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William D. Bonner and Ralph D. Petersen

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Ralph A. Petersen and John D. Stackpole

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An overview of the regularly scheduled sequence of computer analyses and forecasts produced at the National Meteorological Center (NMC) is presented. The available computer resources and time schedule constraints are discussed, the sources and treatment of incoming data are described, the purposes and configurations of the operational analysis/forecasting systems are outlined, and the mechanisms for product distribution are presented.

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David D. Houghton, Ralph A. Petersen, and Richard L. Wobus

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Forecasts from different resolution versions of the National Meteorological Center Nested Grid Model (NGM) are compared for two case studies to assess an optimal ratio of model vertical and horizontal resolutions. Four combinations are considered: 1) 16 layers and 80-km horizontal grid over the United States (the operational version of the model), 2) 32 layers and 80-km horizontal grid, 3) 16 layers and 40-km horizontal grid, and 4) 32 layers and 40-km horizontal grid. Resolution impacts are evaluated for a number of weather system components such as extratropical cyclone evolution, baroclinic and frontal zone structure, jet-stream blow, moisture fields, and precipitation.

Resolution impacts for this limited sample are relatively small for synoptic-scale features such as the position of the extratropical cyclone and main jet-stream flows. Larger impacts are noted for smaller-scale horizontal structure and gradients, frontal zone associated circulations and hydrological cycle components. Vertical resolution enhancement effects on the NGM, which already has added resolution near the lower boundary, are less dramatic in the lower troposphere than those for horizontal resolution, but are important for defining upper-level frontal structures and circulations where the NGM's vertical structure is coarser. Conclusions concerning consistency of horizontal and vertical resolution impacts on baroclinic zone structure and spurious noise generation found in earlier studies with simpler models are confirmed and brought into perspective for comprehensive numerical models and operational weather prediction model applications for the two cases discussed. The effects of the improvements in small-scale forecast accuracy, however, are difficult either to generalize due to the limited number of case studies or to assess because of the lack of high-resolution verification information and evaluation techniques.

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Daniel C. Hartung, Jason A. Otkin, Ralph A. Petersen, David D. Turner, and Wayne F. Feltz

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In this study, atmospheric analyses obtained through assimilation of temperature, water vapor, and wind profiles from a potential network of ground-based remote sensing boundary layer profiling instruments were used to generate short-range ensemble forecasts for each assimilation experiment performed in Part I. Remote sensing systems evaluated during this study include the Doppler wind lidar (DWL), Raman lidar (RAM), microwave radiometer (MWR), and the Atmospheric Emitted Radiance Interferometer (AERI). Overall, the results show that the most accurate forecasts were achieved when mass (temperature and humidity profiles from the RAM, MWR, and/or AERI) and momentum (wind profiles from the DWL) observations were assimilated simultaneously, which is consistent with the main conclusion from Part I. For instance, the improved wind and moisture analyses obtained through assimilation of these observations contributed to more accurate forecasts of moisture flux convergence and the intensity and location of accumulated precipitation (ACPC) due to improved dynamical forcing and mesoscale boundary layer thermodynamic structure. An object-based verification tool was also used to assess the skill of the ACPC forecasts. Overall, total interest values for ACPC matched objects, along with traditional forecast skill statistics like the equitable threat score and critical success index, were most improved in the multisensor assimilation cases.

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Eric Rogers, Geoffrey J. DiMego, Joseph P. Gerrity, Ralph A. Petersen, Brian D. Schmidt, and Deirdre M. Kann

Analyses and forecasts for the first 2 weeks of the Genesis of Atlantic Lows Experiment (GALE) are described. These fields were produced using the National Meteorological Center (NMC) Regional Analysis and Forecast System (RAFS). Two sets of analyses and forecasts were constructed: one using the NMC operational database only (Level IIIa), and one using the NMC data merged with high-density observations taken during GALE (Level IIIb).

During the first 14 days of GALE, supplemental data were collected throughout two Intensive Observing Periods (IOPs). Comparisons of the Level IIIa and IIIb analyses over the GALE observing region in the southeastern United States indicated a worsening of the geopotential height analysis at operational NWS rawinsonde sites using the supplemental IIIb data. This was caused by inconsistencies in the height measurements at the high-density GALE rawinsonde sites. Such patterns were not observed in the wind and temperature analyses.

During IOP No. 1, the Level IIIa and IIIb Nested Grid Model (NGM) forecasts were nearly identical. For IOP No. 2, one forecast cycle saw an improvement in the Level IIIb forecasts due to offshore GALE dropwindsonde data, while another was improved by the inclusion of late-arriving rawinsonde data in the IIIb analysis. The inland, high-density GALE soundings, however, had a negligible impact on NGM forecasts during the entire 12-day period.

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Jason A. Otkin, Daniel C. Hartung, David D. Turner, Ralph A. Petersen, Wayne F. Feltz, and Erik Janzon

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In this study, an Observing System Simulation Experiment was used to examine how the assimilation of temperature, water vapor, and wind profiles from a potential array of ground-based remote sensing boundary layer profiling instruments impacts the accuracy of atmospheric analyses when using an ensemble Kalman filter data assimilation system. Remote sensing systems evaluated during this study include the Doppler wind lidar (DWL), Raman lidar (RAM), microwave radiometer (MWR), and the Atmospheric Emitted Radiance Interferometer (AERI). The case study tracked the evolution of several extratropical weather systems that occurred across the contiguous United States during 7–8 January 2008. Overall, the results demonstrate that using networks of high-quality temperature, wind, and moisture profile observations of the lower troposphere has the potential to improve the accuracy of wintertime atmospheric analyses over land. The impact of each profiling system was greatest in the lower and middle troposphere on the variables observed or retrieved by that instrument; however, some minor improvements also occurred in the unobserved variables and in the upper troposphere, particularly when RAM observations were assimilated. The best analysis overall was achieved when DWL wind profiles and temperature and moisture observations from the RAM, AERI, or MWR were assimilated simultaneously, which illustrates that both mass and momentum observations are necessary to improve the analysis accuracy.

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Rita D. Roberts, Steven J. Goodman, James W. Wilson, Paul Watkiss, Robert Powell, Ralph A. Petersen, Caroline Bain, John Faragher, Ladislaus B. Chang’a, Julius K. Kapkwomu, Paul N. Oloo, Joseph N. Sebaziga, Andrew Hartley, Timothy Donovan, Marion Mittermaier, Lee Cronce, and Katrina S. Virts

Abstract

Up to one thousand drowning deaths occur every year on Lake Victoria in East Africa. Nocturnal thunderstorms are one of the main culprits for the high winds and waves that cause fishing boats to capsize. The HIGHWAY project was established to develop an Early Warning System for Lake Victoria. Prior to HIGHWAY, weather forecasts for the lake were overly general and not trusted. Under the HIGHWAY project, forecasters from weather service offices in East Africa worked with leaders of fishing communities and Beach Management Units to develop marine forecasts and hazardous-weather warnings that were meaningful to fishermen and other stakeholders. Forecasters used high-resolution satellite, radar, and lightning observations collected during a HIGHWAY field campaign, along with guidance from numerical weather prediction models and a 4.4-km resolution Tropical Africa model, to produce specific forecasts and warnings for 10 zones over the lake. Forecasts were communicated to thousands of people by radio broadcasters, local intermediaries, and via smartphones using the WhatsApp application. Fishermen, ferry-boat operators, and lakeside communities used the new marine forecasts to plan their daytime and nighttime activities on the lake. A socio-economic benefits study conducted by HIGHWAY found that ~75% of the people are now using the forecasts to decide if and when to travel on the lake. Significantly, a 30% reduction in drowning fatalities on the lake is likely to have occurred, which when combined with the reduction in other weather-related losses, generates estimated socio-economic benefits of $44M/year due to the HIGHWAY project activities; the new marine forecasts and warnings are helping to save lives and property.

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