We are in the midst of the “Transition Season” where the summer monsoon pattern fades away and the mid-latitude westerlies and low pressure systems move across the area. Another of these events is in progress as a weak closed-low moves across the southwest bringing showers and thunderstorms to the area.
Saturday afternoon we set out for the north side of the San Francisco Peaks hoping that thunderstorms would form over the higher terrain and then move northwestward across Kendrick Park. A few storms did form over the peaks and some of them were briefly photogenic but there was very little in the way of lightning. Eventually, approaching rain chased us from Kendrick Park to the northwest where we set up near Slate Mountain in a large meadow with good views of the peaks.
These slow-moving storms continued to move towards the northwest and this time we got lightning and rainbowsâ€”and rainbows with lightning. As the sun dropped lower in the west the rainbow quickly faded and rain was again approaching our location. We retreated back to Kendrick Parkâ€”this time with the thunderstorms located to our northwest with light from the setting sun still illuminating some clouds. Lightning stikes were frequent and close enough to fill the field of view of the 17-mm focal length lens. Several of these lightning bolts struck the northern flanks of Kendrick Peak.Â About a half-hour after sunset it was over and the storms quickly dissipated.
An early-season trough of low pressure moved across the west on Wednesday and Thursday disrupting the winds associated with the North American Monsoon. As the trough moved across the area, copious amounts of sub-tropical moisture surged northward across Arizona and surrounding areas. Widespread rain with embedded thunderstorms occurred across the area with areas of heavy rainfall and localized flash flooding.
But now the trough has moved northeastward across the Rocky Mountains and into the northern Plains states. The moisture across the southwest has been swept away. This can be seen in the water vapor satellite image. The warm colors are associated with a drier air mass and this has overspread the southwest.
Medium range models such as the GFS (Global Forecast System) suggest that moisture and showers will not return to the area before the end of the month leaving us with an extended break in rainfall.
But there are always some features that can result in different outcomes. For example, Hurricane Grace is moving westward across the Gulf of Mexico and is expected to make landfall in Mexico. The remnants of this tropical cyclone will continue to move to the west and may emerge in the Pacific south of the Gulf of California. If this happens, there might be a surge of moisture moving northward toward Arizona that could bring a return of showers and thunderstorms sooner than models currently suggest.
This is the second year in a row in which the North American Monsoon has failed to deliver its normal weather to Arizona. The monsoon had a late start in July with only a few isolated rain events early in the month and the main event starting around the third week of July. But even that faltered after a week and the final week of July was dry.
August was even worse with no measurable precipitation until after mid-month and even then the amounts were light. The National Weather Service in Flagstaff has posted some climate data for the area for August. It was the hottest August and the 2nd driest on record in Flagstaff and most of the west experienced similar conditions (Figure 1; Figure 2;Â Figure 3).
Photographing summer monsoon storms has been a challenge this year because there were so many dry periods. Even so, there are always interesting weather events and clouds that make it worthwhile. So here is a collection of the most interesting weather photographs from this summer.
A time-lapse movie shows that the ducks are more interesting than the convection.
Full rainbows eluded me this year butI did manage to photograph a rainbow segment.
As with rainbows, lightning was elusive this year. It was typically a case of being in the wrong place on the wrong day and at the wrong time. But I did get lucky with the following image.
And when there is no lightning and no rainbow, one can be content with the sunset.
The monsoon season officially ends in Arizona on September 30 but convective activity ended a week or two ago. But the monsoon provided a great “end-of-season” show.
Several clusters of thunderstorms were moving from the lower elevations up onto the Mogollon Rim on the evening of September 13. I haven’t been able to get any good shots of lighting reflected in water in recent years so I decided to try againâ€”this time along the shores of upper Lake Mary.
I was not disappointed.
The early storms were distant to the west resulting in images with only small flashes. Another cluster of storms was to the southwestâ€”moving to the northeast. Several flashes produced dramatic branches out the top of the storm and into the starry sky.
The storms were moving directly towards me and I had to quit when they got too close. My comfort zone on these storms was about 12 miles. Close enough.
The other day provided a good opportunity to photograph both lightning from thunderstorms and sunset at Grand Canyon. Satellite imagery from the new GOES-16 satelliteÂ indicated that skies remained clear across western Arizona as well as southern Nevada and California. This would allow the setting sun to appear below the cloud deck from the thunderstorms andâ€”maybeâ€”create a great sunset with the clouds glowing from below as the sun approached the horizon.
Close, but it didn’t quite happen that way. The clouds never took on that beautiful glow. On the other hand, an abundance of monsoon moisture in the lower atmosphere allowed the sun to create beams of light and shadow through the depths of the canyon. This was at its best when the sun was briefly obscured by some mid-level clouds creating some shadows at my locationâ€”but with sunlight streaming into the canyon below.
After the sun had dropped below the horizon the beams were gone, of course, but there was still color in the western sky.
The earlier thunderstorms over the area had dissipated but new storms developed about 50 km to my west. This distance meant the visible bolts were fairly small. I wanted big bolts dropping into the canyon near me. What we want and what we get…well, you know.
The radar image shows my location (circle) and the storms to the northwest.
The lightning images are composites of multiple photographs taken over a period of several minutes. The shutter was left open for 15s for each photograph. Some had multiple lightning bolts while others were dark. Even though it was almost 90 minutes after sunset the photographs were still able to pick up twilight colors on the western horizon.
All in all, an illuminating evening (bad pun intended).