Tuesday, August 23, 2016

Upgrade to the RAP and HRRR model


The above link explains that the RAP and HRRR weather models used operationally by the National Weather Service were upgraded to RAPv3 and HRRRv2.

Effective on or about Tuesday, August 23, 2016, beginning with
the 1200 Coordinated Universal Time (UTC) run, the National
Centers for Environmental Prediction (NCEP) will implement
Version 3 of the Rapid Refresh (RAP) and Version 2 of the High-
Resolution Rapid Refresh (HRRR) systems.

Major Changes:

A major change to the RAP will be an expanded computational
domain which will now include Hawaii. This expansion will
facilitate future NCEP plans for ensemble systems and, in time,
improve the initialization of Short Range Ensemble Forecast
(SREF) members that use the RAP for initial conditions.

Analysis Changes:

Both the RAP and HRRR will use an updated version of the
Gridpoint Statistical Interpolation (GSI) analysis code.
Refinements are made to the GSI to improve the assimilation of
surface observations, soil moisture adjustment, and three-
dimensional cloud and precipitation hydrometeors. In addition,
the HRRR will start using the ensemble/hybrid data assimilation;
it is already used in the RAP, but the weighting of the ensemble-
based component in the RAP will increase from 0.50 to 0.75. In
addition, while the RAP already cycles land-surface states, this
cycling is being introduced into the HRRR. In HRRR Version 1, all
runs are independent.

Other analysis changes include:

-Assimilating radial wind and mesonet data
-Applying PBL-based pseudo-innovations for 2-meter temperatures
(already used for 2-meter dew points)
-Changing the cloud-hydrometeor assimilation to avoid METAR-based
cloud building when satellite data shows clear skies at all times
of day (currently used just in daytime)
-Introducing direct use of 2-meter temperature and dew point
model diagnostics in the GSI.

Specific to the HRRR, the application of radar reflectivity data
in the GSI to direct specification of 3-dimensional hydrometeors
is increased to apply to a broader range of weather conditions,
including warm-season events with reflectivity up to 28 dBZ.

Changes to Model:

- The RAP and HRRR will both begin using WRF version 3.6.1; both
will continue to use the ARW core.
- The MYNN planetary boundary layer scheme is being updated to
include the effects of subgrid-scale clouds. The mixing length
formulation in the boundary layer scheme and thermal roughness in
the surface layer are being changed.
- The 9-level RUC land-surface model is being updated to add a
mosaic approach for fractional snow cover, improve the fluxes
from snow cover, and modify the wilting point for cropland use.
- Major updates are being made to the Thompson microphysics
scheme, including making it aerosol-aware with use of an ice-
friendly and water-friendly aerosol field.
- Shortwave and longwave radiation have been changed to use the
RRTMG (RRTM global) scheme that includes the effects of aerosols
and boundary layer subgrid-scale clouds.
- The WRF-ARW diagnostics for 2-meter temperature and dew point
are being improved. 
- The convective scheme in the RAP is changed from the Grell 3-D
scheme to the scale-aware Grell-Freitas scheme. The HRRR, at 3 km
horizontal resolution, explicitly resolves convection and does
not use a convective scheme.

Many of these changes to the data assimilation, land-surface
model, boundary layer scheme, microphysics, radiation, and (in
the RAP only) convective scheme are designed to mitigate the low-
level warm, dry bias in the RAP and HRRR, most notable during
afternoons in the warm season. Significant reduction of these
biases has been evident in extensive testing.

Output Changes:

- The HRRR directory structure will be migrated out of
"nonoperational" on the NCEP ftp and http servers. Data will also
be available on both the primary and secondary servers.

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