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Ira S. Brenner

Abstract

The biases of objective forecasts of maximum and minimum temperature for Phoenix are evaluated relative to the observed temperatures. The temperature forecasts were calculated from regression equations that had been derived from model output statistics (MOS). During the analysis period, from October 1982 through September 1984, significant cold biases of ∼1.5–2.5°F (0.8–1.4°C), were determined for the MOS minimum temperature forecast at 24, 36 and 48 h. The maximum temperature forecasts had warm biases <1.0°F (0.6°C) that were significant only at 24 h. The minimum and maximum temperatures from the most recent 30-year normals (1951–80) were, respectively, ∼5°F (3°C) and 1°F (0.6°C) colder than the observed temperatures during the analysis period. The difference between the climatological and observed minimum temperatures is significant at the 1% level and suggests that a local or regional change in weather conditions may be an important factor in explaining the MOS biases.

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Ira S. Brenner

Abstract

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Ira S. Brenner

The average sea-level pressure gradients that produce sustained surface winds above 8 kt for at least six consecutive hours during the cool season at predetermined key stations in or adjacent to Arizona are investigated. Only wind directions with northerly or easterly components are included in the developmental data sample. Graphs are provided that relate the derived pressure gradients to varying surface wind speeds at each key station.

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Ira S. Brenner

Abstract

Considerable daily variations of summer convective rainfall average areal coverage and rainfall amount were identified in west-central Florida for the period May–September 1997–2000 using a 29-site rainfall network. Pearson correlation coefficients identified the correlations to each from among 16 parameters that can be extracted directly from the 1200 UTC radiosonde data at Ruskin, Florida, and that represent moisture, stability/temperature, and flow. The highest correlations were with all of the moisture parameters—precipitable water, minimum theta- e temperature, wet-bulb zero pressure, and average dewpoints in various layers from the 850- to 500-mb height level.

Multiple linear regression analysis produced a separate prediction equation each for average areal coverage and rainfall amount, which were tested on independent data from May to September 2001. Reliable predictions of the trend direction and magnitude of the change from the observed value of the previous day occurred about 75% of the time with the average prediction error generally within ±10% (areal coverage) and ±0.10 in. (rainfall amount). When the observed trend changed by at least 20% for areal coverage (39 cases), and at least 0.20 in. for average rainfall amount (36 cases), the trend direction was correctly predicted 100% and about 90% of the time, respectively. Of these, the predictions for areal coverage underforecast both the amount of observed increase and decrease by an average of 8% and 6%. For rainfall amount, the predictions underforecast both the magnitude of observed increase and decrease by about 0.18 and 0.06 in., respectively.

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Ira S. Brenner

Abstract

This synoptic study, for the period 13–16 July 1972, involved the use of surface, radiosonde, and radar observations, as well as satellite pictures. Isentropic analysis indicated that the depth of the moisture with this surge of tropical air was of the order of 8000 to 12,000 ft. A unique feature of this type of surge is its resemblance to a giant sea-breeze effect, where the main advective forces result from the low-level pressure gradient between the desert thermal low and the relatively higher pressures over the cooler Gulf of California. This effect is emphasized by the lack of upper-air support, as shown in the mean vector winds from 10,000 to 20,000 ft for the period of concern. Satellite photographs and film loops give a dramatic picture of the movement of the cloud mass initially associated with the surge. They also suggest that one of the mechanisms that may be a factor in the development of the cloudy, showery area at the mouth of the Gulf of California is an easterly wave. These extensive and active cloud areas apparently establish the low-level conditions favorable for the northward push of the surge.

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Ira S. Brenner

Abstract

This synoptic study for the period 22 September to 3 October 1974 involves a case analysis of an unforeseen major precipitation episode. This apparently resulted from the merging of an inactive propagating short–wave trough that moved cast-northeastward out of the subtropics and an inactive extratropical low moving southeastward. Prior to the amalgamation of the two systems, weak upward vertical motion fields allowed only specks of high clouds to be associated with each. Almost immediately with the merging of the two systems, a rapid increase in upward vertical motion around the upper-level extratropical system took place, as evidenced on VHRR satellite imagery by the sudden development of rather organized middle and high cloudiness. Within 24 hours, a distinct vortex comprising all cloud levels was evident on satellite photographs. During the next 24 hours, a major rain-producing storm developed. The major impact of this storm was an abrupt end to the California dry season.

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