929  
FOCN45 CWWG 281900  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT SUNDAY AUGUST  
28 2016.  
 
ALERTS IN EFFECT... RAINFALL WARNING FOR THE URANIUM CITY REGION.  
 
SYNOPTIC OVERVIEW...AN UNUSUALLY TILTED AND HIGH AMPLITUDE UPPER  
LEVEL FLOW LIES OVER MUCH OF CANADA. A LARGE UPPER RIDGE HAS SETTLED  
OVER THE HIGH ARCTIC, WHILE A DEEP EAST-WEST UPPER TROUGH RUNS FROM  
THE GULF OF ALASKA ALL THE WAY THE TO LABRADOR SEA, GIVING RISE TO A  
90 KT EAST TO WEST UPPER LEVEL JET OVER THE NORTHWEST PASSAGE AREA.  
THE JET TURNS SOUTHWARD OVER THE PACIFIC AND FINALLY BACK EAST ALONG  
THE INTERNATIONAL BORDER. SEVERAL CLOSED LOWS OVER HAIDA GWAII AND  
THE MACKENZIE LOOK TO CUT OFF FROM THE MAIN FLOW AND MERGE OVER THE  
GULF OF ALASKA. MEANWHILE, ANOTHER CLOSED LOW OVER BUFFALO NARROWS  
IS MOVING NORTHEASTWARD, WHILE A WEAKER SHORTWAVE IS FOLLOWING ALONG  
THE TRANS-CANADA HIGHWAY NEAR SWIFT CURRENT. AT THE SURFACE, A 1002  
MB LOW MOVING SOUTH OF LA RONGE, WITH A WARM FRONT NORTH AND  
EASTWARD WITH A COLD FRONT SWEEPING SOUTHWESTWARDS INTO MONTANA.  
THIS SURFACE LOW IS MOVING INTO NORTHERN MANITOBA TONIGHT CONTINUING  
TOWARD HUDSON BAY THROUGH MONDAY. A LARGE 1031 MB RIDGE DOMINATES  
OVER THE HIGH ARCTIC.  
 
DISCUSSION...  
 
ALBERTA...BEHIND THE COLD FRONT THE AIRMASS HAS STABILIZED WITH  
RESPECT TO DEEP CONVECTION SO NO THUNDERSTORMS ARE EXPECTED IN THE  
PROVINCE. RAIN WILL CONTINUE OVER THE EXTREME NORTHEASTERN PORTIONS  
OF THE PROVINCE UNDER THE INFLUENCE OF THE TROWAL WRAPPING AROUND  
THE UPPER LOW. THIS PRECIPITATION SHOULD TAPER OFF BY LATE THIS  
AFTERNOON AND PROVIDE ANOTHER 5 MM OF PRECIPITATION BEFORE EXITING  
THE PROVINCE.  
 
TONIGHT CLOUD IS EXPECTED TO CLEAR OUT OF THE PROVINCE AND NEAR  
FREEZING OVERNIGHT LOWS ARE POSSIBLE THROUGH NWRN TO CENTRAL PARTS  
OF THE PROVINCE POSSIBLY BRINGING A FEW FROST PATCHES.  
 
SASKATCHEWAN...EMBEDDED CONVECTION IN THE TROWAL BROUGHT NEAR 45 MM  
OF HEAVY RAIN TO URANIUM CITY LAST NIGHT AND EARLY THIS MORNING.  
WITH THE REGION REMAINING UNDER THE INFLUENCE OF THE TROWAL FOR THE  
NEXT 12 HOURS ANOTHER 10-20 MM OF RAIN IS POSSIBLE BEFORE THE RAIN  
TAPERS OFF ON MONDAY MORNING.  
 
SOUTHEASTERN PORTIONS OF THE PROVINCE SEE A BAND OF SHOWERS AHEAD  
OF THE LOW AND FRONTAL SYSTEM AND ARE MOVING EASTWARD OUT OF THE  
AREA THIS AFTERNOON.  
 
MANITOBA... THE COLD FRONT FROM THE LOW IN NORTHERN SASKATCHEWAN  
IS MOVING INTO THE PROVINCE THIS AFTERNOON. AHEAD OF IT AN AREA OF  
SHOWER IS MOVING AHEAD OF THE LOW AND ASSOCIATED TROF. THE  
TRAILIING COLD FRONT WILL SERVE AS THE POTENTIAL THUNDERSTORM  
TRIGGER LATER THIS AFTERNOON ACROSS THE SOUTH AS IT CONTINUES TO  
PUSH SLOWLY EASTWARD. DEWPOINTS RISING TO HIGH TEENS IN THE  
SOUTHERLY FLOW AHEAD OF THE SYSTEM GIVING MLCAPES APPROACHING  
2000 J/KG WITH INFLOW SHEAR SIGNIFICANT WITH SOUTHERLY 25 KTS AT 850  
MB AND WESTERLY 35 KT AT 500 MB.  
 
STILL MONITORING FOR SUPERCELLS AS THE STORM MODE OF THE LATE  
AFTERNOON AND EARLY EVENING, BUT INVERSION CAP ALOFT MAY INHIBIT  
CONVECTION. CURRENT GEM AND HRRR SHOW INTIATION IN WESTERN MB  
VICINITY BRANDON AND 12 HOUR 50+ MM AREA OF CONVECTIVE PRECIPITATION  
JUST EAST OF LAKE WINNIPEG. WATCHES FOR THIS AREA INCLUDING RED  
RIVER VALLEY AND INTERLAKE EXPECTED THIS AFTERNOON. REQUESTED 21Z  
XWI SOUNDING WILL GIVE BETTER REALTIME IDEA OF STRENGTH OF CAP AND  
STORM MODE POTENTIAL. 30 DEGREES EXPECTED TO BE REQUIRED TO BREAK  
THE CAP AT THIS TIME WITH LARGE HAIL AND HEAVY DOWNPOURS LIKELY IF  
CAP BREAKS. CAN'T RULE OUT TORNADO POTENTIAL WITH THE ABOVE  
MENTIONED SHEAR. IN NORTHERN REGIONS OF MANITOBA, THE LOW PRESSURE  
SYSTEM MOVING THROUGH THE AREA IS EXPECTED TO GIVE UP TO 40 MM OF  
RAIN WITH EMBEDDED THUNDERSTORMS OVER THE NEXT 24-36 HOURS.  
 
WESTERN ARCTIC...EMBEDDED UPPER WAVE OVER GREAT BEAR LAKE IS  
SPREADING SHOWERS IN THE CENTRAL MACKENZIE VALLEY. OTHERWISE NIL  
SIG WX.  
 
EASTERN ARCTIC...PERIODIC FOG CONTINUES TO AFFECT MOST EASTERN  
ARCTIC SITES DUE TO AMPLE LINGERING MOISTURE WITH LIGHT WINDS OR  
WEAK ONSHORE FLOW. WITH THE LOW IN THE AREA DECAYING QUICKLY, SLACK  
WINDS AND THUS MORE PATCHY FOG WILL CONTINUE INTO MONDAY AT LEAST.  
 
OUTLOOK...INCREASING MIDLEVEL INSTABILITY AND A MODERATE 500 MB FLOW  
OVER SWRN AB ON MONDAY WILL LEAD THE POTENTIAL FOR SEVERE  
THUNDERSTORMS OVER THE AREA. AS ALWAYS WITH THIS TIME OF YEAR,  
MOISTURE WILL THE BE THE LIMITING FACTOR IN ANY STORMS THAT DO FORM.  
WITH STRONG SHEARS AND HIGH LCLS, STORMS WILL HAVE TO POTENTIAL TO  
PRODUCE VERY STRONG WIND GUSTS.  
 
END/BUKOSKI/GREENHOUGH  
 
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