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Li-Chuan Gwen Chen and Huug van den Dool

in most studies. The investigation is conducted using the 1982–2010 hindcasts from eight models in the North American Multimodel Ensemble (NMME), and the study area is focused on North America. In the following, section 2 introduces the NMME seasonal forecast data and verification fields. Section 3 describes the weighting methods and system design for deriving the consolidation forecasts. Section 4 explains the cross-validation procedure and performance metrics. Section 5 presents the

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Lee B. Carlaw, Ariel E. Cohen, and Jaret W. Rogers

1. Introduction a. The North American monsoon During the early summer, the upper-air pattern across the Southwest undergoes a substantial evolution as mid- and upper-level winds switch from westerly to easterly or southeasterly. Bryson and Lowry (1955) were among the first to recognize that this was a result of the poleward movement and westward expansion of the Bermuda high during the end of June. Coincident with this alteration to the flow pattern is typically a marked increase in moisture

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Jose-Henrique G. M. Alves, Arun Chawla, Hendrik L. Tolman, David Schwab, Gregory Lang, and Greg Mann

North American Mesoscale Model (NAM) forced GLW system (e.g., wind forcing). a. Spectral resolution Waves can develop over long fetches and propagate long distances in the major oceanic basins, generating wave spectra that may contain measurable amounts of energy in very low frequencies. Therefore, typical wind-wave models resolve discrete energy spectra with frequencies in ranges from 0.03–0.04 up to 0.5–1.0 Hz. In the Great Lakes, geographical features limit the fetch size and propagation

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Jaret W. Rogers, Ariel E. Cohen, and Lee B. Carlaw

1. Introduction This study of North American monsoon convective environments over central and southern Arizona builds on the information from Carlaw et al. (2017 , hereafter CCR ), which provides an overview of environments favorable for lightning and severe weather over the region. Observed soundings and gridded mesoanalysis data are examined to determine which commonly used variables exhibit the most predictive skill for lightning and severe thunderstorm reports across the domain

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Nathaniel C. Johnson, Dan C. Collins, Steven B. Feldstein, Michelle L. L’Heureux, and Emily E. Riddle

Julian 1971 , 1972 ; Zhang 2005 ). The MJO tropical convection anomalies excite large-scale teleconnection patterns, including the two dominant Northern Hemisphere patterns: the Pacific–North American (PNA) pattern ( Knutson and Weickmann 1987 ; Ferranti et al. 1990 ; Higgins and Mo 1997 ; Mori and Watanabe 2008 ; Johnson and Feldstein 2010 ; Riddle et al. 2013 ) and the North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) ( Cassou 2008 ; L’Heureux and Higgins 2008 ; Lin et al. 2009

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Katherine E. Lukens and Ernesto Hugo Berbery

is expected to rise with projected increases in strong-storm frequency and intensity ( Karl et al. 2008 ; Shapiro et al. 2010 ; Kunkel et al. 2013 ; Lawrimore et al. 2014 ). As such, the study of storm tracks and related impacts is critical for understanding the effects of destructive weather and anticipating weather-related fluctuations in the state of the economy, particularly in winter. Winter weather in North America is largely influenced by the zonally oriented Pacific storm track located

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Christopher D. McCray, Eyad H. Atallah, and John R. Gyakum

duration ( Cortinas 2000 ; Ressler et al. 2012 ). Therefore, forecasters attempting to predict the severity of a freezing rain event must determine whether the freezing rain will persist for many hours, transition to another precipitation type, or simply cease. For events to persist for many hours, compensatory mechanisms must be in place to offset the self-limiting diabatic effects. The purpose of this paper is to identify where in North America long-duration freezing rain events (defined in section

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Michael Colbert, David J. Stensrud, Paul M. Markowski, and Yvette P. Richardson

2003 ; Duda and Gallus 2013 ; Kain et al. 2013 ; Burghardt et al. 2014 ; Burlingame et al. 2017 ). It is clear that forecasting CI accurately remains a significant forecast challenge. In this study, we take a different approach and specifically explore the physical processes associated with CI in the North American Mesoscale Forecast System, version 3 (NAMv3; Janjić et al. 2005 ). Two severe weather outbreaks are forecast retrospectively using the NAM 4-km CONUS and 1.33-km Fire Weather nests

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Frederick Sanders

'70 WEATHER AND FORECASTING -OLUME2A S~udy of 500 mb Vorticity Maxima Crossing the East Coast of North America and Associated Surface Cyclogenesis FREDERICK SANDERSMarblehead, M~I 01945(Manuscript receoved 3 November 1986, in final form 9 February 1987 For assessment of the sufficiency of the approach of an upper-level vorticity maximum as a predictor ofexplosive surface cyclogenesis in the

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Gregory B. Goodrich

the time series to change the base period climatology from 1951–1980 to 1971–2000. The Pacific decadal oscillation (PDO) characterizes low-frequency changes in the SST field in the Pacific Ocean with a period of approximately 50 yr. The PDO index is the leading principal component or eigenvector of the mean monthly SSTs in the Pacific Ocean north of 20°N ( Mantua et al. 1997 ). Positive values of the index are associated with above normal SSTs along the west coast of North America and below normal

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