523  
FXCN38 CWUL 231750  
TAF FORECASTER NOTES ISSUED BY THE CANADIAN AVIATION METEOROLOGICAL  
CENTRE AT 1815 UTC TUESDAY 23 MAY 2017.  
 
CYYZ - TORONTO/LESTER B PEARSON INTL.  
 
AN APPROACHING UPPER-LEVEL TROUGH FROM THE WEST WILL BRING  
INSTABILITY AND ALLOW FOR THE DEVELOPMENT OF CONVECTIVE CLOUDINESS  
OVER SOUTHERN ONTARIO TODAY AND TONIGHT.  
 
THIS AFTERNOON..ISOLATED TO SCATTERED TCU UP TO 25 000 FT ARE LIKELY  
TO DEVELOP MAINLY NORTH AND EAST OF THE AIRPORT DURING THE NEXT  
HOURS. ASLO AN ISOLATED CB WITH TOPS AT 32 000 FT WILL BE EMBEDDED IN  
THAT SAME AREA AND IT IS NOT OUT OF THE QUESTION TO HAVE ONE OF THESE  
THAT COULD AFFECT THE AIRPORT SITE: PROBABILITY IS LESS THAN 20% AS  
WE SPEAK. ONE THING FOR SURE, THE NORTHERN (BORDEN) AND EASTERN  
(SIMCOE) BEDPOSTS ARE LIKELY TO BE AFFECTED BY THE TCU AND/OR CB THIS  
AFTERNON AND EARLY EVENING.  
 
TONIGHT..CONDITIONS WILL REMAIN UNSTABLE AND COMBINED WITH THE  
PASSAGE OF A WEAK SURFACE TROUGH, ISOLATED TCU/ACC/CB WITH TOPS  
AROUND 25 000 FT WILL ONCE AGAIN DEVELOP IN THE SAME ABOVE MENTIONNED  
AREA. HENCE STILL THE LOW PROBABILITY (15%) FOR AN ISOLATED CB TO  
AFFECT THE AIRPORT SITE AND ITS ASSOCIATED NORTHERN AND EASTERN  
BEDPOST THROUGH THE NIGHT ESPECIALLY BETWEEN 05 AND 11Z.  
 
WEDNESDAY..GENERALLY CLEAR SKIES AND LIGHT WINDS OVER TORONTO AREA.  
 
OUTLOOK FOR THURSDAY...A SLOW MOVING LOW PRESSURE SYSTEM WILL ARRIVE  
FROM THE OHIO VALLEY AND WILL BRING RAIN, STRATUS CEILINGS AND  
EASTERLY WINDS TO TORONTO REGION.  
 
WEATHER VARIABILITY: LOW.  
 
FORECASTER CONFIDENCE NEXT 3 HOURS: HIGH.  
 
FORECASTER CONFIDENCE NEXT 6 HOURS: HIGH.  
 
END/CMAC-E/F MOREAU  
 
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