Ongoing Refinements to the High-Resolution Ensemble
Forecast System (341)
Matthew Pyle, NCEP/EMC,
College Park, MD
Benjamin Blake, I.M.
Systems Group, Inc. @ NCEP/EMC
Jacob Carley, NCEP/EMC
Abstract:
Ongoing Refinements to the
High-Resolution Ensemble Forecast SystemMatthew Pyle, Benjamin Blake, and Jacob
CarleyConvection-allowing ensembles are an increasingly important tool in
short-term forecasts of high impact weather events, and improving them
continues to be an active area of development. This talk describes ongoing
developments with the High-Resolution Ensemble Forecast (HREF) system, which is
a multi-model convection-allowing ensemble run in NWS operations. The HREF
currently combines forecasts from the two most recent cycles of the
High-Resolution Window (which includes both the NMMB model and two different
WRF-ARW configurations) and the 3 km NAM nest into an eight member system for
product generation. The HREF builds upon the success of SPC's well-known Storm
Scale Ensemble of Opportunity (SSEO), utilizing a similar ensemble membership
and applying comparable product generation techniques. Spread within the HREF,
as with the SSEO before it, comes from the sampling of different dynamical
models, physics schemes, analyses, and initialization times. This approach,
while somewhat ad hoc, provides skillful mean fields and probabilistic guidance
that highlights regions of interest for forecasters. Different forms of
probabilistic product generation (point, neighborhood maximum) will be
described, as both currently are used and each has utility for specific applications.
A newer method for defining probabilities, based on the Ensemble Agreement
Scale (EAS) approach, also will be examined. A switch to EAS probabilities for
certain fields is being considered for a future upgrade, as is adding the
extended 36-h HRRR forecasts as a new HREF model component the impact of these
two changes on HREF forecast skill will be presented.