Schultz Burn Area Flood
July 20, 2010


Preliminary Assessment

Significant flash flooding occurred during the afternoon of July 20th in the neighborhoods downstream from the Schultz wildfire burn area in Coconino County northeast of Flagstaff, AZ, after nearly 2 inches of rain fell in less than one hour over the burn area. Widespread flooding and debris flow occurred across the Timberline, Hutchinson Acres, and Wupatki Trails neighborhoods downstream from the Schultz burn area. Approximately 45 homes in these neighborhoods experienced flooded interiors. Significant flooding also occurred in Doney Park after flood waters crossed U.S. Highway 89, and approximately 40 homes experienced flooded interiors. In addition to flooded interiors, numerous homes sustained property damage such as washed out driveways, fences down, and property laden with ash, among other damages. Flood water depth was estimated to be at least 1 to 2 feet, and higher near washes. Highway 89 was closed for a time as water and debris crossed the road, and required subsequent cleanup before reopening. There was one confirmed fatality associated with this flood event.

flood1 flood2
flood3 flood4
map1

Antecedent Conditions and Preparation

The Schultz wild fire occurred late in June 2010, and severely burned a large portion of the forest along the steep terrain on the east side of the San Fransico Peaks. The pictures below show the nature of the forest and vegetation in the most severely burn area. In this portion of the burn area, there is little if any ground vegetation left to absorb and hold back rainwater. When heavy rain falls over burnt steep terrain, the water quickly rushes downhill carrying loose soils, ash, and debris.

burnt terrain 1

burnt terrain 2

Ever since the Schultz fire occurred back in late June, 2010, the National Weather Service Flagstaff Weather Forecast Office, the US Forest Service, and local law enforcement and emergency management officials have been raising awareness regarding the potential for flash flooding and debris flow downstream of the Schultz burn area. Unfortunately the fear of flash flooding was realized during the early afternoon of July 20, 2010 as a monsoon-season thunderstorm dropped nearly 2 inches of rain over the burn area in less than one hour, and subsequently resulted in flash flooding of several neighborhoods, businesses, and major roadways immediately downstream of the burn area.

Click links below to see examples of how the NWS was raising flood potential awareness prior to the July 20, 2010 flash flood:

July 20, 2010 - The Event

Review of the radar and rain gage data indicated that significant precipitation started falling over the burn area around 1:18 PM and continued through 2:21 PM. The NWS Flagstaff WSR-88D radar indicated that generally 1-3 inches of rain fell in a very short time over much of the burn area. The image below is an NWS Flagstaff radar snapshot from 1:20 PM MST. The Schultz wildfire burn area is outlined in blue and the background image is terrain.

Click on the radar image below for a 3 hour loop from Noon to 3 PM MST.

radar loop


The Storm Total Precipitation image below indicates that the majority of the burn area (outlined in white) received in excess of 1.75 inches of precipitation, with the greatest amounts falling in the western portion of the burn area. The extent of rainfall over the entire burn area was impressive, along with the sharp cutoff to the heavy precipitation. Little or no precipitation fell in the areas that were impacted by the flooding (downstream of the burn area where the heaviest precipitation fell). The rainfall rates were extremely high. Rain gages in the burn area indicated that the initial inch of precipitation fell in approximately 15 minutes, equating to a rainfall rate of approximately 4 inches per hour. The rainfall rates and amounts observed far exceeded the flash flood threshold values that were estimated for this burn area.

storm total precip


NWS Flagstaff Response and Products

NWS Flagstaff automated remote rain gages positioned in the Schultz burn area showed that the first measureable precipitation began at 1:18 PM MST. The NWS Flagstaff meteorologists quickly recognized the threat of flash flooding downstream of the Schultz burn area and issued a flash flood warning at 1:20 PM MST. The first report of flooding was recorded by the NWS Flagstaff in the Timberline area at 1:55 PM MST. Flooding continued to surge and expand over the Timberline area toward Hwy 89 through 2:30 PM MST. The first report of flooding in the Doney Park area near Moonbeam Drive was between 4:30 and 5:00 PM.

The following is a list of the warning products that were issued:

Issue Time Product (click to view)
120 PM MST July 20, 2010 Flash Flood Warning
149 PM MST July 20, 2010 Flash Flood Statement (follow up)
211 PM MST July 20, 2010 Flash Flood Warning
309 PM MST July 20, 2010 Flash Flood Statement (follow up)
346 PM MST July 20, 2010 Flash Flood Statement (follow up)
747 PM MST July 20, 2010 Flood Advisory
150 AM MST July 21, 2010 Flood Advisory (to end event)



Impacts and Summary

The following is a summary of the storm impacts:
You can click this link for the Local Storm Report Summary product.

This storm summary will be updated as additional details and storm damage reports become available. Please direct questions about this report to: