Editor’s Note: Parts of this article original appeared in In&Out Magazine in 2007. It was updated in September 2012 for Anthem News, with more recent information provided by the current state climatologist.
You’ve heard the old adage, “Everybody talks about the weather, but nobody ever does anything about it.” In Anthem, nobody even fully keeps track of it. At least not officially.
The highs, lows and rainfall totals you typically see in local media are rarely if ever 100 percent accurate for our area. Much of what’s presented—including any Internet forecast based on the 85086 zip code—is based on a National Weather Service stations in the North Valley, but none in Anthem.
But Anthem’s climate is different than any of those stations. In summer, it’s significantly cooler here at night than at the weather stations at Sky Harbor or Deer Valley, a bit cooler during the day, and rainfall totals can vary dramatically from one station to another.
“Shooting from the hip, I would say Anthem is similar to Carefree,” said former Chief Meteorologist Anton Haffer at the Weather Service’s Phoenix office in a 2007 interview. But Haffer said there is no real data on Anthem (a fact that remains true today).
“About the only option is to extrapolate from the nearest neighbors,” explained ASU professor Andrew Ellis, who was Arizona’s State Climatologist when we interviewed him for this article in 2007.
Estimates for Anthem
At our suggestion, Ellis kindly chose nearby recording stations he thought relevant—Deer Valley, Carefree and Castle Hot Springs—and did some averaging.
Ellis estimates that Anthem’s average annual rainfall is 12.3 inches, about 60 percent more than at Sky Harbor. Our summer high is typically about two degrees lower than what’s reported at the airport, and our winter lows are typically a couple degrees cooler.
Anthem Temperatures and Rainfall
The elevation of Anthem ranges from 1,760 to 2,428 feet, but most homes are below 2,000 feet. Here is how our altitude and foothills location likely plays out, according to Ellis:
Annual Rainfall July Avg. High Oct. Avg. High Jan. Avg. Low
Sky Harbor 7.6" 105.4 88.2 41.9
Deer Valley 8.4" 105.1 88.0 37.5
Carefree 13.1" 101.7 84.1 40.6
Castle Hot Springs 15.5" 102.8 86.1 40.4
Anthem (estimate) 12.3" 103.2 86.1 39.5
An even more variable number, and one harder to pin down, may be overnight lows in the summer.
In the urban core, asphalt and concrete absorb heat more efficiently than the natural desert. That heat is radiated into the night air, keeping Sky Harbor warmer overnight than rural areas. In Atlanta, where NASA has closely examined this “urban heat island” effect, daytime summer temperatures can be 5 to 8 degrees higher than outlying areas. The very development of Anthem—with all the roads and parking lots paving over natural desert—has likely changed the climate here.
Our higher rainfall is related directly to the mountains around us and to the north, and to our altitude. The Carefree weather station is at 2,530 feet, while Deer Valley’s is at 1,260 feet. Most of Anthem is below 2,000 feet.
Monthly Climate of Anthem
These estimates were made by averaging data from Deer Valley, Carefree and Castle Hot Springs—where conditions and altitudes bracket those here, according to Ellis:
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
High 65.0 68.5 73.0 81.0 90.7 99.9 103.2 100.9 96.2 86.1 73.2 65.2
Low 39.5 41.9 45.3 50.6 59.1 67.8 75.6 74.3 68.7 57.8 46.3 39.7
Rain (inches) 1.34 1.41 1.54 0.51 0.18 0.14 1.08 1.76 1.01 0.97 1.02 1.38
Arizona is at the north edge of the a vast region affected by the monsoon, which dumps an average of 51.8 inches of summer rain in Acapulco, Mexico. In summer, Arizona thunderstorms are more common in the mountains, where there is a greater contrast between the cool air and the warmth generated at the surface by the sun. Monsoon storms are capricious, capable of dumping several inches in one spot and nothing a few miles away.
During winter, rainfall tends to be much more widespread, but more comes down near the mountains. Air is forced upward by the mountain slopes. Rising air cools, and cool air can’t hold as much moisture, so more rain is wrung from clouds over Anthem than over central Phoenix.
Sooner or later, somebody will likely do something about Anthem’s lack of statistics. In fact, you could help, assuming you don’t run afoul of our Del Webb’s landscaping restrictions.
Across the state, there are more than 125 weather stations set up in back yards and monitored by the National Weather Service, which provides the instruments and training. This Cooperative Observer Network “is the most likely type of station for a place like Anthem,” Ellis said. “Anyone can volunteer to be an observer.”
But even now, in 2012, Anthem forecasts are “based on gridded model output from National Weather Service models. They are not based on data,” explained current State Climatologist Nancy J. Selover, also an ASU professor. “The models use data from whatever hourly and daily weather stations they have as inputs to initialize the models. The models are based on physical laws of how heat and moisture move.”
Official weather stations at Carefree, Castle Hot Springs, and Deer Valley Airport are used as the nearest stations, Selover said in an email interview Sept. 23, 2012. “We now also have a few more rain gauges in that area for estimating rainfall. But essentially the method of forecasting for Anthem hasn’t changed.”
Local climate science
Mountains play a big role in our climate, summer and winter. In facts, we tend think of winter in the desert being relatively mild, but since Anthem is nestled near the mountains, the reality is much different than in central Phoenix.
Ellis explains what happens in winter:
“Precipitation is produced from rising motion of the lower atmosphere—rising motion produces cooling, and cool air can hold less moisture, meaning that cooled air eventually has to rid itself of moisture through the creation of liquid water in the form of clouds and precipitation. So, as air flows up the slopes of the terrain toward the higher elevation of Carefree, the additional help in lifting the air produces greater cooling and more precipitation.”
This upslope flow is less a factor in summer.
During summer, thunderstorms like the Great Storm of 2012—in which up to 5 inches of rain fell in 90 minutes—are more frequent at higher elevations. Here’s what happens: The sun heats the ground, and air near the ground is warmed. The air becomes less dense, and it rises—just like bubbles in boiling water.
“Higher-elevation stations, such as Carefree, possess a cooler atmosphere due to elevation, so the heated bubbles detaching from the surface are much less dense than the greater atmosphere, meaning that they rise more quickly,” Ellis said. “At Deer Valley, the greater atmosphere is hotter and in less contrast the warmed bubbles forming at the surface.”
The bottom line: There is more convection in the mountains, so summer rains are more frequent and intense in places like Anthem that are nearer to those mountains, and the effects can be highly localized.
Meteorologists love to confound Valley newbies by explaining that monsoon is not a storm. Rather, it is a seasonal shift in wind. But, wow, what a shift. The monsoon brings fantastic lighting, blinding dust storms and of course torrential rains.
On Aug. 15, 1996, a wind gust of 115 mph was recorded at the Deer Valley airport. In some years, there have been deadly and incredibly destructive high winds in the Valley, and even the occasional tornado. In other years, the monsoon amounts to little more than a good breeze.
And as mentioned above, individual storms during the monsoon are fickle, too. While one part of the Valley can get hammered, another location can experience perfect calm.
Tony Haffer, the meteorologist, watched the monsoon since 1990. “The one thing that has been consistent is the lack of uniformity of the monsoon hazards,” he said. Haffer said dust storms occur ever year, but the density of dust varies greatly by location. And in the North Valley, these storms might be changing.
“With urban sprawl continuing, perhaps there might be less dust observed as one goes north in the Valley,” Haffer explained. Where there was bare desert or dusty farmland, now there are homes and roads, the thinking goes. However, there are no firm studies on this, and Haffer said this perception of reduced dust in recent years could be due simply to the randomness of storm paths.
Historically, the average start date for the monsoon was July 7 and the average end date was Sept. 13. Monsoon was declared only after three consecutive days with the dew point at 55 degrees or higher. It had begun as early as June 17 and as late as July 25.
The problem was, severe monsoon-like weather did not always wait for that definition to be satisfied. So a few years ago Haffer and his colleagues lobbied to set firm start and end dates, as is done with hurricane season. The idea was to put the rightfully feared “monsoon” oomph behind warnings of potentially deadly summer thunderstorms, regardless of when they occur.
So starting in 2008, the anticipation factor was removed: The monsoon officially begins June 15 and ends Sept. 30.
Whatever, it’s still highly unpredictable. With La Nina in place this past winter, history suggests this summer should bring lots of rain. But when Haffer was interviewed for this article two weeks ago, he said “2008 has been anything but typical,” adding “there are no strong signals to indicate what we might expect from Mother Nature during the next couple of months.”
He could not resist making a guess, though: “It is my view we will see a typical monsoon, with some locations seeing nice amounts of rain, while others much less.”
How Monsoon Works
The word “monsoon” is from the Arabic mausim, which means season. Serious monsoons occur in India and in much of Mexico. Acapulco averages 51.8 inches of rain during its summer monsoon and just 3.3 inches the rest of the year.
We are on the fringe of the Mexican monsoon. Much of the year, winds in Arizona blow from the west or northwest. During monsoon, however, they blow from the southwest and bring moisture from the Gulf of Mexico and the tropical Pacific. During monsoon, the soaring temperatures of early June typically moderate into the high 90s and low 100s as humidity rises. Daytime heating causes the moist air to rise, where it condenses and can form violent thunderstorms.
An individual storm is not called a monsoon.
A dust storm during monsoon is called a haboob.
Until the late 1970s, weather experts debated whether ours was truly a monsoon. It was called many things: summer thunderstorm season, Mexican monsoon, Southwest monsoon, and Arizona monsoon. In 2004, scientists decided it is a true monsoon and that like other major climate patterns, it affects weather across a large area, so now it’s called the “North American monsoon.”
• If you hear thunder, stay inside a house or vehicle.
• Lightning can strike up to 60 miles away from any rainfall and 30 minutes after the apparent last rumble.
• Avoid porches, swimming pools, trees and any open, high ground.
• If a dust storm strikes while you are driving, pull off the road. Turn off headlights and taillights, put vehicle in “park” and take your foot off the brake so other motorists don’t follow your taillights and hit you from behind.
• Do not cross flooded roads. As little as one foot of water can float
a car or SUV away.
SOURCE for Safety Tips: National Weather Service