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Short-Range QPF for Flash Flood Prediction and Small Basin Forecasts
Prediction ForecastsDavid Kitzmiller, Yu Zhang, Wanru Wu,
Shaorong Wu, Feng Ding
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Office of Hydrologic DevelopmentNOAA National Weather Service
Silver Spring, Maryland
2 June 2010
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Recent performance of the High Resolution Precipitation Nowcaster (HPN) algorithm in 0-1 hour time frame
Detection of precipitation at 25mm h-1 thresholds Verification at 16 km2 grid resolution (4x4 km)
An approach to QPF in the 0-6-hour range Does blending of physical and extrapolation model precipitation
forecasts improve on either one, in the 0-6-hour time frame? HPN was targeted for FFMP application 0-6h QPF targeted primarily for RFC use, but there are
potential applications to Site Specific
In this discussion:
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Based purely on extrapolation of radar echoes Implemented in OB9.0, following implementation of High-
Resolution Precipitation Estimator (HPE) Produces forecasts of:
Rainfall rate at 15, 30, 45, and 60 minutes 1-hour rainfall total
Forecasts are computed on 4-km grid mesh, output on 1-km grid mesh
Can incorporate gauge/radar bias information from MPE See WDTB flash flood modules:http://www.wdtb.noaa.gov/buildTraining/AWIPS_OB9/index.html
HPN Extrapolation Forecastsin the 0-1 Hour Timeframe:
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HPN verification study:September-October 2009
HPN was run in offline mode over the conterminous U.S., during development of 0-6h QPF algorithm
First two hours of the extrapolation forecast are from HPN algorithm
Input from NMQ radar-only precipitation rate algorithm Forecasts verified relative to subsequent NMQ radar-
only precipitation estimates 30 study hours over 15 days, 15 Sep-31 October Verified detection of ≥12.5mm and ≥ 25mm amounts Documented performance relative to persistence
forecast (initial-time rain rates)
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Example HPN Input/Forecast/Verification
Radar Rainrate1845 UTC24 Sep 2009
NMQ Estimate1845-1945 UTC
HPN Forecast1845-1945 UTC
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
POD FAR CSI
HPN 25mm Persistence 25mm
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
POD FAR CSI
HPN 12.5mm Persistence 12.5mm
HPN verification study: Detection of 4x4km rainfall
23.3 x 106 cases included in statistics
≥12.5mm
≥25mm
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4-km forecasts and verification
0
5
10
15
20
25
0 5 10 15 20 25 30 35
HPN 0-1h forecast, mm
Ra
da
r Q
PE
ve
rifi
ca
tio
n
Mean obs 25th percentile obs 75th percentile obs
Poly. (75th percentile obs) Poly. (25th percentile obs) Poly. (Mean obs)
HPN verification study:Forecast vs Radar-Estimated 4x4km rainfall
22,000 grid boxes with precipitation forecasted, northeastern U.S.
75th pct
25th pct
Mean
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HPN Verification Study:Summary
HPN consistently improves on persistence forecasts in terms of POD and FAR: 40% more detections of 12.5- and 25-mm
amounts 20% fewer false alarms
HPN QPF has little bias overall (0.9 to 1.1) For HPN QPF > 10 mm: Expected (mean)
observation is about 0.67 of the forecast amount For HPN QPF > 10 mm: 25th percentile
observation is about 0.80 of the forecast amount
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Original requests for development from ABRFC Designed to use a statistically-weighted combination of
QPFs from radar extrapolation and from RUC2 Extrapolation/advection model for precipitation rate fields:
Extrapolation based on recent radar echo motion for 0-2 hours Motion vector field is morphed toward RUC2 700-500 hPa wind
field forecast for 3-6 hours
Radar precipitation rate input from NMQ radar-only product (see succeeding NSSL presentation)
Model Output Statistics approach used to determine optimum blend of extrapolation and RUC QPFs
0-6 Hour QPFFrom Radar Extrapolation and RUC forecasts
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Radar Precipitation Rates,1715 UTC, 16 May 2009
From National Mosaic and Multisensor Quantitative Precipitation Estimation system (NMQ)
Yellow: > 10mm 6-h-1
Red: > 25mm 6-h-1
Gray: > 38 mm 6-h-1
Blue: > 75 mm 6-h-1
Radar-Observed Precipitation Rates, 1715 UTC 15 May 2009
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Extrapolation forecasts of rate field, 1715-2315 UTC:
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Forecast products: Probability of 6-hour precipitation ≥ 0.25, 2.5, 12.5,
25, 50, 75 mm Precipitation amount forecast
Gridded forecasts, 4x4 km mesh length Issue forecasts for periods 00-06, 06-12, 12-18,
18-00 UTC (cover entire day) Forecasts use input from the hour preceding
start of valid period RUC-Satellite-Lightning equations will be applied
in radar coverage gaps Forecasts disseminated before start of valid
period
0-6h QPF Product Characteristics
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Regression Equation for 0-6-hPrecip Amount: Southeastern US
Precipitation = 0.52 + 0.31 RADAR QPF(0-3h)+ 0.24 RUC QPF (0-3h)+ 0.26 RUC QPF (3-6h)
+ 0.17 RADAR QPF (3-6h)
given RADAR and/or RUC QPF > 0; forecasts and predictors in mm, spatial area 4x4 km
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Prediction equation based on 40,000 cases: Apr-Sep 2009, Southeastern United States. Mean observed precip = 1.9 mm; R2 = 0.14
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5
10
15
20
25
30
Amount P >2.5mm P > 25mm
RUC+Radar RUC only Radar only Operational
Regression (RUC2+Radar) Forecasts:Correlation to 6-H Rainfall, New England
(17,300 cases Apr-Sep 2009 – 18-00 UTC)
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Red
uct
ion
of
Var
ian
ce (
R2 )
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Explained variance is small at this small spatial scale. However skill increases as accumulating area increases.
Products combining RUC2 and extrapolation QPF could match or improve on skill of current operational guidance
Radar and numerical prediction models are clearly complementary for QPF in 0-6-hour range
0-6h QPF Findings
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Collection of new forecast and verification data on a daily basis
Aim for 3 years’ development data Creation of probability and amount equations
for cool and warm season, and subregions of the conterminous U.S.
Create disaggregation logic to get QPFs for 1-h subintervals in 6-h period
Ongoing Work – 0-6h QPF
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Questions? Suggestions?Thanks to collaborators in NOAA National Severe Storms
Laboratory, Institute of Atmospheric Physics/Czech Republic Academy of Sciences
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Supplementary Slides
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HPN verification study:Detection of 8x8 km rainfall
POD for individual events, 8km
0
0.1
0.2
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
POD for initial rainrate
PO
D f
or
HP
N
POD, 12.5mm POD, 25mm REF
All 12.5mm All 25mm
11,100 grid boxes with precipitation observed or forecasted
FAR for individual events, 8km
0.5
0.6
0.7
0.8
0.9
1
0.5 0.6 0.7 0.8 0.9 1
FAR for initial rainrate
FA
R f
or
HP
N
FAR, 12.5mm FAR, 25mm REF
All 12.5mm All 25mm