1. Hydrometeorological Prediction Center
National Centers for Environmental Prediction (NCEP) Hydrometeorlogical Prediction Center (HPC) Forecast Operations Branch
Dan Petersen
Hydrometeorological Prediction Center
DOC/NOAA/NWS/NCEP
With assistance from Joshua Scheck and Mike Schichtel

2. Goals of Presentation NCEP modeling system update Review HPC Products
HPC Quantitative Precipitation Forecast (QPF) methodology
HPC winter weather desk and temperature biases
HPC medium range forecasts and performance verification
NCEP modeling system update
Answer questions

3. NWS OPERATIONAL FORECAST OFFICES
WFOs
NWS OPERATIONAL
FORECAST OFFICES
CWSUs not depicted
RFCs

4. HPC Products and Services
Model Diagnostics Discussion-
RESOLVE DIFFERENCES BETWEEN MODEL AND ENSEMBLE SOLUTIONS
MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1218 PM EST SAT DEC
VALID DEC 09/1200 UTC THRU DEC 13/0000 UTC
MODEL INITIALIZATION...
MODEL TRENDS...
MODEL DIFFERENCES AND PREFERENCES...

5. HPC Products and Services
National Day One Forecast Chart-highlights precipitation types and potential for heavy precipitation, excessive rainfall, severe convective storms, tropical cyclones

6. HPC Products and Services
Short Range Fronts, Pressures, and Precipitation Type/Intensity 12/24/36/48 hours
New graphics for 6 hr, 60 hr forecasts coming in 2008

7. HPC Products and Services
Surface Analysis

8. HPC Products and Services
Excessive rainfall
Excessive Rainfall for Day One, Two, and Three
(98e,99e)
PEI745 KWBC , discussion QPFERD

9. HPC PRODUCTS AND SERVICES
QPF
Performed on 3 desks (Day One, Days 2/3, Medium Range)
Six-hourly forecasts for Days 1 through 3
Days 4-5, Five Day Total

10. HPC Products and Services QPF Methodology

11. GFS Day Two 24 hr forecast rainfall (left)
HPC QPF Methodology
Ingredients-Based Approach Doswell et. al. December 1996 Weather and Forecasting
Forecaster examine moisture, lift, instability diagnostics
GFS 48 hr forecast mb standardized moisture flux anomalies for 12z Oct
GFS Day Two 24 hr forecast rainfall (left)

12. Verifying low near the AL/MS border
HPC QPF Methodology
Forecasters review model timing and make a decision based on the timing preference
This is the NAM 84 hour forecast for 12z Oct. 25, 2007, resulting in NAM producing rains in the southern Plains and not southeast and Appalachians
Verifying low near the AL/MS border

13. RFC analysis (color-filled) overlaid with GFS Day 3 forecast
HPC analysis of 24 hr rainfall ending 12z Oct 25, 2007 (3 inch isohyet green)

14. RFC analysis (color-filled) overlaid with NAM Day 3 Forecast
RFC analysis (color-filled) overlaid with HPC Day 3 Forecast
RFC analysis (color-filled) overlaid with NAM Day 3 Forecast

15. HPC QPF Methodology Adjust for known biases
‘Long running NAM problem of generating too little warm sector convection, leading to higher amounts in the comma head’
Verifying analysis
NAM 24 hr FCST 12z 30 MAR 2007
Too Much
Too Little

16. HPC QPF Methodology
ECMWF
GFS
Verification

17. HPC QPF Methodology
PRISM is used as an overlay but not part of the qpf blender
5 km gridded HPC QPF available in AWIPS downscaled from 32 km generated by forecaster
Average November rainfall

18. HPC QPF Blender

19. HPC Products and Services
QPF verification

20. HPC Products and Services Winter Weather Desk

21. HPC Winter Weather Desk
Twice daily issuance of product suite based on new model guidance 9/15-5/15
24 hour Snow and Ice accumulation probability graphic for days 1 through 3.
Public and technical versions of low tracks graphic depicting synoptic scale surface low tracks associated with heavy snow or ice.
Heavy Snow and Ice Discussion
Intended to complement the deterministic short term snow and ice forecasts issued by local Weather Forecast Offices

22. HPC Winter Weather Forecast Process
New model guidance arrives
HPC uses model/ensemble blender on left to generate draft graphics sent to NWS WFOs only

23. HPC Winter Weather Forecast Process
Experimental Snow to liquid ratios multiplied by qpf to determine snow accumulations

24. HPC Snow to Liquid Ratio (SLR) Verification
15 Oct 2006 – 1 May 2007 GFS RMSE
Roebber, QPF*10 lowest RMS error for all forecast times
Experimental SLRs consist of a 25% blend of Roebber NAM, Roebber GFS, Climatology SLR, 10:1 ratio

25. HPC Winter Weather Forecast Process
WFO Forecasters receive internal snow/ice accumulation graphics by 1815/0615z and comment (12planet, phone)
HPC/WFO Collaboration UTC on day shift and UTC on night shift
WFOs may request conference call with adjacent WFOs/HPC

26. HPC Winter Weather Forecast Process
Software reviews ensemble data and compiles editable probabilistic snow/ice graphic (right graphic prob of 8 inches)
WFO input is used to modify snow/ice probabilistic forecast
WFO may request change in accumulation

27. HPC Products and Services Winter Weather Desk Probabilistic Snow Forecast

28. Forecaster-Perceived Model Temperature Forecast Biases
NAM
Better at resolving inversions in the 850 to 700 mb layer, which cause snow to melt and refreeze in the shallow, subfreezing air below.
GFS
Persistent with a cold bias throughout layer.
East of the cyclone with a southerly component of flow, the model will be too slow to warm the inversion layer (850 mb to 700 mb).

29. Model Bias Example 1 – Topeka, Kansas F24 GFS and NAM Soundings Valid 1200 UTC 14 Jan. 2007

30. Model Bias Example 1 – Observed Topeka, Kansas Sounding 1200 UTC 14 Jan. 2006

31. Model Bias Example 2 – Norman, Oklahoma F06 GFS and NAM Soundings Valid 1800 UTC 20 Jan. 2007

32. Model Bias Example 2 – Observed Norman, Oklahoma Sounding 1800 UTC 20 Jan. 2007
Norman had 0º C and rain in the hours surrounding 1800 UTC.
The nose of the inversion was about 2º C
Both models were slightly cold at F06, but the NAM was above freezing from 785 hPa to 730 hPa
It took only 6 hours for the GFS bias to result in a -2º C error in the inversion layer

33. Precipitation Type Output Bias
‘Dominant’ precip type among NCEP, revised NCEP, NCEP microphysical algorithm, Ramer, Bourgouin
In case of ties, ZR>SN>IP>R 
NCEP algorithm output favors freezing rain in isothermal near freezing soundings (observed weather was snow on 09z 11/03)

34. Model/SREFMean 48 hr Temperature Performance June 2007-August 2007
SREFMean had lower RMS errors than GFS over summer 2007 in the east-can this last thru the winter?

35. Model/SREFMean 48 hr Temperature Performance December 01 2006-February 28 2007
Over winter , NAM had highest temperature errors mb, GFS lowest errors

36. Model/SREF Mean 84 hr Temperature Performance June 01 2007-August 31 2007

37. Model Temperature Performance Case- 700 mb Observations 10/12/07 00z
Verifying low over eastern PA and -6 to -8 temperatures northern VA into PA/WV

38. Model Temperature Performance 10/12/07 00z NAM 66 hr forecast
NAM forecast low near PA/WV border with minus 9C core over WV

39. Model Temperature Performance 10/12/07 00z GFS 66 hr forecast
GFS forecast low further east over central PA allows freezing air to reach mid Atlantic coast, with no area of -9C forecast

40. Model/SREFmean 48 hour Height rms error 6/01/07-8/31/07
NAM higher height errors extend thru the column mb

41. Winter Weather Desk verification 2006-7
Winter qpf verification mid Atlantic and Appalachian mountain region
Snowfall threat scores over US east of the Rockies
Note high GFS/NAM bias above 1.5 inches
HPC outperformed NCEP models/ensembles most in inch range

42. HPC Products and Services-Winter Weather Desk Low Tracks Graphic

43. HPC Products and Services Low track verification 2006-7
Lowest RMS error-blend of NAM/GFS

44. HPC Products and Services Medium Range Desk
Black (i.e., absence of color) implies high confidence (i.e., absence of uncertainty). Mixtures of red, green, and blue indicate relative amounts of uncertainty due to independent sources.

45. HPC MEDIUM RANGE PRODUCTS
Model Diagnostics Desk
Prelim Day 3-7 Frontal Progs 0900 UTC
Prelim PREEPD UTC
Medium Range Pressure/Fronts
Prelim Day mb Progs 1130 UTC Updated Day 3-7 Frontal Progs 1315 UTC Updated PREEPD UTC
Tropical Hotline Call (seasonal) Noon ET Final Day 3-7 Fronts UTC PMDEPD (Final) UTC
Medium Range Temps/PoPs/QPF
Hawaiian 1-7 Day Discussion UTC
Morning Day 4/5 and 1-5 QPF 1200 UTC Prelim Day 3-7 Min/Max/PoPs UTC Prelim Medium Range Grids 1500 UTC Final Day 3-7 Min/Max/PoPs UTC
Final Medium Range Grids UTC
Afternoon Day 4/5 and 1-5 QPF 2300 UTC
MEDIUM RANGE DESK TWO FORECASTER TEAM
SHIFT HOURS UTC
EVERY DAY OF THE YEAR
288 daily members of model/ensemble height field forecasts

46. HPC DAY MB PROGS
HPC DAY 3-7 FRONTS
HPC DAY 4/5 QPF
HPC DAY 1-5 QPF

47. HPC Products and Services-Medium range Forecast Desk
Blender for sea level pressure/
500 mb forecasts

48. HPC Medium Range Temperature/Probability of Precip Blender

49. HPC Medium Range Available Models/ensembles
Overlay of ECMWF/GFS/ensemble 500 mb height forecasts (left)
HPC can now access ECMWF ensemble mean /700 mb
Heights , 850 mb height/temp/wind , sea level pressure forecasts from both 00z and 12z cycles

50. HPC Days 3-7 Minimum Temperature Verification

51. NCEP Modeling System Update

52. NCEP Modeling System - Short Term Road Map
GFS – Global Forecast System
Changed to use dominant precip type 8/21/07 BALDWIN /NCEP/...REVISED NCEP...RAMER...BOURGOUIN ...AND AN EXPLICIT MICROPHYSICS ALGORITHM
NAM – North American Mesoscale Model
Tweaks to initialization schemes
CONUS 4 km resolution spring 2009
GEFS – Global Ensemble Forecast System
12/4/07 Addition of 20 Canadian model members + 20 GEFS = 40 members (eventual addition of NOGAPS forecast members)
PRODUCTS INCLUDE MEANS/SPREADS/MODES AND AND 90 PERCENT PROBABILITY FORECASTS
SREF – Short Range Ensemble Forecast System
21 members run at approx 34km horiz res 4 cycles per day (upgrade to 12 km December 2007)
10 Eta members, 5 Regional Spectral Model, 6 Weather Research Forecast (WRF)
Convert all members to WRF

53. North American Ensemble Forecast System 186 hr median 2m Temperature Forecast

54. North American Ensemble Forecast System 186 hr 90th percentile 2m Temperature Forecast

55. Questions ???

56. HPC Winter Weather Desk Forecast Process
Average Snow to Liquid Ratio applied to blended qpf amounts

57. Snow to liquid Ratio Verification
Roebber Neural net method
Caribou Method
Climatology

58. Prism-adjusted accumulations for intermountain west

59. Monthly Synergy Meetings
Informal meeting with
EMC, NCO, MMB, NCEP Service Centers, WFOs
Near term model development and super computer/comm systems plans provided
Users can anticipate and accommodate changes
Refer to

60. Flash Flood Forecasting: An Ingredients-Based Methodology Doswell, Brooks, and Maddox Weather and Forecasting   December 1996 pp. 560–581

61. Day six multi-model 500 mb height forecast verification

62. HPC Days 3-7 Forecast Methodology
Forecasters modify max/min temperatures and 12 hr PoPs at up to 384 points.
Dew point, cloud cover, winds, and precipitation type generated from HPC temperature, PoP and surface progs.
Forecasters cannot edit these fields.
Basic philosophy is to generate a set of grids that are consistent with the manually generated forecasts
Forecasters can modify MOS point forecasts directly or use a blending tool.
Blender allows forecasters to select a mix of models, ensembles, and current NDFD grids, assign weights, and use the resultant temperatures and PoPs as a starting point. These can then be manually modified.

63. Methodology Grid Production
Max/min temperature grids are produced by interpolation of manually prepared point forecasts to a grid with PRISM climatology as a background
PoP grids are interpolated from HPC modified stations
Dew points use the HPC temperature forecasts and MOS ensemble with Prism climatology as a background
Cloud cover is based on HPC PoPs and max temps
Winds are based on HPC surface progs
Precipitation type is based on HPC max/min temperature forecasts and on PoPs (for areal coverage)

64. HPC Winter weather desk planned changes for 2007-8
HPC has requested ECMWF provide 6 hourly precipitation amounts and precipitation type forecasts-If yes, HPC will include in the accumulation forecast blender

65. Model/srefmean 84 hour Temperature bias 6/01/07-8/31/07

66. Model/SREFMean Temperature Performance March 01 2007-April 15 2007

67. Model/srefmean 84 hour Height rms error 6/01/07-8/31/07

68. Primary Medium Range Models/Ensembles used at HPC
Cycle (UTC)
Run Duration (Days)
Approx Horizontal Grid Spacing (km)
Members per Day
DGEX
06, 18 8 15 2
ECMWF
00, 12 10 20
ECMWF Ens. 40
102 (2 means)
GFS
00, 06, 12, 18 16 4
GEM Global
10/6
UKMET 6
FNMOC 55
NAEFS 80
40 (2 means)
FNMOC Ens. 00
10 (1 means)
GFS Ens.
80 (4 means)
GEM Ens.
Total: individual runs per day!

69. HPC Days 3-7 Future Plans Continued improvement of methodology
Better algorithms for post processed fields
Changes based on requests from field offices
Use of gridded MOS as background
Investigate alternative means of production
More use of tools such as blenders
More use of ensembles
Faster processing of grids for earlier delivery
Better hardware
Optimize processing
Expand coverage to OCONUS
Day grids for Alaska
Same grids as CONUS

70. HPC Products and Services Low track verification 2005-6
Lowest rms error-blend of NAM/gfs

71. HPC Products and Services
Issue Storm Summaries for widespread heavy precipitation events and post hurricane landfall.
Rainfall statements in Tropical Cyclone Advisories plus backup to National Hurricane Center
Significant River Flood Outlook
Event Driven Forecast support for Government Agencies (i.e. post September 11 attack forecasts for New York and Washington)
Air Quality Forecast Summaries in summer

72. HPC QPF Methodology
GFS 48 hr forecast (l), CPC analysis estimate (magenta 2.5, blue 3.5, yellow 4”)-HPC correctly increased GFS amounts with continuous 2 inch area in sw VA

73. GFS Day 2 forecast (left), HPC Day 2 forecast (right)
HPC QPF Methodology
GFS Day 2 forecast (left), HPC Day 2 forecast (right)

74. HPC Day Two qpf vt 12z 25 Oct 2007 with verifying amounts

75. Day two HPC (left), NAM (right), GFS (bottom)