Flooding and Heavy Rain in Arizona, August 11, 2016

Name: Flooding and Heavy Rain in Arizona, August 11, 2016
Start: 2016-08-11T07:00
End: 2016-08-11T13:45
Location: Arizona

August 11, 2016 · NWS PSR · 3 events in 1 county or zone

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
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Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 3

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS PSR wrote it up.

Scattered to numerous showers and thunderstorms developed across south central Arizona, including the greater Phoenix metropolitan area, during the early morning hours on August 11th. Some of the heavier rains began falling over the southeastern portion of the Phoenix area including communities such as Mesa, Chandler and Queen Creek as of 0400MST and required the issuance of Urban and Small Stream Flood Advisories. Rain continued into the morning hours and led to areal flooding of roads, streams and washes. Numerous roads became closed and extensive street flooding was observed. The Small Stream Flood Advisories were upgraded to Areal Flood Warnings; some of the most significant urban flooding occurred in the community of Mesa and the flooding persisted through the morning and into the early afternoon hours.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Phoenix, AZ wrote its last area forecast discussion before the first event at Aug 11, 3:28 AM MST, 3 hours 32 minutes earlier.

Area forecast discussion, Aug 11, 3:28 AM MST, 3 hours 32 minutes before

Area Forecast Discussion
National Weather Service Phoenix AZ
328 AM MST THU AUG 11 2016

.Update...Aviation and Fire Weather Discussions.

&&

.SYNOPSIS...
The weather pattern will allow for a transition to drier and more
quiet conditions for the end of the week as moisture levels trend
down. With this drying trend, temperatures will also increase
through the weekend and into early next week with readings at or
above normal levels.

&&

.DISCUSSION...
The current synoptic picture shows an upper level trough moving
through the Great Basin with the main shortwave well north of our
area. An unseasonably strong upper level jet currently stretches
from northern Baja northeastward into the central Rockies. This set
up is providing some support for ongoing storms over central and
northern Arizona, but largely more neutral to weakly subsident flow
is seen over southwest and south-central Arizona. Moisture levels
remain quite high over southern Arizona with PWATS of 1.50 - 1.75
inches and ML CAPE values of up to 1000 j/kg. This instability
should be enough to overcome the weak subsidence and should result in
a few isolated showers or thunderstorms this morning.

Daytime heating today will be the main forcing mechanism for any
storms this afternoon and evening. The threat for localized flooding
has mostly ended, but can't rule some minor flooding out a storm or
two this afternoon. Though high-res models have a poor track record
over the last couple days, the vast majority show storm activity
mostly confined to high terrain areas with little activity over the
deserts. The expected little or no activity over the deserts later
today should be because of the drier air aloft mixing down and a
modest southwest steering flow keeping high terrain storms from
propagating into the deserts. May be able to get a few storms over
the deserts this afternoon, but would mostly have to come from
intersecting outflows from high terrain storms.

From Friday into early next week, moisture levels decrease
substantially with 1000-700mb mixing ratios dropping below 8g/kg in
most areas as a high pressure center shifts off the Pacific into the
Great Basin. This northerly flow aloft around the high will bring
even drier air into the Desert Southwest as daytime surface dew
points drop into the 40s to low 50s. Any thunderstorm chances during
this time period will reside mostly over far eastern Arizona which
includes eastern Gila County. As the atmosphere dries, temperatures
will subsequently rise to above normal levels. Highs should even top
110 over southeast California and southwest Arizona and will come
close to Excessive Heat levels in the Imperial Valley by Sunday.
These above normal temperatures will likely persist through Monday
before gradually decreasing, especially over south-central Arizona
where a modest moisture return is forecast for the middle of next
week. Both the GFS and European generally show some monsoon moisture
working back into portions of Arizona starting next Wednesday
bringing a return to storm chances.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL:

Tropical moisture still covers the region. A few disturbances in the
unusually strong southwesterly jetstream winds will develop a few
showers and thunderstorms at times today and early tonight. Through
17z Thu...sct clds near 8 thsd agl with bkn clouds 10 to 14 thsd
agl. Isolated showers and or thunderstorms. Light and variable wind
under 8 knots.  From 17z Thu to 03z Fri...sct clds based 8-10 thsd
ft agl. Tstms developing over the distant mtns n-se of PHX with a
chance of shwrs/tstms in the Phoenix valley during the late
afternoon and evening hours. West wind 6 to 10 knots.

Southeast California/Southwest Arizona including KIPL and KBLH:

Through 03z Fri...sct clds 8-10 thsd agl. South wind 8 to 12 knots.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday...

A drier and warmer airmass will cover the region Saturday and
Sunday. No mountain thunderstorms. Minimum relative humidity will
range from 10 percent in southeast California to 20 percent in
southern Gila County. Afternoon west winds 8 to 15 mph. Excellent
overnight recovery.

From Monday through Wednesday, monsoon moisture will return to the
region providing a slight chance of afternoon and evening mountain
thunderstorms in southern Gila County. Minimum relative humidity
will increase into the 10 to 15 percent range in southeast
California to near 35 percent in southern Gila County. Afternoon
southwest wind 5 to 15 mph. Good overnight recovery.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

Visit us on Facebook...Twitter...and at weather.gov/phoenix

DISCUSSION...Kuhlman
AVIATION...Vasquez
Fire Weather...Vasquez

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

2 flood, 1 heavy rain. Local standard time, as filed.

Flood, Maricopa

When: August 11, 7:00 AM MST to 12:00 PM MST
Where: Maricopa County, 5.37 mi WSW of Chandler Hgts to 4.61 mi SE of Ocotillo
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 33.184, -111.763

Thunderstorms with heavy rain developed over much of the greater Phoenix metropolitan area during the early morning hours on August 11th, and some of the heavier rains occurred over the east and southeast portions including communities such as Chandler, Gilbert and Queen Creek. The heavy rains led to episodes of urban street flooding which led to the closure of various roads. Urban and Small Stream Advisories were issued starting as early as 0400MST and eventually were upgraded to Areal Flood Warnings. At 0740MST, local law enforcement reported that the Hunt Highway was closed between Gilbert Road and Lindsey Road due to areal flooding. The Areal Flood Warning for the area was issued at 0726MST and remained in effect through 1200MST.

Flood, Maricopa

When: August 11, 8:30 AM MST to 1:45 PM MST
Where: Maricopa County, 2.66 mi WSW of Buckhorn to 1.72 mi W of Buckhorn
Cause: Heavy Rain
Reported by: Broadcast Media
Coordinates: 33.409, -111.764

Thunderstorms with heavy rain started to develop during the early morning hours across the eastern portion of the greater Phoenix area, and the stronger storms produced locally heavy rainfall. Some of the heavier rains fell across the community of Mesa. The heavy rain led to widespread street flooding and then areal flooding of roads resulting in road closures. According to a broadcast media report, at 0845MST the intersection of Main Street and Val Vista Drive was completely inundated. This was about 4 miles west of East Mesa. An Areal Flood Warning was issued for the area at 0853MST and it remained in effect until 1335MST.

Heavy Rain, Maricopa

When: August 11, 8:30 AM MST to 12:00 PM MST
Where: Maricopa County, 3.72 mi ENE of Scottsdale Muni
Reported by: Trained Spotter
Coordinates: 33.640, -111.860

Thunderstorms with heavy rain developed over much of the greater Phoenix metropolitan area, especially the eastern portion, during the morning hours on August 11th. Peak rain rates with the heavier showers were in excess of one inch per hour, and the rains eventually led to episodes of urban street flooding in communities such as Scottsdale and Mesa. At 0900MST a trained weather spotter 2 miles northeast of North Scottsdale reported curb to curb flooding at the intersection of Thompson Peak and Bell Roads as well as nearby areas. He also noted that area washes were running. At about 0900MST an Urban and Small Stream Flood Advisory was issued for the area and it remained in effect through 1200MST. Flash flooding was not reported in the area.

What these are

Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Arizona in 2016 Every state in 2016 This day in weather history Warnings in Arizona, August 2016

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 647265, 647255, 647258.