Shakira D. Stackhouse, Stephanie E. Zick, C. Matyas, Kimberly M. Wood, A. Hazelton, G. Alaka
{"title":"Evaluation of Experimental High-Resolution Model Forecasts of Tropical Cyclone Precipitation using Object-Based Metrics","authors":"Shakira D. Stackhouse, Stephanie E. Zick, C. Matyas, Kimberly M. Wood, A. Hazelton, G. Alaka","doi":"10.1175/waf-d-22-0223.1","DOIUrl":"https://doi.org/10.1175/waf-d-22-0223.1","url":null,"abstract":"\u0000Tropical cyclone (TC) precipitation poses serious hazards including freshwater flooding. High-resolution hurricane models predict the location and intensity of TC rainfall, which can influence local evacuation and preparedness policies. This study evaluates 0–72-hour precipitation forecasts from two experimental models, the Hurricane Analysis and Forecast System (HAFS) model and the Basin-scale Hurricane Weather Research and Forecasting (HWRF-B) model, for 2020 North Atlantic landfalling TCs. We use an object-based method that quantifies the shape and size of the forecast and observed precipitation. Precipitation objects are then compared for light, moderate, and heavy precipitation using spatial metrics (e.g., area, perimeter, elongation). Results show that both models forecast precipitation that is too connected, too close to the TC center, too enclosed around the TC center. Collectively, these spatial biases suggest that the model forecasts are too intense even though there is a negative intensity bias for both models, indicating there may be an inconsistency between the precipitation configuration and the maximum sustained winds in the model forecasts. The HAFS model struggles with forecasting stratiform versus convective precipitation and with the representation of lighter (stratiform) precipitation during the first six hours after initialization. No such spin-up issues are seen in the HWRF-B forecasts, which instead exhibit systematic biases at all lead times and systematic issues across all rain rate thresholds. Future work will investigate spin-up issues in the HAFS model forecast and how the microphysics parameterization affects the representation of precipitation in both models.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48292362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Using a reanalysis driven land surface model for initialization of a numerical weather prediction system","authors":"Å. Bakketun, Jostein Blyverket, Malte Müller","doi":"10.1175/waf-d-22-0184.1","DOIUrl":"https://doi.org/10.1175/waf-d-22-0184.1","url":null,"abstract":"\u0000Realistic initialization of the land surface is important to produce accurate NWP forecasts. Therefore, making use of available observations is essential when estimating the surface state. In this work, sequential land surface data assimilation of soil variables is replaced with an offline cycling method. In order to obtain a best possible initial state for the lower boundary of the NWP system, the land surface model is re-run between forecasts with an analyzed atmospheric forcing. We found a relative reduction of 2 meter temperature root mean square errors and mean errors of 6% and 12% respectively, and 4.5% and 11% for 2 meter specific humidity. During a convective event, the system was able to produce useful (fractions skill score greater than the uniform forecast) forecasts (above 30 mm per 12 hour) down to a 100 km length scale where the reference failed to do so below 200 km. The different precipitation forcing caused differences in soil moisture fields that persisted for several weeks and consequently impacted the surface fluxes of heat and moisture and further the forecasts of screen level parameters. The experiments also indicate diurnal and weather dependent variation of the forecast errors that give valuable insight on the role of initial land surface conditions and the land-atmosphere interactions in southern Scandinavia.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41922811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Revisiting Environmental Wind and Moisture Calculations in the Context of Tropical Cyclone Intensification","authors":"Samantha Nebylitsa, S. Majumdar, D. Nolan","doi":"10.1175/waf-d-23-0045.1","DOIUrl":"https://doi.org/10.1175/waf-d-23-0045.1","url":null,"abstract":"\u0000Deep-layer vertical wind shear and mid-tropospheric relative humidity (RH) are explored in and around environments of all intensifying North Atlantic tropical cyclones (TCs) between 1980–2021 using reanalysis data. Shear and RH are averaged within the standard environmental annulus of 200–800-km, along with a 100–600-km annulus, and a 0–250-km radius to represent the inner core and TC itself. Distributions of shear and RH at onset along with a time series of evolution from 48 h prior to and after onset of three different intensification rates: slight (5–10 kt 24 h−1), moderate (15–25 kt 24 h−1), and rapid (≥ 30 kt 24 h−1), are analyzed. RH is also investigated within different shear environments and in shear-relative quadrants around the storm. While low shear and high RH are found to be most favorable for rapid intensification (RI), there is still a significant probability that RI will occur within less favorable environments. RI cases decrease in 850–200-hPa shear in the 24 h leading up to RI, whereas slight intensification cases increase, which is evident in both the standard shear and a shallower layer at 48 h prior to onset. The inner-core RH for RI increases prior to onset whereas it decreases in the environments. RH analysis by shear-relative quadrants demonstrates the importance of moistening in the upshear-right quadrant before onset of RI. Results indicate the potential value of multiple annuli and shear-relative analysis for moisture and a shallower, 925–400-hPa layer for shear in RI forecasting.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43785010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Evaluation of Ensemble Snowfall Forecasts using Operationally-used Snow-to-Liquid Ratios in Five Winter Storms","authors":"Andrew A. Rosenow, H. Reeves, Daniel D. Tripp","doi":"10.1175/waf-d-22-0202.1","DOIUrl":"https://doi.org/10.1175/waf-d-22-0202.1","url":null,"abstract":"\u0000The prediction of snow accumulation remains a forecasting challenge. While the adoption of ensemble numerical weather prediction has enabled the development of probabilistic guidance, the challenges associated with snow accumulation, particularly snow-to-liquid ratio (SLR), still remain when building snow-accumulation tools. In operations, SLR is generally assumed to either fit a simple mathematical relationship or conform to a historic average. In this paper, the impacts of the choice of SLR on ensemble snow forecasts are tested.\u0000Ensemble forecasts from the nine-member High Resolution Rapid Refresh Ensemble (HRRRE) were used to create 24-hour snowfall forecasts for five snowfall events associated with winter cyclones. These snowfall forecasts were derived from model liquid precipitation forecasts using five SLR relationships. These forecasts were evaluated against daily new snowfall observations from the Community Collaborative Rain Hail and Snow network. The results of this analysis show that the forecast error associated with individual members is similar to the error associated with choice of SLR. The SLR with the lowest forecast error showed regional agreement across nearby observations. This suggests that, while there is no one SLR that works best everywhere, it may be possible to improve ensemble snow forecasts if regions where SLRs perform best can be determined ahead of time. The implications of these findings for future ensemble snowfall tools will be discussed.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46686448","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Comparing Polarimetric Signatures of Proximate Pretornadic and Non-Tornadic Supercells in Similar Environments","authors":"Devon J. Healey, Matthew S. Van Den Broeke","doi":"10.1175/waf-d-23-0013.1","DOIUrl":"https://doi.org/10.1175/waf-d-23-0013.1","url":null,"abstract":"\u0000While prior research has shown that characteristics of the supercell environment can indicate the likelihood of tornadogenesis, it is common for tornadic and non-tornadic supercells to coexist in seemingly similar environments. Thus, some small-scale factors must support tornadogenesis in some supercells and not in others. In this study we examined polarimetric radar signatures of proximate pretornadic and non-tornadic supercells in seemingly similar environments to determine if these radar signatures can indicate which proximate supercells are pretornadic and which are non-tornadic. We gathered a collection of proximity supercell groups and developed a method to quantify environmental similarity between storms. Using this method, we selected pretornadic – non-tornadic supercell pairs in close proximity in space and time having the most similar environments. These pairs were run through an automated tracking algorithm which quantifies polarimetric signatures in each supercell. Supercells with larger differential reflectivity (ZDR) column areas were more likely to become tornadic within the next 30 minutes compared to neighboring supercells with smaller ZDR column areas. In about two-thirds of pairs, the pretornadic supercell had a larger ZDR column area than the non-tornadic supercell prior to its maximum low-level rotation, which is consistent with much prior work. ZDR arcs could not discriminate between pretornadic and non-tornadic supercells, and hailfall area was larger in pretornadic supercells. The separation distance between the specific differential phase (KDP) foot and the ZDR arc was larger in pretornadic supercells yet was a limited result due to the small sample size used for comparison.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46544406","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Biases and Skill of Four Two-Moment Bulk Microphysics Schemes in Convection-Allowing Forecasts for the 2018 Hazardous Weather Testbed Spring Forecasting Experiment Period","authors":"M. Johnson, M. Xue, Youngsun Jung","doi":"10.1175/waf-d-22-0171.1","DOIUrl":"https://doi.org/10.1175/waf-d-22-0171.1","url":null,"abstract":"\u0000A proof-of-concept systematic evaluation of convective hazards is applied to short-term (1-6 h) forecasts using the Morrison, National Severe Storms Laboratory (NSSL), Predicted Particle Properties (P3), and Thompson two-moment microphysics schemes for the 2018 NOAA Hazardous Weather Testbed Spring Forecasting Experiment (HWT SFE) period (hereafter “MORR”, “NSSL”, “P3”, and “THOM” experiments, respectively). Four convective line cases are highlighted to elaborate on relative experiment biases/skill. Composite reflectivity and 1-h accumulated precipitation are examined to determine storm coverage/precipitation biases/skill utilizing point-based verification with a neighborhood. Simulated 1-6 km updraft helicity and observed 3-6 km azimuthal shear, and MESH are examined to consider simulated rotation and hail core prediction with object-based scores.\u0000Over the full season, MORR displays little overall storm coverage bias relative to NSSL, P3, and THOM underprediction. The equitable threat score (ETS) and fractions skill score (FSS) of P3 are lower than the other experiments. P3 and THOM underpredict convective regions with intense reflectivity relative to MORR and NSSL overprediction. All experiments underpredict precipitation amounts. P3 light precipitation FSS is lower than other experiments. Rotation object verification exhibits sensitivity to microphysics experiments, as microphysics has an indirect influence on storm dynamics. While P3 has the largest hail object underprediction, all experiments grossly overpredict the number of hail objects in convective line cases despite forecast objects defined with the same product (MESH) and threshold as observations. The importance of microphysics ice parameterization and ongoing scheme updates highlight the need to apply this verification framework to optimal/updated schemes before optimizing ensemble design.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42316332","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Alessandri, N. Pinardi, I. Federico, A. Valentini
{"title":"Storm Surge Ensemble Prediction System for Lagoons and Transitional Environments","authors":"J. Alessandri, N. Pinardi, I. Federico, A. Valentini","doi":"10.1175/waf-d-23-0040.1","DOIUrl":"https://doi.org/10.1175/waf-d-23-0040.1","url":null,"abstract":"\u0000We developed a storm surge Ensemble Prediction System (EPS) for lagoons and transitional environments. Lagoons are often threatened by storm surge events with consequent risks for human life and economic losses. The uncertainties connected with a classic deterministic forecast are many, thus an ensemble forecast system is required to properly consider them and inform the end-user community accordingly. The technological resources now available allow to investigate the possibility of operational ensemble forecasting systems that will become increasingly essential for coastal management. We show the advantages and limitations of an EPS applied to a Lagoon, using a very high-resolution unstructured grid finite element model and 45 EPS members. For five recent storm surge events, the EPS generally improves the forecast skill on the third forecast day compared to just one deterministic forecast, while they are similar in the first two days. A weighting system is implemented to compute an improved ensemble mean. The uncertainties regarding sea level due to meteorological forcing, river runoff, initial and lateral boundaries are evaluated for a special case in the northern Adriatic Sea, and the different forecasts are used to compose the EPS members. We conclude that the largest uncertainty is in the initial and lateral boundary fields at different time and space scales, including the tidal components.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42535180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Weiguo Wang, Jongil Han, Fanglin Yang, Johnathan Steffen, Bin Liu, Zhan Zhang, A. Mehra, V. Tallapragada
{"title":"Improving the intensity forecast of Tropical Cyclones in Hurricane Analysis and Forecast System","authors":"Weiguo Wang, Jongil Han, Fanglin Yang, Johnathan Steffen, Bin Liu, Zhan Zhang, A. Mehra, V. Tallapragada","doi":"10.1175/waf-d-23-0041.1","DOIUrl":"https://doi.org/10.1175/waf-d-23-0041.1","url":null,"abstract":"\u0000A modification to the mixing length formulation in a planetary boundary-layer (PBL) scheme is introduced to improve the intensity forecast of tropical cyclones (TCs) in a basin-scale Hurricane Analysis and Forecast System (HAFS) for the real-time experiment in 2021. The 2020 basin-scale HAFS with the physics suite of the NCEP operational global forecast system performs well in terms of the reduced root mean square (RMS) errors in track and intensity except for the mean intensity bias, compared with NCEP operational hurricane models. To address the large intensity bias issue, the vertical mixing length near the surface used in the PBL scheme is increased to follow the similarity theory, consistent with that used in the surface layer scheme. Test results show that the RMS error and bias in intensity are further reduced without the degradation of the track forecast. An idealized one-dimensional TC PBL model is used to understand the model response to the modification, indicating that the radial wind is strengthened to dynamically balance the enhanced downward momentum mixing. This is also exhibited in the case study of a three-dimensional HAFS simulation, with the improved vertical distribution of the simulated wind speed in the eyewall area. Given the improvement, the modification has been implemented in one of the configurations of the first version of operational HAFS at NCEP. Finally, the adjustment of the parameterization of diffusion and mixing in TC simulations is discussed.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43146396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Bertossa, P. Hitchcock, A. Degaetano, R. Plougonven
{"title":"Coherent Bimodal Events in Ensemble Forecasts of 2-m Temperature","authors":"C. Bertossa, P. Hitchcock, A. Degaetano, R. Plougonven","doi":"10.1175/waf-d-23-0053.1","DOIUrl":"https://doi.org/10.1175/waf-d-23-0053.1","url":null,"abstract":"\u0000A previous study has shown that a large portion of subseasonal-to-seasonal European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecasts for 2-meter temperature exhibit properties of univariate bimodality, in some locations occurring in over 30% of forecasts. This study introduces a novel methodology to identify ‘bimodal events’, meteorological events which trigger the development of spatially and temporally correlated bimodality in forecasts. Understanding such events not only provides insight into the dynamics of the meteorological phenomena causing bimodal events, but also indicates when Gaussian interpretations of forecasts are detrimental. The methodology that is developed allows one to systematically characterize the spatial and temporal scales of the derived bimodal events, and thus uncover the flow states that lead to them. Three distinct regions that exhibit high occurrence rates of bimodality are studied: one in South America, one in the Southern Ocean, and one in the North Atlantic. It is found that bimodal events in each region appear to be triggered by synoptic processes interacting with geographically specific processes: in South America bimodality is often related to Andes blocking events, in the Southern Ocean bimodality is often related to an atmospheric Rossby wave interacting with sea ice, and in the North Atlantic bimodality is often connected to the displacement of a persistent subtropical high. This common pattern of large-scale circulation anomalies interacting with local boundary conditions suggests that any deeper dynamical understanding of these events should incorporate such interactions.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45848551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Long-term observational characteristics of different severe convective wind types around Australia","authors":"Andrew Brown, A. Dowdy, T. Lane, S. Hitchcock","doi":"10.1175/waf-d-23-0069.1","DOIUrl":"https://doi.org/10.1175/waf-d-23-0069.1","url":null,"abstract":"\u0000Regional understanding of severe surface winds produced by convective processes (severe convective winds: SCWs) is important for decision making in several areas of society, including weather forecasting and engineering design. Meteorological studies have demonstrated that SCWs can occur due to a number of different mesoscale and microscale processes, in a range of large-scale atmospheric environments. However, long-term observational studies of SCW characteristics often have not considered this diversity in physical processes, particularly in Australia. Here, a statistical clustering method is used to separate a large dataset of SCW events, measured by automatic weather stations around Australia, into three types, associated with strong background wind, steep lapse rate, and high moisture environments. These different types of SCWs are shown to have different seasonal and spatial variations in their occurrence, as well as different measured wind gust, lightning, and parent-storm characteristics. In addition, various convective diagnostics are tested in their ability to discriminate between measured SCW events and non-severe events, with significant variations in skill between event types. Differences in environmental conditions and wind gust characteristics between clusters suggests potentially different physical processes for SCW production. These findings are intended to improve regional understanding of severe wind characteristics, as well as environmental prediction of SCWs in weather and climate applications, by considering different event types.","PeriodicalId":49369,"journal":{"name":"Weather and Forecasting","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"64708251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}