The year 2011 in Phoenix ended as the (tie) 14th warmest year on record (since 1896) and the 21st driest.

The year started on an exceptional cold note as the high on January 1 was a chilly 49 °F, fourth coldest start to a year on record and the coldest start to a new year in half a century (record low maximum remains 47 °F in 1906). The low temperature at the dawn of the near year dipped below freezing (30 °F) at Phoenix Sky Harbor International Airport (KPHX) - an unusual event happening only 14 other times since 1980. While temperatures moderated back into a more typical range for the rest of January, another abrupt cold snap marked the beginning of February. The high temperature on February 2 was just 44 °F, which set not only a new record low maximum temperature for the date but even marked the coldest high temperature ever recorded during the month of February! Two additional sub-freezing mornings were observed at KPHX (30 °F) on February 3 and 4, making for the coldest back-to-back mornings in February since 1985. Temperatures did warm heading into spring, with the second earliest 100 °F day on record occurring on April 1 (record earliest is March 26, 1988).

Little rain accompanied the often cold pattern across the Southwest. From January 1 through June 30, Phoenix received just 1.04", well below the normal of 3.23" and the 11th driest first half of a year on record.

The summer heat cranked up early, with the 22nd warmest June on record, followed by the (tied) 12th warmest July and finally a brutal August that was not only the warmest August on record but also tied July 2009 as the warmest of any month (July is typically hotter than August). The summer as a whole tied for the 2nd warmest on record, with fourteen daily temperature records set or tied, including the all-time hottest August day on record (117 °F on August 26).

The 2011 Monsoon season, defined as encompassing the period June 15-September 30, was the hottest on record at Phoenix. The average temperature, 95.0 °F, broke the previous record of 94.5 °F established in 2007. The average maximum temperature, 106.7 °F, also set a new record, eclipsing the previous record of 106.4 °F established in 1989, while the average minimum temperature, 83.3 °F, was the second-warmest on record (83.4 °F in 2007). The fact that the average maximum temperature was hottest on record is particularly significant, since daytime high temperatures over the nearby open desert south and west of Phoenix are typically as hot as what occurs at Phoenix's official observation site at Sky Harbor International Airport (urbanization does not have a great impact on high temperatures, although it has a significant impact on nighttime low temperatures and, therefore, average temperatures). Rainfall at KPHX totaled only 0.19" for August-September, which tied for the 6th driest amount on record. Monsoon rainfall totaled 1.60" at KPHX, 36th driest on record. The lack of rainfall during the summer and preceding months resulted in numerous dust storms plaguing central Arizona, including a particularly large one on July 5th that garnered international media attention.

Quickly after the monsoon came to an end, several prolonged periods of cool, cloudy, and at times wet weather set in across the Southwest. The wetter-than-average December was not entirely expected as a moderate La Nina was underway which typically brings about drier conditions for Phoenix. However, the La Nina/ENSO signal was partially overridden by several periods of a strongly positive Arctic Oscillation.