Flood Danger after Fire

HYDROLOGIC OUTLOOK
AZZ015-017-242300-

HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
945 PM MST THU JUN 16 2011

…WILDFIRE BURN AREAS INCREASE RISK OF FLASH FLOODING AND DEBRIS
FLOWS…

IN THE AFTERMATH OF WILDFIRES ACROSS NORTHERN ARIZONA…INCLUDING
THE WALLOW FIRE…LOCUST FIRE…AND 2010 SCHULTZ FIRE…LOCATIONS
DOWNHILL AND DOWNSTREAM FROM BURNED AREAS ARE NOW MORE SUSCEPTIBLE
TO FLASH FLOODING AND DEBRIS FLOWS. A SHORT PERIOD OF MODERATE
RAINFALL ON A BURNED WATERSHED CAN LEAD TO FLASH FLOODS OR DEBRIS
FLOWS. RAINFALL THAT IS NORMALLY ABSORBED CAN RUN OFF EXTREMELY
QUICKLY AFTER SOILS AND VEGETATION HAVE BEEN CHARRED. SEVERELY
BURNED SOILS CAN BE AS WATER REPELLANT AS PAVEMENT.
CONSEQUENTLY…RUNOFF WILL BE GREATER AND MORE RAPID THAN PRIOR TO
THE FIRE. FLOOD WATERS CAN PICK UP LARGE AMOUNTS OF
ASH…SAND…SILT…ROCKS…AND REMNANTS OF VEGETATION. THE FORCE OF
RUSHING WATER AND DEBRIS CAN DAMAGE OR DESTROY
CULVERTS…BRIDGES…ROADWAYS…AND BUILDINGS…POTENTIALLY CAUSING
INJURY OR DEATH.

EACH WILDFIRE BURN AREA POSES ITS OWN UNIQUE RISK OF FLASH FLOODING
DUE TO MANY FACTORS INCLUDING PROXIMITY TO POPULATION CENTERS…BURN
SEVERITY…STEEPNESS OF TERRAIN…AND SIZE OF BURNED DRAINAGE
BASINS. INFORMATION PERTINENT TO INDIVIDUAL BURN AREAS IS INCLUDED
BELOW.

WALLOW FIRE BURN AREA…AFFECTING THE COMMUNITIES OF
ALPINE…EAGAR…GREER…AND NUTRIOSO AS WELL AS PORTIONS OF
HIGHWAYS 180…191…260…261…273…AND 373 WITHIN THE BURNED
AREA OF THE WHITE MOUNTAINS. THE LARGEST WILDFIRE IN STATE HISTORY
HAS BURNED VAST PORTIONS OF THE WHITE MOUNTAINS. PORTIONS OF THE
AREA WERE SEVERELY BURNED…INCLUDING AREAS OF STEEP TERRAIN.
NUMEROUS LOCATIONS WILL BE VULNERABLE TO FLASH FLOODS AND DEBRIS
FLOWS EVEN IN MODERATE INTENSITY RAINS LASTING AS LITTLE AS 10 TO 15
MINUTES. SOME AREA STREAMS AND RIVERS ARE LIKELY TO SEE FLOWS BEYOND
ANYTHING SEEN IN DECADES IF TYPICAL OR ABOVE AVERAGE RAINS OCCUR
THIS SUMMER. RESIDENTS NEAR STREAMS…RIVERS…OR STEEP BURNED
HILLSIDES SHOULD BE ALERT TO FLOODING AND DEBRIS FLOWS. ALL
RESIDENTS SHOULD BE AWARE THAT AREA ROADWAYS MAY BECOME IMPASSIBLE
DUE TO MUD…ROCK…AND DEBRIS SLIDES OR DUE TO STREAMS AND WASHES
OVERWHELMING EXISTING CULVERTS AND BRIDGES. AVOID AREAS OF STEEP
BURNED TERRAIN OR STREAM CHANNELS WHEN RAIN FALLS IN THE AREA.
STUDIES OF THE BURN AREA WILL BE CONDUCTED WHEN POSSIBLE…AND
ADDITIONAL UPDATES ON FLOOD POTENTIAL WILL BE MADE AVAILABLE IN THE
COMING WEEKS.

LOCUST FIRE BURN AREA…AFFECTING THE COMMUNITY OF WHITERIVER. 364
ACRES WERE BURNED ON A STEEP HILLSIDE IMMEDIATELY WEST OF THE
NORTHSIDE…WHISKEY FLATS…AND YUCCA FLATS NEIGHBORHOODS OF
WHITERIVER. RESIDENCES ARE LOCATED WITHIN A FEW HUNDRED FEET OF THE
BURN AREA. DUE TO THE VERY CLOSE PROXIMITY OF RESIDENCES TO THE
BURN AREA…FLASH FLOODING AND DEBRIS FLOWS WILL AFFECT RESIDENCES
VERY QUICKLY AFTER THE ONSET OF MODERATE OR HEAVY RAIN. ONCE RAIN
BEGINS…AS LITTLE AS 5 TO 10 MINUTES OF HEAVY RAIN MAY PRODUCE
FLASH FLOODING AND DEBRIS FLOWS. VULNERABLE LOCATIONS ARE FROM
AROUND LOCUST STREET TO KNOTS LANDING ROAD BETWEEN THE WHITE RIVER
AND THE BURN AREA. DO NOT WAIT FOR A FLASH FLOOD WARNING TO TAKE
PRECAUTIONS TO PROTECT LIFE AND PROPERTY IN THE EVENT OF HEAVY RAIN.
THUNDERSTORMS THAT DEVELOP OVER THE BURN AREA CAN PRODUCE FLASH
FLOODING NEARLY AS FAST AS NATIONAL WEATHER SERVICE RADAR CAN DETECT
THE RAINFALL. FLASH FLOODING MAY BEGIN BEFORE A WARNING CAN BE
ISSUED. IF YOU ARE IN AREAS VULNERABLE TO FLOODING AND DEBRIS FLOWS
FROM THIS BURN AREA…PLAN IN ADVANCE. THERE WILL BE VERY LITTLE
TIME TO SPARE WHEN FLOODING BEGINS.

SCHULTZ FIRE BURN AREA…AFFECTING THE COMMUNITIES OF HUTCHINSON
ACRES…TIMBERLINE…WUPATKI TRAILS…FERNWOOD…AND POTENTIALLY THE
LOW-LYING AREAS IN DONEY PARK EAST OF HIGHWAY 89. ALTHOUGH A YEAR
HAS PASSED SINCE THE FIRE…THE BURN AREA WILL STILL PRODUCE
FLOODING MUCH MORE EASILY THAN BEFORE THE FIRE. EROSION FROM
FLOODING LAST YEAR HAS PRODUCED CHANNELS WHICH CAN CARRY WATER
DOWNHILL EVEN FASTER. IN ADDITION…SOME OF THE SOILS DOWNHILL FROM
THE BURN AREA HAVE BEEN COVERED OVER BY FINE AND RELATIVELY
IMPERMEABLE SEDIMENT FROM LAST YEAR`S FLOODING…AND WILL NOT DRAIN
AS FAST AS BEFORE THE FIRE. ALTHOUGH LESS DEBRIS MAY BE CARRIED BY
FLOOD WATERS THIS YEAR…EXPECT FLOODING TO OCCUR WEST OF HIGHWAY 89
AGAIN THIS SUMMER WHEN MODERATE TO HEAVY RAIN OCCURS FOR 15 TO 30
MINUTES OR MORE OVER PORTIONS OF THE BURN AREA. IN THE EVENT OF
WIDESPREAD AND/OR VERY HEAVY RAINFALL…ENOUGH WATER MAY BE CARRIED
DOWNHILL THAT LOW-LYING PORTIONS OF DONEY PARK EAST OF HIGHWAY 89
MAY BE FLOODED.

RESIDENTS IN FLOOD PRONE AREAS SHOULD HAVE AN EMERGENCY KIT AND A
PLAN TO EVACUATE. IF ROADS ARE BLOCKED OR IT IS UNSAFE TO EVACUATE
DUE TO FLASH FLOODING…DEBRIS FLOWS…HEAVY RAIN…OR POOR
VISIBILITY IT IS BEST TO SHELTER IN PLACE IN A STURDY STRUCTURE.
CALL 911 IF YOU ARE CAUGHT IN A FLASH FLOOD OR DEBRIS FLOW. IF YOU
ARE IN A VEHICLE…DO NOT DRIVE INTO FLOOD WATERS OR DEBRIS FLOWS.

WHEN THE NATIONAL WEATHER SERVICE ISSUES A FLASH FLOOD WATCH FOR
YOUR AREA…IT MEANS THAT THERE IS ENHANCED LIKELIHOOD OF FLASH
FLOODING. YOU SHOULD BE EVEN MORE ALERT TO THE POSSIBILITY OF FLASH
FLOODING. KEEP IN MIND THAT SUMMER WEATHER IN NORTHERN ARIZONA
BRINGS A POSSIBILITY FOR FLASH FLOODING ALMOST EVERY DAY IN
THUNDERSTORMS THAT FORM OVER FLOOD PRONE AREAS AND BURNED AREAS.

WHEN THE NATIONAL WEATHER SERVICE ISSUES A FLASH FLOOD WARNING…IT
MEANS THAT FLASH FLOODING IS ALREADY OCCURRING OR IS LIKELY TO OCCUR
VERY SOON. DO NOT DELAY TAKING PROTECTIVE MEASURES EVEN IF RAINFALL
IS LIGHT AT YOUR LOCATION.

IF YOU HAVE ANY QUESTIONS RELATED TO THE CONTENT OF THIS
PRODUCT…PLEASE CONTACT

GEORGE HOWARD
WARNING COORDINATION METEOROLOGIST
NATIONAL WEATHER SERVICE – FLAGSTAFF
928-556-9161 X223
GEORGE.HOWARD@NOAA.GOV