AMBER Areal Mean Basin Estimated Rainfall COMAP Symposium Heavy Precipitation and Flash Floods Robert S. Davis, Pittsburgh WFO

AMBER Overview AMBER Overview All watersheds in county warning area are defined to a Minimum Basin Area (MBA) of 2 mi 2 to show spatial rainfall distribution. The WSR-88D polar grid (1 o 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 Definitions

National 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.

AMBER Watershed Division All watersheds in the county warning area are divided into hydrologic segments no larger than 10 mi 2. A Minimum Basin Area of 2 mi 2 is used in the initial NSSL stream creation procedure. Each forecast office may modify the NSSL stream database (subdivide or aggregate).

French Creek Allegheny River 02km Allegheny River Patchel Run Franklin Airport Franklin Rocky Grove River Gage

French Creek 02km Allegheny River Patchel Run Franklin Airport Franklin Rocky Grove A B C Franklin 60mm 61mm 42mm 65mm 62mm

Allegheny River French Creek Rocky Grove Patchel Run Patchel Run(2) Patchel Run(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 Flooding ABR in inches FF0 ABR = FFG to < FFG FF1 ABR = FFG to < FFG FF2 ABR = FFG to < FFG FF3 ABR = FFG to < FFG FF4 ABR = FFG to < FFG FF5 ABR = FFG to > FFG + 4.5

Graphical Radar Rainfall OHP – One hour rainfall STP – Storm total rainfall THP – Three hour rainfall

Digital Radar Rainfall DPA – Digital Precipitation Array DHR – Digital Hybrid Scan Reflectivity

Digital Rainfall Estimate 2130 – 2135 UTC Rainfall (mm) Grid size 1km x 1km

ABR and ABR Rate Computations

Digital Rainfall Estimate 2130 – 2135 UTC Rainfall (mm) Grid size 1km x 1km

Average Basin Rainfall = 7.3 mm 2130 – 2135 UTC Rainfall (mm) 7.3 Grid size 1km x 1km

Average Basin Rainfall = 7.3 mm 2130 – 2135 UTC Rainfall (mm) Grid size 1km x 1km

Average Basin Rainfall = 7.3 mm 2130 – 2135 UTC Rainfall (mm) Grid size 1km x 1km

History of NWS Digital Rainfall Products Manually Digitized Radar (MDR: ) 40 km grid / 1 hour RADAP-II digital rainfall ( ) offices. Polar grid (2 o 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: (1 o x 1 km / 5 min.)

Grid size 40 km x 40 km = 1,600 km 2

Digital Precipitation Array (DPA) Time interval (1 hour) Data grid size (4 km x 4 km grid = 16 km 2 ) Rainfall estimates in the WSR-88D polar grid (1 o 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)

Digital Hybrid Scan Reflectivity (DHR) Time interval (5-6 minutes) Grid size (1 degree x 1 km) Reflectivity to the nearest 0.5 dBZ

DHR Grid Area (km 2 ) vs. Radar Range (km)

AMBER DHR Grid Assignment Classes AMBER DHR Grid Assignment 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.

French Creek 02km Allegheny River Patchel Run Franklin Airport Franklin Rocky Grove A B C Franklin 60mm 61mm 42mm 65mm 62mm

Rocky Grove Franklin 02km Franklin Airport 5632 x x x x x x x x x x x x x x x x 16.5 o 99.5km 16.5 o 103.5km 17.5 o 103.5km 18.5 o 100.5km 17.5 o 100.5km French Creek

Radar Rainfall Data Radar 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.

Davis, R. S., 2001: Flash Flood Forecast and Detection Methods. Severe Convective Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor. Soc., in press.

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

15 th Street 13 th Street Franklin Airport Liberty Street Route 8 Route 62 French Creek Chubb Run 0 1km Localization Add small watersheds Area 2.5km 2 MBA 5 km 2

Rocky Grove Franklin 02km Franklin Airport French Creek 5632 Galena Hill 460m Oak Hill 442 m Localization Add urban areas.

Franklin Galena Hill 460 m River Bank km 300 m 350 m 400 m 450 m 15 th Street & Liberty Street Modify FFG for urbanization

Oak Hill 445 m River Bank km 300 m 350 m 400 m 450 m Atlantic St. Grant St. Pacific St. Rocky Grove Modify FFG for 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 # June UTC

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 # June UTC

ABR Allegheny River(67) # June UTC

ABR Patchel Run Sum June UTC

AMBER 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

3 rd Ward 02km Franklin Airport French Creek 5632 Route 322 Route 322 Route 62 Route 8 15 th St Chubb Run

AMBER Data Sources ArcView and the spatial analyst extension. USGS Data (3 arc second DEM data) edcwww.cr.usgs.gov EPA Data (RF3 data files) Ami Arthur (SOO KHNL)

AMBER Case Studies on 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 Cedar City, UT Eastern Ohio Brookville, PA* Dallas, TX* Fort Collins, CO* Kansas City, MO* * Tropical Z/R Cases