Paul J. Kocin

The Interaction of Jet Streak Circulations during Heavy Snow Events along the East Coast of the United States

Abstract 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 processe...

Overview of the 12–14 March 1993 Superstorm

An extratropical cyclone of unusual intensity and areal extent affected much of the Gulf and East Coasts of the United States on 12–14 March 1993. In this paper, the many effects of the storm will be highlighted, including perhaps the most widespread distribution of heavy snowfall of any recent East Coast storm, severe coastal flooding, and an outbreak of 11 confirmed tornadoes. A meteorological description of the storm is also presented, including a synoptic overview and a mesoscale analysis that focuses on the rapid development of the cyclone over the Gulf of Mexico. This is the first part of a three-paper series that also addresses the performance of the operational numerical models and assesses the forecasting decisions made at the National Meteorological Center and National Weather Service local forecast offices in the eastern United States.

A snowfall impact scale derived from northeast storm snowfall distributions

Abstract 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).

Forecast Issues in the Urban Zone: Report of the 10th Prospectus Development Team of the U.S. Weather Research Program

The 10th Prospectus Development Team (PDT-10) of the U.S. Weather Research Program was charged with iden- tifying research needs and opportunities related to the short-term prediction of weather and air quality in urban forecast zones. Weather has special and significant impacts on large numbers of the U.S. population who live in major urban areas. It is recognized that urban users have different weather information needs than do their rural counterparts. Further, large urban areas can impact local weather and hydrologic processes in various ways. The recommendations of the team emphasize that human life and well-being in urban areas can be protected and enjoyed to a significantly greater degree. In particular, PDT-10 supports the need for 1) improved access to real-time weather information, 2) improved tailoring of weather data to the specific needs of individual user groups, and 3) more user-specific forecasts of weather and air quality. Specific recommendations fall within nine thematic areas: 1) development of a user-oriented weather database; 2) focused research on the impacts of visibility and icing on transportation; 3) improved understanding and forecasting of winter storms; 4) improved understanding and forecasting of convective storms; 5) improved forecasting of intense/ severe lightning; 6) further research into the impacts of large urban areas on the location and intensity of urban convec- tion; 7) focused research on the application of mesoscale forecasting in support of emergency response and air quality; 8) quantification and reduction of uncertainty in hydrological, meteorological, and air quality modeling; and 9) the need for improved observing systems. An overarching recommendation of PDT-10 is that research into understanding and predicting weather impacts in urban areas should receive increased emphasis by the atmospheric science community at large, and that urban weather should be a focal point of the U.S. Weather Research Program.

Synoptic scale forecast skill and systematic errors in the MASS 2.0 model

Abstract A large number of predictions from a regional numerical weather prediction model known as the Mesoscale Atmospheric Simulation System (MASS 2.0) am verified against routinely collected observations to determine the models predictive skill and its most important systematic errors at the synoptic scale. The models forecast fields are smoothed to obtain synoptic-scale fields that can be compared objectively with the observation. A total of 23 (28) separate 12 h (24 h) forecasts of atmospheric flow patterns over the United States are evaluated from real-time simulations made during the period 2 April-2 July 1982. The models performance is compared to that of the National Meteorological Centers operational Limited-area Fine Mesh (LFM) model for this period. Temporal variations in normalized forecast skill statistics are synthesized with the mean spatial distribution of daily model forecast errors in order to determine synoptic-scale systematic errors. The mesoscale model produces synoptic-scale for...

Forecasting the 12–14 March 1993 Superstorm

Abstract This paper describes the decision-making process used by the forecasters in the National Meteorological Centers 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 t...

A Report on the Upper-Level Wind Conditions Preceding and During the Shuttle Challenger (STS 51L) Explosion

The synoptic-scale weather conditions preceding and following the ill-fated Space Shuttle Challenger launch are documented, with particular emphasis on the upper-level winds for central and northern Florida. Operational radiosonde data collected by the National Weather Service, visible and infrared imagery from the Geostationary Operational Environmental Satellite, and water-vapor imagery from the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder, ozone data collected by the Total Ozone Mapping Spectrometer aboard the Nimbus-7, and soundings collected at Cape Canaveral (XMR) are described. Analyses derived from these data sets point to the juxtaposition of two distinct jet-stream systems (a polar-front jet [PFJ] and a subtropical jet [STJ]) over north-central Florida on the morning of the launch. Both jets were characterized by regions of significant vertical wind shear, which was especially strong above and below the core of the STJ. Data from a radiosonde released at Cape Canaveral 10 mi...

Advances in Forecasting Extratropical Cyclogenesis at the National Meteorological Center

The National Meteorological Center1 represents one of the major meteorological forecast centers in the world and is the central component of a “forecaster-machine” mix that characterizes the forecast process in the United States. Inthis chapter, the lineage from the concepts of Vilhelm Bjerknes and the Bergen school of the late 1910s to the creation of the National Meteorological Center in 1960 is traced. Furthermore, the improvements made in forecasting cyclogenesis at the National Meteorological Center are examined, with emphasis placed on (1) the advancements in numerical prediction, and (2) the role of the forecasters who have become skillful at understanding the strengths and weaknesses of numerical prediction models and applying them in forecasting on a day-to-day basis.

The use of successive dynamic initialization by nudging to simulate cyclogenesis during GALE IOP 1

SummarySynoptic/diagnostic case studies have increasingly come to rely on numerical simulations started from some initial state after which the model generated fields receive no further information from observed data. The purpose of this paper is to demonstrate the use of a dynamic data assimilation technique based on nudging to create a dynamically consistent high-resolution four-dimensional data set that can be used for synoptic diagnostic studies. The nudging technique is applied in the Goddard Mesoscale Atmospheric Simulation System (GMASS) using the 3-h radiosonde data collected during GALE IOP 1. A unique aspect of this application is nudging toward data analyses for which the areal coverage shifts with time. One of the two nudging simulations assimilates surface pressure in addition to the temperature, mixing ratio, and wind components. The nudging values are determined by linear interpolation between 3-h observation times. Assuming a linear variation of the assimilated value in time leads to estimates of the nudging coefficients which take into account the accuracy of the observations.Both nudging simulations are more accurate in terms of S hand root-mean-square error (RMSE) scores than a control sunulation without successive initialization. The nudging simulation with surface pressure is more accurate than the nudging simulation without surface pressure assimilation for this case. The simulation with surface pressure nudging captures the surface cyclogenesis and the associated strong rise-fall couplet in the 500 hPa height field. It also exhibits the strongest ageostrophic flow and exit region vertical circulation associated with a jet streak on the western side of the intensifying upper-level trough.The data sets made possible by the dynamic assimilation/ simulation cycles are dynamically consistent, have high spatial and temporal resolution and are ideally suited for diagnostic studies. Examples presented include the evolution of the ageostrophic flow associated with the exit region of an upper-level jet propagating toward the base of an intensifying trough with increasing cyclonic curvature of the flow. The nudging simulation with surface pressure provides the resolution and accuracy required to depict the rapid transformation (within a 12-h period) of the exit region ageostrophic flow from predominantly cross contour to along contour as the jet streak approaches the base of the trough.

The great Arctic outbreak and east coast blizzard of February 1899

Abstract 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 du...