Late September provided a chance to photograph storms associated with the passage of an upper-level trough crossing the southwest. Ahead of the trough would be moderate-to-strong upper level winds along with deep-layer shear. So there was a possibility of a few strong thunderstorms that might develop supercellular characteristics. As well, there would likely be a line of storms that formed on the surface cold front pushing southeastward across the state.
The plan was to head north to Cameron, Arizona, then slowly work back to the south as the line of storms moved across the area. I went to Cameron but the storms to the west and northwest were already weakening while storms farther to the southwest were strengthening. So — back south I went with stops at Wupatki NM and Sunset Crater NM while watching the storms. A cluster of storms developed north of the San Francisco Peaks and eventually pushed a strong outflow across the mountains. The leading edge of this outflow had an interesting cloud structure and was briefly very photogenic.
After a few photos, I continued moving across Flagstaff on my way home. Suddenly, the sun dropped low enough to get below the clouds and for a few minutes there was great sunset light on the bottom of the clouds. I shot a few photos at Fort Tuthill County Park with the undersides of the clouds full of sunset colors. And, then just a few minutes later it was over and the light was gone.
So I could have just stayed at home and gone out shooting at the last minute of daylight.
The next day showed potential for a few interesting storms south of Flagstaff. I headed to Sedona and spent a few hours photographing storms.
The past few days have produced interesting storms across northern Arizona.
An isolated storm developed around sunset and produced both wonderful colors and lightning. Most of the lightning, however, was on the other side of the updraft so the storm instead was lit from the inside like a lightbulb. The storm colors and lightning was nicely reflected in the waters of the Kachina Wetlands.
A few days later a large line of convective storms moved southwestward across the state and produced a haboob in the lower (and drier) elevations. As the leading edge of the rain-cooled air moved across the San Francisco peaks the clouds quickly enveloped the mountains. About an hour later, the shelf cloud arrived in Sedona and new storms began to develop.
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.
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 thunderstormsâ€”some severeâ€”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 convectionÂ 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.
Other storms produced very large hail with a report of 2.75″ hail in Holbrook and another of 2.00″ near Tolani Lake.
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.
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.