Afternoon Cloud Formations North of the Valley? (Phoenix, Cottonwood: moving, area)

[New Horizons]

Many days start out totally cloudless and clear outsidet. Then towards early afternoon you see a few whispy clouds north of the valley. As the day goes on the clouds grow thicker and darker. By sunset it looks totally cloudy north of the valley.

This same pattern occurs almost daily and I have a few questions.

What causes these cloud formations? Are the clouds there from the beginning of the day, but the changing sun angle just makes them more visible as the day goes on?

How far away are these clouds? They appear to work their way south, but always stop at a certain point. Most of the valley stays totally clear out.

Thanks! This is something I've wondered about for a few years now.

[new2colo]

Orographic uplifting. There are much taller mountains to the north and east of Phoenix, including the Mogollon Rim. As air hits these higher peaks, it cools and condenses, which creates clouds and occasional precipitation. The clouds/storms will then move in whatever direction or stay pretty much stationary, dependent on numerous factors. The reason that they often fall apart prior to reaching the Valley is the reverse effect of orographic uplifting (the rain shadow effect). As air descends, it warms up and dries out.

[azdr0710]

chemtrails, I tell ya....CHEMTRAILS!......(embarrassing to listen to this!)


https://www.youtube.com/watch?v=A_yFMNR2q5o

[ScottsdaleMark]

Sometimes, orographic lifting will result in rain on the windward side; othertimes it is not severe enough to cause rain and just causes clouds. We see this a lot in this area where clouds form but rain often does not occur.

Lastly, it still occurs even if clouds are not formed; air is always moving so if it's 100 degrees out and bone dry, and no clouds form on the windward side, it doesn't mean air isn't being forced up the mountainside and cooling as it goes; it just means it's not cooling enough to reach the point of condensation for whatever moisture may be in the air.

Similarly, if you have super moist air and that is already fairly cool, even a low, mild obstacle like a hill can potentially cause fog and or/precipitation.

[New Horizons]

I'm understanding things so far. It's 10am right now and as I look northward towards the mountains, there are no visible clouds at all. At some point in the night the clouds must dissipate or retract. Explain please. And that will be my last question.

[Ponderosa]

I was up north yesterday. It rained in the morning and was cloudy all day but as drier air moved in after the storm (the same one that was in Phx a couple days ago) it began to clear.

In general: It starts out much cooler in the north (relative humidty is higher) and the amount of cooling needed to form clouds is less than in the deserts. As the air warms in the daytime it rises into cooler spaces and clouds form. The lifting mechanism is mostly diurnal heating which is very strong in the north - cold nights, warm days. It is solar heat plus warm air coming up from the deserts. In late afternoon, the heating stops in the north, the lift stops, cold air starts to drain into the deserts taking the clouds along. The clouds bump into warmer temps at lower elevations with reduced humidities and dissipate and we get no rain.

[AZDesertBrat]

Originally Posted by New Horizons

I'm understanding things so far. It's 10am right now and as I look northward towards the mountains, there are no visible clouds at all. At some point in the night the clouds must dissipate or retract. Explain please. And that will be my last question.

I was outside at work about 10:30 this morning and I noticed that there WERE clouds along the Rim and I wondered if it was going to rain up there. Not a cloud one from that direction to here in Cottonwood. We have had some clouds lately but mostly clear skies and near perfect temps.. It seems like we have more clouds here in the mornings which make for some really gorgeous sunrises for my drive to work. Now that you've made me aware of it I'll check it out more often. Interesting...


The hot air balloons were out in force this morning! I guess they like the weather.

[locolobo13]

I can remember as a paperboy in the 60s watching clouds form above the Bradshaws on summer afternoons. What was exciting was they would often roll into town after getting into formation. They still form over the Bradshaws but don't make it into town as often.