Western United States Monsoon Pattern (Photo Credit: SPC)

DISCUSSION: As mid-summer approaches, the western United States experiences a monsoonal type pattern. Hot and dry weather typically dominates the early parts of the summer months, as seen this June with record breaking high temperatures across portions of the Desert Southwest. As mid and later July approaches, showers and thunderstorms break out day after day across the western United States. Most of the annual precipitation the Southwestern United States receives is from these showers and thunderstorms that feature frequent lightning, large hail, and heavy downpours.

​These storms can be dangerous to the population in these areas. Flash flooding is frequent under heavy thunderstorms which can stagnate producing inches of rainfall within an hour or less. Just this past weekend, at least 9 people lost their lives in Arizona due to flash flooding. This is not the only danger from these thunderstorms, aside from the fact that lightning and large hail have their own destructive properties, dry microbursts are also a common occurrence in the western U.S.  Temperatures commonly soar from the 90s to over 100 degrees Fahrenheit with dew points 40, to 50+ degrees less than the ambient temperature. Any little shower or thundershower that can survive in this sort of environment has a high probability of mixing winds from upper levels of the atmosphere to the surface that could gust 60 to 70 mph, or more. This poses danger not only to people and property, but transportation as trains could easily derail by the magnitude of these wind gusts. 

Shown above is an example of storm wind/hail reports from SPC for July 17th. One thing to keep in mind, the observations are sparse out in the western U.S. as opposed to abundant in more populated areas such as the Northeast U.S. Many of the storms could be producing high wind gusts but since there are no observations or reports from people, there is no way to know the exact magnitude or number of reports. In this respect, caution is needed with any storms that develop across this area for the potential of high wind gusts and hail. These types of storm reports will be a common occurrence throughout the rest of July, August, and into September.  Out west these storms are beneficial, but as with all good things, too much is harmful.

To learn more about other high-impact weather events affecting North America, be sure to click here! 

ⓒ 2017 Forecaster Joseph DeLizio