National Severe Storms Laboratory

Data Assimilation and Model Updates in the 2013 Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) Analysis and Forecast Systems

Dr. Curtis Alexander
CIRES Research Associate
Boulder, CO

Ming Hu, David Dowell, Steve Weygandt, Stan Benjamin, Eric James, Patrick Hofmann, Tanya Smirnova, John Brown, Joe Olson, Kevin Brundage, and Brian Jamison

04 June 2013, 4:00 PM - 5:30 PM

National Weather Center, Room 1313
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The High-Resolution Rapid Refresh (HRRR) is a CONUS 3-km convection permitting atmospheric prediction system run hourly out to fifteen hours in real-time at the NOAA Earth System Research Laboratory (ESRL). The HRRR uses a version of the Advanced Research WRF (ARW) model with boundary conditions from the ESRL Rapid Refresh (RAP), an hourly-cycled 13-km mesoscale model.

Recent development of the 2013 RAP and HRRR forecast systems has focused on efforts to (1) improve the depiction of the mesoscale environment through refinements to the RAP data assimilation using a hybrid ensemble Kalman filter (EnKF) and 3-D variational background error covariance estimate, (2) introduce 3-km HRRR data assimilation for analysis of storm-scale information and (3) enhance RAP and HRRR model physics for improved land surface and boundary layer prediction using the Mellor-Yamada-Nakanishi-Niino (MYNN) parameterization scheme.

In this presentation we will focus on changes to the real-time RAP and HRRR configurations for 2013 including the establishment of 3-km data assimilation to incorporate storm-scale information using Gridpoint Statistical Interpolation (GSI) that includes sub-hourly 3-km radar data assimilation during a pre-forecast hour, 3-D variational assimilation of conventional observations and a 3-km non-variational cloud and precipitating hydrometeor analysis using radar reflectivity observations to retrieve rain and snow mixing ratios.

Observed radar reflectivities are used as a proxy for HRRR model latent heating specification that replaces the model microphysics latent heating during four fifteen minute periods of a cycled pre-forecast hour with an emphasis on forcing observed convective structures from higher reflectivity regions. Special attention is given to continuity of convective-scale structures, originating from an accurate storm-scale analysis (initial condition), during much of the free forecast period (several hours).

We will also discuss the use of HRRR one hour forecasts as a background in GSI for several hourly 3-km analysis systems including developmental versions of the two-dimensional Real-Time Mesoscale Analysis (RTMA) for improved depiction of current surface conditions and the three-dimensional Rapidly Updating Analysis (RUA) where full-column cloud and precipitating hydrometeor retrievals are accomplished with conventional, satellite and radar reflectivity observations.

RAP and HRRR analysis and forecast improvements, particularly in the first few forecast hours, will be documented with retrospective and real-time verification statistics and case studies from 2012 and 2013.

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