679  
FOCN45 CWWG 301900  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT THURSDAY JUNE  
30 2016.  
 
ALERTS IN EFFECT... HEAT WARNING FOR NORTHERN ALBERTA. THUNDERSTORM  
WATCHES OUT FOR MUCH OF ALBERTA.  
 
SYNOPTIC OVERVIEW...ALOFT A BROAD UPPER RIDGE SITS OVER THE WESTERN  
PRAIRIES WITH SHARP TROUGHS OVER NORTHWESTERN ONTARIO AND THE BC  
COAST. AT THE SURFACE, A 1007 MB LOW SITS OVER NORTHERN QUEBEC WITH  
A COLD FRONT SOUTHWESTWARD INTO SOUTHERN MINNESOTA. A ARCTIC RIDGE  
OF HIGH PRESSURE IS PARKED OVER SASKATCHEWAN AND MANITOBA.  
 
DISCUSSION...  
 
WESTERN PRAIRIES...LIKELY A VERY ACTIVE DAY CONVECTIVLEY OVER MUCH  
OF ALBERTA. THE UPPER TROUGH CURRENTLY MAKING ITS WAY THROUGH  
BC WILL BE THE PRIMARY TRIGGER TODAY. A LEE TROUGH HAS  
FORMED IN ADVANCE OF THIS FEATURE AND IS ALLOWING MOISTURE TO  
POOL THROUGH A DEEP PORTION OF THE PBL. THE ATMOSPHERE REMAINS  
UNSTABLE AND RAIN FROM OVERNIGHT THUNDERSTORMS WILL INCREASE THE  
MOISTURE IN THE LOW LEVELS THAT WILL PROVIDE AMPLE FUEL FOR TODAYS  
THUNDERSTORMS. AS THE UPPER TROUGH CROSSES INTO ALBERTA, STORMS  
WILL FORM ALONG THE FOOTHILLS NORTH OF ROCKY MOUNTAIN HOUSE WHERE  
MLCAPES ARE IN THE 1200-1500J/KG RANGE AND SHEARS ARE 15-20KTS. THE  
SHEAR VECTOR IS ALIGNED PARALLEL TO THE TROUGH SO STORMS WILL LIKELY  
FORM INTO A LINE THAT WILL MOVE SLOWLY TO THE EAST AS THE DAY  
PROGRESSES. THE MAIN THREAT WITH THESE STORMS WILL BE HEAVY RAIN AND  
LOTS OF SMALL HAIL WITH THE ODD PIECE UP TO LOONIE SIZED.  
 
MAIN AREA OF CONCERN IS IN THE SOUTH WHERE CONVECTIVE INITIATION  
WILL BE SLIGHTLY DELAYED IN AREAS SOUTH OF RED DEER AND WILL BE  
COINCIDENT WITH A MODERATE 500MB JET ROUNDING THE BASE OF THE  
APPROACHING UPPER TROUGH. THIS JET IS SUFFICENTLY STRONG TO BRING  
DEEP LAY SHEARS UP TO 30-35KT MAKING HP SUPERCELLS LIKELY OWING TO  
THE INCREASED MLCAPES IN THE 1500-2000J/KG THAT WILL RESULT  
FROM THE DELAYED INITIATION ALLOWING TEMPS TO RISE. THE DEEP LAYER  
SHEAR IS MORE NORMAL TO THE UPPER TROUGH AND AS SUCH STORMS ARE MORE  
LIKELY TO REMAIN DISCRETE AND SLOW MOVING. THIS WILL ALLOW THE  
STORMS TO HAVE UNFETTERED ACCESS TO AMPLE MOISTURE WHICH INCREASES  
THE LIKELIHOOD OF HAIL UP TO AND POTENTIALLY LARGER THAN GOLF BALLS.  
IN THAT SAME AREA, A SELY 850MB 25KT JET WILL INCREASE LOW LEVEL  
STREAMWISE VORTICITY WHICH COULD LEAD TO ISOLATED TORNADOS. SINCE  
THE JETS ALOFT ARE REALTIVELY WEAK, ANY TORNADOS THAT DO FORM ARE  
NOT EXPECTED TO BE LONG LIVED. CURRENTLY THE BEST AREA FOR TORNADIC  
ACTIVITY WOULD OCCUR IN THE BROOKS REGION. THE PRIMARY THREATS WITH  
THESE STORMS WILL BE THE VERY LARGE HAIL, STRONG WINDS AND HEAVY  
RAIN. THE CONVECTION WILL LIKELY CONGEAL INTO A FORWARD-PROPAGATING  
MCS BY EVENING WITH DAMAGING WINDS THE MAIN THREAT UNTIL THE SYSTEM  
EXITS INTO SASKATCHEWAN.  
 
EASTERN PRAIRIES... THUNDERSTORMS FROM ALBERTA LOOK TO MOVE  
INTO EXTREME SOUTHWESTERN SASKATCHEWAN IN THE EVENING HOURS. THE  
LATEST MODEL RUNS CONTINUE TO SLOW THE PROGRESSION OF THE TROUGH  
EASTWARD AND ARE REDUCING SURFACE BASED INSTABILITY ON THE  
SASKATCHEWAN SIDE EARLY ON. STILL, EXPECT A FEW CELLS TO REMAIN  
SEVERE AS THEY CROSS THE BORDER. 850 MB INFLOW WINDS ARE QUITE GOOD,  
FEEDING WARM HUMID AIR AT SOUTHERLY 25 KNOTS - BUT AT 500 MB THE  
WINDS ARE SIMILAR 25 KNOT NORTHWESTERLIES AT 500 MB. STORM MOTION IS  
THUS QUITE LOW SO HEAVY RAIN WILL BE AN INCREASING CONCERN THROUGH  
THE EVENING IN ADDITION TO LARGE HAIL. WITH A NARROW BAND OF  
CONTINUING LOW LEVEL HUMID AIR PROVIDING A GOOD LIFTING PLATFORM,  
THE STORMS WILL BECOME ELEVATED AND SLOWLY SHIFT EASTWARD THOUGH THE  
NIGHT, WITH MUCAPES OF ABOUT 1000-1500 J/KG OR SO. THE SEVERE RISK  
FOR HEAVY CONVECTIVE RAIN AND HAIL CONTINUES OVERNIGHT INTO FRIDAY  
MORNING. INTERESTINGLY, MUCAPE CALCULATIONS APPEAR A BIT  
UNDERDONE IN THE NWP DUE TO THE HIGH LIFTING LEVELS AS IT PUSHES  
INTO THE RIDGE LATE INTO THE NIGHT. AT ANY RATE, THE HIGH RES MODELS  
STILL PICKS UP ON THE POTENTIAL FOR HIGH QPF PUSHING CONVECTIVER  
ACTIVITY AS FAR EAST AS REGINA AND THE BATTLEFORDS. LATER ON FRIDAY,  
MOST OF SOUTHWEST SASKATCHEWAN WILL AGAIN HAVE A RISK OF SEVERE  
WEATHER AS THE TROUGH LINGERS IN THE AREA AND TRIGGERS ANOTHER ROUND  
OF THUNDERSTORMS IN THE AFTERNOON.  
 
MEANWHILE, IN NORTHERN MANITOBA, A SHORTWAVE MOVING SOUTHEAST OUT OF  
KIVALLIQ AND STRONG DAYTIME HEATING OF THE ARCTIC AIR WILL GENERATE  
SCATTERED NON-SEVERE THUNDERSTORMS THIS AFTERNOON ACROSS THE  
NORTHEAST. THE RIDGE WILL OTHERWISE KEEP MANITOBA QUIET TODAY  
AND TOMORROW.  
 
WESTERN ARCTIC...GENERAL INSTABILITY IN THE CENTRAL MACKENZIE  
VALLEY WILL CAUSE THUNDERSTORMS TO ONCE AGAIN INTITATE IN THE EARLY  
AFTERNOON AND CONTINUE UNTIL THE LATE EVENING.  
 
EASTERN ARCTIC...NIL SIG WX.  
 
END/RUSSO/WIELKI  
 
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