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Record Rainfall Deluges Phoenix, Arizona

By: Christopher C. Burt, 7:33 PM GMT on September 09, 2014

Record Rainfall Deluges Phoenix, Arizona

Moisture associated with former Hurricane Norbert swept over southern California, southern Nevada, and Arizona on Monday resulting in record rainfall for parts of Arizona and flash flooding that took the lives of two. The official weather site at Phoenix’s Sky Harbor Int’l Airport picked up an all-time calendar day precipitation amount of 3.29”. Meanwhile, across the country in Virginia, over 12” has fallen near Smithfield in 24 hours.

Although the Phoenix total of 3.29” (all of which fell in seven hours between 2 a.m-9 a.m.) was a calendar day rainfall, beating the 2.91” that fell on September 4, 1939, it was not a record 24-hour amount for the city. On July 1-2, 1911, 4.98” was measured in one 24-hour period at, what was at that time, the city’s official observation site. However, the 3.29” does rank as the 2nd greatest 24-hour rainfall (beating out 3.06” on September 3-4, 1939). The September 1939 event was similar to yesterday’s (September 8th) in that a dissipating tropical storm over the Eastern Pacific was responsible for the inflow of moisture.

Record rainfall totals for Phoenix by time period and month since official observations began in 1896 and through 1995. Monday’s rainfall was a new 24-hour record for the month of September and the 2nd heaviest such on record. Sorry this is hard to read: here is the table from the document. Table from ‘Climate of Phoenix: NOAA Technical Memorandum NWS WR-177.

Hourly METARS at Phoenix Sky Harbor Airport on the morning of September 8th. Note that the greatest single hour of precipitation was 1.02” at the beginning of the storm between 2 a.m.-3 a.m. As the previous table illustrates this fell short of the September single-hour record of 1.41” that occurred during the storm of September 1939. METARS table from NWS-Phoenix.

Even greater amounts of rainfall were measured in the Phoenix suburbs of Tempe and Chandler just southwest of the airport. The top figure was 5.63” at a rain gauge near Alma School in Chandler (an unofficial trained spotter reported 6.09” in northwest Chandler). Note that Phoenix’s average annual rainfall is just 8.03”, so the storm dumped approximately 41% of the entire amount of rain that the city normally sees in a year. In fact, it is more than what was measured for the ENTIRE years of 2002 and 1956 when just 2.82” was recorded (Phoenix’s driest years on record).

Map of rainfall amounts in the greater Phoenix area on September 8th. Note the 5.63” in Chandler located at the very bottom right side of the map. Map from Flood Control District of Maricopa County.

Interstate 10 was submerged by the heavy rainfall with one fatality reported south of Phoenix when a car and its occupant were swept down a wash. Photo courtesy of Arizona Department of Transportation.

Heavy rainfall also occurred in Tucson where a daily record amount of 1.84” was measured and unfortunately an additional fatality occurred, once again a result of an automobile being swept off a road.

Tucson was one of several cities in the Southwest (including Phoenix) that recorded record levels of atmospheric moisture for the month of September this past Monday, as the above graph illustrates. Dew points for many locations were extraordinarily high for desert locations. Blythe, in California’s Mojave Desert, had a dew point of 77° during the night of September 7-8 (with the air temperature between 83°-85°). 12Z upper-air sounding made in Tucson the morning of September 8th.

The Las Vegas area was also pounded by flooding rainfall although the downtown of the city was largely spared (just 0.27” at McCarran Airport). A rain gauge in Weiser Wash (north of Las Vegas near the town of Moapa) measured 4.67” and a dam in the area came within 3” of overflowing.

Big Rains in North Carolina and Virginia

Meanwhile, on the other side of the country, some phenomenal rainfall has also occurred in northeastern North Carolina and southeastern Virginia. A site in North Carolina in Warren County, Warrenton measured 8.81” in 24 hours ending at 5 a.m. ET this morning (September 9th). In Virginia an amazing 12.21” was measured two miles southeast of Smithfield in Isle Of Wight County. 10.71” was measured 1.7 miles southeast of Newport News, Virginia and 9.42” in Cradock, City of Portsmouth. All these 24-hour totals between 7 a.m. September 8 and 7 a.m. September 9.

Radar estimated rainfall map for southeastern Virginia and amounts measured at local airports over the 24-hour period of 7 a.m. September 8 to 7 a.m. September 9th (top table) and other reports from various networks (bottom table). The greatest measured total was 12.21” near Smithfield in Isle of Wight County. Map from NWS-Wakefield, Virginia.

It seems this has been a summer of remarkable extreme precipitation events across the U.S.

Christopher C. Burt
Weather Historian

Precipitation Records Extreme Weather

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.