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TECHNICAL IMPLEMENTATION NOTICE 06-92
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
315 PM EST WED DEC 13 2006

TO:       FAMILY OF SERVICES /FOS/ SUBSCRIBERS...NOAA 
          WEATHER WIRE SERVICE /NWWS/SUBSCRIBERS...EMERGENCY  
          MANAGERS WEATHER INFORMATION NETWORK /EMWIN/  
          SUBSCRIBERS... NOAAPORT SUBSCRIBERS...OTHER 
          NATIONAL WEATHER SERVICE /NWS/ CUSTOMERS AND        
          PARTNERS...NWS EMPLOYEES

FROM:     PAUL HIRSCHBERG
          SCIENCE PLANS BRANCH CHIEF
          OFFICE OF SCIENCE AND TECHNOLOGY 

SUBJECT:  WEATHER RESEARCH FORECAST MODEL CRISIS CHANGES:     
          EFFECTIVE DECEMBER 19 2006.

EFFECTIVE DECEMBER 19 2006...BEGINNING WITH THE 1200 COORDINATED 
UNIVERSAL TIME /UTC/ RUN...SEVERAL CRISIS CHANGES WILL BE MADE TO 
THE WEATHER RESEARCH FORECAST NON-HYDROSTATIC MESOSCALE MODEL  
/WRF-NMM/ RUNNING IN THE NORTH AMERICAN MESOSCALE MODEL 
/NAM/...THE NAM DATA ASSIMILATION SYSTEM /NDAS/...AND THE DGEX. 
THESE CHANGES ARE BEING MADE TO IMPROVE MODEL PERFORMANCE.

THE CRISIS CHANGES INCLUDE:

1. THE DIVERGENCE DAMPING ROUTINE... WHICH DAMPS ALL GRAVITY-
INERTIA AND EXTERNAL MODES IS CHANGED TO INCREASE DAMPING OF THE 
EXTERNAL MODE.

2. DURING THE NDAS... DIVERGENCE DAMPING IS INCREASED TO 5 TIMES 
THAT USED DURING THE 84 HR NAM FREE FORECAST.

3. NUMEROUS CHANGES ARE MADE TO CONVECTIVE PARAMETERIZATION.

4. THREE CHANGES ARE MADE TO THE CLOUD MICROPHYSICS.

5. HORIZONTAL DIFFUSION BETWEEN NEIGHBORING GRID POINTS WITH A 
SLOPE OF LESS THAN OR EQUAL TO 54 M / 12 KM /9 TIMES THAT IN 
OPERATIONAL NAM/ IS ALLOWED.

THE COMBINED IMPACT OF THESE CHANGES HAS LED TO:

1. SLIGHT IMPROVEMENT IN NAM QPF SCORES.

2. A 5-10 PERCENT REDUCTION IN NAM HEIGHT... TEMPERATURE AND 
VECTOR WIND ROOT-MEAN-SQUARE ERRORS COMPARED TO RADIOSONDES 
/POSITIVE IMPACTS INCREASE WITH FORECAST RANGE/. 

3. A SIGNIFICANT REDUCTION IN THE FALSE ALARM RATE FOR TROPICAL 
STORMS.

4. THE NUMERICAL INSTABILITY OBSERVED OFF NEWFOUNDLAND IN OPS NAM 
RUNS FROM 1-4 DECEMBER WAS ELIMINATED BY THESE CHANGES.  

MORE DETAILS ABOUT THE CRISIS CHANGES CAN BE SEEN AT /USE 
LOWERCASE LETTERS/:

HTTP://WWWT.EMC.NCEP.NOAA.GOV/MMB/MMBPLL/PARALOG/PARALOG.NAMY.WRF
NMM_NEW.HTML

A COPY OF THE BRIEFING PACKAGE FOR THE NCEP DIRECTOR CAN BE FOUND 
AT /USE LOWERCASE LETTERS/:

HTTP://WWW.EMC.NCEP.NOAA.GOV/MMB/NAMCHANGES_DEC2006/NAM_UPGRADES.
NOV2006.HTML

THE EFFECTIVE DATE OF THIS CHANGE IS SOONER THAN SPECIFIED BY NWS 
POLICY /NWS INSTRUCTION 10-1805/. THE SHORTER ADVANCE LEAD TIME 
WAS APPROVED TO MEET OPERATIONAL REQUIREMENTS BY REMOVING 
NUMEROUS DEFICIENCIES IN THE NAM NOTED BY NWS FORECASTERS SINCE 
THE JUNE 2006 IMPLEMENTATION. TO ADDRESS THESE ISSUES...THE SET 
OF NAM CHANGES HAVE BEEN UNDER DEVELOPMENT SINCE EARLY FALL 2006 
AND RUN IN PARALLEL BY NCEP.

IF YOU HAVE ANY QUESTIONS CONCERNING THESE CHANGES...PLEASE 
CONTACT: 

	GEOFF DIMEGO
	NCEP...MESOSCALE MODELING BRANCH
	CAMP SPRINGS MARYLAND
	PHONE: 301.763.8000 X7221
	EMAIL: GEOFF.DIMEGO@NOAA.GOV
OR
	ERIC ROGERS
	NCEP...MESOSCALE MODELING BRANCH
	CAMP SPRINGS MARYLAND
	PHONE: 301.763.8000 X7227
	EMAIL: ERIC.ROGERS@NOAA.GOV

THIS AND OTHER NWS TECHNICAL IMPLEMENTATION NOTICES ARE AVAILABLE 
ONLINE AT /USE LOWER CASE LETTERS/:

     HTTP://WWW.NWS.NOAA.GOV/OM/NOTIF.HTM

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