Castle Rock Weather Discussion – Week of July 10, 2017

Castle Rock Weather Forecast | Castle Rock Co Weather | 80109 Weather

This week’s weather outlook.

This week will feature typical July weather for the state of Colorado including us along the Palmer Divide region. We will have some very warm days ahead of us but we won’t get as hot as Denver is expected (forecast high of 98 for Denver on Monday) mainly thanks to our elevation and a chance of storms that will cool us off a bit. You’ll notice that there is increased chances for thunderstorms this week which may be a glimpse of our monsoon season beginning to kick off.

Thunderstorm chances overall will be in the 20-40% range depending on the day and we are hoping monsoonal flow can moisten up the atmosphere to give us rain out of these storms instead of the wind and lightning we’ve had out of most of the storms for the past week. Keep in mind, storms are expected to be relatively scattered so while the chances are higher, us seeing rain is still no sure thing!

What Is The Monsoon and What Does It Mean for Colorado?

Colorado’s monsoon season is part of a larger weather phenomenon often called the “North American Monsoon.” It is caused by a shift in upper level winds and atmospheric patterns that allows moisture to stream into the Southwestern United States. The influx of moisture in addition to daytime heating allows thunderstorms to build and produce areas of heavy rain.

Colorado Monsoon | Castle Rock Co Weather

Source: NWS

What causes this shift in the pattern? Typically we see a large high pressure sit over the region in June and early July that helps to steer storms away from the area and keeps things very warm and dry. As we move into mid July, the high pressure aloft moves to the East; the counter-clockwise flow then sends moisture up from the Gulf of Mexico, across the Desert Southwest and into Colorado.

Keep in mind, our source of moisture is not consistent though… it can ebb and flow from day to day or week to week. It all depends on where the high pressure sets up.

This Accuweather monsoon graphic shows the High further West over Colorado

If the upper level high pressure moves back towards the West and sits over Colorado we will see a return to hot and dry conditions as the monsoon moisture is pushed further West away from Colorado. The trick for Colorado’s monsoon season is that we need to have a decent number of days where this all sets up well for us. The monsoon is critical to providing summer rains and keeping us from getting too crispy in the summer.

Monsoon Thunderstorms in Our Future?

The setup this week looks like our first glimpse of a monsoon pattern in Colorado. We will have to keep a close eye on it to see if it takes hold though as next weekend the high is expected to move West and anchor over Colorado again, effectively shutting of our moisture flow.

Colorado Monsoon | Castle Rock Co Weather

Notice this graphic’s similarity to the one provided by the NWS above

We can use the Precipitable Water graphic above to spot some of the subtropical moisture moving across the Southwest and up into parts of Colorado. This is very encouraging but it still depends on how far East the high pressure moves and if it sets up in a favorable area. Much like the storms we see in the winter, a wobble 50 miles East or West can make all the difference!

Did You Know?

The term “Monsoon” is often thought of or associated with “heavy flooding rains.” In its simplest terms the word Monsoon actually just means “a change in the wind.”

It’s the change in the wind from more of a Westerly/Northwesterly direction to a South or Southwesterly direction that brings the big change in our weather in Colorado during monsoon season.


John R. Braddock
Storm Chaser/ Amateur Meteorologist at Mountain Wave Weather
John R. Braddock is a NOAA/NWS Certified Storm Chaser and Amateur Meteorologist living in Castle Rock, Colorado. A graduate of Colorado State University with a Bachelor's in Computer Science and a Colorado native, he specializes in short range forecasting, severe weather and mountain weather dynamics.

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