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NATIONAL TECHNICAL IMPLEMENTATION MESSAGE 98-17
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
230 PM EDT FRI JUL 17 1998
TO: FAMILY OF SERVICES /FOS/ SUBSCRIBERS...NOAA WEATHER
WIRE SERVICE /NWWS/ SUBSCRIBERS...OTHER NATIONAL
WEATHER SERVICE /NWS/ CUSTOMERS...NWS EMPLOYEES
FROM: LEROY SPAYD...CHIEF...SCIENCE AND TRAINING CORE
SUBJECT: CHANGES TO THE NCEP GLOBAL ANALYSIS/FORECAST
SYSTEM...EFFECTIVE JULY 21 1998
BEGINNING WITH THE 12Z GLOBAL MODEL RUN ON JULY 21 1998...SEVERAL
CHANGES WILL BE IMPLEMENTED INTO THE GLOBAL ANALYSIS AND FORECAST
SYSTEM /BOTH AVN AND MRF RUNS/...THEIR EFFECTS ARE TO REDUCE A
TENDENCY FOR SPURIOUS TROPICAL SYSTEMS TO DEVELOP IN THE FORECAST
AS WELL AS THE MODEL WARM BIAS OVER LAND MASSES...A CONVECTIVE
ADJUSTMENT IS ADDED TO THE GRID-SCALE PRECIPITATION
PARAMETERIZATION TO REMOVE LOCAL STATIC INSTABILITY THAT HAS NOT
BEEN ELIMINATED BY THE CONVECTION SCHEME...FULL RESOLUTION TESTS
SHOW THAT TROPICAL VORTICES ARE SYSTEMATICALLY DAMPED...LOW LEVEL
WARM BIAS HAS BEEN REDUCED BY TEMPORARILY ELIMINATING AEROSOL
ABSORPTION BY SHORTWAVE RADIATION AS WELL AS INCREASING
EVAPORATION FROM VEGETATION...ON-LINE DOCUMENTATION OF THE
CHANGES WILL BE ADDED TO THE DRAFT TECHNICAL PROCEDURES BULLETIN
AT HTTP://WWW.NWS.NOAA.GOV/OM/TPB/INDDRAFT.HTM /NUMBER
449/.../USE LOWER CASE FOR URL/. FORECASTERS WILL SEE BOTH FEWER
SPURIOUS TROPICAL SYSTEMS AND A COOLER MODEL LOWER TROPOSHERE
OVER LAND...AEROSOL EFFECTS WILL BE REINTRODUCED AT A FUTURE
TIME...ROUTINE MONITORING OF THE EFFECT OF THESE CHANGES WILL
CONTINUE AND FUTURE MODEL ADJUSTMENTS WILL BE MADE WHERE
NECESSARY.
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