NOCN02 CWAO 271930 
GENOT FAX NO. 012
 
GENOT NO. 014 EST LA VERSION FRANCAISE DU GENOT NO. 012.

MODIFICATIONS TO THE REGIONAL FORECAST SYSTEM AT CMC...
PART 2 OF 2...

7.  EVALUATION OF THE GEM 24 KM MODEL IN PARALLEL RUN.

THE NEW MODEL HAS BEEN RUN IN PARALLEL FOR SEVERAL MONTHS, AND HAS 
BEEN EVALUATED BOTH OBJECTIVELY AND SUBJECTIVELY. FORECAST 
PRECIPITATION IS THE FIELD THAT EXHIBITED THE MOST DIFFERENCES 
BETWEEN THE NEW AND CURRENTLY OPERATIONAL MODEL. THE NEW MODEL 
PROVED SUPERIOR SEVERAL TIMES IN HANDLING PRECIPITATION ASSOCIATED 
TO CONVECTIVE LINES SUCH AS COLD FRONTS AND SQUALL LINES. 
PRECIPITATION PATTERNS ASSOCIATED TO THESE FEATURES ARE MORE 
REALISTIC, MAXIMUM VALUES ARE OFTEN CLOSER TO OBSERVED VALUES, AND 
THE REDUCED PRECIPITATION TRACE IS BETTER THAN IN THE OPERATIONAL 
MODEL. FOR AIRMASS TYPE OF CONVECTION, THE NEW MODEL BEHAVES 
DIFFERENTLY FROM THE OPERATIONAL MODEL, BUT THE DEGREE OF 
IMPROVEMENT IS NOT AS CLEAR. THESE LARGE DIFFERENCES BETWEEN 
FORECAST PRECIPITATION FROM BOTH MODELS ORIGINATE MOSTLY FROM THE 
DIFFERENT DEEP CONVECTION SCHEMES USED IN THE MODELS;  FORECAST 
PRECIPITATION IN CASES WHERE CONVECTION IS INACTIVE IS RELATIVELY 
SIMILAR IN BOTH MODELS (E.G. IN WINTER OVER THE CONTINENT).

THE TENDENCY EXHIBITED BY THE 35 KM VERSION OF GEM TO OVERDEVELOP 
OCEANIC LOWS TO WHICH IS ASSOCIATED DEEP CONVECTION IS CLEARLY 
IMPROVED IN THE NEW VERSION OF THE MODEL; FOR SEVERAL OF THESE 
CASES THE NEW MODEL WAS NOT DEVELOPING THE ASSOCIATED LOW AS MUCH 
AS THE OPERATIONAL MODEL AND VERIFIED MUCH BETTER. IT IS 
ANTICIPATED THAT THE BENEFITS WILL EVEN BE MORE SIGNIFICANT NEXT 
WINTER, ESPECIALLY IN OCEAN AREAS EAST OF THE NORTH AMERICAN 
CONTINENT WHERE THIS TYPE OF DEVELOPMENT IS FREQUENT. HOWEVER, ONE 
CANNOT CONCLUDE THAT THE NEW MODEL SYSTEMATICALLY DEVELOPS THESE 
SYSTEMS LESS THAN THE CURRENT OPERATIONAL MODEL SINCE WE HAVE 
OBSERVED A NUMBER OF EXPLOSIVE DEVELOPMENTS THAT HAVE BEEN WELL 
CAPTURED BY THE GEM 24 KM VERSION.

8.  POST-PROCESSING.

SOME CHANGES HAVE BEEN DONE TO THE SCRIBE SYSTEM TO TAKE INTO 
ACCOUNT SOME OF THE CHARACTERISTICS OF CERTAIN FIELDS OF THE NEW 
MODEL THAT ARE DIFFERENT, AND ALSO TO REFINE THE TERMINOLOGY OF 
THE FORECASTS BASED ON THIS SYSTEM.

THE POST PROCESSING APPLIED TO STATISTICAL FORECASTS HAS BEEN 
MODIFIED SO AS TO REDUCE THE INCONSISTENCIES THAT HAVE BEEN NOTED 
PREVIOUSLY IN THE PROBABILITY OF PRECIPITATION AND TEMPERATURE 
FORECASTS.

SOME CHANGES HAVE BEEN DONE TO THE AVIATION PACKAGE CHARTS:

A)  THE TURBULENCE FIELD HAS BEEN RECALIBRATED SO AS TO TAKE
INTO ACCOUNT IMPROVEMENTS TO THE FORECAST MODEL OVER THE PAST
FEW YEARS. THE THRESHOLDS FOR THE DVSI DEPICTED ON THE CHARTS
WILL BE MODIFIED FROM 30, 60, 90 AND 120 TO 30, 50, 150 AND
240.

B)  LOW LEVEL MOMENTUM FLUX AND MID-LEVEL CLEAR AIR
TURBULENCE FIELDS DEPICTED ON CHARTS A0776C TO A0783C WILL BE ON 
DIFFERENT CHART PANELS, SO AS TO IMPROVE READABILITY. TO MAKE ROOM 
FOR THIS NEW PANEL, FORECASTS OF CLOUD CEILINGS FOR PERIODS 6-24 
HOURS WILL BE GROUPED ON A NEW SINGLE 4-PANEL CHART, WITH ID'S 
A0784C (FOR 00 UTC RUN) AND A0785C (FOR 12 UTC RUN). MOREOVER, 
CHART DESCRIPTORS FOR A0776C TO A0783C WILL BE MODIFIED TO REFLECT
THE FACT THAT CLOUDS FORECASTS ARE NO LONGER PART OF THESE CHARTS
(THE WORD CLOUD WILL BE REMOVED FROM THE DESCRIPTOR).

STANDARD 4-PANEL CHARTS HAVE BEEN MODIFIED AS FOLLOWS TO IMPROVE 
READABILITY:

A)  CONTOURS OF 10% AND 30% FOR RELATIVE HUMIDITY HAVE BEEN REMOVED.

B)  A FILTER IS APPLIED TO THE QPF FIELD. CONTOURS DEPICTED WILL BE
0.5, 5, 10, 25, 50 AND 100 MM; THE 1 MM CONTOUR WILL BE REMOVED. 
MOREOVER, THE VERTICAL MOTION FIELD IS NO LONGER REPRESENTED ON THE
QPF PANEL SINCE THIS FIELD IS AVAILABLE SOMEWHERE ELSE IN THE 
SEVERE WEATHER PACKAGE. ON THESE CHARTS, THE VERTICAL MOTION
CONTOURS DEPICTED WILL BE 3, 9, 15, 25, 75,... MICROBAR/S.

C)  THE 500 HPA VORTICITY FIELD WILL BE FILTERED.

FINALLY, SOME COSMETIC CHANGES HAS ALSO BEEN DONE ON THE CONVECTION
INDICES CHARTS:  THE LIFTED INDEX WILL BE COMPUTED ACCORDING TO ITS
TRUE DEFINITION, AND THEREFORE WILL NO LONGER REPRESENT THE MOST
UNSTABLE INDEX OBTAINED BY LIFTING AN AIR PARCEL FROM EACH OF THE
LOWEST 4 ETA LEVELS OF THE MODEL. IN ADDITION, THE VALUE 0 OF THE
INDEX WILL BE ENHANCED, INSTEAD OF THE -4 CONTOUR. THE SHOWALTER
INDEX WILL BE CONTOURED AT 4 UNITS INTERVALS.

MCBEAN/ADMA/TORONTO