PRELIMINARY RESULTS FOR THE 0-1 PRELIMINARY RESULTS FOR THE 0-1 HOUR MULTISENSOR PRECIPITATION HOUR MULTISENSOR PRECIPITATION

NOWCASTERNOWCASTER

Shucai Guan and Feng DingShucai Guan and Feng DingRS Information Systems/Hydrology LaboratoryRS Information Systems/Hydrology Laboratory

Richard Fulton and David KitzmillerRichard Fulton and David KitzmillerHydrology LaboratoryHydrology Laboratory

Office of Hydrologic DevelopmentOffice of Hydrologic DevelopmentNational Weather Service, NOAANational Weather Service, NOAA

Silver Spring, MarylandSilver Spring, Maryland

32nd Conference on Radar Meteorology32nd Conference on Radar Meteorology26 October 2005, Albuquerque, NM26 October 2005, Albuquerque, NM

6R.4

OutlineOutline

IntroductionIntroduction Description of the Multisensor Description of the Multisensor

Precipitation Nowcaster Precipitation Nowcaster (MPN)(MPN) Analysis Method and Results Analysis Method and Results ConclusionsConclusions

IntroductionIntroduction

NWS mission includes warning operations for NWS mission includes warning operations for flash flash flooding conditionsflooding conditions, currently the greatest storm-, currently the greatest storm-related threat to life in the United States.related threat to life in the United States.

MPN is developed for NWS Weather Forecast MPN is developed for NWS Weather Forecast Offices to provide additional automated forecast Offices to provide additional automated forecast guidance and lead-time for issuance of flash flood guidance and lead-time for issuance of flash flood warnings. warnings.

The purpose: evaluate the accuracy of a scaled-The purpose: evaluate the accuracy of a scaled-down MPN (no gage data and no mosaicking) down MPN (no gage data and no mosaicking) forecasts of rainrate and establish a baseline of forecasts of rainrate and establish a baseline of performance.performance.

Description of MPNDescription of MPN 4-km resolution, updated every 5 min; forecast 1-hour 4-km resolution, updated every 5 min; forecast 1-hour

accumulated precipitation and 0-1 hour rain rates.accumulated precipitation and 0-1 hour rain rates. Can use rain gauge data to adjust the radar rainrates.Can use rain gauge data to adjust the radar rainrates. Mosaics regional radar data before making the forecast. Mosaics regional radar data before making the forecast. Uses a standard local pattern-matching scheme to Uses a standard local pattern-matching scheme to

estimate storm motion.estimate storm motion. Three options for the smoothing: 1) no smoothing, 2) Three options for the smoothing: 1) no smoothing, 2)

adaptable smoothing using the Flash Flood Potential adaptable smoothing using the Flash Flood Potential method, or 3) a method proposed by Bellon and Zawadski method, or 3) a method proposed by Bellon and Zawadski (1994) (hereafter called BZ94). (1994) (hereafter called BZ94).

Growth/decay of local rain ratesGrowth/decay of local rain rates. .

7 7 flash flood cases in the MD-VA-PA region are flash flood cases in the MD-VA-PA region are investigated. investigated.

Six statistics (Bias, RMSE, COR, POD, FAR, Six statistics (Bias, RMSE, COR, POD, FAR, and CSI) are used to evaluate and compare the and CSI) are used to evaluate and compare the accuracy of the parameter tests.accuracy of the parameter tests.

There are13 algorithm configurations for each There are13 algorithm configurations for each case: 2(growth/decay; N or G) X 3 smoothing case: 2(growth/decay; N or G) X 3 smoothing (none, FFP method, BZ94 method; N or F or B) (none, FFP method, BZ94 method; N or F or B) X 2 (local vs. area-averaged storm motion; L or X 2 (local vs. area-averaged storm motion; L or A) + persistence (A) + persistence (PRS). For example, NFL is ). For example, NFL is test with turning off growth/decay, using FFP test with turning off growth/decay, using FFP smoothing and local storm motion.smoothing and local storm motion.

13 algorithm configurations and their 13 algorithm configurations and their test namestest names

Growth/decay No No No No No No No Yes Yes Yes Yes Yes Yes

Smoothing No No No FFP FFP BZ94 BZ94 No No FFP FFP BZ94 BZ94

Motion No Avg Loc Avg Loc Avg Loc Avg Loc Avg Loc Avg Loc

Test name PRS NNA NNL NFA NFL NBA NBL GNA GNL GFA GFL GBA GBL

Example of Example of observed and observed and forecasted 60-forecasted 60-minute rain minute rain rate and one-rate and one-hour hour accumulation accumulation images for images for June 13, 2003June 13, 2003

(MPN with (MPN with option NFL)option NFL)

Average Bias and RMSE for 60-min forecasted rain rate.

0

0.5

1

1.5

2

Bia

s

0123456

RM

SE

(m

m/h

)

Bias RMSE

The bias is ∑(forecasted rain rate)/ ∑(observed rain rate).

Correlation coefficient and CSI (>5mm/h) for 60-min forecast rain rate.

0

0.1

0.2

0.3

0.4

Corr

elat

ion

0

0.05

0.1

0.15

0.2

0.25

Criti

cal S

ucce

ss

Inde

x

Correlation CSI

POD and FAR of rain rate > 5 mm/h at 60-min forecast.

00.10.20.30.40.50.6

POD

0.6

0.65

0.7

0.75

0.8

FAR

POD FAR

0

10

20

30

40

50

60

70

80

90

1st Qtr 2nd Qtr 3rd Qtr 4th Qtr

East

West

North

Growth/decay option as implementedcauses positive bias in forecasts

Smoothing option reducesbias in forecasts

Turning off growth/decay option results a Turning off growth/decay option results a perceptible improvement on RMSE after perceptible improvement on RMSE after the 30 minute forecastthe 30 minute forecast

Smoothing option reduces RMSEreduces RMSE

The smoothing option increases correlationThe smoothing option increases correlation

Turning on the growth/decay Turning on the growth/decay option has negligible improvement option has negligible improvement on correlationon correlation

Turning on the growth/decay Turning on the growth/decay option and smoothing option option and smoothing option improve PODimprove POD

The effect of the growth/decay option The effect of the growth/decay option is much larger than that of the is much larger than that of the smoothing option at 60 minutes into smoothing option at 60 minutes into the forecastthe forecast

Turning on the growth/decay Turning on the growth/decay option increases FARoption increases FAR

The smoothing produces The smoothing produces notable improvement on FAR notable improvement on FAR after the 30 minute forecastafter the 30 minute forecast

The smoothing improves CSIThe smoothing improves CSI

The growth/decay option has The growth/decay option has small mixed effect on CSIsmall mixed effect on CSI

Comparison of average POD, FAR, and CSI of rain rate > 15 mm/h at 60 minute

forecast between persistence and nogr_smffp_loc runs.

0

0.2

0.4

0.6

0.8

1

POD FAR CSI

PRN

NFL

Comparison of average POD, FAR, and CSI of rain rate > 5 mm/h at 60 minute

forecast between persistence and nogr_smffp_loc runs.

0

0.2

0.4

0.6

0.8

1

POD FAR CSI

PRS

NFL+71%

-11%

+67% +32%

-10%

+54%

Comparison of average POD, FAR, and CSI of rain rate > 15 mm/h at 60 minute

forecast between persistence and nogr_smffp_loc runs.

0

0.2

0.4

0.6

0.8

1

POD FAR CSI

PRS

NFL+32%

-10%

+54%

ConclusionsConclusions

MPN substantially improves all six statistics MPN substantially improves all six statistics relative to persistence method.relative to persistence method. The The progressive progressive spatial smoothing spatial smoothing creates major improvement for creates major improvement for all six statisticsall six statistics..

Comparing with persistence, MPN:– Reduces RMSE by 24%.Reduces RMSE by 24%.– Raises POD by 71% for rainrate > 5 mm/h.– Raises POD by 32% for rainrate >15 mm/h.– Decreases FAR by about 10%.– Increases CSI by 67% Increases CSI by 67% for rainrate > 5 mm/h.– Increases CSI by 54% Increases CSI by 54% for rainrate > 15 mm/h.