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Dennis G. Baker

A new scoring scheme for verification of fixed-width, credible interval temperature forecasts, which penalizes forecasts of low probabilities for their uncertainty, has been developed. This scoring scheme encourages the forecaster to maximize the proportion of verifying forecasts and to provide probabilities that reflect his true confidence. Results of the use of this scoring scheme in the University of Michigan Forecast Game indicate that a forecaster should strive first for accuracy of the temperature forecast and second for having well-calibrated associated probabilities.

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Dennis G. Baker

Abstract

Root-mean-square errors of the 24 h operational, objective, maximum-minimum temperature forecasts derived from primitive equation model predictions and model output statistics are evaluated in terms of synoptic-scale and mesoscale contributions. Eight regions of the United States are examined for the period from December 1974 through November 1976. Climatology and persistence are used for comparison. For the operational forecasts, the synoptic-scale and mesoscale contribute approximately equally to the error. On the synoptic scale, the objective predictions are significantly more accurate than persistence and climatology. However, on the mesoscale, the predictions have approximately the same accuracy as climatology for minimum temperatures and only slightly more accuracy than climatology for maximum temperatures.

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Dennis G. Baker

Abstract

During an experiment in mesoscale weather forecasting in the Michigan area, consensus improved over NWS guidance in maximum/minimum temperature and probability of precipitation forecasts out to 24 hours. Forecasts were generally best in the vicinity of the forecast site. Climatology, persistence, NWS guidance and consensus forecast errors in maximum/minimum temperature and precipitation probability forecasts were divided into synoptic and mesoscale contributions. The errors of the climatology and persistence forecasts resulted substantially more from the synoptic scale than the mesoscale. NWS guidance and consensus forecasts improved over climatology on the synoptic scale with much less or no improvement on the mesoscale. For temperature, consensus showed improvement over guidance only on the synoptic scale. For precipitation, no relationship to scale was evident. In terms of remaining errors, errors were distributed approximately equally between the synoptic scale and mesoscale for temperature. For precipitation, the errors were significantly greater from the mesoscale than the synoptic scale. The implications of these results for zone forecasts and future improvements in mesoscale forecasting accuracy are discussed.

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Dennis G. Baker

Abstract

The mesoscale air temperature and dew point fields in a synoptic situation where air with a temperature at least 25°C colder than lake water temperature passed over the western Great Lakes is investigated. The airflow experienced an average temperature rise of 8°C and a dew point rise of 15°C from one shore of Lake Michigan to the other. Leeward of Lake Michigan the surface air temperature and dew point of the airflow decreased approximately 2°C and 4°C, respectively, as the air moved inland. Strong temperature gradients, referred to as lake–end pseudofronts, were found perpendicular to the flow downwind from the end of the lakes. The lake-end pseudofront at the southern end of Lake Michigan was 25–50 km wide, extended over 100 km downstream, and had an average magnitude of 0.5°C (5 km)−1. A band of heavy snow was associated with it. Ice on the lakes, coupled with a transitory wind shift, allowed unmodified cold air to penetrate into lower Michigan for several hours. Low dew points accompanied this cold air penetration with the region covered by low dew points being greater than that covered by low temperatures.

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Dennis G. Baker, Anita Baker-Blocker, Bernard H. DeWitt, and Dennis W. Dixon

Abstract

Objective predictions of first permanent ice formation and freeze-up on the Great Lakes were made by use of cumulative freezing degree-day totals, by the Lisitzin-Rodhe-Bilello equation, by use of departures from normal air temperature and by use of 30-day temperature outlooks. The four objective methods yield similar improvement over use of the mean date of freeze-up in prediction of these ice events, although freezing degree-day totals appear to represent the best method. Lake Superior ice cover can be predicted using the freezing degree-day method extrapolated to mid-lake locations with better results than a climatological prediction based on the use of long-term mean freeze-up dates.

Ice breakup on the Great Lakes was predicted using thawing degree-day totals and a correlation between stations approach. Both of these predictive techniques are superior to use of the mean date of breakup as a prediction.

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Edward Ryznar, Dennis G. Baker, and Harry Moses

Twenty-five meteorological stations are in operation inland from two nuclear power plants located on the Lake Michigan shoreline in southwestern lower Michigan. Their purpose is to provide data to enable meteorological effects of mechanical-draft cooling towers at the Palisades Nuclear Plant and a once-through cooling system at the Donald C. Cook Nuclear Plant to be evaluated. Temperature, relative humidity, and precipitation are measured at all stations, total solar radiation and wind velocity at four, and visibility at three. The stations, equipment, and calibration methods are described, and examples of types of meteorological analyses are presented.

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