Transcript Document

Improving Flash Flood Nowcasting
at the National Weather Service
W. Scott Lincoln, Hydrologist/Cartographer
NWS Lower Mississippi River Forecast Center
Overview
• Why care about flash flooding?
• Why improve flash flood warnings?
• What new nowcasting techniques are being
evaluated?
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Why care about flash flooding?
• Flooding (either flash or river) is frequently
cited as #1 cause of weather fatalities
– Based upon 30 year average
– No discrimination of flash flooding vs. river flooding
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Why care about flash flooding?
• Detailed weather fatality/injury/damage
statistics available over shorter 19 year period
(1994-2012)
• Among short-fuse weather events, flash
flooding is just shy of #1* in:
– Number of fatalities
– Crop/property damage
*NOTE: Ignoring the big tornado year of 2011, flash
flooding would be approximately the same as tornadoes.
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Flash Flooding Statistics
U.S. Weather Fatalities:
All
U.S. Weather Fatalities:
Short-fuse events
Source: National Weather Service Office of
Climate, Water, & Weather Services
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Flash Flooding Statistics
1994-2012 (OCWWS)
~75% of fatalities due to
flash flooding, ~25%
river flooding
1959-2005 (Ashley &
Ashley 2007)
~71% of fatalities due to
flash flooding, ~29%
river flooding
Hurricane Camille
Rapid City flash flood
Buffalo Creek #3 Dam failure
Big Thompson Canyon flash flood
Teton Dam failure
Kelly Barnes Dam failure
Laurel Run dam break
Kansas City flash flood
Sources: National Weather Service Office of
Climate, Water, & Weather Services; Ashley &
Ashley (2007)
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Flash Flooding Statistics
1959-2005 (Ashley & Ashley 2007)
Vast majority of persons killed by
flooding (any type) are in vehicles.
Source: Ashley & Ashley (2007)
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Flash Flooding Statistics
1959-2005 (Ashley & Ashley
2007)
States with highest flash flood
fatality rates (normalized by
population) span multiple
landform regions.
A single big event
can drive the statistics
Source: Ashley & Ashley (2007)
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Why improve flash flood warnings?
• Tornado/Severe warnings:
–
–
–
–
Scientific reasoning
Specific location of threat
Threat severity information
Predicted movement and evolution
• Flash Flood warnings:
– Frequently cover large areas
– Frequently lack severity information
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Flash Flooding Warnings
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE
1212 AM CST WED FEB 26 2014
THE NATIONAL WEATHER SERVICE IN …HAS ISSUED A
* FLASH FLOOD WARNING FOR...
ST. TAMMANY PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...SLIDELL...MANDEVILLE...EDEN ISLE...
COVINGTON...
HANCOCK COUNTY IN SOUTHERN MISSISSIPPI...
THIS INCLUDES THE CITIES OF...WAVELAND...DIAMONDHEAD...
* AT 1206 AM CST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
FROMDETECTED
THUNDERSTORMS OVER THE WARNED AREA.
* AT 1206 AM FLASH
CST...NATIONALFLOODING
WEATHER SERVICE METEOROLOGISTS
* UNTIL 215 AM CST
FLASH FLOODING FROM THUNDERSTORMS OVER THE WARNED AREA.
* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO STENNIS
SPACE CENTER...PEARL RIVER...MADISONVILLE...ABITA SPRINGS AND KILN
$$
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Flash Flood Warnings
FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE …
605 PM CDT WED MAY 1 2013
...A FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 715 PM CDT FOR
NORTHEASTERN HARRISON AND NORTHERN JACKSON COUNTIES...
AT 555 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
FLASH FLOODING OVER THE WARNED AREA. THE COVERAGE OF THE FLASH
FLOOD WARNING HAS BEEN EXPANDED TO INCLUDE GULFPORT...BILOXI AND
SOUTHWEST JACKSON COUNTY. ISOLATED AREAS BETWEEN GULFPORT AND
BILOXI HAVE RECEIVED UP TO 6 INCHES OF RAINFALL IN THREE HOURS
ACCORDING TO RADAR.
AT 555 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
FLASH
OVER THE WARNED AREA.
ADDITIONAL RAINFALL
AMOUNTSFLOODING
OF 1 TO 2 ARE POSSIBLE IN
PRECAUTIONARY/PREPAREDNESS ACTIONS...
THE WARNED AREA SOUTHEAST HARRISON COUNTY AND CENTRAL PARTS OF
JACKSON COUNTY.
ISOLATED AREAS BETWEEN GULFPORT AND
BILOXI HAVE RECEIVED UP TO 6 INCHES OF RAINFALL IN THREE HOURS
ACCORDING TO RADAR.
EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF SMALL
CREEKS AND STREAMS...URBAN AREAS...HIGHWAYS...STREETS AND UNDERPASSES
AS WELL AS OTHER DRAINAGE AREAS AND LOW LYING SPOTS.
MOST FLOOD DEATHS OCCUR IN AUTOMOBILES. NEVER DRIVE YOUR VEHICLE INTO
AREAS WHERE THE WATER COVERS THE ROADWAY. FLOOD WATERS ARE USUALLY
DEEPER THAN THEY APPEAR. JUST ONE FOOT OF FLOWING WATER IS POWERFUL
ENOUGH TO SWEEP VEHICLES OFF THE ROAD. WHEN ENCOUNTERING FLOODED
ROADS MAKE THE SMART CHOICE...TURN AROUND...DONT DROWN.
$$
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2% rainfall event underway
(3hr rainfall duration)
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Flash Flood Warnings
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE …
258 PM PDT SAT AUG 24 2013
THE NATIONAL WEATHER SERVICE IN … HAS ISSUED A
* FLASH FLOOD WARNING FOR...
WEST CENTRAL IMPERIAL COUNTY IN SOUTHEAST CALIFORNIA...
* UNTIL 600 PM PDT
* AT 249 PM PDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
THUNDERSTORMS WITH VERY HEAVY RAIN BETWEEN SALTON CITY AND
* OTHER AREAS IN THE WARNING INCLUDE WESTMORLAND... ANDHIGHWAY 86
BRAWLEY.
BETWEEN SALTON CITY AND WESTMORLAND.
* AT 249 PM PDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
THUNDERSTORMS WITH VERY HEAVY RAIN BETWEEN SALTON CITY AND
BRAWLEY. MOVEMENT OF THE STORMS WAS SLOWLY SOUTHEAST.
RADAR ESTIMATES THAT STORMS IN THIS AREA HAVE PRODUCED OVER 3
INCHES OF RAIN SINCE 2 PM. THIS AMOUNT OF RAIN IS SUFFICIENT TO
PRECAUTIONARY/PREPAREDNESS
ACTIONS...
PRODUCE
RUNOFF AND FLASH FLOODING.
RADAR ESTIMATES THAT STORMS IN THIS AREA HAVE PRODUCED OVER 3 INCHES
OF RAIN SINCE 2 PM. THIS AMOUNT OF RAIN IS SUFFICIENT TO PRODUCE
RUNOFF AND FLASH FLOODING.
CAMPERS...HIKERS...AND OFF ROAD VEHICLE RIDERS SEEK HIGHER GROUND
IMMEDIATELY. AVOID WASHES AND STREAMS. DO NOT ATTEMPT TO CROSS
SWIFTLY FLOWING WATER OR WATER OF UNKNOWN DEPTH.
MOST FLOOD DEATHS OCCUR IN MOTORIZED VEHICLES. WHEN ENCOUNTERING
FLOODED ROADS...MAKE THE SMART CHOICE...TURN AROUND...DONT DROWN.
$$
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Flash Flood Warnings
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE …
131 PM MST TUE JUL 31 2012
THE NATIONAL WEATHER SERVICE IN … HAS ISSUED A
* FLASH FLOOD WARNING FOR...
NORTH CENTRAL YUMA COUNTY IN SOUTHWEST ARIZONA...
CENTRAL LA PAZ COUNTY IN WEST CENTRAL ARIZONA...
* UNTIL 330 PM MST/330 PM PDT/
* AT 118 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED
SCATTERED SHOWERS AND THUNDERSTORMS CONTINUING TO MOVE ACROSS
PORTIONS OF THE WARNED AREA PRODUCING VERY HEAVY RAINFALL. BETWEEN
TWO AND THREE INCHES HAVE FALLEN BETWEEN 11 AM AND 1 PM IN SOME
LOCATIONS. THIS IS A SIGNIFICANT EVENT...WITH RAINFALL
TOTALS APPROACHING THE 100 YEAR AVERAGE RECURRENCE INTERVAL EVENT.
* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO BUCKSKIN
MOUNTAIN PARK...PARKER DAM AND BOUSE
BETWEEN TWO AND THREE INCHES HAVE FALLEN BETWEEN 11 AM AND 1 PM
IN SOME
LOCATIONS. THIS IS A SIGNIFICANT EVENT...WITH RAINFALL TOTALS
PRECAUTIONARY/PREPAREDNESS
ACTIONS...
APPROACHING THE 100 YEAR AVERAGE RECURRENCE INTERVAL EVENT.
A FLASH FLOOD WARNING MEANS THAT PEOPLE ALONG THE BANKS OF WASHES AND
CREEKS SHOULD MOVE TO HIGHER GROUND IMMEDIATELY. NORMALLY DRY WASHES
AND STREAMS WILL SUDDENLY HAVE RUNNING WATER AND MAKE UNBRIDGED
CROSSINGS IMPASSABLE. STREETS...UNDERPASSES...AND LOW SPOTS WILL
BECOME INUNDATED MAKING DRIVING HAZARDOUS IN THE WARNED AREA.
MOST FLOOD DEATHS OCCUR IN MOTORIZED VEHICLES. WHEN ENCOUNTERING
FLOODED ROADS...MAKE THE SMART CHOICE...TURN AROUND...DONT DROWN.
$$
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Flash Flood Warnings
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE …
128 AM CDT FRI MAY 4 2012
THE NATIONAL WEATHER SERVICE IN … HAS ISSUED A
* FLASH FLOOD WARNING FOR...
NORTHEASTERN DEKALB COUNTY IN NORTHWEST MISSOURI...
NORTHERN DAVIESS COUNTY IN NORTH CENTRAL MISSOURI...
SOUTHERN GENTRY COUNTY IN NORTHWEST MISSOURI...
* UNTIL 730 AM CDT
* AT 122 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
SLOW MOVING THUNDERSTORMS WITH VERY HEAVY RAINFALL ACROSS THE
WARNED AREA. DOPPLER RADAR ESTIMATED THAT UP TO 4 INCHES OF RAIN
HAVE FALLEN SINCE 11 PM ACROSS NORTHERN DAVIESS AND SOUTHERN
GENTRY COUNTIES.
NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED SLOW MOVING
THUNDERSTORMS WITH VERY HEAVY RAINFALL ACROSS THE WARNED AREA.
DOPPLER RADAR ESTIMATED THAT UP TO 4 INCHES OF RAIN HAVE FALLEN SINCE
* RUNOFF FROM THIS EXCESSIVE RAINFALL WILL CAUSE FLASH FLOODING TO
11 PM
NORTHERN
DAVIESS AND SOUTHERN GENTRY COUNTIES.
OCCUR. SOME LOCATIONS
THAT ACROSS
WILL EXPERIENCE FLOODING
INCLUDE...
JAMESPORT...KING CITY AND PATTONSBURG. THIS RUNOFF IS LIKELY TO
CAUSE DOWNSTREAM FLOODING OF THE GRAND RIVER AFFECTING JAMESON AND
GALLATIN.
RUNOFF FROM THIS EXCESSIVE RAINFALL WILL CAUSE FLASH FLOODING TO
THIS WILL IMPACTOCCUR.
I-35 BETWEEN MILE MARKERS 71 AND 82.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
ADDITIONAL RAINFALL AMOUNTS OF ONE TO TWO INCHES ARE POSSIBLE IN THE
WARNED AREA THROUGH 3 AM.
&&
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Current nowcasting tools
• Site-Specific Headwater Predictor (SSHP)
• Gridded Flash Flood Guidance (GFFG) utilized
by Flash Flood Monitoring and Prediction
(FFMP)
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SSHP
• Substantial period of record
required
• Calibrated to observations
• Specific locations only
Soil moisture
adjustment
]
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GFFG and FFMP
• Gridded product that provides
flood/no-flood rainfall value over
set durations
• Based upon land cover, slope,
and soil type
• Shows where runoff is
generated, not where
accumulating
Realtime rainfall…
ratio of GFFG in FFMP
Adjusted for
soil moisture
4x daily
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New techniques under evaluation
• Rainfall average recurrence interval (ARI)
• Simulated streamflow ARI
– FLASH/CREST
– DHM-TF
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Rainfall ARI
• Comparison of realtime rainfall estimates to
historical context
• Historical context provided by rainfall
frequency analysis done by NWS
Hydrometeorological Design Studies Center
http://hdsc.nws.noaa.gov/hdsc/pfds/index.html
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Rainfall ARI
• Strengths
– Provides severity information
– Can narrow down area expecting flooding
• Weaknesses
– Does not provide any routing information
– Based upon rainfall, not surface water flow
– Does not take into account land cover differences or seasonality
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Ouachita Mts., AR: June 2010
Rainfall ARI
•
Rainfall Source: RFC
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Vancleave, MS: May 2013
Rainfall ARI
•
Rainfall Source: RFC
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Springfield, MO: June 2013
Rainfall ARI
•
Rainfall Source: RFC
From:
“Analysis of the 15 June
2013 Isolated Extreme
Rainfall Event in Springfield,
Missouri”
Currently in peer review.
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Streamflow ARI: FLASH
• Streamflow model run from 2002-2010 using
hourly StageIV precipitation
• Frequency analysis done to annual peak flows
from model run
• Q3 radar-only rainfall product drives model in
realtime; results compared to historical
context
http://flash.ou.edu
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Streamflow ARI: FLASH
• Strengths
– Provides severity information
– Simulating accumulation of flow
– Frequent updates due to radar-only rainfall product
• Weaknesses
– Mismatch in rainfall sources for base period vs. realtime could cause
bias
– Nine (9) year base period short; higher uncertainty in peak flow
estimates
– Radar-only rainfall can be biased without gauge adjustment
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Springfield, MO: June 2013
Streamflow ARI
•
•
Model: FLASH
Rainfall Source: Q2
From:
“Analysis of the 15 June
2013 Isolated Extreme
Rainfall Event in Springfield,
Missouri”
Currently in peer review.
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Streamflow ARI: DHM-TF
• Streamflow model run from 2003-2012 using
hourly LMRFC precipitation
• Frequency analysis done to annual peak flows
from model run
• RFC gauge bias-corrected rainfall drives model
in realtime; results compared to historical
context
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Streamflow ARI: FLASH
• Strengths
– Provides severity information
– Simulating accumulation of flow
– Bias-corrected rainfall product reduces rainfall uncertainty
• Weaknesses
– Ten (10) year base period short; higher uncertainty in peak flow
estimates
– Bias-corrected rainfall has substantial delay (up to 1.5hr)
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Ouachita Mts., AR: June 2010
Streamflow ARI
•
•
Model: DHM-TF
Rainfall Source: RFC
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Springfield, MO: June 2013
Streamflow ARI
•
•
Model: DHM-TF
Rainfall Source: RFC
From:
“Analysis of the 15 June
2013 Isolated Extreme
Rainfall Event in Springfield,
Missouri”
Currently in peer review.
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Summary
• Flash flooding remains one of the top weather
hazards in the U.S.
• Flash flood warnings are typically lacking
when compared to other short-fuse warnings
• Nowcasting techniques with potential to
improve flash flood warnings already exist;
some have been in development for many
years
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Questions/Comments?
W. Scott Lincoln
Hydrologist, Cartographer
NWS Lower Mississippi River Forecast Center
[email protected]
Always follow safe procedures
while surveying flash flooding!
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