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Greater Phoenix Climate Overview
(Excerpted
from Robert Schmidli's comprehensive The
Climate of Phoenix online
publication.)
Phoenix is located in
about the center of the Salt River Valley, a broad,
oval-shaped, nearly flat plain. The Salt River runs from
east to west through the valley, but, owing to
impounding dams upstream, it is usually dry. The climate
is of a desert type with low annual rainfall and low
relative humidity. Daytime temperatures are high
throughout the summer months. The winters are mild.
Nighttime temperatures frequently drop below freezing
during the three coldest months, but the afternoons are
usually sunny and warm.
 At an elevation of about 1100 feet, the station is in a
level or gently sloping valley running
east and west.
The Salt River Mountains, or South Mountains as they are
commonly called, are located 6 miles to the south and
rise to 2600 feet MSL. The Phoenix Mountains lie 8 miles
to the north with Squaw Peak rising to 2600 feet MSL.
The famous landmark of Camelback Mountain lies 6 miles
to the north-northeast and rises to 2700 feet MSL.
Eighteen miles to the southwest lie the Sierra Estrella
Mountains with a maximum elevation of 4500 feet MSL, and
30 miles to the west-northwest are found the White Tank
Mountains with a maximum elevation of 4100 feet MSL. The
Superstition Mountains are approximately 35 miles to the
east and rise to 5000 feet MSL.
The central floor of the Salt River Valley is irrigated
by water from dams built on the Salt River system. To
the north and west of the gravity flow irrigated
district, there is considerable agricultural land
irrigated by pump water.
There are two separate rainfall seasons. The first
occurs during the winter months from November through
March when the area is subjected to occasional storms
from the Pacific Ocean. While this is classified as a
rainfall season, there can be periods of a month or more
in this or any other season when practically no
precipitation occurs. Snowfall occurs very rarely in the
Salt River Valley, while light snows occasionally fall
in the higher mountains surrounding the valley. The
second rainfall period occurs during July and August
when Arizona is subjected to widespread thunderstorm
activity whose moisture supply originates in the Gulf of
Mexico, in the Pacific Ocean off the west coast of
Mexico and in the Gulf of California.
The spring and fall months are generally dry, although
precipitation in substantial amounts has fallen
occasionally during every month of the year. During the winter months, the temperature is marginal
for some types of crops. Areas with milder temperatures
around the edges of the valley are utilized by these
crops. However, the valley is subjected to occasional
killing and hard freezes in which no area escapes
damage.
The valley floor, in general, is rather free of strong
wind. During the spring months southwest and west winds
predominate and are associated with the passage of
low-pressure troughs. During the thunderstorm season in
July and August, there are often local, strong, gusty
winds with considerable blowing dust. These winds
generally come from a northeasterly to southeasterly
direction. Throughout the year there are periods, often
several days in length, in which winds remain under 10
miles per hour.
Sunshine in Phoenix area averages 86 percent of
possible, ranging from a minimum monthly average of
around 78 percent in January and December to a maximum
of 94 percent in June. During the winter, skies are
sometimes cloudy, but sunny skies predominate and the
temperatures are mild. During the spring, skies are also
predominately sunny with warm temperatures during the
day and mild pleasant evenings. Beginning with June,
daytime weather is hot. During July and August, there is
an increase in humidity, and there is often considerable
afternoon and evening cloudiness associated with cumulus
clouds building up over the nearby mountains. Summer
thundershowers seldom occur in the valley before
evening.
The autumn season, beginning during the latter part of
September, is characterized by sudden changes in
temperature. The change from the heat of summer to the
mild winter temperatures usually occurs during October.
The normal temperature change from the beginning to the
end of this month is the greatest of any of the twelve
months in central Arizona. By November, the mild winter
season is definitely established in the Salt River
Valley region. |
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For current radar and
satellite imagery of the Phoenix area, visit the National
Weather Service.
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