Forecasters have recently gained access to two new convection allowing (CAM) WRF ensemble model forecasts. One ensemble is provide by NSSL and is a nine-member, WRF-ARW ensemble initialized daily at 00 UTC while the other is a ten-member, WRF-ARW ensemble initialized daily at 00 UTC and is provided by NCAR/MMM. These two modeling systems appear to be one of the first, regular and widely available convection allowing (CAM) ensembles.
CAMs have proven to be a great utility for forecasters as they can provide information about features smaller than those resolved by coarser resolution models, and in addition, they can predict convective mode, convective system propagation, diurnal cycle, and other characteristics of convection far better than models run with a convective parametrization. More information on CAMs is available at this reference.
In addition, the web sites in which these two modeling systems are available contain an easy to use graphical interface, the ability to zoom over regions, and access to several unique fields. Some of the fields include hourly max and updraft helicity probabilities, composite convective parameters, simulated satellite imagery, and ensemble max fields.
While these modeling systems were not likely created to provide guidance for tropical or sub-tropical weather systems, the developing storm system near the Bahamas provides an interesting example to view one set of output, the 1-km or composite reflectivity products in figures 1 and 2.
Nine-member NSSL WRF-ARW Ensemble initialized daily at 0000 UTC
The 9 ensemble members utilize the WRF-ARW V3.4.1 at 4-km grid length with similar configurations but varied initial conditions. The members are comprised of the regular NSSL-WRF, which uses the 0000 UTC initialized NAM for ICs and LBCs, one member that uses the 0000 UTC initialized GFS for ICs and LBCs, and 7 members that use different members of NCEP’s 2100 UTC initialized SREF system for ICs and LBCs. The SREF system ICs/LBCs include 3 WRF-ARW members (the control member and two perturbed members), 2 NMM members (the control and one perturbed member), and 3 NMMB members (the control and two perturbed members). The domain and physics parametrizations for each NSSL-WRF ensemble member are identical to the regular NSSL-WRF and include MYJ BL/turbulence parametrization, WSM6 microphysics, RRTM longwave radiation, Dudhia shortwave radiation, and
Noah land-surface model.
Ten-member NCAR/MMM WRF-ARW Ensemble initialized daily at 0000 UTC
The 10 ensemble members utilize the WRF-ARW V3.6.1 at 3-km grid length with similar configurations but varied initial conditions. Initial conditions provided by down scaled members of 0000 UTC WRF/DART EAKF analyses with perturbed lateral boundary conditions originating from GFS forecasts. The domain and physics parametrizations for each NCAR/MMM WRF ensemble member are the same and include MYJ BL/turbulence parametrization, Thompson microphysics, RRTMG longwave radiation, Dudhia shortwave radiation, and Noah land-surface model.