HAS QPF Process

Referencing National Weather Service Instruction 10-911 - River Forecast Center Operations, ..."the basic HAS shift functions include assimilation and quality assurance of observed and forecast data sets for use in the hydrologic modeling process, production of hydrometeorological discussions and other coordination products, and coordination activities with forecasters in associated WFOs and the Hydrometeorological Prediction Center (HPC) of the National Centers for Environmental Prediction (NCEP).

RFCs in the conterminous United States receive QPF guidance from the HPC and make adjustments as necessary before entering it into their operational hydrologic modeling system. RFCs coordinate with HPC and affected WFOs when operationally significant changes are made to QPF guidance. RFC QPF products are made available to the public and media customers over NWS-supported public dissemination pathways and are posted on the Internet."

While many River Forecast Centers cross-utilize the HAS function with other hydrologic functions within the RFC, the CNRFC focuses the HAS function on the task of providing the most accurate QPF possible for input to the NWSRFS hydrologic model. The basic steps of the QPF process are outlined here:

• HPC provides the initial point value QPF guidance (AWIPS text product QPFRSA).
• Using Mountain Mapper software, the HAS forecaster adjusts point QPF based on a thorough review of latest model guidance, observational datasets, and application of forecaster experience.
• QPF is converted to MAP (mean areal precipitation) values for use in NWSRFS.
• Locally developed software (MM2RFS) reformats the QPF MAP data into a format acceptable to NWSRFS and allows one final opportunity to adjust basin QPF prior to running the NWSRFS model.
• QPF text and graphics products are generated for AWIPS and the web.

The HAS forecaster has several tools available to review and adjust QPF, including:

• AWIPS numerical model guidance
• AWIPS observational data, including observations and derived products from satellite, upper air sounding data, the NEXRAD WSR-88D radar network, and ASOS and other sources of surface data
• Real-time precipitation networks available from other federal, state, and local agencies
• Research datasets such as PACJET wind profilers
• Rhea Orographic Aid QPF guidance
• Forecast products and discussions from the WFOs, HPC, and NCEP

Under normal staffing conditions, the CNRFC hours of operations are 6:00 AM to 6:00 PM on weekdays and 6:00 AM - 2:00 PM on weekends. HAS products released during these hours of operation are issued directly by the HAS forecaster unless changes to HPC QPF were deemed unnecessary. Manual QPF issuance times are optional and only done at the discretion of the HAS forecaster. A series of AWIPS text products are generated at fixed times throughout the day along with unscheduled updates when necessary.

Table 1 below shows the QPF products schedule for a complete hydrologic day.

Table 1.
HAS QPF product issuance times

The CNRFC auto-processes HPC QPF for the day 4 12UTC-00UTC period (highlighted by the green cells in the table above) to fill in a gap that exists in the gridded QPF from the CNRFC HAS and the DGEX high resolution QPF grids used by the WFOs for days 4-7. Note that this QPF will be HPC only and not adjusted by the HAS forecaster.]

During the hours that the CNRFC is closed, QPF products continue to be processed and HPC QPF is automatically reissued as HAS QPF products. The AWIPS product RNOHD8RSA contains the latest issuance of the HAS QPF. Located near the top of the RNOHD8RSA product is a text line stating whether the QPF was either modified or unmodified by the HAS forecaster.

The HAS Forecaster has the option to set controls to override this process and can force the most current HAS QPF forecast to be reissued, and this is commonly done for the late evening issuance of HAS QPF products. Understandably, there is decreased confidence to override HPC QPF for the early morning products issued after 3 AM PST, and hence HPC QPF is generally reissued as HAS QPF shortly after at 3:15 AM PST. The HAS forecaster day shift in normal operations begins at 6:00 AM PST and a HAS QPF update to the HPC QPF is available by 7:30 AM PST . So, this leaves a period of about 4 hours that HPC QPF will be the primary HAS QPF product available.

In 2005, the CNRFC began issuing gridded QPF for the WFOs to use as their initial gridded QPF field. The QPF grids are transmitted to Western Region Headquarters where they are redistributed to the WFOs for ingest into their Grid Forecast Editors (GFE). The grid resolution is 4 kilometers. The QPF grids are typically available to the WFOS approximately 15 minutes after the issuance times shown in table 1 and graphical QPF products on the CNRFC website typically appear within a half hour of these issuance times. Because of the afternoon NWSRFS run, it is common during wet weather that the HAS forecaster include an early afternoon update prior by 1:00 pm PST, in order to incorporate the latest QPF guidance from the 18UTC NAM model run as well as account for trends in the latest observational data.

The hours of operation at the CNRFC are defined by established criteria based on hydrologic activity as shown in the following table:

Below is a complete timeline summary of the entire 24-hour QPF process at the CNRFC during normal operational status:

During significant flooding, the CNRFC provides full 24-hour operational support to its users with hydrologic products issued at 6-hour intervals. This includes complete river forecast guidance updates at 8:00 am, 2:00 pm, 8:00 pm, and 2:00 am. This necessitates HAS QPF/snow level updates two hours earlier at 6:00 am, 12:00 pm, 6:00 pm, and 12:00 am.

Page last modified: July 31, 2006