The increase in skill of numerical model guidance and the use of consensus forecast techniques have led to significant improvements in the accuracy of tropical cyclone track forecasts at ranges beyond 72 h. Identification of instances when the forecast track from an individual numerical model may be in error could lead to additional improvement in the accuracy of tropical cyclone track forecasts. An objective methodology is tested to characterize the spread among the three primary global numerical model forecast tracks used as guidance by the Joint Typhoon Warning Center. Statistically-significant principal components derived from empirical orthogonal functions of mid-tropospheric height and vorticity forecast fields identify cases of large spread among model forecasts. Cases in which the three-model average forecast track resulted in a large error were characterized by a distribution of principal components such that one component was significantly different from the other two. Removal of the forecast track associated with the outlying principal component resulted in a reduced forecast error. Therefore, the objective methodology may be utilized to define a selective consensus by removing forecast tracks from consideration based on the projection of forecast fields onto empirical orthogonal functions and inspecting the distribution of the resulting principal components.

Accurate weather forecasts are vital to air combat operations. Quantitative assessments of forecasts and their operational impacts are essential to improving weather support for war fighters. We adapted an existing U.S. Navy, web-based, near-real time system for collecting and analyzing data on the performance and operational impacts of military forecasts. We used the adapted system to collect and analyze data on Air Force Weather (AFW) forecasts, and the planning and execution of flying operations, at six Air Combat Command and Pacific Air Forces bases. We analyzed the data to develop quantitative metrics of forecast performance and operational impacts. Our results indicate that planning weather forecasts (PWFs) have a higher potential for making positive contributions to air operations than do mission execution forecasts (MEFs). This is notable because AFW units spend significantly less time developing PWFs than MEFs. Surface visibility, cloud ceilings, and cloud layers caused most negative mission impacts, indicating these phenomena should be a focus of future research and training. We found high levels of mission success even when forecasts were inaccurate, perhaps due to aircrew and mission flexibility. Our analyses revealed a need for improved education of flying units on the nature and availability of AFW products.

Cold air outbreaks (CAOs) occur when large scale atmospheric circulations allow for the incursion of polar air masses into middle and lower latitudes, influencing wintertime temperatures regionally. The January 2004 CAO is identified as a major CAO in the Deep South of the United States in terms of wind chill equivalent temperature or a temperature-only criterion. Surface air temperature, horizontal winds, specific humidity, and Ertel potential vorticity are analyzed for this event using several reanalysis products: National Aeronautic and Space Administration Modern Era Retrospective-Analysis for Research and Application (MERRA), the National Centers for Environmental Prediction National Center for Atmospheric Research (NCEP-NCAR), and the National Centers for Environmental Prediction North American Regional Reanalysis (NARR). We perform an intercomparison of the reanalysis products and parallel surface station observations during the synoptic evolution of the leading cold front associated with CAO onset. The key synoptic, mesoscale, and dynamical features associated with onset are studied to determine the relative accuracy of the respective reanalysis products in representing the key features. The comparative evaluation revealed pronounced temperature and moisture biases in the NCEP-NCAR reanalysis products that limit its utility in portraying the synoptic features characteristic of CAO onset. Conversely, both MERRA and NARR accurately represent the detailed thermodynamic and moisture structural evolution associated with CAO onset indicating their utility in future observationally-based studies of CAO events. Ertel potential vorticity analyses indicate that the onset of the 2004 CAO is strongly linked to an incipient tropopause fold feature that developed over the Great Lakes region.

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A two-level diagnostic baroclinic model is constructed for the purpose of examining the role of latent heat release in the production of vertical motion and rainfall. Incorporated in the model are terrain and frictional inflow effects and a variable level of non-divergence. The computations are carried out on a 300 point standard rectangular grid covering the North American continent. [...]

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Thesis (M.Sc. Earth Sciences)--University of Waikato, 2008. / Title from PDF cover (viewed February 23, 2009) Includes bibliographical references (p. 72-75)