong winds in extratropical cyclones. Although previous studies identified the release of conditional symmetric instability as a cause of sting jets, the mechanism to initiate its release remains unidentified. To identify this mechanism, a case study was selected of an intense cyclone over the North Atlantic Ocean during 7–8 December 2005 that possessed a sting jet detected from the NASA Quick Scatterometer (QuikSCAT). A couplet of Petterssen frontogenesis and frontolysis occurred along the bent-back front. The direct circulation associated with the frontogenesis led to ascent within the cyclonically turning portion of the warm conveyor belt, contributing to the comma-cloud head. When the bent-back front became frontolytic, an indirect circulation associated with the frontolysis, in conjunction with alongfront cold advection, led to descent within and on the warm side of the front, brin...
TL;DR: In this article, an operational inner-shelf wave forecasting system was implemented for the Oregon and southwest Washington coast in the U.S. Pacific Northwest (PNW), where a series of nested grids with increasing resolution were implemented to achieve a 30-arc-second resolution at the shelf level.
Abstract: An operational inner-shelf wave forecasting system was implemented for the Oregon and southwest Washington coast in the U.S. Pacific Northwest (PNW). High-resolution wave forecasts are useful for navigational planning, identifying wave energy resources, providing information for site-specific coastal flood models, and having an informed recreational beach user group, among other things. This forecasting model is run once a day at 1200 UTC producing 84-h forecasts. A series of nested grids with increasing resolution shoreward are implemented to achieve a 30-arc-second resolution at the shelf level. This resolution is significantly higher than what the current operational models produce, thus improving the ability to quantify the alongshore variations of wave conditions on the PNW coast. Normalized root-mean-squared errors in significant wave height and mean wave period range from 0.13 to 0.24 and from 0.13 to 0.26, respectively. Visualization of the forecasts is made available online and is present...
TL;DR: In this article, the authors employed large-scale reanalysis data to diagnose SAW through synoptic-scale dynamic and thermodynamic factors using mean sea level pressure gradient and lower-tropospheric temperature advection, respectively.
Abstract: Santa Ana winds (SAW) are among the most notorious fire-weather conditions in the United States and are implicated in wildfire and wind hazards in Southern California. This study employs large-scale reanalysis data to diagnose SAW through synoptic-scale dynamic and thermodynamic factors using mean sea level pressure gradient and lower-tropospheric temperature advection, respectively. A two-parameter threshold model of these factors exhibits skill in identifying surface-based characteristics of SAW featuring strong offshore winds and extreme fire weather as viewed through the Fosberg fire weather index across Remote Automated Weather Stations in southwestern California. These results suggest that a strong northeastward gradient in mean sea level pressure aligned with strong cold-air advection in the lower troposphere provide a simple, yet effective, means of diagnosing SAW from synoptic-scale reanalysis. This objective method may be useful for medium- to extended-range forecasting when mesoscale mo...
TL;DR: It is found that variance in SOM nodes is reduced compared to the overall dataset, indicating that this is a viable classification method and simple skill scores are computed for each SOM to evaluate the relative potential of each variable for future development as a method of probabilistic forecasting.
Abstract: The self-organizing map (SOM) statistical technique is applied to vertical profiles of thermodynamic and kinematic parameters from a Rapid Update Cycle-2 (RUC-2) proximity sounding dataset with the goal of better distinguishing and predicting supercell and tornadic environments. An SOM is a topologically ordered mapping of input data onto a two-dimensional array of nodes that can be used to classify large datasets into meaningful clusters. The relative ability of SOMs derived from each parameter to separate soundings in a way that is useful in discriminating between storm type, location, and time of year is discussed. Sensitivity to SOM configuration is also explored. Simple skill scores are computed for each SOM to evaluate the relative potential of each variable for future development as a method of probabilistic forecasting. It is found that variance in SOM nodes is reduced compared to the overall dataset, indicating that this is a viable classification method. SOMs of profiles of wind-derived ...
TL;DR: In this article, the echo top is computed by interpolating between elevation scans that bracket the echo-top threshold, which results in smaller errors when higher-elevation scans are available.
Abstract: It is demonstrated that the traditional method, in widespread use on Next Generation Weather Radar (NEXRAD) and other radar systems, to compute echo-top heights results in both under- and overestimates. It is proposed that echo tops be computed by interpolating between elevation scans that bracket the echo-top threshold. The traditional and proposed techniques are evaluated using simulated radar samples of a modeled thunderstorm and by sampling a high-resolution range‐height indicator (RHI) of a real thunderstorm. It is shown that the proposed method results in smaller errors when higher-elevation scans are available.
TL;DR: New features introduced in WAVEWATCH III have allowed the operational model to increase spatial resolution and extend the global domain closer to the North Pole, while at the same time optimizing the computational cost.
Abstract: A new operational wave forecasting system has been implemented at the National Centers for Environmental Prediction (NCEP) using the third public release of WAVEWATCH III. The new system uses a mosaic of grids with two-way nesting in a single model. This global system replaces a previous operational wave modeling suite (based on the second release of WAVEWATCH III). The new forecast system consists of nine grids at different resolutions to provide the National Weather Service (NWS) and NCEP centers with model guidance of suitable resolution for all areas where they have the responsibility of providing gridded forecast products. New features introduced in WAVEWATCH III, such as two-way nesting between grids and carving out selected areas of the computational domain, have allowed the operational model to increase spatial resolution and extend the global domain closer to the North Pole, while at the same time optimizing the computational cost. A spectral partitioning algorithm has been implemented to...
TL;DR: In this paper, a severe thunderstorm wind gust climatology spanning 2003-09 for the contiguous United States is developed using measured Automated Surface Observing System (ASOS) and Automated Weather Observating System (AWOS) wind gusts.
Abstract: A severe thunderstorm wind gust climatology spanning 2003–09 for the contiguous United States is developed using measured Automated Surface Observing System (ASOS) and Automated Weather Observing System (AWOS) wind gusts. Archived severe report information from the National Climatic Data Center publication Storm Data and single-site volumetric radar data are used to identify severe wind gust observations [≥50 kt (25.7 m s−1)] associated with thunderstorms and to classify the convective mode of the storms. The measured severe wind gust distribution, comprising only 2% of all severe gusts, is examined with respect to radar-based convective modes. The convective mode scheme presented herein focuses on three primary radar-based storm categories: supercell, quasi-linear convective systems (QLCSs), and disorganized. Measured severe gust frequency revealed distinct spatial patterns, where the high plains received the greatest number of gusts and occurred most often in the late spring and summer months. S...