Atmospheric River Over Arizona

December 24, 2021 / Add comment

We had a very wet period from late afternoon Thursday through early evening Friday (12/23-12/24) as an atmospheric river (AR) moved across the southwest and Arizona. From the Wikipedia site:

An atmospheric river (AR) is a narrow corridor or filament of concentrated moisture in the atmosphere. Other names for this phenomenon are tropical plume, tropical connection, moisture plume, water vapor surge, and cloud band.

GOES-17 water vapor channel showing the moisture plume.

An approaching trough of low pressure was able to tap into tropical moisture and move it across the southwest into Arizona overnight. Interestingly, the moisture plume aloft initially moved above a drier layer of air. Precipitation falling into this drier air experienced strong wet bulbing and evaporative cooling which lowered snow levels to ~6500 feet—putting Flagstaff into the snow. As the plume continued, these cooling effects diminished and the snow turned into rain. So we had about 4-6″ of snow followed by day-long rain. What a mess.

The Center for Western Weather and Water Extremes provides forecasts for ARs moving into the West. Below are some of the products valid at 5 A.M. Friday (12/24/2021) that clearly show the plume of moisture.

Integrated water vapor (iwv): Note how the moisture is depleted as it crosses the Mogollon Rim with very little moisture available across NE Arizona.

It’s great to get all this moisture although it would have been much better if had been either all rain or all snow. Mixed precipitation is always a mess.

Comet C/2021 A1 (Leonard)—III

December 21, 2021

Comet C/2021 A1 (Leonard) remains a visually interesting object in the evening twilight. It is only visible for short time each evening between the time it gets dark enough to see it and when it gets too low on the horizon and is obscured by dust or clouds.

Comet C/2021 A1 (Leonard) at 1833 MST 20 December 2021. Image has been inverted to help show the fine structore of the tail.

Comet C/2021 A1 (Leonard) at 1833 MST 20 December 2021.

The comet has undergone a rapid brightening in the past few days. From Spaceweather.com:

The outburst might signal a fragmentation event in the comet’s core. This would come as no surprise. The comet is heading for its closest approach to the sun (0.61 AU) on Jan. 3rd. Increasing heat may be liberating new jets of gas and dust from the comet’s core—or worse, blowing away huge chunks of ice and rock.

There have been numerous magnificent images posted to the Spaceweather.com website:

In the southwest we are heading into an extended period of cloudy skies with rain and snow so it is unknown when I will get another chance to shoot photographs of the comet.

A Frosty Morning in Sedona

December 15, 2021

Last week we headed down to Sedona for a trail run. Because of a recent rain event followed by a very cold night there was frost on the ground and some of the vegetation. Especially wonderful was the spiky frost on many rocks and tree roots.

It was beautiful—and it didn’t last long.

Aspen Leaves and Autumn Color

October 20, 2021 / 1 Comment

The changing color of aspen leaves has peaked in many locations — and just now peaking in others. It’s always interesting to see which areas go early and which hang on until later.

Here are some photos of aspen around northern Arizona this past week.