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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.

Reader Comments

Are we able to prevent this from happening again or reduce the effects? Or is it that global warming will result in even greater floods of this nature?
Thanks for writing these blogs. Always something new and interesting. I really like the fact that you always put the data into context and give a historical perspective. And especially glad that, unlike some other media mavens, you don't just say: "Wow! What a heavy rain they had!" or "Was that HOT, or what?!" Thanks again, and please keep 'em coming!
I enjoyed the write-up and appreciate the visual data. Interesting data to find out that the all time PHX rainfall record occurred way back in 1911. I'm an enthusiastic believer in conservation and good stewardship of the earth. However, I'll stop short and just say that the weather is gonna do what its gonna do...regardless of us and our idea that we can somehow change the thermostat of the planet. Just flying around a single CB cloud formation, you get the true sense of just how small we really are. The earth barely knows that we are here!
Quoting 3. oldpilotsclub:

I enjoyed the write-up and appreciate the visual data. Interesting data to find out that the all time PHX rainfall record occurred way back in 1911. I'm an enthusiastic believer in conservation and good stewardship of the earth. However, I'll stop short and just say that the weather is gonna do what its gonna do...regardless of us and our idea that we can somehow change the thermostat of the planet. Just flying around a single CB cloud formation, you get the true sense of just how small we really are. The earth barely knows that we are here!


Whether or not we can affect the climate can be broken down into 2 questions as follows: Are we significantly changing the carbon dioxide content of the atmosphere over time? Can significantly changing the carbon dioxide content of the atmosphere affect the climate? There are ways of addressing each of these questions.
Quoting 1. mysticloud:

Are we able to prevent this from happening again or reduce the effects? Or is it that global warming will result in even greater floods of this nature?


With an average 8 inches per year of rainfall, Phoenix may have a drainage system designed to work properly for storm events of a magnitude far less than this recent deluge. By comparison, Philadelphia receives around 40 inches per year of rain. A rain even of 40% its annual total in one day would be 16 inches and I suspect that its drainage system is not designed for that. Add to that the fact that the ground in Phoenix is probably hard as cement from dryness and that there may be considerable paved area, and you have ideal conditions for instant runoff without any attenuation.

This rain event was directly attributable to a moisture feed from a tropical system. Had these storms formed 50 miles west over the empty desert, it would have been an interesting event, but not a news story. Absent such a tropical system (the cause of the 1939 event) such a rainfall total would be unlikely. If climate change does result in a greater frequency of west pac storms getting closer to the US and funneling moisture into the desert southwest, then we could expect more like this. That is open to conjecture.

I suspect that Phoenix will look at its existing drainage system and see what upgrades it can make to mitigate future storm impacts. I doubt they will spend billions to overhaul the entire system, but targeted changes may be effective.
Yeah, people don't like to hear it, but people need to.

Overnight -



The Weather Channel reported rainfall rates of more than five inches per hour in Nebraska.

Link
Quoting 3. oldpilotsclub:

... Just flying around a single CB cloud formation, you get the true sense of just how small we really are. The earth barely knows that we are here!

This is a specious argument. If that were true in general, then viruses would never be able to make anyone sick. I mean, look how small viruses are in comparison to the size of a human. How can that tiny Ebola virus possibly do any damage? Perhaps because sheer numbers often matter more than relative size?
Quoting 8. EstherD:


This is a specious argument. If that were true in general, then viruses would never be able to make anyone sick. I mean, look how small viruses are in comparison to the size of a human. How can that tiny Ebola virus possibly do any damage? Perhaps because sheer numbers often matter more than relative size?


Small things -

Shift in Arabia sea plankton may threaten fisheries

In a study published this week in Nature Communications, the researchers show how the millions of green algae living within Noctiluca's cells allow it to exploit an oxygen-starved dead zone the size of Texas. They hypothesize that a tide of nutrient-rich sewage flowing from booming cities on the Arabian Sea is expanding the dead zone and feeding Noctiluca's growth.

"These blooms are massive, appear year after year, and could be devastating to the Arabian Sea ecosystem over the long-term," said the study's lead author, Helga do Rosario Gomes, a biogeochemist at Lamont-Doherty.

Until recently, photosynthetic diatoms supported the Arabian Sea food chain. Zooplankton grazed on the diatoms, a type of algae, and were in turn eaten by fish. In the early 2000s, it all changed. The researchers began to see vast blooms of Noctiluca and a steep drop in diatoms and dissolved oxygen in the water column. Within a decade, Noctiluca had virtually replaced diatoms at the base of the food chain, marking the start of a colossal ecosystem shift. ................................. The study has attributed much of Noctiluca's rise to growing sewage flows into the Arabian Sea, an intriguing connection that should be followed up on, says Andrew Juhl, a microbiologist at Lamont-Doherty who was not involved in the study. "It's unusual for Noctiluca to bloom in the open sea and return year after year," he said "All of these observations suggest that something dramatic has changed in the Arabian Sea."


Link
Pakistani authorities have breached a strategic dyke in flood-affected Punjab to ease pressure on flood defences downstream and protect urban areas.

More than 700,000 villagers have been forced to flee their homes.

Much of the water is reaching Pakistan from Indian-administered Kashmir where flood levels are now falling.

There have been chaotic scenes at one of the region's main airports, Srinagar, as tourists and migrant workers struggle to leave.

The death toll in the two countries has passed 450, with troops deployed to rescue people and provide assistance.


Link
As of 8 am EDT Wednesday, 10.54" was recorded in 12 hours in Browning, MO, with 9.61" inches falling at Chillicothe. Moisture from Norbert will spread all the way into Michigan's Upper Peninsula on Wednesday afternoon, and an Areal Flood Watch is posted there for flooding rains of 1 - 3".

Link
And 9.60" in Kirksville, Missouri in 24 hours ending at 1:30 p.m. today (Sept. 10). The city's greatest 24-hour rainfall on record. Precipitation records began in 1893 in Kirksville.

Quoting 11. ColoradoBob1:

As of 8 am EDT Wednesday, 10.54" was recorded in 12 hours in Browning, MO, with 9.61" inches falling at Chillicothe. Moisture from Norbert will spread all the way into Michigan's Upper Peninsula on Wednesday afternoon, and an Areal Flood Watch is posted there for flooding rains of 1 - 3".

Link
Quoting 3. oldpilotsclub:

I enjoyed the write-up and appreciate the visual data. Interesting data to find out that the all time PHX rainfall record occurred way back in 1911. I'm an enthusiastic believer in conservation and good stewardship of the earth. However, I'll stop short and just say that the weather is gonna do what its gonna do...regardless of us and our idea that we can somehow change the thermostat of the planet. Just flying around a single CB cloud formation, you get the true sense of just how small we really are. The earth barely knows that we are here!
My take on your note on 'the true sense of just how small we really are' evoked my response of how truly vulnerable we are in the greater scheme of this ever-expanding universe and also how important we appear to be about ourselves as, well, silly and overrated. I had noted your being 'an enthusiastic believer in conservation and good stewardship of the earth' as a promise, of sorts. I, too, do much and prefer to say little to those who prefer to say much and perhaps do little. I thank you for your comments.
Quoting 13. srqthymesage:

My take on your note on 'the true sense of just how small we really are' evoked my response of how truly vulnerable we are in the greater scheme of this ever-expanding universe and also how important we appear to be about ourselves as, well, silly and overrated. I had noted your being 'an enthusiastic believer in conservation and good stewardship of the earth' as a promise, of sorts. I, too, do much and prefer to say little to those who prefer to say much and perhaps do little. I thank you for your comments.

As I said in my earlier response, "how small we are" matters little in comparison to how many we are and how much damage each one of us can do. I point this out again only because the "look how small we are" rationalization has recently become a common denialist theme song used to peremptorily dismiss any possibility that we could be responsible in any way for what's happening to our environment. As for the rest, I'm pretty much in agreement with what you and the oldpilot have to say. Just avoid joining the "tiny little me" denialist parade and we'll get along fine.
Regardless of whether we are important or unimportant, and regardless of whether or not we are considered to be small individually or collectively, our burning of fossil fuels has increased the atmospheric carbon dioxide content by about 40%, and this change is in the process of altering climate. Our carbon dioxide emissions have also resulted in more acidic oceans.
Quoting 14. EstherD:


As I said in my earlier response, "how small we are" matters little in comparison to how many we are and how much damage each one of us can do. I point this out again only because the "look how small we are" rationalization has recently become a common denialist theme song used to peremptorily dismiss any possibility that we could be responsible in any way for what's happening to our environment. As for the rest, I'm pretty much in agreement with what you and the oldpilot have to say. Just avoid joining the "tiny little me" denialist parade and we'll get along fine.


Can't agree with you more! It's high time for us to stop complaining how powerless we are in front of the nature and be responsible!

Highly Efficient End of Lease Cleaners
The percentage of carbon dioxide in the atmosphere is relatively small, at about 0.040% (it was about 0.028% before the industrial revolution), but, being a greenhouse gas, it has a disproportionately large effect on warming. Carbon dioxide is an "active ingredient" of the atmosphere, with respect to the greenhouse effect, whereas the bulk of the atmosphere consists of "inactive ingredients", with respect to the greenhouse effect.

If you were to take a small pill with a large glass of water, it wouldn't make much sense to argue that the pill would have virtually no effect because it was relatively small compared to the water that you took it with, as the pill would contain an active ingredient, whereas the water would be inactive with respect to medicinal effect.

"The pill is small compared to the water that I drank it with, and even smaller compared to my body, therefore it cannot have a significant effect", wouldn't be a valid argument, especially if there is overwhelming evidence that taking the pill has a significant effect.
Torrential rain is causing floods and landslides in northern Japan, nearly one million residents displaced

Link
Quoting 17. DCSwithunderscores:

The percentage of carbon dioxide in the atmosphere is relatively small, at about 0.040% (it was about 0.028% before the industrial revolution), but, being a greenhouse gas, it has a disproportionately large effect on warming. Carbon dioxide is an "active ingredient" of the atmosphere, with respect to the greenhouse effect, whereas the bulk of the atmosphere consists of "inactive ingredients", with respect to the greenhouse effect.

If you were to take a small pill with a large glass of water, it wouldn't make much sense to argue that the pill would have virtually no effect because it was relatively small compared to the water that you took it with, as the pill would contain an active ingredient, whereas the water would be inactive with respect to medicinal effect.

"The pill is small compared to the water that I drank it with, and even smaller compared to my body, therefore it cannot have a significant effect", wouldn't be a valid argument, especially if there is overwhelming evidence that taking the pill has a significant effect.

Excellent analogy! Better than any I've been able to come up with so far. Will file that away for future use. Thanks!
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