TR pointed out a weather warning earlier this week. The warning mentioned that precipitation would mostly fall to the west of a line from Page to Black Canyon City. What could be interesting about such a line? In this case, a combination of where the moisture was and the prevalent wind direction that day caused the line. Sure enough, looking at the radar estimated precipitation the next day, one could clearly make out most of that line.
As I looked at weather forecasts at Lake Powell for the weekend, I started in Page. As of this morning Page is showing a 50% chance of rain on Saturday. (Page Weather forecast from NWS) I then scrolled their “Click Map For Forecast” tool to the Lone Rock Area which is on the Utah side of the border. I’m more interested in a better estimate of temperatures, but notice only a 30% chance of rain. I scrolled a bit east to the southern edge of Padre Bay, but still in Utah. The chance of rain there is 40%. Then I drop south of the border into Labyrinth Canyon. I find 50% here. Next I go up by Cookie Jar. Only 30% here. Deep into Last Chance Canyon, 30%. It seems that if you are in Utah on Lake Powell, on Saturday, you have a lower chance of rain. Also, the Arizona-side will be 2-3 degrees cooler.
Why would the state line make a difference? As it turns out, the Flagstaff National Weather Service is responsible for the Arizona-side of the lake. The Salt Lake City NWS is responsible for the Utah-side of the lake. So, the forecasting office could be the cause. But, as I look that the North American Mesoscale model for the next 84 hours(below), an issue seems to be right around the border. An area of heavier precipitation seems to be centered around Page and south of the border. I may have to go up there and see for myself.
Arizona is going to be wet all over this weekend. Enjoy it! We need the water.