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Paul J. Kocin

A collection of detailed surface weather observations is used to construct an analysis of the legendary “Blizzard of '88,” an intense cyclone that was accompanied by unusually heavy snowfall, high winds and cold temperatures across the northeastern United States from 11 to 14 March 1888. The analysis follows the cyclone from genesis along a slow-moving frontal system, through rapid development and occlusion along the Middle Atlantic and southern New England coasts. Unusual aspects of the cyclone are highlighted. These include the limited areal extent of heavy snow accumulations, the establishment of very cold air across western New England and the Middle Atlantic states, a persistent stationary frontal zone across central New England that separated frigid continental air from maritime air, and the slow movement and rapid warming associated with the decay of the storm.

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Paul J. Kocin and Louis W. Uccellini

A Northeast snowfall impact scale (NESIS) is presented to convey a measure of the impact of heavy snowfall in the Northeast urban corridor, a region that extends from southern Virginia to New England. The scale is derived from a synoptic climatology of 30 major snowstorms in the Northeast urban corridor and applied to the snowfall distribution of 70 snowstorms east of the Rocky Mountains. NESIS is similar in concept to other meteorological scales that are designed to simplify complex phenomena into an easily understood range of values. The Fujita scale for tornadoes and the Saffir–Simpson scale for hurricanes measure the potential for destruction to property and loss of life by wind-related damage (and storm surge for Saffir–Simpson) through use of a categorical ranking (0 or 1–5).

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Paul J. Kocin and and Louis W. Uccellini

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Paul J. Kocin and and Louis W. Uccellini

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Louis W. Uccellini and Paul J. Kocin

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The interaction of transverse vertical circulations associated with two separate jet steak/trough systems is found to be a common feature of cyclogenetic events which produce heavy snow along the East Coast of the United States. The transverse circulations are identified for eight cases that span the period from 1960 to 1987 utilizing an isentropic analysis of the operational radiosonde data. The analyses depict the interaction of 1) a direct circulation located within the confluent entrance region of an upper-level jet streak over the northeastern United States or southeastern Canada with 2) an indirect circulation in the diffluent exit region of a jet streak associated with a trough nearing the East Coast. This interaction contributes to differential moisture and temperature advections and vertical motions necessary to produce heavy snowfall along the coast. It is suggested that the circulation patterns associated with the jet streak establish an environment within which boundary layer processes (e.g., cold-air damming, coastal frontogenesis, the development of a low-level jet Streak) can further contribute to cyclogenesis and the development of severe winter weather conditions.

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Paul J. Kocin, Alan D. Weiss, and Joseph J. Wagner

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An unprecedented period of extreme cold accompanied by an intense East Coast blizzard during February 1899 is documented through an examination of detailed surface weather charts constructed from original data. The surface weather analyses depict the passage of several anticyclones of Canadian or polar origin that propagated southward, spreading progressively colder temperatures throughout the central, eastern, and southern United States. This series of cold outbreaks culminated in the southward plunge of one final, massive anticyclone that yielded the coldest temperatures on record for much of the south-central and southeastern United States. The final cold wave was associated with the development of a cyclone that left measurable snow over most of the Gulf Coast and Florida and then produced severe blizzard conditions along much of the East Coast.

To place this period in historical perspective, minimum temperatures recorded during February 1899 are compared with minimum temperatures measured during more recent cold air outbreaks. Snowfall records set during February 1899 that have never been exceeded are also documented. Examples of extreme weather events such as this enable forecasters and students to gain practical experience by visualizing the meteorological patterns these events are associated with, by acquiring a historical perspective when assessing other events, and by gaining an appreciation of the limits of severity that atmospheric phenomena can attain.

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Steven E. Koch, Mary desJardins, and Paul J. Kocin

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An objective analysis scheme based on the Barnes technique and designed for use on an interactive computer is described. In order to meet the specific needs of the research meteorologist, the interactive Barnes scheme allows real-time assessments both of the quality of the resulting analyses and of the impact of satellite-derived data upon various meteorological data sets. Display of a number of statistical and mapped analysis quality control indicators aid the impact assessments. Simple means for taking account of the spatially clustered nature typical of satellite data are included in the internal computations of the relative weights of data at grid point locations.

An analyst is allowed the capability of modifying values of certain input parameters to the interactive Barnes scheme within internally set limits. These constraints were objectively determined and tested in a number of different situations prior to implementation. The following constraints are employed: 1) calculation of the weights as a function of a data spacing representative of the data distribution; 2) automatic elimination of detail at wavelengths smaller than twice the representative data spacing; 3) placement of bounds upon the grid spacing by the data spacing; and 4) setting of a fixed limit on the number of passes through the data to achieve rapid and sufficient convergence of the analyzed values to the observed ones. A mathematical analysis of the convergence properties of the Barnes technique is presented to support the validity of the latter constraint.

Despite these constraints, the interactive Barnes scheme remains versatile because it accepts limited inputs to the data and grid display areas, to the data and grid spacings, and to the rate of convergence of the analysis to the observations. Input parameter values are entered through a series of questions displayed on a computer video terminal and by manipulation of display function devices. The analyst immediately sees a plot of the data, the contoured grid values, superimposed in various colors if desired, and the effects of choice of analysis options. Examples of both meteorological and satellite data analyses are presented to demonstrate the objectivity, versatility and practicality of the interactive Barnes scheme.

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Louis W. Uccellini, Paul J. Kocin, Russell S. Schneider, Paul M. Stokols, and Russell A. Dorr

This paper describes the decision-making process used by the forecasters in the National Meteorological Center's Meteorological Operations Division and in Weather Forecast Offices of the National Weather Service to provide the successful forecasts of the superstorm of 12–14 March 1993. This review illustrates 1) the difficult decisions forecasters faced when using sometimes conflicting model guidance, 2) the forecasters' success in recognizing the mesoscale aspects of the storm as it began to develop and move along the Gulf and East Coasts of the United States, and 3) their ability to produce one of the most successful heavy snow and blizzard forecasts ever for a major winter storm that affected the eastern third of the United States.

The successful aspects of the forecasts include the following. 1) Cyclogenesis was predicted up to 5 days prior to its onset. 2) The unusual intensity of the storm was predicted three days in advance, allowing forecasters, government officials, and the media ample time to prepare the public, marine, and aviation interests to take precautions for the protection of life and property. 3) The excessive amounts and areal distribution of snowfall were predicted two days in advance of its onset. 4) An extensive number of blizzard watches and warnings were issued throughout the eastern United States with unprecedented lead times. 5) The coordination of forecasts within the National Weather Service and between the National Weather Service, private forecasters, and media meteorologists was perhaps the most extensive in recent history.

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Louis W. Uccellini, Ralph A. Petersen, Paul J. Kocin, Keith F. Brill, and James J. Tuccillo

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A series of numerical simulations is presented for the February 1979 Presidents' Day cyclone in order to understand more fully the roles played by upper-level jet streaks the oceanic planetary boundary layer (PBL), and latent heat release in the development of a low-level jet (LU) and secondary cyclogenesis along the East Coast of the United States. Mesoscale model simulations with and without sensible and latent heating show that the diabatic processes, along with the jet streak circulation patterns, contribute to the enhancement of the low-level winds and the initial development of the coastal cyclone. However. none of the mechanisms acting alone is sufficient to yield a satisfactory simulation of the LIJ and secondary cyclogenesis. Furthermore, the model-based diagnostic analyses indicate that a synergistic interaction must exist among these processes to account for the substantial increase in the magnitude of the low-level winds and the decrease in the sea level pressure that mark the secondary cyclogenesis for this case.

The following sequence is derived from the model diagnostic study: 1) Temporally increasing divergence along the axis of an upper-tropospheric jet streak located near the crest of an upper-level ridge is associated with the development of an indirect circulation that spans the entire depth of the troposphere and is displaced to the anticyclonic side of the jet. The lower branch of the indirect circulation appears to extend northwestward from the oceanic PBL up sloping isentropic surfaces toward 700 mb over the Appalachian Mountains. 2) Sensible heating and associated moisture flux within the oceanic PBL warm and moisten the lower branch of the indirect circulation, enhancing precipitation rates and latent heat release west of the coastline. 3) The combination of a shallow direct circulation associated with a developing coastal front, sloping lower-tropospheric isentropic surfaces just to the west of the coastline, and latent heat release contributes to a vertical displacement of parcels within the lower branch of the indirect circulation as they cross the coastline. 4) The vertical displacement of the parcels in a baroclinic environment (in which the pressure gradient force changes with height) results in the rapid increase in the magnitude of the ageostrophic wind and associated unbalanced flow. This imbalance contributes to parcel acceleration resulting in the formation of a LLJ in the lower branch of the indirect circulation over a 2 to 4 h period. 5) The increasing wind speed associated with the developing LLJ is, in turn, responsible for an increase in the horizontal mass flux divergence in the entrance region of the LLJ. The increase in the mass flux divergence in the lower troposphere just above the boundary layer makes a significant contribution to the decreasing sea-level pressure that constitutes the initial development phase of the secondary cyclone along the coast.

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George J. Maglaras, Jeff S. Waldstreicher, Paul J. Kocin, Anthony F. Gigi, and Robert A. Marine

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The complex combination of synoptic- and mesoscale interactions topographic influences, and large population densities poses a multitude of challenging problems to winter weather forecasters throughout the eastern United States. Over the years, much has been learned about the structure, evolution, and attendant precipitation within winter storms. As a result, numerous operational procedures, forecast applications, and objective techniques have been developed at National Weather Service offices to assess the potential for hazardous winter weather.

An overview of the challenge of forecasting winter weather in the eastern United States is presented, including a historical review of several legendary winter storms, from the Blizzard of 1888 to the Halloween Nor'easter of 1991. The synoptic-scale features associated with East Coast winter storms are described. The mesoscale nature of many eastern winter weather events is illustrated through an examination of the Veterans' Day Snowstorm of 11 November 1987, and the Long Island Snowstorm of 13 December 1988. The development of applied forecast techniques and the potential for new remote sensing technologies (e.g., Doppler weather radar and wind profilers) and mesoscale models to improve operational forecasts of winter weather hazards are also discussed. Companion papers focus on cyclogenesis, terrain-related winter weather forecast considerations in the Southeast, and lake effect snow forecasting.

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