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Colorado W i n d

John McGinley drew on his years of experience with the National Oceanographic and Atmospheric Administration to put together the mechanisms & indicators  for sailors' wind on the western edge of the Great Plains, in the lee of the Rocky Mountains. He presented as part of SAIL's Winter Racing Seminars on April 12th, 2006.

The presentation has material of interest to Wyoming, New Mexico, & western Nebraska sailors.

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A short summary:

Winds on the Great Plains are dominated by the circulation around the Bermuda High. Winds in the Rockies are dominated by monsoon or  local circulations. The Front Range sits right in between these countervailing effects. sometimes one dominates, sometimes another.

The "Dry Line" is the line separating the southerly winds of the Bermuda High from the mountain winds. It shifts from as far east as the Kansas-Colorado border to the Rockies' foothills.

"Colorado Monsoon" is the term given to moisture-laden air circulating from off the west coast of Mexico in mid- to late-summer. Warm moist air flows north until it meets cools over the mountains and drops its water.

McConaughey Reservoir -- near Ogallala Nebraska -- receives mostly the Bermuda High southerlies. Carter Lake, Chatfield Reservoir, and Cherry Creek Reservoir are in the Front Range area of variable winds. Dillon, Ruedi, Grand Lake & Granby are mountain lakes winds are "steered" by the surrounding peaks & valleys.

Four Main Weather Regimes:

•  Westerly downslope - dangerous gusts. Also known as  Chinook, or Foehn winds. Characteristics:
  • Cap Cloud over mountains. Lenticular (lens-shaped) clouds drift eastward.
  • Vertical "rotors" can bring reverse flow down to surface.
  • In winter, known as "The Snoweater". Compression heating melts snow.
    
•  Post cold front upslope – cloudy with showers.
  • The upslopes bring snow in winter.
  • Often terminate Dry Line at Palmer Divide (near town of Monument Colorado)
     
•  Mountain upslope breeze - light and nutty winds.
  • Caused by the sun heating the eastern side of the mountains in the morning.
  • May disappear by mid-morning, engendering hours of calm.
     
•  Bermuda high southerlies - Denver Cyclone and thunderstorms.
  • Most often, late summer
  • Dry Line shifts west to the Front Range.
  • Mixing westerlies & southerlies produce rotation.