-------- Original Message --------
319
NOUS41 KWBC 132017
PNSWSH
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@xxxxxxxx
OR
ERIC ROGERS
NCEP...MESOSCALE MODELING BRANCH
CAMP SPRINGS MARYLAND
PHONE: 301.763.8000 X7227
EMAIL: ERIC.ROGERS@xxxxxxxx
THIS AND OTHER NWS TECHNICAL IMPLEMENTATION NOTICES ARE AVAILABLE
ONLINE AT /USE LOWER CASE LETTERS/:
HTTP://WWW.NWS.NOAA.GOV/OM/NOTIF.HTM
$$
--
Linda Miller - lmiller@xxxxxxxxxxxxxxxx
Community Services, Unidata
University Corporation for Atmospheric Research
P.O. Box 3000
Boulder, CO 80307-3000
303-497-8646 fax: 303-497-8690
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