Colorado Wind

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.

Here's 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 (caused by low pressure areas in, or off the west coast of, Mexico) 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.

Four Main Weather Regimes:

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