Tucson's Climate: Perfect

In the shadow of the Santa Catalina Mountains, which tower to 9185 feet atop Mount Lemmon, we find the teeming metropolis of Tucson. Perched on the edge of the Sonora Desert but influenced by the high mountains to the east, Tucson, at an elevation of 2410 feet, enjoys a unique climate whose outstanding features are sunshine, pleasantly warm winters, hot summers and low annual rainfall.

Tucson is located in an area of the United States that enjoys the greatest number of sunny days. Actually, based on nine years of record at Tucson's airport, 86 per cent of possible sunshine has been registered. When many other sections of the nation experience stormy, cloudy and disagreeable weather, Tucson shows a remarkably high percentage of sunshine. December's average of possible sunshine stands at 82%, January 78% and February 85%. April, May and June bring with them 90 to 93% of possible sunshine. When we begin to compare the percentage of possible sunshine on an annual basis, we find that Tucson's 86% is almost twice as great as that recorded over much of the Great Lakes area. Even the southeastern corner of the United States can only boast of 60 to 70% of possible sunshine. Coastal areas of the Pacific Northwest and northern California with about 40 to 45% sunshine doubtlessly cast longing eyes toward the azure sunny skies of Tucson when they experience long cloudy periods of weather.

According to U.S. Weather Bureau records, relative humidity values in the Tucson area are among the lowest in the United States. A comparison of noontime average relative humidity values shows Tucson with 30% while other localities are considerably more moist. For instance, Atlanta's noontime humidity averaged over an annual period stands at 56%, Buffalo 61%, Jacksonville, Florida 55%, Los Angeles 49%, New York City 59%, San Francisco 65%, Washington D.C. 51%, Boston 56% and Chicago 61%.

Relative humidity records at Tucson show that noontime values range from an average of 40% in January to the low value of 13% in May and June. It is not unusual for relative humidities to drop as low as 5% during the latter part of the Spring season. Due to the dryness of the air, evaporator coolers are utilized to a great extent for air conditioning of homes and commercial buildings. With outdoor temperatures near the 100 degree mark it is not difficult to bring indoor temperatures into the low 80's with the aid of evaporator coolers. Hence, living conditions are quite comfortable even with extremely high outside temperatures. Also, refrigerated air conditioning is becoming more popular so that “climate control” indoors isbecoming an every day reality.

Speaking about high temperatures, the University of Arizona weather station in Tucson registered 112 degrees on several occasions. Actually, every year since records began back in 1892, temperatures have climbed to the 105 to 110 degree zone. One should not get the impression though, that the climate of Tucson is as hot as the "proverbial inferno." The average annual temperature of 67 degrees compares very favorably with that found in such far away places as Lima, Peru and Athens, Greece.

The winter months of December, January and February show an average daily maximum temperature of 65 to 68 degrees while early morning low temperatures drop to an invigorating 35 to 38 degree value. The lowest temperature of record on the University campus was 6 degrees above zero which occurred in January, 1913. It is not rare to have low temperatures near the 20 degree mark but normally these cold spells do not last for more than a day or two in January or February. Tucson enjoys a growing season which extends over a 250 day period. The average date of the last killing frost in the Spring is around the 15th of March while the average date of the first killing frost in the Autumn occurs around the 20th of November.

Snows are rare in Tucson and normally do not cover the ground for more than a day or two at a time. On the University campus, three months since 1892 have seen a total snow cover which added up to 6.0 inches, namely January 1896 and 1937 and March, 1922. Usually only about an inch or two of snow falls and is rapidly melted as soon as skies clear which ordinarily occurs on the following day after a snow storm. However, should one wish to find deep snows in the winter, all that need be done is to drive to the winter sports area on Mount Lemmon, about 45 miles from Tucson. Located at the 7000 to 8000 foot level, it is not unusual to find from two to three feet of snow with ideal skiing and tobogganing conditions. Be sure to take along warm wraps though, as temperatures get as low as 5 to 15 degrees above zero at the winter sports area during cold spells!

March and April find delightful weather with Spring flowers (if it rains) in full bloom by mid-March. If winter rains on the desert are adequate, a thrill of a lifetime will be experienced. Literally millions of wildflowers raise their petals to the warm rays of a questing sun. Mariposa lilies, blue lupins, mallow in shades of delicate pink to deep bronze, splashes of brilliant cadmium yellow in the bouquet-like brittle bush, with magenta, red and yellow wax-like petals of the cactus blooms opening by late April or early in May.

Average daily high temperatures in March reach 74 degrees with low values around 42. April sees the mercury climb to 82 degrees for average maximum temperature values while daily low readings remain at a relatively cool value of 47 degrees. May sees the first signs of the long summer days ahead. High temperatures average 90 degrees with lows near 55. June through September are the hot months of the year with average daily high temperatures reaching 99 in June, 100 degrees in July, 97 in August and 95 in September. Even though maximum temperatures are quite high in June and September, we find that low temperatures are quite comfortable, averaging around 64 to 65 degrees during these two months.

The arrival of tropical air from the Gulf of Mexico is heralded by towering cumulus clouds against the deep blue Arizona sky. They first appear during the closing days of June or by the 4th of July. Night-time temperatures immediately reflect the arrival of this moist air and we find daily average low temperatures in the 71 to 73 degree zone throughout much of July and August. Cool temperatures are never far away from Tucson, even during the hottest time of the year. An extensive summer colony is found at Summerhaven, well up the slopes of the Santa Catalina Mountains. Beautiful cottages snuggle in the big pines with the 7700 foot altitude assuring cool nights and pleasant afternoon temperatures. While Tucson may swelter in temperatures in the 100 degree bracket, we find temperatures at Summerhaven near 75 degrees with early morning readings in the 49 to 54 range this during the hot months reaching from June through September! Thus, within a mere 45 miles of paved road one can experience a complete change in climate from that found in Tucson.

Spectacular displays of lightning and the deep roll of thunder mark the summer rainy season which brings almost one-half of the annual precipitation. Average rainfall during July is 2.01 inches, August 2.12 and September 1.13 inches for a combined total of 5.26 inches for these three months. With an average annual precipitation value of 10.83 inches we can readily see that the remaining nine months of the year must provide the balance of moisture.

Winter rains from about mid-November through March account for almost 3.50 additional inches of moisture. Thus the Spring months of April, May and June are relatively free from rainy weather. May, with an average of only 0.19 inch of rain, is the driest month, followed by June with 0.28 and April with 0.39 inch.

On rare occasions torrential rains in thunderstorms cause flash flooding in washes draining into lowlands from surrounding mountains. Records at the Soil Conservation Service station at Tucson Nursery, just to the north of town, show that rain up to 2.85 inches can occur in a one day period. Due to the slope of the ground in the Tucson area, flood waters from these "gully washers" run off rapidly and within a few hours after rains stop most of the water has drained into main river channels.

As mentioned earlier, tropical air arriving from the Gulf of Mexico is primarily responsible for the heavy rains of July and August. Almost all of this rainfall occurs in thunderstorms. July has an average of 13 days with thunderstorms while August has 12. During some years the thunderstorm season extends into the early part of September so that an average of about 5 days with thunderstorms can be expected during that month. All other months of the year experience only one or two thunderstorms. In most cases they accompany a cold frontal passage or storm system moving into the area from the north or west bringing rainfall to the Southwestern desert thus accounting for moisture during all other months than the "Summer monsoon" season of July, August and early September in some cases.

Hail, fog, sleet and other weather phenomena usually found over other sections of the United States is rare in Tucson. So much so, often a complete year passes without a single occurrence of hail fog or sleet. No record has been made of tornadoes in the Tucson metropolitan area. Hurricanes, of course, are unheard of in the desert Southwest. On rare occasions heavy rains in September occur as remnants of a decayed hurricane drift into Arizona. However, no hurricane winds accompany the "tail end" of these storms which are so destructive at times on the Gulf of Mexico and east coasts.

Strongest winds in Tucson are usually connected with thunderstorms. For a brief period winds "kick up" to about 40 to 45 miles per hour, raising great clouds of dust. Within about a 15 or 20 minute period rain commences and the dust storm is at an end. A cold front passage in February of 1952 caused the strongest wind recorded in the past 9 years at Tucson's airport when a speed of 59 miles per hour was reached for a one minute period. Ordinarily winds are gentle, being dominated to a great extent by the mountain-valley drainage of air. Average wind velocity at the University campus is only 6 miles per hour with no particular month being more windy than another-April with an average of 6.8 miles per hour is the highest with December's 5.5 miles per hour value standing on the low side.

Sharp and clear stand the sentinels of Tucson. To the northeast the towering Santa Catalina Mountains, to the southeast the sweeping slopes of the Rincons... while to the west the craggy tops of the Silver Bell and Sierrita Mountains are backed up by the towering ramparts of the Roskruge and Baboquivari Ranges. Rare is the day that visibility is lower than 40 to 60 miles and often from the higher slopes, mountain ranges up to 100 miles away can be seen outlined against an Arizona sky that so often is "bluer than blue" a "big" sky that covers the "big country" surrounding the busy and modern city of Tucson.