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RUSSELL J. YOUNKIN

Abstract

The relationship between circulation and heavy snowfall over the western United States is studied as a means of improving operational forecasts for that region. The models developed relate occurrence of heavy snowfall in 12-hr. periods to initial circulation features and are suitable for direct use on available circulation prognoses.

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WARREN SMITH and RUSSELL J. YOUNKIN

Abstract

The jet stream is recognized as an important atmospheric mechanism for vertical exchange processes. It follows that certain jet stream positions relative to moisture source regions bring about occurrences of extensive heavy rainfall. One type of such occurrence, mainly in the central United States, is identified with a “digging” polar jet stream. To better understand the meteorological relationships involved, we developed composite models from seven representative cases and studied one unusually heavy rainfall situation in more detail. For this type, there is a tendency for heavy rainfall to occur in an ellipsoidal pattern in advance of the polar jet stream.

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THEODORE W. KLEINSASSER and RUSSELL J. YOUNKIN

Abstract

The daily net energy available for heating the air from 0300 GMT to the following afternoon, as determined by Myers, is used to compute objectively the maximum temperature expected under static, clear-sky conditions at 12 cities in the power distribution area of the Tennessee Valley Authority. The maximum temperatures thus obtained are plotted and analyzed to resolve irregular features of the isotherm patterns. The analysis is then adjusted subjectively primarily for the effect of temperature advection but also for cloudiness, precipitational cooling, and vertical motion—to take account of changes expected by mid-afternoon of the current day and also of the following day. Verification results for seven cities in the TVA area during 1954 and 1955 are presented. The current-day forecast errors are approximately 50 percent less than persistence forecast errors.

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Harry E. Brown and Russell J. Younkin

The worst east coast storm of 1971–72 developed very rapidly and reached maturity at extreme southerly latitudes. To a large degree, the development was forecast more than two days in advance by use of the National Meteorological Center 6-layer primitive equation (P.E.) model. However, the P.E. prognosis contained systematic errors. Most were eliminated by the limited area fine mesh model (LFM) and NMC forecasters. NMC's total performance with the storm was nearly the best possible with the current state-of-the-art. The successful forecast of cyclogenesis led to equally successful forecasts of precipitation quantities, heavy snow, and storm surges, among other things. Examples are presented.

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JERROLD A. La RUE and RUSSELL J. YOUNKIN

Abstract

During the past two years, the Quantitative Precipitation Forecast Unit of the National Meteorological Center has collected, as a by-product of its verification program, a large quantity of data relating to observed precipitation amounts. A technique is developed to process these data into precipitation volumes for varying time periods. The technique is simple and provides a fast method of obtaining large-scale precipitation volumes on a day-to-day basis. Similarly, monthly volumes can be easily estimated.

The volumes for a number of larger precipitation storms for periods of one to five days are presented, as well as monthly and annual volumes. An attempt was made to determine a normal isohyetal gradient for individual storms but was successful only with amounts exceeding 3 inches. The volumetric contribution by isohyetal intervals is examined and only in cases of the heaviest storms were the larger amounts found to be important to total volume.

The distribution of heavy precipitation, as portrayed by isopleths of the number of times areas were enclosed by the 1 inch isohyet, is given for each month and for the year. Although the distribution is not too different from that which might be expected, the authors know of no other source for this information.

An addendum permits a comparison of the 1961 and 1962 monthly and annual precipitation volumes. The significant decrease in the 1962 volume emphasizes the deficient rainfall reported over much of the Nation.

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JERROLD A. LARUE and RUSSELL J. YOUNKIN

Abstract

No Abstract Available.

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PAUL A. GOREE and RUSSELL J. YOUNKIN

Abstract

Verification shows that recent guidance and official heavy snowfall forecasts have achieved only a modest degree of success. Therefore, the synoptic-climatological relationship of heavy snowfall to those, surface and upper-air features which are routinely forecast, is studied in an attempt to improve, operational forecasting of heavy snowfall east of the Rockies. The relationship is modeled in a way suitable for direct use on available circulation prognoses. The models relate percentage frequency of occurrence of heavy snowfall in 12-hr. periods to the initial 500-mb. absolute vorticity maximum, the 500-mb. height contours, the 1000–500-mb. thickness contours, and the surface low pressure center.

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RICHARD F. BROWNE and RUSSELL J. YOUNKIN

Abstract

It is generally known that certain relationships exist between the production of heavy snow and low-level dynamic and thermodynamic parameters, such as vorticity, moisture, and temperature advection patterns. This statistical synoptic climatological study at the 850-mb level is made to understand better these relationships and also to improve operational forecasting of heavy snow over the central and eastern United States. Models relating percentage frequency of heavy snowfall in 12-hr periods to initial and subsequent 850-mb height and temperature patterns are developed. Also, considerable other statistical information is arranged in tabular form for forecaster evaluation.

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Russell J. Younkin, Jerrold A. LaRue, and Frederick Sanders

Abstract

This article describes and illustrates an objective technique of forecasting clouds, precipitation and precipitation amounts. The system is tailored to fit the specific operation of the National Meteorological Center in the use of data routinely available. It attempts to eliminate or to alleviate a number of difficulties which have plagued other objective techniques.

The method follows rather closely the earlier work of Frederick Sanders, but departs importantly in the method of obtaining vertical motion and in the form and manipulation of the moisture parameter. The vertical motion is computed from objective 1000-mb and 500-mb prognoses through an adiabatic approach. Saturation thickness is used as the moisture parameter in a manner which eliminates the need for reference to specific and relative humidities.

Two forecasts are illustrated in detail. The first example employs a form which obtains directly a vertical motion field, while the second by-passes this step.

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