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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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Ning Lin, James A. Smith, Gabriele Villarini, Timothy P. Marchok, and Mary Lynn Baeck

areas were obtained from USGS Digital Elevation Model (DEM) data, which were based on the North American Vertical Datum (NGVD) and adjusted to the mean sea level (see Shen et al. 2005 ). ADCIRC simulations were carried out for astronomical tides in normal days and for storm tides (the sum of the astronomical tide and storm surge) during Hurricane Isabel’s passage. In the first case, ADCIRC was forced by tidal constituents along the ocean boundary. In the second case, ADCIRC was forced by tidal

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Sen Zhao, Malte F. Stuecker, Fei-Fei Jin, Juan Feng, Hong-Li Ren, Wenjun Zhang, and Jianping Li

operational seasonal forecasting, the use of multimodel ensemble prediction generally results in improved skill due to error compensation and greater consistency and reliability between models ( Hagedorn et al. 2005 ; DelSole et al. 2014 ). The North American Multimodel Ensemble (NMME) system ( Kirtman et al. 2014 ) was recently developed to harness this idea. The NMME system is used for seasonal predictions since 2011 and was made an operational forecast system in 2016. Many studies have shown that the

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Lance F. Bosart

SEPTEMBER 1990 LANCE F. BOSART 527 Degradation of the North American Radiosonde Network LANCE F. BOSARTDepartment of Atmospheric Science, State University of New York at Albany, 1400 Washington Avenue, Albany, New York(Manuscript received 27 April 1990, in final form 7 May 1990) Over the last five years the National Oceanic andAtmospheric Administration (NOAA) has

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James Wallmann, Rhett Milne, Christopher Smallcomb, and Matthew Mehle

show its usefulness in forecasting the general locations of important features relevant to the lightning outbreak two or more days in advance. The GFS is used in this case because it is run later than the North American Mesoscale version of the Weather Research and Forecasting Model (NAM-WRF), so the assimilation scheme has more observations that are not available for the NAM-WRF, such as late upper-air observations ( NCEP 2010 ). Generally speaking, this should result in a better synoptic

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Jonny William Malloy and Randall S. Cerveny

Sonoran Desert also makes the area subject to influences by the summer North American monsoon (NAM). The NAM is a large-scale atmospheric circulation phenomenon affecting primarily the U.S. Southwest and northern Mexico ( Adams and Comrie 1997 ; Douglas et al. 1993 ). The NAM is characterized by 1) atmospheric instability ( Diem and Brown 2009 ; Heinselman and Schultz 2006 ), 2) intermittent rainfall ( Carleton 1986 ; Mullen et al. 1998 ), 3) severe weather hazards ( Brazel and Nickling 1986

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Philip N. Schumacher, Gregory Frosig, Jason L. Selzler, and Robert A. Weisman

Saskatchewan across Alberta into northwestern Montana. In the central plains, a weaker temperature gradient existed with implied warm-air advection across the eastern Dakotas and Minnesota. At 700 hPa, the trough was also observed from eastern Montana into eastern New Mexico ( Fig. 2c ). The primary thermal gradient was located from the Canadian Prairie Provinces into North Dakota and northern Minnesota. Two jet streaks were located across the North American plains at 300 hPa ( Fig. 2d ). An intense

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Brian F. O’Hara, Michael L. Kaplan, and S. Jeffrey Underwood

1. Introduction Translated as “snow-covered mountain range” in Spanish, the Sierra Nevada (especially the elevations of the High Sierra around Mount Whitney) can be snow covered for most of the year. The range is known for heavy and even legendary snowfalls including the infamous Donner Pass snowstorm of January 1952 ( Ludlum 1952 ). Since snowfalls in the Sierra Nevada can be extreme, relative to most of North America, they require considerable analyses to understand their trends and unique

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Loren D. White

regression slopes in this easternmost segment seems to be related to greater static stability in an area of rain-cooled air extending across Mississippi and western Alabama. This rain-cooled area was even more evident in the National Centers for Environmental Prediction (NCEP) North American Mesoscale (NAM) model (12-km resolution) at 2100 UTC ( Fig. 13 ). Approximate potential temperature lapse rates implied are 10 K km −1 between 91° and 90.8°W and 14 K km −1 between 90.8° and 90.5°W, based on linear

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Martin A. Baxter and Philip N. Schumacher

were missing during the period studied. To create composites of atmospheric fields, the North American Regional Reanalysis (NARR) was used as a proxy for observed atmospheric fields. The NARR, with data available every 3 h, has a grid spacing of 32 km and 45 vertical layers to 100 hPa ( Mesinger et al. 2006 ). NARR data were chosen for use because of their high temporal and spatial resolution relative to observations and also because of the consistency of the modeling system used throughout the

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