ESRL – Some Recommendations for Mesoscale Ensemble Forecasts Consolidate all NCEP regional storm-scale model runs perhaps under HRRRE (or other) banner (including NAM-nest, Hi-Res Windows, SPC runs, Fire-Weather nests) David Dowell on CAMs – Weisman Grid spacing should be ≤ 4km – Increased realism of convective structures from 4 to 3 to 2km (Weisman, Kain, others) Recommend – use 3km, better to add ensemble members and retain 3km dx. – Another advantage for 3km (for now): much research experience now available with 3km (NCAR, ESRL, WoF for outer next.) Question – Use ARW and NMMB equally? (ESRL and EMC have assumed yes for now for HRRRE). No difference in ARW vs. NMMB run time at same res. – Therefore run both at same resolution. Mesoscale Ensembles Toward 2020 – Stan, David Dowell, Curtis, Steve Weygandt

2 2019? High-Resolution Rapid Refresh ENSEMBLE (HRRRE) Each member of NARRE contains 3 km nests – CONUS/Gulf/Carib, Alaska, Hawaii nests – The two control runs initialized with radar data & other hi-res obs This capability puts NWS/NCEP[+OAR/ESRL] in a position to – Provide NextGen Enroute AND Terminal guidance – Provide PROBABILITY guidance with full Probability Density Function specified, hence uncertainty information as well – Provide a vehicle to improve assimilation capabilities using hybrid (4d- ens-var) technique with current & future radar & satellite – Address Warn-on-Forecast as resolutions evolve towards ~1 km NAM nests are extensions of the 00z, 06z, 12z & 18Z runs. HRRRE requires an increase in HPCC funding over and above that required for the NARRE From Geoff DiMego, Dec 2011, NCEP Model Review

DRAFT Storm Prediction Center Desired Numerical Guidance Attributes 3

DRAFT Storm Prediction Center Desired Numerical Guidance Attributes 4 Possible alternative NWP 2-member suite Global ensemble – as shown by EMC  10-12km global member ensemble runs to Day 14 twice daily (to 7d at 06z, 18z) hourly assimilation cycle with 24h runs init hourly Single regional model/assimilation ensemble - SSEF SSEF (equivalent to HRRRe) – 2-3km Initialize hourly (or subhourly), run to 24h Every 6h, run out to 48-60h 2-3km EnKF/hybrid/other DA Multi-species microphysics with at least 2-moment rain Include aerosols/fire/smoke for all runs with aerosol- aware microphysics No separate HWRF or fire-weather runs or AQ/dust run km multi-WFO nest where needed (WoF) SSEF analysis = RUA, no separate products

From HRRR/HRRRe to WoF Radar-DFI-LH effective start at 13km/3km Mesoscale environment via GSI enhancements for RAPv2+ critical for HRRR 3km/80-member hourly updated GSI-hybrid data assimilation over HRRR-CONUS domain plausible – Estimated needed 10,000 cores (Jeff W. / Stan) Model design for HRRR – most accurate numerics possible necessary for identification of storm structure (line vs. supercells vs. cell vs. MCS variations) – ARW, less 6 th order diffusion, 5 th -order vertical advection WoF options – discussion with NSSL, ESRL, EMC, U.OK, SPC partners, NCEP/PSR participants – direct nest inside HRRR/HRRRe within same executable – Separate system using HRRR/HRRRe lateral BCs/background 5 Mesoscale Ensembles Toward 2020 – Stan, David Dowell, Curtis, Steve Weygandt