Flash Flooding and Flooding in Arizona, July 24, 2017

Name: Flash Flooding and Flooding in Arizona, July 24, 2017
Start: 2017-07-24T07:30
End: 2017-07-24T17:45
Location: Arizona

July 24, 2017 · NWS PSR · 6 events in 2 counties and zones

Where it happened

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

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Tropical storms and surge
Floods
Wind
Hail
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: $35,000
Crop damage: None recorded
Events: 6

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 much of south-central Arizona, including the greater Phoenix metropolitan area, during the morning hours on July 24th. Many of the storms produced locally heavy rainfall with peak rain rates in excess of two inches per hour, and this led to episodes of flooding and flash flooding across the lower deserts. At 0938MST a mesonet weather station 5 miles west of the Ahwatukee Foothills measured 2.09 inches of rain within one hour. Flash flooding occurred in Apache Junction; the Weekes wash experienced flash flooding due to very high flow, and a live swift water rescue occurred at 0917MST about 1 mile southwest of Apache Junction. Flash flooding in Sacaton partially submerged a truck and washed away several palm trees. Flooding persisted into the early afternoon hours across the east and southeast portions of the Phoenix area; at about 1400MST many roads near Santan were flooded and closed and shortly afterwards, multiple lanes of an intersection were closed due to flooding 5 miles east of East Mesa. Flash Flooding also occurred over far west Phoenix in the towns of Tonopah and Wintersburg; washes such as the Delaney Wash were impassable due to high water shortly after noon.

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 Jul 24, 7:00 AM MST, 30 minutes earlier.

Area forecast discussion, Jul 24, 7:00 AM MST, 30 minutes before

Area Forecast Discussion
National Weather Service Phoenix AZ
700 AM MST Mon Jul 24 2017

.UPDATE...
Updated Fire Weather section.

&&

.SYNOPSIS...
Thunderstorm activity can be expected across the region today,
especially over northern and southwestern Arizona. Cloud cover
and a moist atmosphere will lead to cooler temperatures today.
This will be followed by drier southwesterly flow aloft leading to
warmer temperatures along with fewer storms across the region
Tuesday through Thursday. More active monsoon conditions return by
next weekend.

&&

.DISCUSSION...
Convection has begun developing in portions of southwest Arizona
as HRRR and NAM Nest had been indicating. However, there is also
new convection developing over south-central AZ. HRRR only recently
changed it's mind on keeping things relatively quiet there. Made
upward adjustments to the PoPs and QPF. Cells are not stationary
and anticipate that flash flooding potential will be limited but
there will be some pretty intense short lived showers causing
nuisance flooding.

&&

.Previous Discussion...
After all of last night's convection, there are multiple MCVs
floating around Arizona. One prominent one is departing northern
Maricopa County early this morning and moving into northern
Arizona. Scattered light showers are the result. Speaking of the
earlier convection, a lot of the 00Z hi-res models did a rather
poor job of depicting it for our area - despite only being a 1-4
hour forecast. There are a variety of different solutions amongst
those models for our forecast area. Some of them, especially the
ones that were so underdone with last evening's activity, depict
convection redeveloping over south-central Arizona. However,
multiple runs of the HRRR have the focus further west -
specifically over La Paz County. The 06Z NAM Nest does as well.
They appear to be generating convection on the western periphery
of the aforementioned MCV. Have leaned toward this scenario but
still a lot of question about how much destabilization there will
be given all of the cloudiness. With so much moisture in place,
anticipate there will be some sort of showers (if not full fledged
thunderstorms) there. The influence of the mid level inverted
trough should also help to get at least isolated coverage over
other lower elevation locations with better chances higher
terrain. On the back side of the inverted trough, drier air starts
moving in later today. Anticipate that things will be fairly quiet
by early evening if not sooner.

Tuesday through Thursday Sunday...
With a lot less moisture available, look for quiet a downtrend in
PoPs (limited to south-central AZ - mainly higher terrain). Temps
climb as well but not out of hand. Late in the week and over the
weekend, a more favorable flow pattern sets up. Plus it appears
there will be a tropical storm of some sort passing south and west
of Baja which helps advect moisture back into the region. Thus a
gradual return of PoPs from east to west. Temps nudge down as
well.

&&

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

Showers and isolated thunderstorms will be off and on from now
through about 22Z this afternoon. Storms aren't expected to be
strong, but they will be capable of producing some good rainfall.
Activity will be on a downward trend after 22Z, with mostly dry
conditions expected for the remainder of the TAF period. Winds
will primarily be out of the east, with some variableness expected
near showers/storms. Low level cloud decks will be around 5 to 8
kft, with gradual clearing and lifting after 00Z.

Southeast California/Southwest Arizona including KIPL and KBLH:

Showers and isolated thunderstorms will be off and on between 13Z
this morning and 22Z this afternoon. Storms aren't expected to be
strong, but they will be capable of producing some good rainfall.
Activity will be on a downward trend after 22Z, with mostly dry
conditions expected for the remainder of the TAF period. Winds
will primarily be out of the southeast at KIPL and out of the
south at KBLH, with some variableness expected near
showers/storms. Low level cloud decks will be around 5 to 8 kft,
with gradual clearing and lifting after 00Z.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday:

Storm chances will be minimal on Wednesday with only slight
chances limited to the higher terrain of south-central Arizona.
Humidities and storm chances begin to increase Thursday with
chances reaching southeast California by Saturday. Temperatures
will be near normal Wednesday and Thursday (a bit above normal
near and west of the Lower Colorado River Valley) before beginning
to decrease late this week. Apart from thunderstorms, winds will
follow familiar warm season patterns.

&&

.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...AJ
AVIATION...Hernandez
FIRE WEATHER...AJ

In the hours before

Local storm report, Jul 24, 6:14 AM MST, 1 hour 16 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
614 AM MST MON JUL 24 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0612 AM     HEAVY RAIN       1 SE APACHE JUNCTION    33.40N 111.53W
07/24/2017  E0.59 INCH       PINAL              AZ   TRAINED SPOTTER

            TRAINED SPOTTER REPORTED MINOR FLOODING JUST
            NORTH OF TOMAHAWK AND US 60. SAYS WATER IS
            UP TO THE CURB ON THE RIGHT LANE.

&&

BH

The radar

The Phoenix radar (KIWA), 22 km away, was scanning. The volume nearest the first event began at 14:32 UTC.

Open the radar archive at this moment

Event by event

4 flash flood, 2 flood. Local standard time, as filed.

Flash Flood, Pinal

When: July 24, 7:30 AM MST to 10:15 AM MST
Where: Pinal County, 1.42 mi NNW of Sacaton to 0.46 mi S of Sacaton
Cause: Heavy Rain
Property damage: $20,000
Reported by: Public
Coordinates: 33.099, -111.741

Thunderstorms with locally heavy rainfall developed across much of the greater Phoenix area during the morning hours on July 24th, and with peak rain rates reaching 2 inches per hour at times, episodes of flash flooding developed as a result. One of the communities affected by flash flooding was the town of Sacaton, to the southeast of Phoenix. According to a report from the public, at 0900MST flash flooding occurred about 3 miles southeast of Sacaton; flood waters partially submerged a truck and they also washed away a number of palm trees located roughly at Sacaton and highway 87. A Flash Flood Warning was in effect at the time, but it was slightly north of the location of the flash flooding, over portions of Apache Junction and Queen Creek.

Flash Flood, Pinal

When: July 24, 8:15 AM MST to 12:55 PM MST
Where: Pinal County, 5.81 mi SW of Apache Jct to 3.88 mi SSE of Palm Spgs
Cause: Heavy Rain
Property damage: $10,000
Reported by: Broadcast Media
Coordinates: 33.359, -111.620

Thunderstorms with locally heavy rainfall developed across the eastern portion of the greater Phoenix area during the morning hours and the intense rainfall eventually led to episodes of flash flooding which affected the community of Apache Junction. A trained spotter just southeast of Apache Junction reported heavy rain at 0612MST which had already caused minor street flooding. Intense rain continued in the area with peak rain rates approaching 2 inches per hour at times. A Flash Flood Warning was issued for areas including Apache Junction at 0719MST and at 0917, local broadcast media reported that a live swift water rescue was underway at 16th Avenue at Saguaro, approximately 1 mile southwest of Apache Junction. No injuries were reported due to this flash flooding.

Flash Flood, Maricopa

When: July 24, 9:00 AM MST to 12:00 PM MST
Where: Maricopa County, 1.3 mi NNE of Perryville to 1.83 mi NW of Litchfield Jct
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 33.446, -112.459

Thunderstorms with locally heavy rainfall developed across much of the greater Phoenix area, including the western communities such as Goodyear, during the morning hours on July 24th. Peak rain rates reached to at least 2 inches per hour with some of heavier showers and this intense rainfall resulted in episodes of flooding and flash flooding during the morning hours. According to local law enforcement, at 1030MST flash flooding occurred about 2 miles northwest of Goodyear. Cotton Lane near McDowell Road was closed due to the flash flooding. No injuries were reported however. A Flash Flood Warning was in effect at the time of the flash flooding.

Flash Flood, Maricopa

When: July 24, 11:50 AM MST to 5:45 PM MST
Where: Maricopa County, 14.79 mi WSW of Tonopah to 11.96 mi SE of Dixie
Cause: Heavy Rain
Property damage: $5,000
Reported by: Mesonet
Coordinates: 33.425, -113.170

Scattered to numerous showers and thunderstorms developed across much of the greater Phoenix area during the morning hours on July 24th, and some of the heavier rainfall affected the far western portions including the towns of Tonopah and Wintersburg. During the late morning hours, rain gauges in the area reported amounts of up to around two inches and this resulted in episodes of flash flooding as area washes ran heavily and flowed across area roads making them impassible. As of 1150MST, stream gages reported significant flow in both the Waterman Wash and the Delaney Wash. At 1228MST flash flooding was observed 3 miles south of Tonopah; according to a Maricopa County Flood Control stream gage the Delaney Wash at 411th Avenue was impassible due to flood waters. At about 1300MST another stream gage reported that the Delaney Wash 3 miles northwest of Wintersburg was flooding and impassible at the Salome Highway. A Flash Flood Warning was in effect for the area at the time of the flooding; it was issued at 1152MST and remained in effect through 1445MST. Due to continued flow in the area washes, the Flash Flood Warning was re-issued for the same area and remained in effect through 1745MST.

Flood, Pinal

When: July 24, 1:00 PM MST to 4:00 PM MST
Where: Pinal County, 4.03 mi SW of Casa Blanca to 0.56 mi NNW of Casa Blanca
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 33.087, -111.967

Thunderstorms with locally heavy rainfall developed over much of the east and southeast portions of the greater Phoenix area during the morning hours on July 24th; peak rain rates as high as 2 inches per hour were observed and this led to episodes of flash flooding which continued into the early afternoon. One of the areas affected by the heavy rain was the community of Santan, to the southeast of Phoenix. After the initial, flash flood producing rains had subsided, considerable water was left behind, inundating roads and leading to episodes of areal flooding. At 1358MST an Emergency Manager reported that many roads in the area around Santan were flooded and closed. Additionally, a Maricopa County stream gage around 3 miles northwest of Santan indicated that flood stage had been exceeded. Flooding continued into the afternoon hours before the water subsided.

Flood, Maricopa

When: July 24, 1:00 PM MST to 4:00 PM MST
Where: Maricopa County, 3.07 mi SSE of Desert Sands to 4.67 mi ESE of Desert Sands
Cause: Heavy Rain
Reported by: Law Enforcement
Coordinates: 33.362, -111.643

Thunderstorms with heavy rain developed across the eastern portion of the greater Phoenix area during the morning hours on July 24th, affecting communities such as Mesa and Apache Junction. Peak rain rates with the stronger storms reached 2 inches per hour and this resulted in episodes of morning flash flooding. After the initial flash flood producing rains subsided, there was significant water remaining which resulted in lingering flooding over portions of Mesa. According to local law enforcement, at 1430MST multiple lanes of an intersection were closed due to high water, approximately 5 miles southeast of East Mesa. Areal flood warnings were not in effect at the time.

What these are

Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

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

The same day elsewhere

Every storm in Arizona in 2017 Every state in 2017 This day in weather history Warnings in Arizona, July 2017

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: 709813, 709807, 709823, 709830, 709832, 709833.