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ATMS 373- Mountain Meteorology

This article explores the factors that determine mountain climates in North America, including latitude, altitude, continentality, and regional circulations. It also examines the impact of mountains on regional weather patterns and microclimates.

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ATMS 373- Mountain Meteorology

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  1. ATMS 373- Mountain Meteorology • Packet#2 • Mountain climates http://www.ils.unc.edu/parkproject/webcam/webcam.html

  2. ATMS 373- Mountain Meteorology • Outline • Mountain climates (Chaps. 1, 2) • Background • Lee cyclogenesis (Article 1) http://www.ils.unc.edu/parkproject/webcam/webcam.html

  3. ATMS 373- Chapter 1 • Four factors that determine climate • (1.1) Latitude, determines • Length of day • Angle of incoming sunlight • Amount of solar radiation received at site Fig 1.1, 1.2, 1.3

  4. ATMS 373- Chapter 1 • Four factors that determine climate; (1.1) Latitude • Near the equator • Length of days ~ same year-round • Noon sun is nearly overhead year-round little seasonal variability in the weather Fig 1.1

  5. ATMS 373- Chapter 1 • Four factors that determine climate; (1.1) Latitude • Near the poles • Dark in winter • Sunny in summer • Low diurnal variability high seasonal variability in the weather Fig 1.1

  6. ATMS 373- Chapter 1 • Four factors that determine climate; (1.1) Latitude • Mid-latitudes • moderate diurnal varibility • moderate seasonal variability in the weather Fig 1.1

  7. ATMS 373- Chapter 1 • Four factors that determine climate; (1.1) Latitude • Altitude angle of sun • High angle  sun is nearly overhead  more heating per unit area • Low angle  sun is near the horizon  less heating per unit area Fig 1.2

  8. ATMS 373- Chapter 1 • Four factors that determine climate; (1.1) Latitude • Semi-permanent pressure belts • Equatorial, sub-polar lows • Sub-tropical and polar highs • Shift north (south) in summer (winter) • Names • Bermuda high, Pacific high Aleutian low Fig 1.3

  9. ATMS 373- Chapter 1 • Four factors that determine climate • (1.2) Altitude, as it increases: • Temperature generally decreases • Incoming solar radiation increases • Wind speeds generally increase • Air density (pressure) decreases http://www.viveier.com/?p=67

  10. ATMS 373- Chapter 1 • Four factors that determine climate; (1.2) Altitude • High “changeability” of mntn weather • Air at high altitudes has a quick response to heat input • Rapid transport of warm and cold air, clouds, and storms by strong winds http://www.viveier.com/?p=67

  11. ATMS 373- Chapter 1 • Four factors that determine climate • (1.3) Continentality • Locations at the center of a continent experience larger diurnal and seasonal temperature changes than locations near large bodies of water (differences in specific heat) http://www.jyi.org/articleimages/224/originals/img0.jpg

  12. Figure 11: Temperature data for San Francisco, California (37°N), and Richmond, Virginia (37°N) - two cities with the same mean annual temperature.

  13. ATMS 373- Chapter 1 • Four factors that determine climate; (1.3) Continentality • Coastal locations • Less sunshine, more cloudiness, more moisture, more precipitation, moderate temperatures • Coastal mountains; heavy precipitation on windward side than inland locations http://www.jyi.org/articleimages/224/originals/img0.jpg

  14. ATMS 373- Chapter 1 • Four factors that determine climate • (1.4) Regional Circulations • Seasonal dependence Fig 1.4 (a, b)

  15. ATMS 373- Chapter 1 • Four factors that determine climate; (1.4) Regional Circulations • Summer dominated by sub-tropical high pressure • Bermuda high; carries warm tropical air northward into central U.S. • Pacific high; fog, cool weather along U.S. west coast • California low Fig 1.4 (a)

  16. ATMS 373- Chapter 1 • Four factors that determine climate; (1.4) Regional Circulations • Winter semi-permanent lows become strong • Extensive wintertime precipitation as maritime air is lifted over coastal barriers on west coast • Arctic and Great Basin Highs • Ocean currents • Gulf Stream, Kuroshio Fig 1.4 (b)

  17. ATMS 373- Chapter 2 • Mountain Climates of North America • The Appalachians • The Coastal Range • The Alaska range • The Cascade Range • The Sierra Nevada • The Rocky Mountains Fig 2.1

  18. ATMS 373- Chapter 2 • Mountain Climates of North America • The Appalachians • The Coastal Range • The Alaska range • The Cascade Range • The Sierra Nevada • The Rocky Mountains maritime influence ? continental influence

  19. ATMS 373- Chapter 2 • Mountain Climates of North America • Mntn range can itself affect the regional climate • By acting as a barrier to regional flows • For example, arctic air mass outbreaks from northern Canada [see following slide] http://www.theodora.com/wfb/photos/china/china_photos_18.html

  20. Average upper-level wind flow (heavy arrows) and surface position of anticyclones (H) associated with two extremely cold outbreaks of arctic air during December. Numbers on the map represent minimum temperatures (°F) measured during each cold snap.

  21. ATMS 373- Chapter 2 • Mountain Climates of North America –two challenges in creating detailed descriptions • Microclimates • Lack of high-altitude climate measurement (e.g. precipitation) stations

  22. ATMS 373- Chapter 2 • Mountain Climates of North America • (2.1) The Appalachians • 1500 mile mntn range • Highest peak at Mt. Mitchell (6684 ft) • Climate of Appalachians is determined primarily by latitude Fig 2.2

  23. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.1) The Appalachians • Northern climate • Spruce and fir forests • Less extensive clusters of mountains • Mt. Washington (NH) experiences some of the worst weather on the continent • Cool climate • Most winter precip falls as snow • Snow cover remains for most of winter http://www.72hourchallenge.org.uk/preparation.htm

  24. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.1) The Appalachians • Southern climate • Hardwood and pine forests • Series of long ridges • Mt. Mitchell highest point east of the Mississippi River • Temperate and rainy climate • Most winter precip falls as rain • Snow cover remains for a few days, at most in only the highest summits http://www.72hourchallenge.org.uk/preparation.htm

  25. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.1) The Appalachians, summer • Bermuda High • Warm humid air from Gulf of Mexico • Traps pollutants and natural hydrocarbon emissions  dense haze (Great Smoky Mntns) • Thunderstorms common • Tropical storms and hurricanes can bring heavy rain and flooding to eastern slopes Frances http://www4.ncsu.edu/~nwsfo/storage/cases/20040908/track.20040917.frances.jpg

  26. ATMS 373- Chapter 2 (3) • Mountain Climates of North America; (2.1) The Appalachians, winter • Synoptic-scale storms • Lee cyclones from Rocky Mntns, heavy precip, then cold, arctic outbreaks (1) • Coastal cyclones, heavy precip on the east on the east side of the range (2) • Locally-generated cyclones (3) L (1) (2)

  27. ATMS 373- Chapter 2 • Mountain Climates of North America • (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada • Parallel west coast of North America • Lie perpendicular to prevailing westerlies of mid-latitudes Fig 2.3

  28. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada • Highest peaks and ridges of C.R. are found in Alaska • Mt. Olympus (7965 ft) highest point of C.R. in lower 48 states • Temperate rain forest at the base of the Olympic Mntns • Alpine tundra above 5000 ft of Olympic Mntns Fig 2.3

  29. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada • Largest mntn range in Alaska • Highest peak on the North American continent (20,320 ft) • Extensively glaciated Fig 2.3

  30. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada • Highest peaks are volcanoes (Mt. Rainier, 14,410 ft) • Mean crest height of Cascades considerably below elevations of isolated volcanoes • Most extensive glaciation in the lower 48 states Fig 2.3

  31. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada • Immediately south of Cascade Range • Steep-sloped barrier parallel to lower elevation coastal range • Mt Whitney (14,495 ft) highest peak in lower 48 Fig 2.3

  32. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada • Significant barriers to maritime air masses • Heavy precipitation occurs on windward slopes of the ranges [100-200 in. AK, 150 in. WA, 120 in. OR, 50 in. N. CA] Fig 2.3

  33. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada • Rain shadows in lee of mntn ranges • Sequim, WA; 16 in. per year • Death Valley, CA; 2 in. per year (80 miles east of Mt. Whitney) • Rainfall is seasonal and is influenced by Aleutian Low and Pacific high Fig 2.3

  34. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada, winter • Aleutian low dominates • Nearly continuous precip along southeast AK, western Canada, and in the Pacific Northwest • Rain in coastal range, snow at higher ranges inland (sometimes rain)  freezing level is watched closely Fig 2.3

  35. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.2) The Coast Range, the Alaska Range, the Cascade Range, and the Sierra Nevada, spring andsummer • Pacific High moves northward • Milder, drier weather • Subsidence associated with high pressure suppresses clouds and precipitation (except fog) Fig 2.3

  36. ATMS 373- Chapter 2 • Mountain Climates of North America • (2.3) The Rocky Mountains • Extend over 3000 miles from northwestern AK to northern New Mexico • Largest mntn range in North America • Two climate zones • Northern Rockies [NR] (AK to central Wyoming) • Southern Rockies [SR] (central Wyoming to New Mexico) http://www.peakbagger.com/range.aspx?rid=14

  37. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.3) The Rocky Mountains • NR; heavily glaciated and support coniferous forests • SR; sparse glaciers and forests  lower precip amounts (40 in. per year) • Wide range of “life zones” (prairie, foothills, montane, sub-alpine, alpine) http://www.peakbagger.com/range.aspx?rid=14

  38. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.3) The Rocky Mountains • Typical continental climate • Large daily and seasonal temperature ranges • Intermntn valleys receive meager amounts of precip (12 in. per year) • Powder snow common; lower water content (2-7%) http://www.peakbagger.com/range.aspx?rid=14

  39. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.3) The Rocky Mountains; winter • NR; impacted by storms forming near Aleutian Low • SR; jet stream brings strong winds aloft http://www.peakbagger.com/range.aspx?rid=14

  40. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.3) The Rocky Mountains; summer • NR; isolated afternoon thunderstorms, light precip, hazard of lightning-ignited forest fires • SR; Bermuda High brings moisture to eastern foothills producing afternoon thunderstorms, monsoon winds http://www.peakbagger.com/range.aspx?rid=14

  41. ATMS 373- Chapter 2 • Mountain Climates of North America • (2.4) Between the Mountains • Large plateus, basins, plains, and valleys • Climates characterized by limited precip and extreme temperatures Fig 2.4

  42. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains • Largest region “Great Plains” between Rocky Mntns and the Appalachians • Coast Range  Rockies, Rocky Mntn Trench • Central Valley (CA) • Great Basin, between Rockies and Sierra Nevada • Columbia Basin, between Rockies and Cascades Fig 2.4

  43. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains, Great Plains • “invaded” by arctic and polar air masses from north (northern Canada) and maritime tropical air from south (Gulf of Mexico) Fig 2.4

  44. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains, Brooks-Coast range • Extremes in temperature due to seasonal changes in solar insolation (incoming solar radiation) • Records; -80oF, 100oF for Alaska both found between ranges • Permafrost is found here Fig 2.4

  45. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains, Rocky Mntn Trench • Cold air from arctic outbreaks collects in the trench • When cold air is deep enough, it drains westward through gaps in the coastal range  gap winds • Low annual precipitation Fig 2.4

  46. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains, Central Valley • Sacramento Valley (north) and San Joaquin Valley (south) • Drain into the Pacific Ocean through the Caracena Straits near San Francisco • Tulle fog; cold moist maritime air flows eastward off the Pacific into the valley through the Caracena Straits, a problem during winter Fig 2.4

  47. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains, Great Basin • 200,000 sq miles of desert • Variations of elevation are substantial; Mt. Whitney (14,495 ft) to Death Valley (282 ft below sea level) • Precip falling from clouds often evaporates before reaching the ground Fig 2.4

  48. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains, Great Basin • Generally protected from arctic and polar air masses • Winter temperatures low due to high elevations • Record high temperature for western hemisphere (134oF, Death Valley, CA) Fig 2.4

  49. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains, Columbia Basin • Fertile land in WA, OR, and western Idaho • Must be irrigated due to low annual precipitation Fig 2.4

  50. ATMS 373- Chapter 2 • Mountain Climates of North America; (2.4) Between the Mountains • “breaks” in a single range (gaps) • Narrow; strong winds… issues with blowing snow and forest fire containment • Broad; similar climate to valleys, limited precipitation and a large diurnal and seasonal temperature range Fig 2.4

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