Monsoon season is in full swing across parts of the western United States as areas from Nevada to Oklahoma — including most of the state of Colorado — are under a flash flood watch for the next couple of days. Parts of the region could see three to four inches of rain by the time the event is over on Wednesday.

Flash flood watches are in effect for all of the counties shaded in green on the map above. A flash flood watch means that conditions are favorable for heavy rainfall to develop and produce sudden, intense flooding in low-lying areas with little or no warning.

Heavy rains are already occurring this afternoon across parts of Utah, Wyoming, and Colorado, with several flash flood warnings in effect. Flooding is ongoing in some places, including around Cheyenne, Wyoming, and east of Albuquerque, New Mexico. Heavy rains over a burn scar west of Las Vegas yesterday caused a five-foot deep debris flow in the small town of Mount Charleston, according to The Weather Channel.

Latest rainfall forecasts from the Weather Prediction Center show a bullseye of three to four (or more) inches of rain possible across parts of central and eastern Colorado, with a wider swath of two to three inches extending down through Oklahoma and into New Mexico.

According to the latest flash flood guidance, it won't take much heavy rain to create flash flooding in the area. In much of central and eastern Colorado, it will just take one to two inches of rain in falling in three hours to trigger flash floods. The three-hour rainfall limit for flash flooding sits between two and three inches across northeastern New Mexico, and between two-and-a-half and three-and-a-half inches across the Texas Panhandle and western/central Oklahoma.

It goes without saying that nobody should ever drive through a flooded roadway — "turn around, don't drown" as the National Weather Service's saying goes — since it only takes a few inches of swiftly-moving water to pose a threat to both people and cars.

[Images: NWS, Google Earth, NWS]