741  
FOCN45 CWWG 281900  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT WEDNESDAY JUNE  
28 2017.  
 
ALERTS IN EFFECT...NONE.  
 
SYNOPTIC OVERVIEW...DOMINANT UPPER FEATURE TODAY IS A REX BLOCK  
FORMED BY A RIDGE CENTERED OVER THE WESTERN KITIKMEOT, AND A COLD LOW  
OVER CENTRAL AB. THIS COLD LOW WILL MEANDER THROUGH THE PRAIRIES OVER  
THE REMAINDER OF THE WEEK PUSHING INTO MB ON FRIDAY. OTHERWISE  
RIDGING OVER B.C., A SHORTWAVE TROF PUSHING THROUGH THE PAULATUK  
AREA, AND A FILLING UPPER LOW OFF THE COAST OF LABRADOR.  
 
AT THE SURFACE, A TRIPLET OF LOWS IN EAST-CENTRAL AB, THE MANITOBA  
INTERLAKE, AND WESTERN MINNESOTA CONNECTED BY A SHARP TROUGH OF LOW  
PRESSURE. ANOTHER LOW VICINITY PAULATUK SLOWLY MOVING EAST. A FINAL  
LOW WAS ANALYZED WITH THE 12Z MAP VICINITY SK/AB/MT BORDER  
INTERSECTION. THE DOMINANT BAROCLINICITY LIES WITH THE MINNESOTA LOW  
GRADUALLY TRACKING EASTWARD TOWARDS THE GREAT LAKES. OTHERWISE, A  
1021 MB HIGH NEAR KUGAARUK BUILDS SOUTHWARDS, AND WEAK TROUGHING  
CONTINUES OVER EASTERN BAFFIN BAY.  
 
DISCUSSION...  
 
ALBERTA...UPPER LOW AND ASSOCIATED SHOWERS SLUMPING SOUTHWARDS.  
GOOD VORTICITY OVER EASTERN ALBERTA TODAY WITH THE UPPER LOW AND  
SURFACE TROUGH MAY BRING FUNNEL CLOUDS. THUNDERSTORMS FORECAST  
THROUGH SOUTHERN ALBERTA WITH THE FOCUS NEAR A SURFACE TROUGH RUNNING  
FROM ROUGHLY CLARESHOLM TO OYEN. POCKETS OF MLCAPE NEAR 1000 J/KG AND  
SHEARS NEAR 30 KNOTS EARLY IN THE AFTERNOON. AS THE DAY PROGRESSES  
SHEARS DROP OFF TO 20. SLIGHT CHANCE OF SEVERE GUSTS BUT MOSTLY  
NON-SEVERE STORMS. IN NORTHEASTERN SASKATCHEWAN SOME AREAS MAY  
APPROACH RAINFALL CRITERIA. AN AREA OF THUNDERSTORMS GAVE A QUICK 30  
MM TO FLIN FLON OVERNIGHT AND SIMILAR COULD OCCUR THROUGH PELICAN  
NARROWS TOWARDS LA LOCHE.  
 
MANITOBA...SHOWERS CONTINUE ALONG THE TROWAL (WHICH HAS NOW MOVED  
EAST OF WINNIPEG) AS OF EARLY THIS AFTERNOON WITH 5-15 MM OF RAIN  
FORECAST BY THURSDAY MORNING AND LOCALLY 25+ MM POSSIBLE IN  
THUNDERSTORMS. THIS SYSTEM IS VERY SLOW MOVING AND ISOLATED  
THUNDERSTORMS MAY REDEVELOP THIS AFTERNOON, BUT THE PRECIPITATION  
SHOULD MOVE ENTIRELY OUT OF SOUTHERN MANITOBA TONIGHT.  
 
SASKATCHEWAN...SURFACE BASED CONVECTION IS FORECAST TO DEVELOP IN SK  
UNDER THE UPPER LOW. WITH CAPES GENERALLY IN THE 400 TO 1000 J/KG  
RANGE, AND 0 TO 6 KM BULK SHEAR VALUES OF 20 TO 30 KNOTS, SEVERE  
THUNDERSTORMS ARE UNLIKELY. THAT SAID, FUNNEL CLOUDS ARE POSSIBLE IF  
NOT LIKELY UNDER THE UPPER LOW AS IT DRIFTS INTO WEST CENTRAL  
SASKATCHEWAN THIS AFTERNOON. ALSO OF CONCERN IS A SMALL DISTURBANCE  
MOST READILY IDENTIFIED ON SATELLITE IMAGERY ALONG THE SK/MT BORDER.  
AREA OF MID-LEVEL INSTABILITY AS EVIDENCED BY MORNING ACC (FROM  
SATELLITE/WEBCAMS) FROM ROUGHLY CYYN-CYMJ-CYQR-WAQ. ALTHOUGH SURFACE  
DEWPOINTS ARE LOW, WEAK CYCLOGENISIS LIKELY FROM SK/AB/MT LOW SEEMS  
TO ADVECT LOW-LEVEL MOISTURE INTO THIS AREA THIS AFTERNOON. SUBTLE  
SHORT WAVE IN MT DRIFTING NE COMBINED WITH FALLING HEIGHTS FROM  
APPROACH OF AB UPPER LOW TRIGGERING A FEW THUNDERSTORMS IN THIS AREA  
AT THE MOMENT, AND THESE STORMS HAVE THE POTENTIAL TO INCREASE IN  
SEVERITY AS THE DAY WEARS ON AND SHEAR VALUES INCREASE. CONDITIONAL  
RISK OF SEVERE THUNDERSTORMS WILL EXIST IN THIS AREA THIS AFTERNOON,  
DEPENDENT UPON HOW THE SITUATION EVOLVES.  
 
MB/SK THURSDAY...A SIMILAR SITUATION IS EXPECTED ON THURSDAY WITH THE  
UPPER LOW TRIGGERING SURFACE BASED CONVECTION OVER SOUTHEAST  
SASKATCHEWAN AND SOUTHERN MANITOBA. FUNNEL CLOUDS WILL ONCE AGAIN BE  
A POSSIBILITY THURSDAY OVER EXTREME SOUTHEASTERN SK AND SOUTHWESTERN  
MB. CAPE VALUES ARE EXPECTED TO APPROACH 1500 J/KG IN THAT AREA,  
HOWEVER LOW LEVEL SHEAR IS EXPECTED TO BE A LIMITING FACTOR FOR  
SEVERE CONVECTION, HOWEVER BRIEF LANDSPOUT TORNADOES MAY BE A  
POSSIBILITY. SHOWERS WILL CONTINUE ON THURSDAY ALONG THE TROWAL  
EXTENDING THROUGH CENTRAL MB INTO WEST CENTRAL SK.  
 
CANADA DAY OUTLOOK...IT LOOKS LIKE MAINLY SUNNY SKIES IN STORE FOR  
SASKATCHEWAN AND WESTERN MANITOBA AS THE UPPER RIDGE BUILDS INTO THE  
WESTERN PRAIRIES. THERE IS A FAIR AMOUNT OF DISAGREEMENT BETWEEN THE  
MODELS WITH REGARDS TO THE POSITION OF THE UPPER TROUGH ON SATURDAY,  
HOWEVER A SHOWERY COOL DAY OVER EASTERN MANITOBA REMAINS A  
POSSIBILITY. LATE DAY SHOWERS OR THUNDERSTORMS APPEAR LIKELY FOR  
ALBERTA. STAY TUNED...  
 
WESTERN ARCTIC...RISK OF THUNDERSTORMS IN THE CENTRAL MACKENZIE.  
 
EASTERN ARCTIC...NIL SIG WX.  
 
END/FULTON/MACKAY  
 
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