Monday, July 28, 2014

On Again, Off Again, the Monsoon is a Fickle Creature

Staff Writer, DL Mullan
Weather / Air Quality

The monsoon will take a break in the western part of the state and bring with it hotter temperatures. Tuesday through Thursday will begin this on and off pattern. The coming weekend will see a return of storm chances and air quality concerns with dust storm formation.

Until then, keep your oven mittens in the car, July is not over and August is setting up to be as hot as ever.
Forecast Discussion: It has been an active few days now on the weather front! It started with the unusually large dust event that affected portions of Mexico on Thursday. This was likely caused by what is called a Mesoscale Convective System. This dust then moved northward into Arizona Thursday and Friday with a moisture surge. A pronounced haze was widespread. As a result PM-10 and PM-2.5 were already elevated before significant thunderstorm activity and multiple outlfows triggered a dust storm that impacted much of the Valley during the early evening on Friday. Ultimately, six Maricopa County monitors exceeded the PM-10 health standard. Then another round of strong winds, locally heavy rainfall, and blowing dust struck the Phoenix Metropolitan late last night into the early morning hours. This would account for the lingering haze seen today along with higher current PM readings. We remain in an unstable environment. Models are consistent in showing thunderstorms forming once again over the higher terrain. These then move westward under east-southeasterly steering winds into the Phoenix area during the early evening. Stronger outflows dropping out the higher terrain from the north and east versus the south will help limit the dust threat, but localized blowing dust is still possible. The steering flow is then expected to turn southwesterly by Monday, which is unfavorable for bringing convection into the Valley. Generally, ozone readings are running lower than this time yesterday, likely to due to this morning's cloud cover and the clearing winds from last night. We expect ozone to stay around the lower Moderate range through Tuesday.
North looking toward the Estrella Mountains

Source: AIRNow, Visibility Cameras,