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Central Highlands Planning Area Climate

The high country of the Mogollon Rim is a significant topographic barrier to regional airflow, making the climate of the Central Highlands Planning Area wetter and cooler than the rest of the state.  The area-weighted average of water-year precipitation for the National Oceanic and Atmospheric Administration (NOAA) Arizona Climate Divisions 3 and 4 (covers Yavapai and Gila counties, respectively) is 16.8 inches, which is greater than the statewide average of 12.1 inches.  A climate division is a region within a state that is generally climatically homogeneous.  Arizona is divided into seven climate divisions. 

The area-weighted average water-year temperature for the planning area is 59.3°F, compared to the statewide average of 59.9°F. While average temperatures are slightly cooler than the statewide average, they have been warming during the last 70+ years (Figure 5.0-7).  Recent studies show an observed increase, throughout much of the West, in the fraction of winter precipitation falling as rain, rather than snow, at low-to-middle elevations (up to around 8,000 feet).  If this trend continues, the timing, amount and distribution of spring runoff is likely to be affected.

Figure 5.0-7 Average Temperature and Total Precipitation in the Central Highlands Planning Area from 1930-2002

Click to view Figure 5.0-7

Horizontal lines are average temperature and precipitation, respectively. Light lines are yearly
values and highlighted lines are 5-year moving average values, Data are from U.S. Historical
Climatology Network. Figure author: CLIMAS

Precipitation in the Central Highlands Planning Area has a bi-modal pattern (both winter and summer precipitation peaks) characteristic of Arizona (Figure 5.0-8); however, the planning area receives a greater fraction of its precipitation during the winter months than, for example, southeastern Arizona. During winter, precipitation comes during the passage of frontal storm systems moving west-to-east guided by the jet stream, typically located north of Arizona, but occasionally traversing the state.  As moist air masses encounter the Mogollon Rim they are lifted and cooled, which condenses water vapor and enhances precipitation.  Winter precipitation stored as snow is important for planning area water resources.  Cooler temperatures and less intense sunlight during winter combine to reduce evaporation, and, in most years, allow snow cover to persist until spring, when gradually melting snow replenishes surface water supplies.

During the summer monsoon season, atmospheric circulation shifts and brings moisture from the south and east to the planning area.  Storms during this season are driven primarily by convection (heat-driven upward motion), aided by topography, which can force air parcels upward to heights where water vapor condenses.  Summer convective thunderstorms tend to occur in spatially scattered cells.  Many storms originate over the high elevations in the Central Highlands Planning Area and move downward and outward over the deserts.  The planning area receives over 37% of its annual precipitation during July-September, which helps replenish streamflow and recharge groundwater aquifers, especially in the shallow fractured aquifers near Payson. However, summer precipitation is generally less hydrologically effective than winter precipitation because of greater evaporation rates and the spatial discontinuity of the storms.

Figure 5.0-8 Average Monthly Precipitation and Temperature in the Central Highlands Planning Area, 1930-2002

Click to view Figure 5.0-8

Data are from the U.S. Historical Climatology Network. Figure author: CLIMAS

Figure 5.0-9 shows long-term changes in area-weighted average winter (November-April) precipitation for NOAA Arizona Climate Divisions 3 and 4 based on three-ring reconstructions.  The record indicates recurrent drought in each century, with notable winter dry periods in the mid-1100s, late 1500s, late 1600s, and late 1700s. Notable winter wet periods include the early 1200s, the mid-1800s, and early 1900s. Precipitation variability on time scales of 10-30 years is likely related to shifts in Pacific Ocean circulation patterns, though recent research also points to the influence of the North Atlantic Ocean. Shorter-term variations can be attributed to ocean-atmosphere variations related to the El Niño-Southern Oscillation. During El Niño episodes, there are greater chances for above-average winter precipitation, as storm tracks across North America are shifted farther south than normal. La Niña conditions are reliably associated with below-average winter precipitation.

Figure 5.0-9 Arizona NOAA Climate Divisions 3 & 4 Winter (November-April) Precipitation
Departures from Average, 1000-1988, Reconstructed from Tree Rings

Click to view Figure 5.0-9

Data are presented as a 20-year moving average to show variability on decadal time scales. Data:
Fenbiao Ni, The University of Arizona Laboratory of Tree-Ring Research and CLIMAS. Figure


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References and Supplemental Reading for the Central Highlands Planning Area Overview

Colorado River Central Highlands Planning Area Download entire Central Highlands Planning Area Atlas in pdf Verde River Lake Pleasant