AMBERAMBERAreal Mean Basin Estimated Rainfall

COMAP Symposium

Heavy Precipitation and Flash Floods

Robert S. Davis, Pittsburgh WFO

AMBER OverviewAMBER Overview

• All watersheds in county warning area are defined to a Minimum Basin Area (MBA) of 2 mi2 to show spatial rainfall distribution.

• The WSR-88D polar grid (1o by 1 km) is mapped to the defined watersheds.

• Average Basin Rainfall (ABR) is computed for each watershed every volume scan.

• An hourly ABR rate is determined from the single volume scan (5-6 min.) of ABR.

Stream Basin Stream Basin DefinitionsDefinitions

National Basin DelineationNational Basin Delineation

• 30Sep1999 – NWS agrees to fund the AMBER National Basin Delineation project by NSSL for all of the United States.

• ArcInfo used to define the watershed boundaries.

• USGS 1 arc second (30 m) DEM data supplied by EROS Data Center.

• www.nssl.noaa.gov/teams/western/basins

AMBER Watershed DivisionAMBER Watershed Division

• All watersheds in the county warning area are divided into hydrologic segments no larger than 10 mi2.

• A Minimum Basin Area of 2 mi2 is used in the initial NSSL stream creation procedure.

• Each forecast office may modify the NSSL stream database (subdivide or aggregate).

FrenchCreek

AlleghenyRiver

0 2km

AlleghenyRiver

PatchelRun

FranklinAirport

Franklin

RockyGrove

RiverGage

FrenchCreek

0 2km

AlleghenyRiver

PatchelRun

FranklinAirport

Franklin

RockyGrove

5632

5624

5623

5618

5622

A

B

C

Franklin60mm

61mm

42mm

65mm

62mm

AlleghenyRiver

FrenchCreek

56625663

5661

5632RockyGrove

PatchelRun

PatchelRun(2)

PatchelRun(1)

48mm

31mm

35mm

60mm

ABR vs FFG

Determining the Flash Flood Threat

Flash Flood Guidance (FFG)

• ABR in a specific time period (1, 3 hours) to initiate flooding on streams.

• Assumes stream at low flow level.

• Assumes no rainfall since data cutoff

• FFG is the amount of ABR needed to produce threshold runoff (climatic average runoff needed to start flooding of streams)

FF Scale for Flash FloodingFF Scale for Flash FloodingABR in inchesABR in inches

• FF0 ABR = FFG to < FFG + 0.5

• FF1 ABR = FFG + 0.5 to < FFG + 1.5

• FF2 ABR = FFG + 1.5 to < FFG + 2.5

• FF3 ABR = FFG + 2.5 to < FFG + 3.5

• FF4 ABR = FFG + 3.5 to < FFG + 4.5

• FF5 ABR = FFG + 4.5 to > FFG + 4.5

Graphical Radar Graphical Radar RainfallRainfall

OHP – One hour rainfall

STP – Storm total rainfall

THP – Three hour rainfall

Digital Radar Digital Radar RainfallRainfall

DPA – Digital Precipitation Array

DHR – Digital Hybrid Scan Reflectivity

Digital Rainfall Estimate

2130 – 2135 UTC Rainfall (mm)

10.4

9.6

9.8 9.4

7.4 3.6

5.0

7.54.1

6.2

Grid size 1km x 1km

ABR and ABR Rate ABR and ABR Rate

ComputationsComputations

Digital Rainfall Estimate

2130 – 2135 UTC Rainfall (mm)

10.4

9.6

9.8 9.4

7.4 3.6

5.0

7.54.1

6.2

Grid size 1km x 1km

Average Basin Rainfall = 7.3 mm

2130 – 2135 UTC Rainfall (mm)

7.3

7.3

7.3 7.3

7.3 7.3

7.3

7.37.3

7.3

Grid size 1km x 1km

Average Basin Rainfall = 7.3 mm

2130 – 2135 UTC Rainfall (mm)

10.4

9.6

9.8 9.4

7.4 3.6

5.0

7.54.1

6.2

Grid size 1km x 1km

Average Basin Rainfall = 7.3 mm

2130 – 2135 UTC Rainfall (mm)

9.3

9.3

9.3 6.4

6.4 6.4

6.4

9.35.2

5.2

Grid size 1km x 1km

History of NWS Digital History of NWS Digital Rainfall ProductsRainfall Products

• Manually Digitized Radar

(MDR:1975-1993) 40 km grid / 1 hour• RADAP-II digital rainfall (1977-1993)

10-12 offices. Polar grid (2o x 2.2 km / 10 min.)• WSR-88D Digital Precipitation Array

(DPA:1993-current) 4 km grid - 1 hour• WSR-88D Digital Hybrid Scan Reflectivity

(DHR:1999-current) Polar grid: (1o x 1 km / 5 min.)

ABCDEFGH

JI

KLMNOPQRSTUVWXY

A B C D E F G H I J K L M N O P Q R S T U V W X Y

250nm

125nm

MDR

GRIDRadar inBox MM

LJ352

3 5 2

ROB DigitalReport:

Grid size 40 km x 40 km = 1,600 km2

Digital Precipitation Array Digital Precipitation Array (DPA)(DPA)

• Time interval (1 hour)

• Data grid size (4 km x 4 km grid = 16 km2)

• Rainfall estimates in the WSR-88D polar grid (1o x 2 km) are averaged to produce a single rainfall estimate in each grid box.

• Used for RFC Stage 1-3 precipitation estimation and for FFMP(AWIPS Build 5.0)

MDR vs. HRAP 4kmAllegheny County, PA

Pine Creek

HRAP 4kmGrid

Little Pine Creek

4.2km at 40oN

727 mi2

68 mi2

6 mi2

Manually Digitized Radar

Digital Hybrid Scan Digital Hybrid Scan Reflectivity (DHR)Reflectivity (DHR)

• Time interval (5-6 minutes)

• Grid size (1 degree x 1 km)

• Reflectivity to the nearest 0.5 dBZ

DHR Grid Area (kmDHR Grid Area (km22) ) vs. Radar Range (km)vs. Radar Range (km)

0

0.5

1

1.5

2

2.5

3

3.5

4

0 50 100 150 200

AMBER DHR Grid AMBER DHR Grid Assignment ClassesAssignment Classes

• DHR grid is mapped to all defined watershed segments. This allows ABR computation in 5-6 minute time steps.

• DHR grid is mapped to all urban areas to compute ABR urban rainfall.

• Single 1km DHR bins are assigned to location of all rain gages, allowing gage comparison with radar estimated rainfall.

FrenchCreek

0 2km

AlleghenyRiver

PatchelRun

FranklinAirport

Franklin

RockyGrove

5632

5624

5623

5618

5622

A

B

C

Franklin60mm

61mm

42mm

65mm

62mm

RockyGrove

Franklin

0 2kmFranklinAirport

5632x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x16.5o 99.5km

16.5o 103.5km

17.5o 103.5km

18.5o 100.5km

17.5o 100.5km

FrenchCreek

Radar Rainfall DataRadar Rainfall Data• Radar provides 3 rainfall measurements,

location, time, and quantitative estimate.• Radar grid size determines the minimum

basin area (MBA) for ABR computations.• Sample rate determines time interval, but

product time interval may be larger.• Z/R relationship determines rainfall

estimate. (Sources of error important!!)

Scale of Flash Flood Storms

• Thunderstorms producing heavy rainfall (>25 mm hr-1) are small in area and short in time duration.

• Cell lifetime generally < 30 minutes.

• Areal coverage is Z/R dependent, larger areas with Tropical Z/R, smaller areas with standard convective Z/R.

40 dBZ

0 10 km

20km25km2

70km2

2575

125

Rainfall RateStandard Z/R mm hr-1Z = 300 R 1.4

Davis, R. S., 2001: Flash Flood Forecast and Detection Methods. Severe Convective

Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor. Soc., in press.

40 dBZ

0 10 km

32km2

40km2

80km2

2575

125

Rainfall RateTropical Z/R mm hr-1

Z = 250 R 1.2

Davis, R. S., 2001: Flash Flood Forecast and Detection Methods. Severe Convective

Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor. Soc., in press.

AMBER Localization

Modifications to the NSSL database done at the NWSFO

AMBER Localization

• Subdivide defined NSSL watersheds

• Add smaller watersheds

• Add urban areas

• Create rain gage database

• Modify FFG for individual streams

15th

Street

13th

Street

FranklinAirport

LibertyStreet

Route 8

Route 62

French Creek

ChubbRun

0 1km

LocalizationAdd small watersheds

Area 2.5km2

MBA 5 km2

RockyGrove

Franklin

0 2kmFranklinAirport

FrenchCreek

5632Galena

Hill460m

OakHill

442 m

LocalizationAdd urban areas.

Franklin

Galena Hill460 m

RiverBank

0 0.5 1.0 1.5 km300 m

350 m

400 m

450 m

15th Street &Liberty Street

Modify FFGfor urbanization

Oak Hill445 m

RiverBank

0 0.5 1.0 km

300 m

350 m

400 m

450 m

Atl

anti

c St

.

Gra

nt S

t.

Paci

fic

St.

Rocky Grove

Modify FFGfor steep terrain

Rain Gage Verification of Z/R

• Include all rain gages in AMBER database

• Latitude/Longitude of gage only needed.

• Single DHR bin with gage used for WSR-88D rainfall estimate.

Gage: Franklin Airport #105921-22 June 2001 2331-0040 UTC

0

20

40

60

80

100

120

140

2331

2336

2341

2346

2351

2355

0002

0007

0011

0016

0021

0026

0035

0040

ABR RateABR

AMBERGIS Graphic Products

• ABR Rate Time Lapse

• 30 minute ABR Time Lapse

• 120 minute ABR Total

• Graphics produced for 15, 30, 60, 90, 120 and 180 minutes. (User selectable).

• ABR/ABR Rate line graphs.

ABR French Creek #563221-22 June 2001 2331-0040 UTC

0

20

40

60

80

100

120

2331

2336

2341

2346

2351

2355

0002

0007

0011

0016

0021

0026

0035

0040

ABR RateABR

ABR Allegheny River(67) #562321-22 June 2001 2331-0040 UTC

0

20

40

60

80

100

120

140

2331

2336

2341

2346

2351

2355

0002

0007

0011

0016

0021

0026

0035

0040

ABR RateABR

ABR Patchel Run Sum21-22 June 2001 2331-0040 UTC

0

10

20

30

40

50

60

70

80

2331

2336

2341

2346

2351

2355

0002

0007

0011

0016

0021

0026

0035

0040

ABR RateABR

AMBER SummaryAMBER Summary• ABR provides basin specific rainfall to

determine flash flood risk (ABR-FFG)• ABR rate focuses forecaster attention on

critical streams before flooding occurs.• History of ABR helpful in adjusting FFG

for multiple rainfall events.• Basin specific ABR allows forecaster to

mention “threat area” in warning text.

Flood Damage Path

Stream Specific Warnings

3rd Ward

0 2kmFranklinAirport

FrenchCreek

5632

Route 322

Route322

Route 62Route 8

15th StChubb Run

AMBER Data SourcesAMBER Data Sources• ArcView and the spatial analyst extension.

www.esri.com• USGS Data (3 arc second DEM data)

edcwww.cr.usgs.gov• EPA Data (RF3 data files)

www.epa.gov/OST/BASINS/gisdata.html• Ami Arthur aarthur@enterprise.nssl.noaa.gov• Paul.Jendrowski@noaa.gov (SOO KHNL)

AMBER Case StudiesAMBER Case Studieson COMET Websiteon COMET Website

• buff.ppt 13Jul96 • epgh99.ppt 18May99• pitcairn.ppt 01Jul97• zion.ppt 27Jul98• ohio98.ppt 26Jun98• redbank.ppt 19Jul96• dallas95.ppt 05May95• ftc97.ppt 28Jul97• kc1998.ppt 05Oct98

• Buffalo Creek, CO• Pittsburgh, PA• Pittsburgh, PA• Cedar City, UT• Eastern Ohio• Brookville, PA* • Dallas, TX*• Fort Collins, CO*• Kansas City, MO*

* Tropical Z/R Cases