Meteors and Comets

The past few nights have been interesting. On the evening of December 13–14 was the peak of the Geminid meteor shower. This year the expected peak was around 100–120 meteors per hour and various meteor counts appear to confirm that number.

At the same time, Comet 46P/Wirtanen has been getting a lot of attention. On December 16 it made its closest approach to Earth—only 11.5 million km away. That’s about 30 lunar distances for reference.

From SpaceWeather.com: “Although the comet is very close to Earth, it is not very bright. 46P/Wirtanen is a relatively small comet and, thus, barely visible to the unaided eye despite its proximity. It is nevertheless an easy target for digital cameras. Even a short exposure reveals the comet’s spherical form and emerald green hue.”

During the late evening of December 13, I traveled to Wupatki National Monument because of its dark skies. I shot a sequence of photos—each of 30 seconds duration—of the night sky hoping to catch a few meteors. One bright meteor blazed across the sky and I was able to catch part of it before it moved out of the frame of the camera. At the same time, the crescent Moon was setting in the west and gently illuminating Wukoki Pueblo. At the very top center of the photograph is Comet 46P/Wirtanen.

Geminid meteor, Comet 46P/Wirtanen and Wukoki Pueblo.
Geminid meteor, Comet 46P/Wirtanen and Wukoki Pueblo.

After about 1/2 hour of shooting meteors, I shot longer exposures of the comet. On this night, the comet formed a triangle with the Pleiades and Hyades star clusters. The image shown here is from ten 60-second images stacked using Deep Sky Stacker (DSS) and post-processed using  rnc-color-stretch.

Comet 46P/Wirtanen with the Pleiades and Hyades star clusters.
Comet 46P/Wirtanen with the Pleiades and Hyades star clusters.

A few nights later, the comet had moved so that it was between the Pleiades and Hyades clusters. Again, I shot a sequence of 60-second exposures totaling about one hour in duration—this time from the Mormon Lake overlook. The motion of the comet is quite apparent in this sequence of images. The first image shows the motion of the comet against the stars; the second is a time-lapse movie of the same sequence.

The motion of Comet 46P/Wirtanen is seen as a short streak in this one-hour composite image.
The motion of Comet 46P/Wirtanen is seen as a short streak in this one-hour composite image.

Time lapse movie showing the motion of Comet 46P/Wirtanen during a period of one hour.

Comet 46P/Wirtanen is now moving farther from Earth and will slowly dim in brightness but it will remain visible through binoculors, telescopes, and with digital cameras for many weeks or more. There is still plenty of time to see the comet if you haven’t already.

A Transition Season Severe Weather Event

Lightning behind Wukoki Pueble in Wupatki National Monument.

September 1 marks the first day of “meteorological autumn” and it started out with a severe weather event across portions of northern Arizona. Severe storms are more likely during what is often called the “transition season” as we make the switch from the North American Monsoon weather pattern into a fall pattern.

In the transition season the westerlies begin to push southward again as the large area of high pressure over the southwest weakens. Disturbances in the westerlies along with stronger jet-level winds can combine with copious amounts of residual tropical moisture to bring severe thunderstorms to the area.

250 mb pattern for 1200 UTC 01 September 2018. (Image from NOAA/Storm Prediction Center.)
250 mb pattern for 1200 UTC 01 September 2018. (Image from NOAA/Storm Prediction Center.)
Upper air sounding for KFGZ at 1200 UTC 01 September 2018.
Upper air sounding for KFGZ at 1200 UTC 01 September 2018.

A short-wave trough and moderate jet stream were present across Arizona at 1200 UTC 01 September. Monsoon moisture was also present. The first hint that something was up was the development of thunderstorms—some severe—before sunrise. This patch of storms moved to the east and northeast and, in its wake, left a pool of cooler air across northeastern Arizona along with an outflow boundary. Outflow boundaries can often play an important role in subsequent convection with increased severity and rotation as the storm moves across the boundary. (Maddox et al. 1980; Rasmussen et al. 1998)

Afternoon runs of the HRRR model showed storms developing along an east-west line across northern Arizona and that some of these would interact with that boundary, become severe and turn to the right moving southeast. And that’s pretty much what happened. Score one for the HRRR model.

HRRR simulated radar forecast for the afternoon of 01 September. (Animated GIF courtesy of College of DuPage.)
HRRR simulated radar forecast for the afternoon of 01 September. (Animated GIF courtesy of College of DuPage.)
Reflectivity from KFSX radar at 1607 MST.
Reflectivity from KFSX radar at 1607 MST.

Other storms produced very large hail with a report of 2.75″ hail in Holbrook and another of 2.00″ near Tolani Lake.

View of rapidly developing convection east of Wupatki National Monument (Panorama from northeast through south).
View of rapidly developing convection east of Wupatki National Monument (Panorama from northeast through south).

I was watching and photographing these storms from the southern portions of Wupatki National Monument. There was explosive vertical growth in these storms along with some generally unorganized rotation. The storm also developed a rear-flank downdraft. And I was able to hear the “hail roar” (i.e., a roaring sound that originates in the storm cloud caused by large hailstones hitting the ground or colliding in mid-air). I’ve occasionally heard hail roar in High Plains storms but never in Arizona.

Low clouds, fog, and a K-H wave in the cold pool behind the storm.
Low clouds, fog, and a K-H wave in the cold pool behind the storm.
Cumulonimbus mammatus behind the storm.
Cumulonimbus mammatus behind the storm.

Behind the storm, cold outflow dominated and low clouds and fog quickly developed across the low hills of Wupatki National Monument. A broad area of mammatus clouds was also present.

Lightning behind Wukoki Pueblo in Wupatki National Monument.( Single exposure of 1/4 second.)
Lightning behind Wukoki Pueblo in Wupatki National Monument.( Single exposure of 1/4 second.)

And the lightning was impressive.

Lightning map for 01 September 2018. (Courtesy of WeatherBell.)
Lightning map for 01 September 2018. (Courtesy of WeatherBell.)

Arizona Monsoon Clouds—July 2018

Late afternoon sun briefly lights up Cathedral Rock in Sedona.

The North American Monsoon arrived in northern Arizona during the first week of July—which is an average start date. Within just a few days, we quickly transitioned from Extreme Fire Danger to High—and within a week or two—to Moderate.

Summer monsoon season is my second storm chase season—the first is in late spring across the High Plains. Second season is more about lightning, clouds with dramatic scenery, and colors at sunset. This July has been a bit more challenging than other seasons but still successful.

Here are some photographs of storms and storm-related activity during July 2018.

Early stage Cumulonimbus

A pair of developing cumulonimbus as seen from Kachina Wetlands.
A pair of developing cumulonimbus as seen from Kachina Wetlands.

Cumulonimbus over Hart Prairie.Cumulonimbus over Hart Prairie.

Outflow boundaries and arcus clouds

Gust front and arcus clouds advance across Wupatki National Monument.
Gust front and arcus clouds advance across Wupatki National Monument.
Gust front and arcus clouds continue to advance across Wupatki National Monument.
Gust front and arcus clouds continue to advance across Wupatki National Monument.

This complex of storms was moving westward across Wupatki National Monument. I had originally planned to photograph the system from the Doney Mtn. Picnic Area but the system arrived at that location before I did. So I retreated back to US-89 and the entrance to the Monument. Both of these images are panoramas that span the northeast through south. The San Francisco Peaks can be seen at the far right of both images.

Rainbows (and maybe a tornado?)

A rainbow (and possible vortex).
A rainbow (and possible vortex).

As convection approached a rainbow developed and I was busy trying to reset the camera to capture the full bow. Only later, when examing the images, did I notice what might be a vortex bisecting the rainbow. Because I did not see it in real time I cannot say whether there was any rotation. It may just be a random bit of cloud debris.

Lightning

The best part of the thunderstorm season is trying to capture lightning. It’s more than just getting a photograph of lightning—it’s important to get lightning in an interesting location.

Lightning visibile from South Rim of Grand Canyon with Desert Tower in the distance.
Lightning visibile from South Rim of Grand Canyon with Desert Tower in the distance.
Lightning over the Painted Desert as seen from South Rim of Grand Canyon.
Lightning over the Painted Desert as seen from South Rim of Grand Canyon.
Lightning over the Painted Desert.
Lightning over the Painted Desert.
A composite of four images showing multiple lightning strikes on the San Francisco Peaks. These storms dropped almost 6 inches of rain in under 3 hours.
A composite of four images showing multiple lightning strikes on the San Francisco Peaks. These storms dropped almost 6 inches of rain in under 3 hours.

Menacing thunderstorms

Sometimes I chase storms—other times they chase me. We were mountain biking on Observatory Mesa when this thunderstorm developed and enveloped the San Francisco Peaks. It was definitely time to turn around.

A thunderstorms envelopes the San Francisco Peaks.
A thunderstorms envelopes the San Francisco Peaks.

Sunset after the storm

And, of course, sunset after the storms can be pretty amazing,

Sunset over Grand Canyon as seen from Lipan Point.
Sunset over Grand Canyon as seen from Lipan Point.
A distant thunderstorm is backlit by the setting sun at Grand Canyon.
A distant thunderstorm is backlit by the setting sun at Grand Canyon.
Late afternoon sun briefly lights up Cathedral Rock in Sedona.
Late afternoon sun briefly lights up Cathedral Rock in Sedona.
Dark skies behind Cathedral Rock.
Dark skies behind Cathedral Rock.
The setting sun lights up the clouds as shadows race up the face of Cathedral Rock.
The setting sun lights up the clouds as shadows race up the face of Cathedral Rock.

Reflections

Reflections in pools of water can produce interesting images. Several days of heavy rain resulted in ponds of water at Crescent Moon Picnic Area.

The setting sun illuminates Cathedral Rock which is reflected in a small pond.
The setting sun illuminates Cathedral Rock which is reflected in a small pond.

Rainfall amounts

As is typical, rainfall amounts can vary widely over even just a few miles. Here is a map showing the rain gauge amounts for July on the east side of the San Francisco Peaks southward through Flagstaff and beyond. Amounts range from 2.5 to 14.5 inches.

Rain gauge totals for July 2018.
Rain gauge totals for July 2018.

August continues to bring thunderstorms, lightning, and flooding to northern Arizona.