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873
NOUS41 KWBC 171832
PNSWSH
PUBLIC INFORMATION STATEMENT...TECHNICAL IMPLE. NOTICE 00-06
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
130 PM EST FRI MAR 17 2000
TO FAMILY SERVICES/FOS/SUBSCRIBERS...NOAAPORT
SUBSCRIBERS...OTHER NATIONAL
WEATHER SERVICE /NWS/ CUSTOMERS...NWS EMPLOYEES
FROM THERESE Z PIERCE...CHIEF...HYDROMETEOROLOGICAL SERVICES
SUBJECT CHANGES TO THE NCEP NESTED GRID MODEL...EFFECTIVE MARCH
15 2000
I. RATIONALE FOR CHANGES
AT 1200 UTC 15 MARCH 2000 (TENTATIVE) A SERIES OF CHANGES TO THE
INITIALIZATION PROCEDURE FOR THE NCEP NESTED GRID MODEL WERE MADE.
SINCE THE DISABLING OF THE NCEP CRAY C-90 COMPUTER ON 27 SEPTEMBER
1999...THE NGM HAS BEEN RUN ON A CRAY J-90 WHICH IS 3-4 TIMES
SLOWER THAN THE C-90. THUS... NGM PRODUCTS ARE NOW AVAILABLE ABOUT
ONE HOUR LATER THAN BEFORE.
SINCE NWS FIELD FORECASTERS AND OUTSIDE CUSTOMERS ARE STILL
HEAVILY DEPENDENT ON TIMELY NGM AND NGM MOS PRODUCTS... AND
BECAUSE THERE ARE NO FUNDS TO MAINTAIN THE CRAY J-90 IN
OPERATIONS BEYOND MARCH 2000...THERE WAS A NEED FOR NCEP'S
ENVIRONMENTAL MODELING CENTER (EMC) TO CONVERT THE NGM TO RUN ON
THE NEW IBM-SP COMPUTER. CONVERSION OF THE ENTIRE SUITE OF CODES
WHICH RAN ON THE C-90 (INCLUDING THE REGIONAL OPTIMUM
INTERPOLATION (ROI) ANALYSIS) USING IBM'S MESSAGE PASSING
INTERFACE (MPI) WAS ESTIMATED TO TAKE 2 PERSON YEARS OF WORK.
SUCH AN EFFORT WAS NEITHER FEASIBLE NOR COST EFFECTIVE.
TO SATISFY BOTH THE USERS' REQUIREMENTS FOR A TIMELY
NGM FORECAST AND NCEP'S REQUIREMENTS FOR A MAINTAINABLE
NGM SYSTEM...THE FOLLOWING CHANGES WERE MADE:
- NGM INITIAL CONDITIONS WILL BE OBTAINED FROM THE
MESO ETA ANALYSIS OVER NORTH AMERICA...AND FROM A
6-H AVN FORECAST OVER THE REST OF THE NORTHERN
HEMISPHERE...INSTEAD OF FROM THE HEMISPHERIC ROI ANALYSIS.
- SINCE THE ETA ANALYSIS DOES NOT EXTEND BEYOND THE
NORTH POLE INTO EUROPE AND ASIA...THE HIGH RESOLUTION
NGM C-GRID WAS MODIFIED TO BE SIMILAR IN SIZE TO THE
ETA COMPUTATIONAL GRID.
USE OF THE ETA ANALYSIS/AVN FORECAST TO INITIALIZE THE
NGM WILL HAVE ADVANTAGES AND DISADVANTAGES WHICH WILL CAUSE
IMPROVEMENT OR DEGRADATION OVER THE CRAY NGM SYSTEM:
CURRENT AND FUTURE ADVANTAGES
1) SINCE THE NGM IS INITIALIZED FROM THE ETA ANALYSIS...IT
CAN START ONE HOUR EARLIER ON THE IBM THAN IT DID ON CRAY J-90.
ALTHOUGH THE NGM RUNS SLOWER ON THE IBM THEN IT DID ON THE CRAY
C-90...THE EARLIER START TIME ON THE IBM WILL COMPENSATE FOR
THIS...AND NGM PRODUCTS FROM THE IBM WILL BE AVAILABLE AT ABOUT
THE SAME TIME AS BEFORE THE DISABLING OF THE C-90.
(ABOUT 50 MINUTES SOONER THAN TODAY).
2) ETA ANALYSIS USES MORE DATA TYPES THAN REGIONAL OPTIMUM
INTERPOLATION ANALYSIS...SUCH AS AIRCRAFT TEMPERATURES...WSR-88D
VAD WINDS...SSM/I OCEANIC WIND SPEEDS...SURFACE WIND OBSERVATIONS
OVER LAND...AND PRECIPITABLE WATER FROM THE GOES AND SSM/I
SSM/I SOUNDER.
3) THE ETA ANALYSIS WILL CONTINUE TO BE IMPROVED BY
ALGORITHM CHANGES AND BY NEW DATA SOURCES (SATELLITE
RADIANCES...ASSIMILATION OF OBSERVED PRECIPITATION AND
CLOUD...WSR-88D RADIAL WINDS).
4) CONTINUED IMPROVEMENTS IN THE AVN FORECAST SUITE.
5) THE IBM VERSION OF THE NGM COULD BE RUN WELL INTO
THE FUTURE TO PROVIDE EARLY MOS GUIDANCE AND TO PROVIDE
EMC WITH A BASELINE FOR THE MEASUREMENT OF MESO ETA SKILL.
DISADVANTAGES
1) SMALLER INNERMOST GRID WHICH STOPS AT THE NORTH POLE.
2) OCCASIONAL PROBLEMS WITH ETA ANALYSIS IN PACIFIC WHICH
ADVERSELY IMPACT THE NGM FORECAST ON THE IBM. THIS COULD BE THE
RESULT OF FEWER OBSERVATIONS BEING AVAILABLE TO THE
ETA ANALYSIS DUE TO THE EARLY (T+70 MINUTES) DATA CUTOFF TIME.
3) USE OF A 6-H AVN FORECAST INSTEAD OF AN ROI ANALYSIS TO
INITIALIZE ANY PART OF THE NGM GRIDS OUTSIDE OF THE ETA
COMPUTATIONAL GRID. AT THE EARLY DATA CUTOFF TIME OF THE ETA
THERE WOULD BE LITTLE IF ANY OBSERVATIONS AVAILABLE FOR AN
ANALYSIS IN THE EASTERN HEMISPHERE.
II. RESULTS
EMC HAS PERFORMED TWO PARALLEL TESTS OF THE IBM VERSION OF THE
NGM: A REAL-TIME TEST WHICH STARTED AT 1200 UTC
16 DECEMBER 1999...AND A WARM SEASON RETROSPECTIVE TEST FOR JULY
1999. EMC'S QUANTITATIVE SKILL SCORES (FIT TO RAWINSONDE DATA
AND 24-H QUANTITATIVE PRECIPITATION FORECASTS (QPF)
SCORES) FOR THESE TESTS CAN BE FOUND AT
HTTP://SGI62.WWB.NOAA.GOV:8080/NGMSTATS/ . THE TECHNIQUES
DEVELOPMENT LABORATORY (TDL) RAN THE NGM MOS PACKAGE FROM THE
PARALLEL NGM FORECASTS; THESE RESULTS CAN BE FOUND AT
HTTP://WWW.NWS.NOAA.GOV/TDL/SYNOP/NGMCAFTI.HTM .
DURING THE JULY 1999 TEST...THE EMC SCORES AND THE TDL
MOS VERIFICATIONS SHOW SMALL DIFFERENCES IN THE
QUALITY OF THE PARALLEL NGM WHEN COMPARED TO THE
OPERATIONAL NGM. QPF SKILL FROM THE PARALLEL NGM WAS
SLIGHTLY BETTER IN THE EASTERN U.S. AND SLIGHTLY WORSE
IN THE WESTERN U.S....WHILE THE FIT TO RAWINSONDE DATA
WAS GENERALLY BETTER FOR ALL VARIABLES.
FOR THE CURRENT COOL SEASON TEST...THERE ARE LARGER
DIFFERENCES IN QUALITY BETWEEN THE OPERATIONAL AND
PARALLEL NGM...WITH DEGRADATION MORE COMMON AT UPPER LEVELS THAN
IN THE WARM SEASON TEST. GREATEST DIFFERENCES WERE
SEEN IN WINDS (WORSE ABOVE 700 MB)...TEMPERATURE AND HEIGHTS
(COMPARABLE OR BETTER BELOW 400 MB BUT WORSE ABOVE DUE TO
A GROWING WARM BIAS) AND SURFACE TEMPERATURE (BETTER AT
AT 12-H AND 24-H RANGE BUT SLIGHTLY WORSE AT 48-H). QPF
SKILL IS COMPARABLE OR SLIGHTLY BETTER IN THE EASTERN U.S. BUT
WORSE IN THE WESTERN U.S.
TDL PRODUCED AVERAGE VERIFICATION STATISTICS FROM 700+
SITES IN THE CONUS AND ALASKA FOR BOTH THE OPERATIONAL
AND PARALLEL NGM. FOR THE TWO NGM RUNS THE ERRORS ARE
COMPARABLE THROUGH THE 12-36 H PERIOD...WITH SLIGHT
DEGRADATION (4% FOR THE COOL SEASON TEMPERATURE) FOR
THE PARALLEL NGM'S 60-H MOS TEMPERATURE FORECAST.
FURTHER DETAILS CAN BE FOUND IN THE NWS TECHNICAL
PROCEDURES BULLETIN #464..."CHANGES TO THE NCEP REGIONAL
ANALYSIS AND FORECAST SYSTEM (RAFS): INITIAL CONDITIONS FOR FOR
THE NESTED GRID MODEL" AT
HTTP://SGI62.WWB.NOAA.GOV:8080/NGMTPB/
THE 3/1/2000 PRESENTATION TO THE NWS COMMITTEE ON
ANALYSIS AND FORECAST TECHNIQUES IMPLEMENTATION (CAFTI)
ON THE NGM CHANGES IS ALSO AVAILABLE ONLINE AT
FTP://FTP.NCEP.NOAA.GOV/PUB/EMC/WD20ER/NGMCAFTI6/INDEX.HTM
NOTE TO FORECASTERS
USERS SHOULD NOT EXPECT TO SEE AN EXACT MATCH BETWEEN
THE ETA ANALYSIS AND THE NGM 00-H FIELDS DERIVED FROM
THE ETA ANALYSIS IN ALL SITUATIONS FOR THE FOLLOWING
REASONS:
1) THE NGM IMPLICIT NORMAL MODE INITIALIZATION IS PERFORMED ON
THE INTERPOLATED ETA ANALYSIS BEFORE THE NGM MODEL
INTEGRATION.
2) VERTICAL RESOLUTION DIFFERENCE : THE OPERATIONAL MESO
ETA MODEL HAS 45 VERTICAL LEVELS...WHILE THE NGM HAS 16
LEVELS. CERTAIN FEATURES (SUCH AS NARROW JET STREAKS
OR SHARP VERTICAL MOISTURE GRADIENTS) WHICH ARE RESOLVED
IN THE ETA ANALYSIS MAY NOT BE CAPTURED WITH THE SAME
DETAIL WHEN INTERPOLATED TO THE THICKER NGM VERTICAL
LAYERS.
3) MODEL TERRAIN HEIGHT DIFFERENCES : THE 32-KM ETA MODEL
TERRAIN HEIGHT IS DERIVED FROM HIGH RESOLUTION 30 SECOND
DATA OVER THE CONUS...WHILE THE NGM USES MUCH SMOOTHER
TERRAIN BASED ON R40 SPECTRAL RESOLUTION. THUS...THERE ARE MANY
REGIONS WITH SIGNIFICANT DIFFERENCES IN MODEL TERRAIN HEIGHT.
DURING THE ETA-TO-NGM INTERPOLATION...THE FIRST STEP IS TO
RECOMPUTE THE ETA ANALYSIS SURFACE PRESSURE BASED ON THE NGM
TERRAIN HEIGHT. IF THE NGM TERRAIN HEIGHT IS LESS THAN THE ETA
TERRAIN HEIGHT...ONE MUST EXTRAPOLATE THE WIND...
TEMPERATURE...AND MOISTURE FROM THE FIRST ATMOSPHERIC ETA
LAYER TO GET VALUES AT NGM LEVELS BELOW THE ETA MODEL
TERRAIN.
4) FORECASTERS WHO USE THE MESO ETA AND NGM FORECAST HOURLY
STATION PROFILES PACKED IN BUFR FORMAT SHOULD BE AWARE THAT THE
STATION DATA IN THE ETA MODEL IS TAKEN FROM THE MODEL GRID POINT
CLOSEST TO THE STATION LOCATION...WHILE THE NGM PERFORMS A
BILINEAR INTERPOLATION FROM THE FOUR GRID POINTS CLOSEST TO THE
STATION. THEREFORE...THE 00-H ETA AND NGM PROFILES MAY NOT
ALWAYS AGREE EVEN FOR STATIONS CLOSE TO SEA LEVEL...ESPECIALLY
IN REGIONS WITH STRONG GRADIENTS.
END
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