Monsoon storms dumped 3.8 inches on Payson in July, the most ever recorded — and a full inch ahead of the second highest total, the National Weather Service reported on Monday.
The furious monsoon storms that have doubled July’s already generous rainfall averages will likely continue through the week — but then take at least a brief break, say National Weather Service meteorologists.
Friday’s storms added several inches to July’s already sodden total, said Flagstaff-based weather service technician Dave Vonderheide.
Payson rainfall records go back only to 1948. But this year drowned the last high water mark — 2.78 in 1956 — thanks to more than 2 inches added to the tally on Friday afternoon and early Saturday.
A flash-flood warning remained in effect for most of northern Arizona on Monday, with a 50 percent chance of afternoon thundershowers today through Thursday, dropping to about 30 percent heading into the weekend.
The Salt and Verde rivers are both swollen with runoff. Salt River Project on Monday reported 4,900 cubic feet per second flowing into Roosevelt Lake in the Salt River. That’s 15 times the normal flow of 338. Tonto Creek at its juncture with Roosevelt Lake had 282 cubic feet per second, compared to a normal flow of 16. That’s about 17 times the normal flow. The Verde River had 596 csf, about four times normal.
The freakish year in Rim Country produced near-record rainfall in January, a bone-dry spring and now a series of drenching, July monsoon storms.
The NWS has not yet compiled complete, year-to-date figures for Payson, although unofficial totals stand at about 16 inches. Flagstaff has gotten 15.66 inches so far this year, compared to the long-term average of 12.58. However, in July, Flagstaff got 5.94 inches, compared to the normal 3.54 inches.
The culprit simmers and glowers about 18,000 feet above Arkansas and Louisiana — a huge mass of high pressure. This mass of slightly more dense air has set up a gyre of air moving around the edges. Above Arizona and New Mexico, this clockwise air pattern has been drawing warm, wet air out of the Gulf of Mexico and the Gulf of California.
This mass of moist air then hurls itself at the superheated desert. Great billows of hot air rise from the desert floor into the wet air drawn in off the gulf, causing the monsoon storms.
The storms have demonstrated the moodiness of the monsoon season, with intense storms several miles across rather than the winter storms on a front of hundreds of miles rolling in off the Pacific.
“Wherever you’ve got the warm, moist air and localized heating, you get the storms,” said meteorologist George Howard. “That’s the hit and miss nature of the storms we’re seeing — so you’ve got a thunderstorm over here and another one behind you — and then one popping up over yonder. Any particular storm may be only a couple of miles wide and the movement of the air depends on a particular peak or ridge.”
As a result, certain portions of Payson got so much rain on Friday that it caused serious flooding (see related story on page 1) — while just outside of town the rain was gentle.
In East Verde Estates, one rain gauge recorded an unofficial 10.5 inches of rain in July — most of that in the last two weeks.
So far, the season has included all three of the critical ingredients to mix up a monsoon storm. First, we have the moist air imported from the gulf. Second, we have an unstable atmosphere, so that rising cells of hot air sustain themselves. Finally, we have localized lift — the topography of hills, mountains and canyons that makes Rim Country among the most thunderstorm prone areas in the country.
The year stands in sharp contrast to last summer, when a decently wet winter yielded to a dry monsoon season.
Some analysts have associated a strong El Niño warming of the East Pacific with wet monsoons in the Southwest, but Howard said the link is tenuous.
“Last year, we had systems moving in off the Pacific, ushering in dry air. This year, we just haven’t seen that sort of flow,” said Howard.
It’s the weather, dude.
So does that mean we’re in for a sopping wet August?
Maybe. Maybe not.
Howard predicted a return to normal monsoon conditions in August — with lighter afternoon thundershowers that will deliver another couple of inches, maybe half of what we had in July. Flagstaff, for instance, normally gets 2.25 to 2.75 inches in August.
But then — who knows?
“We might end up with a slightly more moist August than normal, but we’ll probably see a normal variability for monsoons.”