What’s Happening at WeatherSure - July 2012

I thought that this month we’d talk a little about Colorado weather- for newcomers or lifelong residents, Colorado weather can be awe inspiring, scary, confusing and more- the one rule about the weather here is it’s always changing, and there’s no such thing as unusual weather- hurricane force winds, draught conditions, flash flooding- if you’ve been here a while, you’ve seen a lot of varied conditions. The meteorologists throw out terms like “upslope” and “monsoon”, and let’s take a look from a scientific perspective - 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. I am reproducing part of his discussion here, and the full presentation can be found on the “Sailing Association of Intermountain Lakes” website. 

The summer weather pattern. Winds in the Plains are dominated by the Bermuda High; mountains are dominated by monsoon and local circulations: Denver sits between.  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.

Four Main Weather Regimes:

  • ·      Westerly downslope
  • ·      Post cold front upslope - Often terminate Dry Line at Palmer Divide (near town of Monument Colorado)
  • ·      Mountain upslope breeze
  • ·      Bermuda high southerlies
    • Most often, late summer