Tuesday afternoon brought the passage of a weak cold front across northern Arizona. It was mostly clear much of the day but by late afternoon clouds were increasing and spreading southward. Because there was a distinct west edge to the clouds it was likely that the setting sun would be able to illuminate the overhead clouds.
As the band of convective snow showers progressed southward it took on the characteristics of an outflow boundary and even developed a bit of a shelf cloud on the leading edge.
As the sun dropped lower in the western sky this cloud band briefly took on the colors of sunset.
Time lapse video showing the southward progression of the convective snow showers.
And, then, a few minutes later the light was gone.
It’s always fun to head out at the tail end of a winter storm and capture photographs of the sunrise with the new snow. This winter has had only a few periods with real winter weather—the most notable was the last 10 days of December. Since then storms and snow have been infrequent.
Of course I was interested in taking advantage of our latest weather event—even though it was fairly weak and delivered only a skiff of snow. A quick check of satellite imagery before sunrise showed that skies were mostly clear and that there was a cap cloud on top of the San Francisco Peaks.
I arrived a bit before sunrise at the Mormon Lake overlook and started taking both photographs and video. The clouds were already dissipating over the peaks resulting in much less of a cap cloud than I hoped.
No matter—it’s always fun to out there before sunrise shooting photos. Here are a few photos from before sunrise and just after as the sun began to illuminate the peaks.
Below is a time-lapse video showing the movement of the clouds over the summits of the San Francisco Peaks.
Time lapse video (50x) of the sunrise over the San Francisco Peaks.
I was also intrigued by the tire tracks left in the snow of the parking area.
Finally—here is a sunrise photo from New Years Day—the last day in which we had significant snow here.
It’s been awhile since the last post about the comet—but cloudy skies with lots of rain and snow have made observations difficult. Finally, we had a break in the weather on New Year’s Day and I was able to capture additional images.
The comet has dropped lower in the sky making it difficult to get good images because the comet is now located in the band of twilight glare. Only at the end of astronomical twilight is the sky dark enough but by this time the comet is very low on the horizon leaving only minutes to shoot until it sets.
Below are two images of the comet. The first is a set of images taken between 1832 and 1850 MST. The best 30 images were combined and averaged in Starry Sky Stacker then histogram stretched using rnc-color-stretch. Individual images were shot at 85mm, ƒ/4, ISO 100, and 15 seconds. The resulting image shows the tail extending nearly to the upper left corner.
The second image is a single image taken at 1901 MST at 85mm, ƒ/1.8, ISO 500 and 30 seconds. This image shows how close the comet was to the horizon. The glow at the bottom of the image is the light dome from Phoenix about 200 km to the south.
The comet is moving away from us and lower in the sky. I’m not certain I will be able to get another chance to capture any images. For those in the southern hemisphere, the comet is better placed in the night sky for viewing and photography and there have been some amazing images captured. Spaceweather.com noted that “…Intense solar heat has given the comet one of the most beautiful tails astronomers have ever seen…”
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.
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.
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.
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: