The Big Fog

December 14, 2014

Widespread, dense fog covered portions of northern Arizona for more than a week in early December. The fog appeared at Winslow, Arizona (KINW), during the evening of December 3 and finally dissipated on the afternoon of December 12. Similar conditions were experienced in Flagstaff, Arizona (KFLG), with fog appearing on the afternoon of December 4 and finally dissipating in the evening of December 10. For some locations, including Flagstaff, the fog was episodic with periods of dense fog interspersed with clear conditions. Farther to the northeast, including places such as Winslow and the Chinle Valley, the fog was more persistent.

A sea of fog across northern Arizona at sunrise.

The fog was the result of a heavy rainfall event across northern Arizona December 2–4. Many locations received between 1 and 2 inches of rain. Following the rain, high pressure developed across the southwest and a strong thermal inversion developed. The inversion was finally removed when a trough moved across the region bringing strong southwest winds and steeper lapse rates.

Visible satellite image showing extensive areas of fog across northern Arizona.

It should be noted that thermal inversions are not rare. Quite the contrary. An inversion commonly occurs at night and during the winter when the angle of the sun is very low in the sky. After last years fog event in the Grand Canyon, some in the media declared that thermal inversions are rare and that the inversion was the cause of the fog. Not really. Both then and now the moisture evaporated out of the soils but was trapped near the ground by the inversion. And, slowly but surely, the moisture content of the lowest few hundred meters of the atmosphere became saturated and fog developed.

Well—enough of the meteorological explanation. What did it look like?

When these shallow fog events occur it is possible to find hills and mountains that are above the inversion so that an observer can look down on the fog. This often results in some amazing photographic opportunities. Anticipating that the fog would occur, I was ready to travel to the Grand Canyon to capture images of the fog filling the canyon. Well, it didn’t quite fill the canyon—at least, not like last year. But there were still photographic opportunities.

I also found myself on the lower slopes of the San Francisco Peaks north of Flagstaff and was able to capture images and video of the fog streaming across the pass between the San Francisco Peaks and O’Leary Peak as well as the sea of fog across the Little Colorado River Valley.

And the rains (and hail) came…

July 7, 2014

It’s been a dry spring—and before that, a dry winter—but the rains have finally arrived. The North American Monsoon has started across Arizona and it’s right on time. The rains usually arrive during the first two weeks of July. Rain started falling on the 2nd of July and hasn’t stopped yet. The average rainfall for July at the Flagstaff airport is 2.61″. We have already had 2.64″ and it’s only the first week. At least one location around town has had even more as shown by the rainfall map below.

Some of these storms have produced copious amounts of small hail. As the vast quantities of hail on the ground chill the near-surface air fog forms and is known appropriately as hail fog.

Most of this hail was pea sized or smaller—nothing large or severe. Even hours after the hail fell there were still piles of it along the side of the road.

It’s only the first week of the rainy season and I’m ready for a day with sunshine.

Winter returns to West Fork Oak Creek

December 12, 2013

Winter has arrived in northern Arizona with snow and very cold temperatures. On this morning (09 December), the temperature fell to -9°F in Flagstaff and -23°F at Grand Canyon Airport. That’s getting cold enough for West Fork Oak Creek to start freezing over allowing wintertime travel. It had snowed a few days earlier and with fresh powder this had the potential to be an interesting hike and photo trip.

Dry grasses poke through the shallow snow.

But the creek wasn’t frozen enough. Where there were rocks or logs crossing the creek was possible — if not easy. But in spots where one had to cross an expanse of ice — well, no, not yet. Nothing quite like stepping out onto the ice and having it crack in spider web fashion under your feet — with knee deep water below. So, we were unable to travel more than about 1 ½ miles upstream before returning.

We ran into only one other group of hikers on the trail. Although from California, they have lived in cold climes before and were not daunted by the cold and snow in the canyon. But they, too, turned around at the icy crossing.

Giant icicles hang from the sandstone walls of West Fork Oak Creek.

There will be other chances later in the winter when the ice may be safely passable. Or, maybe not. It’s always a bit of a mystery on what we will find when we arrive at West Fork Oak Creek.

A winter walk along West Fork Oak Creek

January 16, 2013

It’s been cold around these parts lately. How cold? Well, we’ve seen -24ºF in Bellemont, -19ºF in Tusayan, and -9ºF in Flagstaff. These are all northern Arizona communities that are used to the cold — but not for this many days in a row. This is the coldest 5-day period in Flagstaff in over three decades.

One of many icy crossings of West Fork Oak Creek.

There are some benefits. With prolonged cold some of the streams in the canyons will freeze. With this in mind, we took a hike up West Fork Oak Creek. The trail was snow packed and icy. Wisely, we all had foot traction gear including instep crampons and microspikes.

An icy rock and log crossing of West Fork Oak Creek.

The trail crosses the creek numerous times and the first few crossings were tricky but doable. That is, the logs and/or stepping stones were ice covered but sure footing could be found using care and caution.

One of stream crossings, though, stymied us. For whatever reasons, the water and ice level had increased substantially in this location so that all the stepping stones were well under water and ice. And the flow of water had become concentrated along one side of the channel so that the ice was eroded. After studying it for awhile, we reluctantly agreed that the risk of crashing through the ice was too great. We turned back.

Canyon wall reflections in icy West Fork Oak Creek (2007).

In previous years we had easily moved through this crossing and many others farther upstream including the “subway” passage. We had hoped to make it this far and, possibly, even farther upstream. It wasn’t to be.

A deep pool crossing in the "subway" made easy with ice in West Fork Oak Creek (2007). — A deep pool crossing in the “subway” made easy with ice in West Fork Oak Creek (2007).

Still, it’s never a bad day when you are out hiking with no one else around except your friends in an environment not often experienced by most.

Edit: 01 Feb 2013 – fixed typos.

“Science experiments” with boiling water on a cold day

January 1, 2013

It seems that we get extraordinarily cold mornings on New Years Day. It was -17°F for a low temperature in Bellemont, Arizona today. Two years ago, on New Years Day 2011, it was -30°F. Both times we had fun tossing boiling water into the air and watching it freeze before it hits the ground.

Yeah, sure, folks up north do this all the time in the winter. But, remember, this is Arizona!