# Presentation: 461626

##  Brian McInerneyHydrologistNational Weather Service Southern Utah Flood Event  Oct. 5th & 6th, 2006 August 2007

## Antecedent Conditions

- A closed low pressure system is parked over Southern California
- Subtropical moisture is moving from the south pacific south of Baja Mexico
- The two interact and produce widespread long duration rainfall
- Model guidance indicates rainfall amounts could produce over 6+ inches of rainfall over parts of south central Utah
- Things get serious

## Antecedent Conditions

- Model Guidance 66 hours prior to event indicating 6.25 inches of rainfall possible for storm total

## Antecedent Conditions

- On Wednesday, Oct. 4th, around noon, NWS issues Flash Flood Watch
- Calls all NPS offices, BLM offices, GSENM offices, County Dispatch, and City EM’s to give heads up on storm and probable flooding
- Roads closed, backcountry permits denied, and other actions taken by appropriate agencies
- Around 4am on Thursday, Oct. 5th, 2006 Precipitation began to fall on Southeastern Utah
- On Oct. 5th, 1pm NWS issues Flash Flood Warning

## Beginning of Storm

- Rainfall begins in earnest on Thursday, Oct. 5th during the early afternoon hours.
- Radar is overshooting majority of storm activity
- Radar is considered unreliable to be used for this event for precipitation estimates
- However, radar is used to track storm activity

## Active Storm Event

- Intense rainfall is covering Southeast Utah as of Thursday, Oct. 5th in the afternoon hours
- Amounts are being recorded at over 1.5 inches at 4pm
- Amounts increase to 2.5 inches in some areas
- The start of widespread flash flooding is occurring region wide

## Active Storm Event

- Active precipitation continues through night
- Widespread flooding continues over southeastern Utah
- Smaller drainages are receding in parts of the area as heaviest rainfall has moved on to Colorado
- Mainstem rivers are peaking during early morning hours of Friday, Oct. 6th
- Widespread amounts are being recorded at over 2.5 to 3.5 inches on Friday morning
- Road from Capitol Reef NP to Hanksville is damaged and closed.
- Hanksville receives record 24 rainfall amount of 3.73 inches
- Tavaputs Plateau recorded 5.75 inches for a storm total

## Active Storm Event

- Satellite view indicating widespread heavy precipitation across southeast Utah
- Heavy precipitation also across Arizona and Nevada
- Flow is southwest
- Training storms (storms that reform over a specific area) are a problem

## Active Storm Event

-  24 hour lightning plot ending at 8pm on Oct. 6th, 2006

## Active Storm Event

-  GOES Satellite Total precipitable Water Friday 10pm Oct. 5th, 2006

- SE Utah

-  Gray areas indicate 3+ inches of precipitation total from GOES Satellite ending midnight Oct. 6th, 2006

## Damage

## Flood

## Venturing Into a Flash Flood

## Venturing Into a Flash Flood

## How Much Does a Flash Flood Weigh?

- _Volume_
- 1 ac-ft. = 325,851.43 gallons
- 1 gallon – 8.345 lbs
- 1 ac-ft. = 2,437,528.4 lbs
- Largest Elephant = 24,000 lbs
- 1 ac-ft. = 113 Large Elephants
- _Flow_
- 1 cu ft. = 7.4805 gallons
- 1 cu ft. = 62.42 lbs
- 1000 cu ft./sec = 62,420 lbs/sec
- 1000 cfs = 2.6 Large Elephants rolling by each second

- 7000 cfs per average flow per day in the Dirty Devil River = 18.2 large elephants rolling by every second, all day

## Not one injury or death

## Flood

## Hydrographs

## Frequency of Flash Flooding In Southern Utah

## New thoughts on Flash Flooding

- In the past, it was thought that flash flooding was over by September
- Convective flash flooding is indeed slowed and finished by that time
- However, long duration widespread rainfall is just beginning
- We now gear up to address this type of phenomenon
- Flash flooding continues through late October
- We had learned more of this phenomenon by talking with our customers

## Paria River near Lees Ferry ClimatologyNumber of days exceeding river flows of 700 cfs1924 through 2004

- Month

## Paria River near Lees Ferry Climatology Number of events exceeding river flows of 700 cfs1924 through 2004

- Month

## North Fork Virgin River near Springdale Climatology Number of days exceeding river flows of 700 cfs1923 through 2003

- Month

## North Fork Virgin River near Springdale Climatology Number of events exceeding river flows of 700 cfs1923 through 2003

- Month

## Fremont River near Cainville Climatology Number of days exceeding river flows of 300 cfs1964 through 2004

- Month

## Fremont River near Cainville Climatology Number of events exceeding river flows of 300 cfs1964 through 2004

- Month

## Contact Information

- Additional Information
- Contact
- Brian McInerney
- Hydrologist
- National Weather Service
- 801-971-2033 c
- brian.mcinerney@noaa.gov