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Louis W. Uccellini, Paul J. Kocin, Joseph Sienkiewicz and, Robert Kistler, and Michael Baker

Abstract

Fred Sanders' career extended over 55 yr, touching upon many of the revolutionary transformations in the field of meteorology during that period. In this paper, his contributions to the transformation of synoptic meteorology, his research into the nature of explosive cyclogenesis, and related advances in the ability to predict these storms are reviewed. In addition to this review, the current status of forecasting oceanic cyclones 4.5 days in advance is presented, illustrating the progress that has been made and the challenges that persist, especially for forecasting those extreme extratropical cyclones that are marked by surface wind speeds exceeding hurricane force. Last, Fred Sanders' participation in a forecast for the historic 1947 snowstorm (that produced snowfall amounts in the New York City area that set records at that time) is reviewed along with an attempt to use today's operational global model to simulate this storm using data that were available at the time. The study reveals the predictive limitations involved with this case based on the scarcity of upper-air data in 1947, while confirming Fred Sanders' forecasting skills when dealing with these types of major storm events, even as a young aviation forecaster at New York's LaGuardia Airport.

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Paul J. Kocin, Philip N. Schumacher, Ronald F. Morales Jr., and Louis W. Uccellini

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.

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Louis W. Uccellini, Paul J. Kocin, Ralph A. Petersen, Carlyle H. Wash, and Keith F. Brill

Abstract

The Presidents' Day cyclone of 18–19 February 1979 was an intense and rapidly developing storm which produced heavy snowfall along the East Coast of the United States. An analysis of the cyclone is presented which isolates three jet streaks that appear to have played important roles in the development of two separate areas of heavy snow. One area of heavy snow developed prior to cyclogenesis and is linked, in part, to an increasingly unbalanced subtropical jet streak (STJ) and a noticeably ageostrophic low-level jet. The second area of heavy snow developed in conjunction with the explosive cyclogenesis off the East Coast as a polar jet streak and midtropospheric trough propagated toward the coastal region from the north-central United States.

This paper examines the STJ in detail. The maximum wind speeds associated with the STJ increased by 15 to 20 m s-1 between 1200 GMT 17 and 1200 GMT 18 February 1979 as the jet propagated from the south-central toward the eastern United States. During the 24 h period, the flow in the STJ became increasingly supergeostrophic and apparently unbalanced. Ageostrophic wind speeds increased to greater than 30 m s-1, with a significant cross-contour component directed toward lower values of the Montgomery streamfunction, as the flow along the STJ became increasingly divergent with time. The increased wind speed, ageostrophic flow, and divergence along the axis of the STJ are linked to the increasing confluence in the entrance region of the jet streak and the decreasing wavelength of the trough-ridge system in which the jet streak was embedded. The upper level divergence and upward vertical motion near the axis of the STJ along with the moisture transport associated with the LLJ are found to be important factors in the development of the first area of heavy snow.

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Paul J. Kocin, David A. Olson, Arthur C. Wick, and Robert D. Harner

Abstract

The preparation of surface weather analyses at the National Meteorological Center (NMC) is currently under review. The availability of advanced graphics workstations and consideration of revisions to conceptual models of cyclogenesis and frontal analysis present challenges and opportunities for improving surface analysis at NMC. In this paper, current procedures and surface analysis products are reviewed. The adaptation of workstation technology to one surface weather analysis product, the Daily Weather Maps, Weekly Series, is described and presented as a preliminary experiment for assessing the utility of performing surface analyses on interactive workstations. Finally, issues that will impact the future of surface analysis at NMC, such as workstation development, utilization of gridded datasets and their manipulation for improving objective analyses, possible revisions to frontal symbology, incorporation of mesoscale symbology, and changes to sea-level pressure computations, are discussed.

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Steven E. Koch, William C. Skillman, Paul J. Kocin, Peter J. Wetzel, Keith F. Brill, Dennis A. Keyser, and Michael C. McCumber

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 model's predictive skill and its most important systematic errors at the synoptic scale. The model's 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 model's 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 forecasts at an overall level of performance equivalent to that of the LFM model. Lower tropospheric mass fields are, for the most part, predicted significantly better by the MASS 2.0 model, but it is outperformed by the LFM at and above 500 mb. The greatest improvement made by the mesoscale model is a 73% reduction of cold bias in LFM forecasts of the 1000–500 mb thickness field, primarily over the western United States. The LFM bias is the combined result of model overforecasts of surface anticyclone intensity and underforecasts of surface cyclone intensity and nearby 500 mb geopotential heights.

The poorer forecasts by the MASS 2.0 model in the middle and upper troposphere result primarily from a systematic mass loss which occurs only under a certain synoptic flow pattern termed the mass loss regime. Problems with specification of the lateral boundary conditions and, to a lesser extent, erroneous computation of the map factor seemed to contribute most to the systematic mass loss. This error is very significant since MASS 2.0 performance either equaled or surpassed that of the LFM model in forecasts of virtually every meteorological field studied when mass loss regime days were excluded from the sample.

Two other important systematic errors in MASS model forecasts are investigated. Underforecasts of moisture over the Gulf Coast states are found to be due in large part to a negative bias in the moisture initialization. Also, overforecasts of surface cyclone intensity and 1000–500 mb thickness values over the Plains states are traced to excessive latent beating resulting from the absence of a cumulus parameterization scheme in the model. Awareness of these synoptic-scale forecasts errors enables more effective use to be made of the (unfiltered) mesoscale forecast fields, which are evaluated in the companion paper by Koch.

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Louis W. Uccellini, Keith F. Brill, Ralph A. Petersen, Daniel Keyser, Robert Aune, Paul J. Kocin, and Mary des Jardins

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 min after the shuttle accident combined with radiosonde and jimsphere wind measurements before the shuttle launch reveal that, over XMR, the magnitude of the maximum wind in the PFJ was increasing with time while the magnitude of the STJ was decreasing. Even with the decreasing magnitude of wind speeds in the core of the STJ over XMR, large vertical wind shears and low Richardson numbers were still diagnosed near the PFJ and beneath the core of the STJ at the time of launch (1639 GMT). The low Richardson numbers associated with the presence of vertical wind shear indicate that conditions were favorable for shear-induced turbulence at the time of the shuttle explosion.

The results from the analyses of the synoptic radiosonde data are inconclusive due to the poor temporal and horizontal spatial resolution of the observational data base and the large number of missing data reports at numerous stations in the southeastern United States (including XMR). In an attempt to overcome this deficiency, numerical simulations of the atmospheric conditions were conducted using a mesoscale numerical model. The simulations initialized at 1200 GMT 28 January confirm the juxtaposition of two distinct jet systems over north-central Florida at the time of the shuttle launch and the presence of large vertical wind shears and low Richardson numbers associated with these jets.

Given the rapid temporal evolution of atmospheric flow regimes which involve strong wind shears, we recommend that consideration should be given to 1) augmenting the observations (both in time and space) upstream and around the Cape Canaveral launch facility, 2) enhancing the analysis and display capabilities of these data, and 3) using numerical-model output to provide the best possible diagnosis and forecast of the meteorological conditions for future shuttle launches.

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Walter F. Dabberdt, Jeremy Hales, Steven Zubrick, Andrew Crook, Witold Krajewski, J. Christopher Doran, Cynthia Mueller, Clark King, Ronald N. Keener, Robert Bornstein, David Rodenhuis, Paul Kocin, Michael A. Rossetti, Fred Sharrocks, and Ellis M. Stanley Sr.

The 10th Prospectus Development Team (PDT-10) of the U.S. Weather Research Program was charged with identifying 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 convection; 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.

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