NMQ Verification System (QVS) Tutorial

Figure 17. Default Q2 tab image showing Q2RAD_HSR.

Figure 18. Different Z-R relations. Only the convective, stratiform and tropical are used in Q2 at this time. Additional Z-Rs used by the NWS will be incorporated in algorithm updates.

Figure 19. Gauge-only analysis.

Tabs: Q2

Next-generation QPE (Q2) products are experimental in nature. Q2 products can be derived from single or multiple sensors and can be combined in various ways. Figure 17 (at right) shows the default Q2RAD_HSR 24h image.

Hourly gauge data are FTPed from NCEP every 10 min. Just after the top of the hour, the number of gauges is small. All gauges are in after 6 hours.

The following products are available for testing and comparison:

HYDRO_EST: Hydroestimator NWS operational satellite precipitation product.
STAGE II from NCEP: The following are excerpts from the NCEP documentation :

NCEP 'Stage II' refers to the real-time, hourly, multi-sensor National Precipitation Analysis (NPA) developed at the National Centers for Environmental Prediction (NCEP) in cooperation with the Office of Hydrology (OH). This analysis merges two data sources that are currently being collected in real-time by OH and NCEP. Approximately 3000 automated, hourly raingage observations are available over the contiguous 48 states from ASOS and via the GOES Data Collection Platform (DCP). In addition, hourly radar estimates of precipitation ('DPA', for Digital Precipitation Arrays) are obtained as compressed digital files via the ASOS network. The DPA estimates are created by the WSR-88D Radar Product Generator on a 131 x 131 4-km grid centered over each radar site. The data analysis routines, including a bias adjustment of the radar estimates using the gage data, have been adapted by NCEP on a national 4-km grid from algorithms developed by OH ("Stage II") and executed regionally at NWS River Forecast Centers (RFC).

At the present time, the NCEP Stage II does not have manual quality control steps that are a hallmark of the RFC MPE analyses.

Stage II [Gauge only] – Gauge-only analysis

Stage II [Multisensor] – A local gauge correction of the gauge-adjusted fields following Seo (1998).

Stage II [Radar Only] – Composite of raw WSR-88D DPA data

Stage II [Gauge Adj Rad] – Composite of radar DPAs each having a mean field gauge bias. The radar bias adjustment algorithm follows Smith and Krajewski (1991).
STAGE IV— Precipitation Analysis from NCEP: The following is an excerpt from the NCEP documentation :

Mosaicked into a national product at NCEP, from the regional hourly/6-hourly multi-sensor (radar+gauges) precipitation analyses (MPEs) produced by the 12 River Forecast Centers over CONUS. Some manual QC done at the RFCs. Mosaic done at NCEP within an hour of receiving any new hourly/6-hourly data from one or more RFC.
Q2 [All Gauge]: An objective analysis of all gauges from NCEP with a 3 hr delay.
Q2 [QC'ed Gauge]: Q2 with a local gauge adjustment that includes a gauge-radar bias QC application
Q2 [Radar Only]: "Radar-based precipitation rate and accumulations over various time periods (1- to 72-hour). The rate is derived from the hybrid scan reflectivity using convective, stratiform and tropical Z-R relations (see Figure 18 at right) identified by the precip_flags (that are in turn identified by VPRs). Note the additional optional Z-Rs used by the NWS.
Q2 [Radar Only US + CA]: Q2 with the addition of Canadian radars. Note that there is no QC applied to the additional radars.
Q2 [Gauge Adj Rad]: Local gauge corrected radar QPE fields. The local gauge correction is applied onto the 1-h Q2RAD_HSR precipitation field. It runs hourly and uses hourly rain gauge observations from the HADS (Hydrometeorological Automated Data System) data sets at NCEP. In the local gauge correction scheme, radar-gauge biases are calculated at each gauge site and then interpolated onto the NMQ grid using an inverse distance weighted (IDW) mean scheme. The two parameters in the IDW scheme, exponent and radius of influence, are determined through a cross-validation procedure. The interpolated radar-gauge bias field is applied back to the Q2RAD_HSR 1-h precipitation field and a local gauge bias corrected 1-h precipitation field is obtained. Longer-term accumulations are computed by aggregating the 1-h local gauge corrected precipitation fields.

Analysis Tools allows product comparisons (see Mosaic 3D Derived).

References

Seo, D.-J., 1998: Real-time estimation of rainfall fields using rain gauge data under fractional coverage conditions. J. Hydrol., 208, 25–36.

Smith, J.A., and W.F. Krajewski, 1991: Estimation of the Mean Field Bias of Radar Rainfall Estimates. J. Appl. Meteor., 30, 397–412.