Monsoon??

Monsoon thunderstorm facts from someone who has never seen one:

The Arizona monsoonal circulation does not produce thunderstorms every day during the months of July-September but rather occurs in a pattern that has "Bursts" and "Breaks". According to climatologist Andrew Carleton:
"Burst": a movement into Arizona of a weak trough in the upper level westerlies (normally during summer these winds are far north of this location) which spreads upper level cold air into the region. In lower levels, during a "burst", there is strong surface heating and strong southerly or southeasterly transport of moisture into Arizona. This creates intense atmospheric destabilization and leads to strong widespread thunderstorm outbreaks.
"Break": an enhanced ridging of the upper level Bermuda and North Pacific subtropical high pressure systems which acts to stabilize the atmosphere and thereby cutoff widespread thunderstorm activity. Our own meteorologists suggest that a break usually occurs when the subtropical ridge re-develops over NW Mexico and drier air spreads into Arizona.




Prior to 2008 the Phoenix area monsoon was considered to have started when there were three consecutive days when the dew point averaged 55 degrees or higher. In 2008 the National Weather Service decided to take the guesswork out of monsoon start and end dates. After all, monsoon is a season, and most people should not be concerned with whether or not a particular dust storm was defined as monsoon storm or not. Beginning in 2008, June 15 will be the first day of monsoon, and September 30 will be the last day. Now we can be more concerned with monsoon safety and less concerned with definitions. More About Phoenix Monsoon

Meteorologists still track and report dewpoints and study monsoon weather patterns. Here are some technical monsoon facts for our area.

• The average starting date of the monsoon in Phoenix is July 7.
• The average ending date of the monsoon is September 13.
• The earliest start date for the monsoon was June 16, 1925.
• The latest start date for the monsoon was July 25, 1987.
• The average date of the first break in the monsoon is August 16.
• The average total number of monsoon days (where a monsoon day is considered one with an average dewpoint of 55 degrees or higher) is 56.
• The greatest number of monsoon days was 99, recorded in 1984.
• The fewest number of monsoon days was 27, recorded in 1962.
• The greatest number of consecutive monsoon days was 72, from June 25 through September 4, 1984. This was also the greatest number of consecutive days with dew points of 60 degrees or higher.
• In Phoenix, normal rainfall during July, August and September is 2.65 inches.
• The wettest monsoon occurred in 1984 when we had 9.38 inches of rain.
• The driest monsoon occurred in 1924 with only 0.35 inches.

By the way, the term "monsoons" as in "when the monsoons arrive ..." is a meteorological no-no. There is no such beast. The word should be used in the same manner that "summer" is used. Consequently, the proper terminology is "monsoon thunderstorms" not "monsoons."