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Clifford F. Mass

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Clifford F. Mass

For over a half-century, the Bergen School conceptual model of cyclone structure and development has dominated the practice of synoptic meteorology, especially regarding the techniques by which surface synoptic charts are analyzed. Although the Norwegian paradigm captures some of the essential features of cyclone evolution, research and practical application over the last 60-odd years have revealed significant deficiencies, several of which are discussed in this paper. The Bergen model has also been applied in regions and under conditions quite unlike those for which the model was originally developed. Knowledge of these problems by many in the research and operational communities has had little impact on the manner in which synoptic charts are analyzed or the way the subject is described in many textbooks. Deficiencies in the underlying conceptual model of cyclone development have been compounded by a lack of consistent and well-defined procedures for defining fronts and for analyzing surface synoptic charts. Several examples of confusing and inconsistent surface analyses are presented in this paper.

To resolve these problems, the meteorological community should follow a two-pronged approach. First, the research and operational insights gained over the last half-century should be combined with recent numerical modeling and observational studies to establish improved conceptual models of cyclone evolution. Second, a clear and consistent methodology for analyzing synoptic charts should be devised. Several possible approaches for implementing these suggestions are presented in this paper.

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Clifford F. Mass

This paper describes the current application of compact discs (CD-ROM) to the storage and distribution of datasets for atmospheric sciences and related disciplines. CD-ROM technology is reviewed, currently available discs are listed, and a look at future developments is provided.

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Clifford F. Mass
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Clifford F. Mass

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The coastal regions of southern Oregon and northern California can be considerably warmer than locations to the north and south when air descends the substantial mountain barrier to the east. This paper describes the event of 27 February 1985, during which Brookings, Oregon experienced the highest February temperature ever observed in that state.

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Clifford F. Mass
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Clifford F. Mass
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Robert Conrick
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Clifford F. Mass

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The OLYMPEX field campaign, which took place around the Olympic Mountains of Washington State during winter 2015/16, provided data for evaluating the simulated microphysics and precipitation over and near that barrier. Using OLYMPEX observations, this paper assesses precipitation and associated microphysics in the WRF-ARW model over the U.S. Pacific Northwest. Model precipitation from the University of Washington real-time WRF forecast system during the OLYMPEX field program (November 2015–February 2016) and an extended period (2008–18) showed persistent underprediction of precipitation, reaching 100 mm yr−1 over the windward side of the coastal terrain. Increasing horizontal resolution does not substantially reduce this underprediction. Evaluating surface disdrometer observations during the 2015/16 OLYMPEX winter, it was found that the operational University of Washington WRF modeling system using Thompson microphysics poorly simulated the rain drop size distribution over a windward coastal valley. Although liquid water content was represented realistically, drop diameters were overpredicted, and, consequently, the rain drop distribution intercept parameter was underpredicted. During two heavy precipitation periods, WRF realistically simulated environmental conditions, including wind speed, thermodynamic structures, integrated moisture transport, and melting levels. Several microphysical parameterization schemes were tested in addition to the Thompson scheme, with each exhibiting similar biases for these two events. We show that the parameterization of aerosols over the coastal Northwest offered only minor improvement.

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Clifford F. Mass
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David Ovens

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The Camp Fire event was associated with dry, northeasterly winds that descended the western slopes of the Sierra Nevada of Northern California during the early morning hours of 8 November 2018. The downslope winds peaked around sunrise, with strong winds pushing the fire rapidly toward Paradise, California. Similar to recent central/Northern California wildfires associated with downslope winds, the synoptic pattern was characterized by building sea level pressure over the Intermountain West and a trough along the coastal zone, with both the synoptic evolution and low-level winds skillfully forecast by operational models. The maximum wind gusts along the western Sierra Nevada slopes ranged from 10–20 kt (1 kt ≈ 0.51 m s−1) at sheltered locations to 50–60 kt at exposed sites on the mid- to upper slopes of the barrier. The highest winds were not climatologically exceptional, and low-level temperatures were cooler than normal over and to the east of the Sierra Nevada, near normal over the western slopes, and warmer than normal over coastal California. Drier-than-normal conditions prevailed during the ∼3 days preceding and during the event, as a result of downslope winds. The origin of the fire can be traced to strong winds interacting with a failing electrical transmission infrastructure, with highly flammable surface fuels fostering rapid fire movement between the ignition source and Paradise.

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Justin Sharp
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Clifford F. Mass

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This paper quantifies the impact of the Columbia Gorge on the weather and climate within and downstream of this mesoscale gap and examines the influence of synoptic-scale flow on gorge weather. Easterly winds occur more frequently and are stronger at stations such as Portland International Airport (KPDX) that are close to the western terminus of the gorge than at other lowland stations west of the Cascades. In the cool season, there is a strong correlation between east winds at KPDX and cooler temperatures in the Columbia Basin, within the gorge, and over the northern Willamette River valley. At least 56% of the annual snowfall, 70% of days with snowfall, and 90% of days with freezing rain at KPDX coincide with easterly gorge flow.

Synoptic composites were created to identify the large-scale patterns leading to strong winds, snowfall, and freezing rain in the gorge. These composites showed that all gorge gap flow events are associated with a high-amplitude 500-mb ridge upstream of the Pacific Northwest, colder than normal 850-mb temperatures over the study region, and a substantial offshore sea level pressure gradient force between the interior and the northwest coast. However, the synoptic evolution varies for different kinds of gorge weather events. For example, the composite of the 500-mb field for freezing rain events features a split developing in the upstream ridge with zonal flow at midlatitudes, while for easterly gap winds accompanied by snowfall, there is an amplification of the ridge.

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