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

Staff Writer, DL Mullan

Weather / Air Quality
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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,

Do You Want a Dust Storm with Dinner?

Staff Writer, DB Holmes

Weather / Air Quality
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The start of the weekend looks good but there is the possibility of a dust storm from dry thunderstorms coming in from the west and southwest. Then Phoenix will be headed into the triple digits once again. A tropical storm is ramping up in the southwestern waters off Mexico. What will happen? Nothing so far in the forecast seems to indicate any problems from this tropical depression as it strengthens.

Still for those people with respiratory problems, stay inside with filtered air at any signs of dusty air.

Forecast Discussion: The lingering area of low pressure to the west finally opens up and and catches a ride on the main jet stream over the weekend. Before this happens, however, Arizona will see an influx of moisture into the eastern half of the state. Models also show possible dry thunderstorms developing in southwestern Arizona Friday afterno

Saturday's Air Quality Forecast

on near Yuma and Gila Bend. The outflow could generate some dust moving in all directions. The first PM10 monitor that would impacted in the Valley would be the Buckeye monitor. Models have the wind field (and possible dust) moving east across the Valley between 6 and 8 pm. This is the second consecutive day the models have had this solution. We have raised the PM10 forecast to reflect this possibility. Ozone levels may also increase on Saturday in response to Friday's outflow. The same model shows possible thunderstorm outflow moving south from Prescott into north Phoenix Saturday afternoon on the back side of the eastward-moving low pressure system. This would potentially affect the Surprise/Dysart/Sun City/north Peoria area the most. It's going to be a very active, interesting couple of days weather-wise which increase air quality uncertainty.

Source: AIRNow, Weather Channel 

Last of April's Hours Don't Bring May Flowers

Staff Writer, DB Holmes

Weather / Air Quality

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Phoenix is going to be hot in the beginning of this week but temperatures will be tapering off into the mid to upper 80's by next weekend. Watch out for more wind associated with low pressure systems making their way down the jet stream.

Forecast Discussion: Daytime highs in Phoenix will warm to the middle 90s through Tuesday with high pressure moving through the region. We will see ozone levels edge up each day, reaching the middle Moderate range by Tuesday, ahead of the next disturbance on Wednesday. The mid-week system will bring cooler air, dropping afternoon highs into the upper 80s. This wave will be lacking moisture, so no rain is expected for the deserts. Winds may exceed 15-20 mph at times. We'll be watching the models of changes to speeds and directions of the wind which could result in some blowing dust. For now, it doesn't appear to be a big dust-maker for the Phoenix area.

Source: AIRNow, Weather Channel  

Spring into Summer, Phoenix is Dry and Hot

Staff Writer, DB Holmes

Weather / Meteorology
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It is that time of the year again when temperatures rise as well as ozone concentrations. The rainless wind episodes have helped further dry out the deserts. Potential for blowing dust is still relevant as breezy conditions come into the Valley this weekend with windy conditions set up for the middle of next week.

Forecast Discussion: The official high in Phoenix on Wednesday was 95°F. As expected, we saw ozone concentrations go up around the forecast area under the light, west-to-east flow. The baseline for Thursday is higher, so it’s likely that levels will go higher as well under sunny skies and relatively light winds. An approaching upper-level system could boost levels further on Friday into the middle Moderate range before dropping off Saturday with increased surface breezes and atmospheric mixing. PM10 levels also bounced higher, into the lower Moderate range on Wednesday. The South Phoenix and West 43rd Avenue monitors registered 53 and 55 AQI, respectively. Buckeye was not far behind at 50 AQI. This is a testament to how dry the soil has become, and long-range models suggest there will be no rain expected over the next 2 weeks. We don’t anticipate any significant blowing dust this weekend, but it’s possible to see some pockets along the desert floor between Phoenix and southern California Saturday into early Sunday. Daytime temperatures are forecast to drop into the upper 80s, close to 90°F on Saturday and Sunday, warming slightly once again by Monday.

Source: AIRNow