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Douglas K. Miller, David Hotz, Jessica Winton, and Lukas Stewart

Mexico border. The upper-wave orientation resembled the anticyclonic Rossby wave breaking scenarios identified by Bosart et al. (2017) and Moore et al. (2016) as frequent precursors of extreme weather events (EWEs) and extreme precipitation events (EPEs). Composite means of geopotential height at the 300-hPa ( Fig. 5c ) and 500-hPa ( Fig. 5d ) levels of the non-AR extreme events showed lower-amplitude troughs and ridges, a pattern indicative of weak synoptic-scale atmospheric dynamics over the

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Ariel E. Cohen and John P. Cangialosi

1. Introduction Forecasters at the Tropical Analysis and Forecast Branch (TAFB) of the National Oceanic and Atmospheric Administration’s (NOAA) National Hurricane Center in Miami, Florida, are responsible for providing high-seas forecasts to the Gulf of California, also known as the Sea of Cortez. High-seas forecasts provide event-driven forecasts of strong wind [20 kt (10.3 m s −1 ) or higher] and high-wave [8 ft (2.4 m) or higher] areas. The gulf is an oft-traversed waterway and provides a

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Jeffrey S. Gall, Isaac Ginis, Shian-Jiann Lin, Timothy P. Marchok, and Jan-Huey Chen

high-resolution atmospheric model run with prescribed SSTs (e.g., Bender et al. 1993 ; Bender and Ginis 2000 ). As the resolution increases to a level that can support compact and strong TCs, it then becomes imperative that atmosphere–ocean interaction be accounted for in the forecast model, and to a lesser degree, in the assimilation system. Leaving a high-resolution atmospheric model detached from the ocean often leads to the overprediction of TC intensity. Coupling to a wave model Given HiRAM

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James E. Overland

excellent forecasts to over 140 fishing vessels in Alaskanwaters during !ate January 1989, the worst icing episode of the decade. This case suggests that current-generationatmosphere models are capable of providing reliable 36-h forecasts of cold-air advection, and thus indicatingregions of heavy icing. A wave height/wind speed threshold for the onset of topside icing is 5 m s-~ for a 15m vessel, 10 m s-~ for a 50-m trawler and 15 m s-~ for a 100-m vessel, developed from seakeeping theory.These wind

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D. Hudson, A. G. Marshall, O. Alves, G. Young, D. Jones, and A. Watkins

fortnight of the heat wave both one and two weeks in advance. The forecasts also effectively warned that the month of January would be associated with extreme heat. In contrast to January, the extreme heat in September was related to strong forcing from climate drivers that are associated with an increased chance of having extreme heat over Australia. The anomalous atmospheric circulation during the periods of heat included a strong negative SAM, MJO activity (phases 1/2 and 5/6), a persistent region of

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Shawn M. Milrad, Eyad H. Atallah, John R. Gyakum, and Giselle Dookhie

1. Introduction a. Motivation Quantitative precipitation forecasts (QPFs) remain an important challenge in meteorology, especially during heavy precipitation events ( Sisson and Gyakum 2004 ; Milrad et al. 2009b ). Roebber and Bosart (1998) and Sisson and Gyakum (2004) pointed out that while forecast skill of mass fields (e.g., 500-hPa height) has improved greatly, QPF skill lags behind. As shown by the National Oceanic and Atmospheric Administration (NOAA) Weather Prediction Center QPF

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

outbreaks culminated in the southward plunge of one final, massive anticyclone thatyielded the coldest temperatures on record for much of the south-central and southeastern United States. Thefinal cold wave was associated with the development of a cyclone that left measurable snow over most of theGulf 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

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Shih-Yu Wang, Tsing-Chang Chen, and S. Elwynn Taylor

to Midwestern flash floods, have been observed to couple with serial short-wave perturbations in the midtroposphere (e.g., Maddox et al. 1979 ; Johns 1984 ; Changnon and Kunkel 1999 ). Sub-synoptic-scale cyclonic perturbations at midlevels can sustain long-lived, progressive MCSs across the Upper Midwest (e.g., Bosart and Sanders 1981 ). Trier et al. (2006) noted that a series of preexisting perturbations embedded in the midlevel northwesterly flow induced a series of progressive MCSs in

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Qiaoping Li, Song Yang, Tongwen Wu, and Xiangwen Liu

region, a zonally oriented upper-tropospheric wave train is found, with a strong and southward-expanded SH and a strengthened and southwestward-extended Aleutian low, leading cold air from the high latitudes to southern China. The CFSv2 gives a reasonable prediction of these anomalous patterns; however, the SH and the northerly wind over eastern China are underpredicted with increasing lead time. When cold surges occur in southern China, the atmospheric patterns are similar to those of cold surges

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David H. Bromwich, Richard I. Cullather, and Robert W. Grumbine

of research activities on the Antarctic continent. Additionally, the use of atmospheric numerical analyses plays an increasingly important role in research on climate variability and change (e.g., Kalnay et al. 1996 ). Section 2 provides an overview of the NCEP Global Data Assimilation System (GDAS) and the operational global spectral model. A discussion is also given of the prevailing conditions during the FROST July 1994 SOP, the subject of this paper. In section 3 , an evaluation of the

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