506  
FOCN45 CWWG 181900  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT WEDNESDAY  
SEPTEMBER 18 2019.  
 
ALERTS IN EFFECT...SEVERE THUNDERSTORM WATCH FOR PORTIONS OF SOUTHERN  
AND CENTRAL MANITOBA. RAINFALL WARNING FOR CAPE DORSET, WITH IQALUIT  
AND KIMMIRUT UNDER CONSIDERATION.  
 
SYNOPTIC OVERVIEW...UPPER RIDGE CONTINUES TO SHIFT EASTWARD, NOW FROM  
THE GREAT LAKES THROUGH NORTHERN QUEBEC. UPPER LOW NEAR SEATTLE AND  
ANOTHER NEAR LUPIN WITH UPPER TROUGH RUNNING BETWEEN. STRONG VORTMAX  
IN SW MB PUSHING NORTHEASTWARD. UPPER RIDGE OVER THE NORTHEASTERN  
PACIFIC WITH AN EASTWARD MOVING UPPER LOW OVER EASTERN ALASKA.  
 
AT THE SURFACE, 995 MB LOW OVER MANITOBA INTERLAKE TRACKING  
NORTHEAST. WARM FRONT FROM THIS LOW UP TOWARDS GILLAM, WHICH THEN  
CURVES SOUTHEAST OVER NORTHWESTERN ONTARIO. COLD FRONT FROM THIS LOW  
SOUTHWARD THROUGH WESTERN MANITOBA. 997 MB LOW NEAR CHESTERFIELD  
INLET ALSO TRACKING NORTHEAST. WARM FRONT EAST AND COLD FRONT  
SOUTH-SOUTHWEST FROM THIS LOW. HIGH PRESSURE RIDGE FROM MONTANA TO  
NORTHERN BC. ANOTHER HIGH PRESSURE RIDGE FROM QUEBEC UP THROUGH DAVIS  
STRAIT.  
 
DISCUSSION...  
 
PRAIRIES...ANOTHER VERY WARM NIGHT OVER EASTERN SASKATCHEWAN AND MUCH  
OF MANITOBA WITH DEW POINTS WELL UP INTO THE TEENS. THUNDERSTORMS  
PERSISTED MUCH OF THE NIGHT OVER EASTERN SASKATCHEWAN THEN MOVED INTO  
WEST-CENTRAL MANITOBA PROMPTING WATCHES AND WARNINGS. ALTHOUGH  
HIGHEST THETA-E AIR IS MOVING OFF INTO NW ONTARIO, STRONG DYNAMICS IN  
VICNINTY AND NORTH OF THE VORT CENTRE ARE CONTRIBUTING TO ONGOING  
SEVERE THUNDERSTORMS, AND WE ANTICIPATE THAT THE CURRENT WATCHES WILL  
BE MAINTAINED FOR MOST OF THE AFTERNOON.  
 
THE HEAT AND HUMIDITY OF THE PAST COUPLE OF DAYS WILL ALSO DISPERSE  
AS THE COLD FRONT MOVES THROUGH.  
 
GENERALLY CLEAR AND COOL THROUGH ALBERTA EARLY THIS MORNING, WITH  
RISKS OF FROST OVERNIGHT THROUGH MUCH OF THE PROVINCE. THE UPPER LOW  
NEAR SEATTLE IS SLOWLY TRACKING EAST TOWARD ALBERTA, BRINGING SOME  
WEAK INSTABILITY TO THE NORTHERN FOOTHILLS. AN AREA OF SHOWERS AND  
NON-SEVERE THUNDERSTORMS WILL DEVELOP AND SLUMP SOUTHEASTWARD,  
BRINGING LOCAL AMOUNTS OF 5-10 MM OF RAIN TO AREAS NORTH OF CALGARY  
BEFORE MOVING IN TO SOUTHERN SASKATCHEWAN ON THURSDAY. THE SYSTEM  
WILL CONTINUE TO RAMP UP ON FRIDAY AS IT EDGES INTO MANITOBA  
ENCOUNTERING HIGHER DEWPOINTS FURTHER EAST. MORE SEVERE THUNDERSTORMS  
ARE POSSIBLE FRIDAY.  
 
ARCTIC...CHESTERFIELD INLET LOW WILL INTENSIFY AS IT TRACKS NORTHEAST  
OVER THE NEXT COUPLE OF DAYS. THE 25 MM IN 24 HOURS RAINFALL WARNING  
THRESHOLD WILL LIKELY BE MET IN SEVERAL COMMUNITIES OVER THE NEXT  
COUPLE OF DAYS. RAINFALL WARNING FOR CAPE DORSET AS THEY ARE FIRST TO  
GET THE RAIN. WARNING MAY HAVE TO BE ISSUED FOR OTHER SOUTH BAFFIN  
COMMUNITIES OVER THE NEXT DAY OR SO AS THE SYSTEM CONTINUES TO  
ADVANCE. SOUTHEAST WINDS AHEAD OF THE SYSTEM WILL GUST TO 80 KM/H  
HERE AND THERE, ALONG WITH GALES IN SOME OF THE ADJOINING WATERS.  
NORTHWEST WINDS BEHIND THE SYSTEM WILL ALSO PRODUCE GALES.  
 
END/FULTON/PATTEN  
 
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