Monsoon upon us Published July 1, 2010 By Staff Sgt. Jasmine Reif 56th Fighter Wing Public Affairs LUKE AIR FORCE BASE, Ariz. -- Monsoon is upon us and the Air Force Weather agency is predicting an average season and forecasts it will begin soon. In Arizona, Monsoon occurs when winds reverse directions seasonally, which determines the weather of large regions. The change of wind directions is caused by the greater annual temperature differences over large areas of land than over nearby waters. "Monsoon weather is characterized by continued high temperatures and increasing humidity," said Staff Sgt. John Mitchem, 56th Operations Support Squadron Weather Flight acting mission weather element NCO in charge. "When an air mass is forced from a low elevation to a higher elevation, it most commonly triggers thunderstorms in the mountains. When the weather cools in the evenings the storms begin to move into the valley." The main forecast challenges for Luke Air Force Base under the Monsoon system are thunderstorms, heavy rain and strong convective winds. The Monsoon is the most significant weather-producing feature in the Southwest desert. "Monsoon accounts for about 70 percent of all rainfall in Arizona, and during flash floods, cars on base can get stuck in small bodies of water," said Staff Sgt. Jason Chalmer, 56th OSS Weather Flight airfield services element NCO in charge. "It is very important for people to be aware of weather forecasts. In Arizona, there is a law called the 'stupid motorist law' and if someone drives onto a road marked 'flooded' and gets stuck, the cost to save them must be repaid to the city." Luke is located on the northwest boundary of the monsoonal zone. As a result, it is directly affected by the strongest of monsoonal patterns. Periodic high intensity surges may produce conditions that will bring about short-term thunderstorm outbreaks generally lasting three to five days. Monsoon occurs every year in Arizona and during thunderstorms there can be frequent flash flooding on base. There are four types of Monsoons: Type 1: Four Corner High This is the most common of the four types of monsoonal flows. A high sets up over Four Corners, subsequently opening the Gulf of Mexico and pushing moisture toward Arizona. Small, single cell thunderstorms build over the mountains and quickly collapse. The result is stronger thunderstorms over the base. This can quickly escalate and turn into a severe weather event. Wind warnings, hail warnings and lightning watches are most likely to be issued for this type of storm. Type II: Rim Shot/Great Basin High A Great Basin High sets up over southern Nevada, causing the flow to come into Arizona from the northeast. It is sometimes referred to as a "backdoor cold front." Most of the thunderstorm activity is over the Mogollon Rim. This is the typical set up for severe thunderstorms in the Phoenix area. High winds, hail, lightning and heavy rain warnings may be issued. Type III: Trapping High A Bermuda high shifts west to Texas, resulting in a gulf surge. This creates an immense moisture source allowing for the development of massive thunderstorms. Flash flooding is the most common in this type and a warning for lightning and more than two inches of rain in 12 hours is likely to be issued. Type IV: Transitional This type of monsoonal flow most represents thunderstorms in the Midwest. In August and late September weather returns to normal patterns. Massive thunderstorms can result and even produce tornadoes for Arizona. Severe winds, hail and rain could occur in this pattern. If a tropical system is captured by the system, flash flooding could occur. The most common weather with monsoonal thunderstorms are lightning, sudden sustaining high winds, dust storms and flash flooding. "It's important to be aware of these storms while commuting or participating in recreational activities," Sergeant Mitchem said. "If participating in water activities remember just because it's not raining where you are at doesn't mean there couldn't be a flash flood heading your way." If storms are in the mountains and a downpour occurs, that water may travel to bodies of water located at lower elevations. "It is best to avoid flooded roads all together," he said. "If you are caught in a dust storm while driving, it's best to pull off the road and park in a safe place until the storm passes. Being aware of your surrounding environment and using good judgment skills are the best overall ways to avoid bad situations."