Cold Air Damming by the Front Range of the Colorado Rockies and its Relationship to Locally Heavy Snows

Dunn, Lawrence B.

doi:10.1175/1520-0434(1987)002<0177:cadbtf>2.0.co;2

Cited by 30 publications

(20 citation statements)

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“…Hypothetically, usingthe lifted parcel calculation for the 8-9 December 1985 storm, and a similar cold pool slope for CHR (Dunn, 1987 does not present a thermodynamic sounding) yields saturation at the upper boundary of the cold pool approximately 25 km west of the convergence line, which is in close agreement with snowfall maxima observations (see Dunn, 1987, figs. 3 and 16; the snowfall maximum occurred 15-20 km west of the convergence line).…”

Section: The Role Of Moisture Content In the Upslope Layersupporting

confidence: 75%

“…lb ), produced a similar upslope pattern to the 8-9 December 1985 situation reported by Dunn (1987). Note the extension of heavy snowfall onto the plains just east of the foothills near the FCL area.…”

Section: I 30-31 March 1988supporting

confidence: 72%

“…This line developed as a cold pool formed against the foothills. The meso-front is similar to the one analyzed in Dunn (1987;his figs. 13-18).…”

Section: I 30-31 March 1988supporting

confidence: 70%

“…A critical difference exists in the moisture content of the incoming surface easterly flow {inflow) in the 30-31 March 1988 storm when compared to the 8-9 December 1985 storm presented in Dunn (1987). This difference exerts a major influence on the corresponding snowfall distribution.…”

Section: The Role Of Moisture Content In the Upslope Layermentioning

confidence: 97%

“…For example, blocking-induced convergent motion and precipitation can occur on sloping plains well east of the foothills (Lilly, 1981). Schultz et al (1985) and Dunn (1987) found that the interaction of topography with synoptic-scale upslope can create low-level convergence zones associated with cold air damming. Dunn presented a case study (8-9 December 1985) of a blocking-induced convergence line, or meso-front, oriented approximately north-south which enhanced upward motion in the low levels during a snowstorm.…”

Section: Introductionmentioning

confidence: 99%

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Observations of blocking-induced convergence zones and effects on precipitation in complex terrain

Wesley

Pielke

1990

Atmospheric Research

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Wesley, D.A. and Pielke, R.A., 1990. Observations of blocking-induced convergence zones and effects on precipitation in complex terrain. Atmos. Res.,.Through an extensive set of observations, including standard surface measurements, Doppler radar, routine National Weather Service radiosondes and special Cross-chain Loran Atmospheric Sounding System (CLASS) data, two case studies of wintertime storms on the east slopes of the Rocky Mountains of Colorado are presented (9-10 February 1988 and 30-31 March 1988). The emphases are the effects of blocking-induced convergence zones on snowfall distributions, snow crystal production mechanisms and banded reflectivity structure. As shown by the analysis of a typical Front Range storm, cold air damming can frequently lead to convergence zones and enhanced precipitation east of the mountains. The meso-fronts often form in place just east of the foothills, and are sensitive to the nature of the low-level synoptic easterly flow. For other upslope situations, the convergence zone does not appear as a meso-front, but as a less distinct area of convergence. Measured vertical profiles associated with the blocked surface patterns reveal a distinctly layered temperature and wind structure. These soundings, along with surface measurements of wind, moisture and snow crystal types, enable some microphysical interpretation to be made concerning snowfall production in zones of ascent aloft, which are related to frontal surfaces as well as lifting at the top of the blocking-induced cold pool. Predominance of heavily rimed, dendritic aggregates implies lifting associated with the layered vertical structure in both storms. Bands of enhanced Doppler reflectivity exhibit significant correlation with snowfall intensity. The two case studies demonstrate that distinctly different patterns of blocking and convergence can appear in Colorado Front Range storms, each resulting in a unique snowfall distribution. RESUME A l'aide d'un ensemble fourni d'observations, incluant des mesures classiques au sol, des donndes de radar Doppler, des radiosondages du rdseau du National Weather Service, et des sondages spdciaux du "Cross-chain Loran Atmospheric Sounding System" (CLASS), on pr~sente deux dtudes de cas de perturbations hivernales sur la pente orientale des Montagnes Rocheuses du Colorado (9-10 fdvrier 1988, et 30-31 mars 1988). On montre spdcialement les effets des zones de convergence induites par blocage sur la distribution des chutes de neige, les mdcanismes de production des cristaux de neige, et la structure en bande de la rdflectivit~. Comme le montre l'analyse d'une 0169-8095/90/$03.50

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Section: The Role Of Moisture Content In the Upslope Layersupporting

confidence: 75%

Section: I 30-31 March 1988supporting

confidence: 72%

“…This line developed as a cold pool formed against the foothills. The meso-front is similar to the one analyzed in Dunn (1987;his figs. 13-18).…”

Section: I 30-31 March 1988supporting

confidence: 70%

Section: The Role Of Moisture Content In the Upslope Layermentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Observations of blocking-induced convergence zones and effects on precipitation in complex terrain

Wesley

Pielke

1990

Atmospheric Research

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An air mass‐derived cool season climatology of synoptically forced Appalachian cold‐air damming

Ellis

Marston

Nelson

2017

Intl Journal of Climatology

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An air mass approach was used to identify episodes of cool season cold-air damming (CAD) within the central Appalachian Mountains region of the eastern United States. Daily air mass type data were used to identify days on which moist polar (MP) air was regionally evident east of the mountains, while non-MP air was in place at nearby stations west of the mountains. Over a 35-year study period, 219 CAD days were identified (>6 per year) with the annual frequency exhibiting no trend but suggesting that El Niño (La Niña) coincides with a greater (lesser) frequency of CAD days in winter (December-February). Synoptic atmospheric composites reveal west-to-east migration of a parent anticyclone to a classic position along the border of the northeastern United States and southeastern Canada. This coincides with a pattern of amplifying and slowly eastward-moving 500 hPa height anomalies characterized by positive (negative) values over eastern (western) North America that are signalled a few days in advance by the index representing the Pacific-North American teleconnection pattern. Confinement of the CAD below the 850 hPa level is evident in the synoptic wind field, while the composite vertical profile of the atmosphere within the CAD environment further depicts the shallow nature of the surface-based cool, moist air. Northeasterly winds at the surface veer to southeasterly within a few hundred metres above the surface, and then southwesterly at less than one km above the surface, at the 850 hPa level. The air mass approach to CAD identification appears to successfully identify regional occurrences of synoptically forced CAD, although it likely does not detect local and/or diabatically forced CAD.

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Surface airflow around Windless Bight, Ross Island, Antarctica

O'Connor

Bromwich

1988

Quart J Royal Meteoro Soc

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SCJMMARYRoss Island, Antarctica is located along the Transantarctic Mountains and is subjected to a strong southerly mountain-parallel wind regime. Despite this, Windless Bight on the island's southern coast is a region of anomalous calm. The atmospheric boundary layer dynamics that gives rise to this phenomenon is analysed both theoretically and observationally. It is the strong static stability of the boundary layer air encountering the high steep topography of' Ross Island, that causes a stagnation zone resulting in the calm conditions of Windless Bight.Direct and proxy observations of boundary layer winds provide a detailed description of airflow around the island. The anomalous (with respect to the synoptic pressure field) but persistent north-easterly winds at Scott Base are due to the deflection of highly stable, low-level air around Hut Point Peninsula. By contrast, the less frequent, strong southerly winds which override the peninsula are associated with the influx of warm maritime air from cyclonic systems to the east. It is inferred that flow of air around the terrain of Ross Island gives rise to locally strong winds; these are responsible for the ice breakout and polynya occurrences in McMurdo Sound.Thc surface airflow past Ross Island can be modelled by a two-dimensional, steady, frictionless, irrotational, incompressible flow past an obstacle, with a shape bascd on an island height contour. The flow is assumed to separate from the eastern and western sides of the island and form a wake downstream. A solution for this flow is presented, based on potential theory for streaming motion past an obstacle. The streamline and isobar patterns clearly depict the stagnation region in Windless Bight. For approaching winds of 20 m s ' thc local pressure field is perturbed by several millibars.

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Cold Air Damming by the Front Range of the Colorado Rockies and its Relationship to Locally Heavy Snows

Cited by 30 publications

References 0 publications

Observations of blocking-induced convergence zones and effects on precipitation in complex terrain

Observations of blocking-induced convergence zones and effects on precipitation in complex terrain

An air mass‐derived cool season climatology of synoptically forced Appalachian cold‐air damming

Surface airflow around Windless Bight, Ross Island, Antarctica

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