Monsoonal Moisture to Further Threaten the Southwest US and Southern Rockies with Heavy Rain and Flash Flooding

Monsoonal moisture threatens the Southwest US and Southern Rockies again this week, causing potential heavy rain and flash flooding across the regions, according to the National Weather Service (NWS).

The weather system is likely to continue in the coming days, even during the weekend.

While rainfall and floodwaters pose the greatest risk, other weather hazards, such as strong winds lightning, and thunderstorms could still occur.

Indirect yet related risks also include electrocution. Power outages and disruption to travel, as well as to businesses are possible.

The inclement weather is part of the so-called "North American Monsoon," which brings rainfall not only to portions of Canada and the United States but also to countries in Central America.

The mentioned monsoon is often compared as a lesser form of the Asian monsoon. However, various sources have shown it is also the same weather phenomenon.

The NWS weather forecast of the North American Monsoon comes as a "dangerous heat" continues to impact most parts of the Central US and Northeast US.

In recent days and weeks, a renewed heat wave or heat dome shattered all-time high temperature records in multiple cities.

Monsoonal Moisture Forecast

Along with other weather advisories, the NWS' Weather Prediction Center (WPC) issues on Wednesday, July 20, its new short-range forecast regarding the persistent monsoonal moisture that will bring localized torrential rain and isolated flash floods to some portions of the said Western US regions.

The WPC forecast is valid from Thursday to Saturday, July 21 to July 23, which contains other weather hazards like the potential severe thunderstorms from the Ohio Valley to New England and even parts of the Southeast US on Thursday.

The US weather agency also retains its "Excessive Heat Warnings" and "Heat Advisories" for the latter half of the week, with over 100 million Americans under the heat alerts.

Intense heat in the form of above-average temperatures could result in heat-related illnesses, the NWS says.

The North American Monsoon

The National Oceanic and Atmospheric Administration (NOAA) stated that the North American Monsoon is an annual climate phenomenon, particularly prevalent in the Southwest US and Northwest Mexico.

Defined as a seasonal change within the atmosphere, the NOAA says this occurs as the summer heat or summer sun makes the continental land mass to become hotter.

The warming makes the prevailing wind to become dry over the so-called "monsoon region" consisting of Northwest Mexico, Arizona, and New Mexico.

Furthermore, the summer heat buildup over North America enables the formation of high pressure over the monsoon region, bringing the dry wind into a southward direction to bring moisture from areas between the Gulf of California and the Pacific Ocean.

US Southwest Monsoon Season

While the US has already entered its summer season, which approximately spans from June to September, the southwestern part of the country has its separate yet integrated season pertaining to the North American Monsoon.

In 2008, NWS officials made a decision to consider the period between June 15 and September 30 to be the US Southwest Monsoon Season in Arizona or the Southwestern Monsoon, according to the University of Arizona's Climate Assessment for the Southwest (CLIMAS).