DECEMBER 2007 FLOOD EVENT

PART 2: FORECAST VERIFICATION

December 2007 Event Verification

The verification discussion is divided into two sections.In the first section the primary meteorological input, quantitative precipitation forecast (QPF), is evaluated.Evaluation of the hydrologic forecasts follows.

 

Meteorological Verification

This was the first major event where hydrometeorologists at the NWRFC utilized GFE to generate forecasted mean areal precipitation (FMAP) for input to hydrologic models.Hydrometeorolgical forecasters started using GFE generated QPF operationally this season.Each morning the HAS forecaster initializes NWRFC's QPF field using a mix of WFO ISC, HPC, and various model (GFS and NAM) QPF data.The forecaster uses GFE tools to derive a 10 day QPF product.PRISM climatological relationships are utilized to account for the influence of elevation.From the GFE grids QPF amounts are generated for the network of precipitation sites that was used in the NWSRFS model calibration.The FMAP is computed from these points using the calibration MAP weights.

 

Presentation of QPF verification will start off with spatial products generated during the event.This will be followed by basin specific analysis of point forecasts.Figure 1 displays the 24 hour QPF field in GFE for day 1. The derived calibration point precipitation values for that same 24 hour period are shown in figure 2.These can be compared with the image of observed precipitation displayed on the verification web page (see figure 3).


Figure 1 NWRFC GFE display ofday 1 QPF from 12/02/2007 12Z to 12/03/2007 12Z.

Figure 2 NWRFC point QPF plot for day 1 plot from 12/02/2007 12Z to 12/03/2007 12Z

Figure 3 Observed cumulative precipitation from 12/02/2007 12Z to 12/03/2007 12Z.


In fig. 1 there is a 7.45 inch 24 hour day-1 forecast accumulation sample value in the north Oregon Coast Range, along with 7.09 inch accumulation centered over the Washington Olympic Mountains. At the same fig. 1 sample points, the day-2 forecast 24 hour accumulations in fig. 4 are respectively 6.83 and 6.61 inches.The cumulative 2 day precipitation for this two areas are 14.28 and 13.7 inches respectively, which was in the range of observed values.

 

The day 2 GFE QPF grid shown in figure 4 showed that less precipitation was forecasted for Monday. The point QPF product displayed in figure 5 shows that the day 1 GFE QPF grid generated Monday morning (not shown) was an improvement over the forecast two days out.

 

Figure 4 NWRFC GFE display of  day 2 QPF from 12/03/2007 12Z to 12/04/2007 12Z.

 

Figure 5NWRFC point QPF plot for day 1 plot from 12/03/2007 12Z to 12/04/2007 12Z.

Figure 6Observed cumulative precipitation from 12/03/2007 12Z to 12/04/2007 12Z.


Wilson Basin

 

Figures 7 and 8 Comparison of Precipitation Forecasts for the Wilson River Basin.

Figures 9 and 10Scatter Diagrams of Observed Precipitationand NWRFC QPF for the Wilson River Basin.

 

 

Dec 1-3 2007 Event Verification Summary - Wilson Basin Sites

Event Performance Statistics

Event Performance - MAJOR EVENTS

 

 

Event Performance - MAJOR EVENTS

1.00"+ in 6-hour Time Period

 

 

4.00"+ in 24-hour Time Period

 

NWRFC

HPC

PQR

 

 

 

NWRFC

HPC

PQR

POD

0.47

0.77

0.30

 

 

POD

0.50

0.83

0.00

FAR

0.18

0.08

0.10

 

 

FAR

0.40

0.00

1.00

CSI

0.42

0.72

0.29

 

 

CSI

0.38

0.83

0.00

 

 

 

 

 

 

 

 

 

 

Event Performance - MODERATE EVENTS

 

 

Event Performance - MODERATE EVENTS

0.50"+ in 6-hour Time Period

 

 

2.00"+ in 24-hour Time Period

 

NWRFC

HPC

PQR

 

 

 

NWRFC

HPC

PQR

POD

0.90

0.93

0.71

 

 

POD

1.00

0.92

0.75

FAR

0.12

0.11

0.03

 

 

FAR

0.00

0.00

0.00

CSI

0.81

0.83

0.70

 

 

CSI

1.00

0.92

0.75

 

 

 

 

 

 

 

 

 

 

Event Performance - MINOR EVENTS

 

 

Event Performance - MINOR EVENTS

0.25"+ in 6-hour Time Period

 

 

1.00"+ in 24-hour Time Period

 

NWRFC

HPC

PQR

 

 

 

NWRFC

HPC

PQR

POD

0.89

0.93

0.88

 

 

POD

0.89

0.89

0.78

FAR

0.09

0.07

0.09

 

 

FAR

0.00

0.00

0.00

CSI

0.82

0.87

0.81

 

 

CSI

0.89

0.89

0.78

Table 1 Event QPF Verification Statistics for the Wilson River Basin.

 

Dec 1-3 2007 Event Verification Summary - Wilson Basin Sites

Daily Forecast Performance Statistics

Forecast Bias (Mean Algebraic Error)

 

 

Forecast Bias (Mean Algebraic Error)

6-hour Time Period, All Stations

 

 

24-hour Time Period, All Stations

 

NWRFC