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The NCEP North American Mesoscale Modeling System: Recent Changes and Future Plans

The NCEP North American Mesoscale Modeling System: Recent Changes and Future Plans. Eric Rogers Geoff DiMego Thomas Black Michael Ek Brad Ferrier George Gayno Zavi š a Janji ć Ying Lin Matthew Pyle Vince Wong Wan-Shu Wu Mesoscale Modeling Branch, EMC/NCEP Jacob Carley

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The NCEP North American Mesoscale Modeling System: Recent Changes and Future Plans

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  1. The NCEP North American Mesoscale Modeling System: Recent Changes and Future Plans Eric Rogers Geoff DiMego Thomas Black Michael Ek Brad Ferrier George Gayno Zaviša Janjić Ying Lin Matthew Pyle Vince Wong Wan-Shu Wu Mesoscale Modeling Branch, EMC/NCEP Jacob Carley Perdue University AMS 23st WAF / 19th NWP Conference, Omaha, NE 1 June 2009 Where the Nation’s climate and weather services begin

  2. Overview of Presentation • Summarize March 2008 and December 2008 NAM implementations • Discuss some of the specific changes in more detail • Planned NAM changes in 2010 • More details can be found in extended abstract and at underlined hyperlinks

  3. PRE-2008 NAM HISTORY • June 2006 : WRF-NMM and GSI analysis replace Eta model / 3DVAR analysis in the NAM • December 2006 • Extensive tuning of convection / microphysics • New divergence damping scheme with extra damping of external mode gravity waves; 5x higher damping of both internal and external modes during NDAS to reduce noise in analysis increments

  4. MARCH 2008 NAM CHANGES • Expanded (~18%) computational domain • Model changes • Gravity wave drag / mountain blocking • Unified Noah Land-surface physics • Modified advection of passive substances (q, cloud water, TKE) • Two minor changes in radiation • Improved computation of surface longwave radiation • Fix bug for climatological O3 • Analysis changes • Retuned background error covariances • New observations : AIRS & GOES SFOV radiances, EUMETSTAT & MODIS satellite winds, surface mesonet winds from sites on NCEP use list • Adjust NDAS soil moisture outside of CONUS using 00Z 12-36 h NAM QPF • Smoother model terrain

  5. Gravity Wave Drag & Mountain Blocking (GWD) • “Mountain blocking” (Lott & Miller, 1997; Alpert 2004) • Wind flow around subgrid orography • Low-level flow is blocked below a dividing streamline (air flows around, not over barrier) • Gravity wave drag (Alpert et al., 1988, 1996; Kim & Arakawa,1995) • Mountain wave stress, pressure drag • Vertical distribution of the wave stress, changes winds aloft (momentum deposition) • Parallel testing : GWD can improve NAM synoptic forecasts, greatest impact seen on upper troposphere winds/height and lower troposphere temperatures

  6. Control GWD Control 1016 hPa 1024 hPa 1032 hPa In GWD run: • High pressure breaks down over Canada & New England • Low pressure forms over western NC and SC Impact of GWD: 12Z 20 Dec 2006 Runs: 72-h SLP (500 hPa and QPF in extended abstract)

  7. Example of the impact of GWD on lower tropospheric vertical profiles : valid 12z 10/28/07 Black= Omaha (OAX) raob Red= Ops NAM 48-h fcst Blue = Parallel NAM (with GWD) 48-h fcst Model soundings are from grid point closest to OAX Much better depiction of low-level inversion in GWD run

  8. Hurricane Dean: 24-h SLP forecast valid 12z 18 Aug 07 OPS NAM Pll NAM TPC Best Track Position (Franklin, 2008)

  9. Hurricane Dean: 48-h SLP forecast valid 12z 19 Aug 07 Pll NAM OPS NAM TPC Best Track Position (Franklin, 2008)

  10. Hurricane Dean: 72-h SLP forecast valid 12z 20 Aug 07 Pll NAM OPS NAM TPC Best Track Position (Franklin, 2008)

  11. Hurricane Dean: 84-h SLP forecast valid 00z 21 Aug 07 Pll NAM OPS NAM TPC Best Track Position (Franklin, 2008) TPC predicted position (issued 12z 8/17) valid 06z 8/21

  12. DECEMBER 2008 CHANGES • NDAS “Partial Cycling” • Model Changes • Vertically mix/diffuse each hydrometeor species • Radiation change : double absorption coefficients for water and ice in clouds • Land-sfc model changes to address problematic 2-m dew point temps over snow cover • Analysis Changes • New observations : MetOp-a radiances and TAMDAR/AMDAR aircraft data • New version of radiative transfer model w/default climatology • Use hi-res (23 km) AFWA snow depth analysis

  13. NDAS Configuration • 12-h spin-up; 4 successive analyses & 3-h model forecasts; last 3-h forecast is first guess for NAM analysis • Prior to July 1998, 12-h NDAS was started from a 6-h forecast from the NCEP Global Data Assimilation System (GDAS) • Since July 1998, NDAS was fully cycled (3-h model forecast from previous cycle used to initiate NDAS) • Rationale for full cycling • Eliminates adjustments/inconsistencies if a model forecast with different characteristics (resolution, physics) is used as a first guess…..but

  14. NDAS Configuration • GFS tends to outperform NAM • WRF-NMM forecasts initialized off GFS initial conditions sometimes produce better synoptic-scale forecasts • Issues still exist with respect to “noisy” analysis increments in the NDAS • Not practical to run ops NAM off global analysis (GFS runs after NAM, NDAS is necessary to provide fully cycled soil states) • Revisit use of 6-h GDAS forecast to provide atmospheric first guess states to initiate the NDAS while using fully cycled NDAS soil states (NDAS Partial Cycling, or “NPCY”)

  15. Impact of NDAS Partial Cycling during parallel testing • Tended to improve NAM forecast (sometimes more “GFS-like”, especially at day 2-3) • Occasional significant improvement in QPF over ops NAM • Occasionally, parallel NAM would do worse than ops NAM when GFS had a “dropout” forecast (see example in extended abstract) • NPCY method implemented in Dec 2008 bundle, is considered temporary while more advanced techniques to control noise in the NDAS mature, such as digital filter initialization (Colón, paper 18A.2)

  16. 72-h forecast – GDAS anl 500 hPa height difference valid 00z 8 Oct 08 • NPCY NAM has lower errors associated w/trough over central US and Gulf of Alaska Ops NAM Pll NAM w/NCPY Ops GFS

  17. 24-h QPF valid 12z 8 Oct 2008 72-h Ops NAM forecast 72-h Pll NAM forecast w/NPCY • Parallel NAM improves 24-h QPF across Iowa, Northern Illinois, Wisconsin and U.P. of Michigan • Parallel NAM shifts heaviest precip further east into central KY/TN than ops NAM CPC 1/8 deg observed pcp analysis

  18. Impact of March 2008 changes and partial cycling : Vertical profile of cumulative RMS errors from December 2007 – March 2008 Temp - Solid = Ops NAM - Dash = Pll NAM with 3/08 changes - Dash-dot = Pll NAM with 3/08 changes + NDAS Partial Cycling Black = 24-h Fcst Red = 48-h Fcst Blue = 72-h Fcst Height RH Vector Wind

  19. Impact of radiation change • 12 February 2008 Mid-Atlantic Freezing Rain Case; Poor forecast by NAM for DC area 2-m Temperature (°F): Black line is 32oF isotherm CTL Significant Cold Air Damming RUC Analysis of 2-m T at 00z 13 Feb 2008 Control WRF-NMM 12-hr forecast of 2-m T valid 00z 13 Feb 2008

  20. Impact of radiation change • Increase cloud optical depths by doubling absorption coefficients of water and ice in clouds • Intended effect is to reduce the amount of incoming solar radiation reaching the ground and warming the surface, thus keeping the surface slightly cooler beneath cloud Result: more pronounced damming signature Experimental WRF-NMM 12-hr forecast of 2-m T valid 00z 13 Feb 2008

  21. NAM 2010 Plans • December 2008 bundle is the last major set of changes to WRF-based NAM • NAM changes planned in fall 2010 • Change to ESMF-based NOAA Environmental Modeling System (NEMS) framework (Black, paper 2A.6) • Replace E-grid NMM with B-grid NCEP Nonhydrostatic Multiscale Model (NMMB, Janjić, paper 5A.1) • Use physics packages developed for WRF • Parent NAM domain will remain at 12km resolution and 84-h forecast range • Add ~3-6 km runs nested in NAM over CONUS and Alaska, out to 36-48 h (try to match or better NDFD grid resolution) • Possibly add ~3 km nests over Hawaii/Puerto Rico

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