131  
FOCN45 CWWG 071200  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 7:00 AM CDT TUESDAY JULY  
7 2020.  
 
ALERTS IN EFFECT...NONE.  
 
SYNOPTIC OVERVIEW...ALOFT THERE IS AN UPPER LOW OVER THE YUKON WITH A  
LONG WAVE TROUGH EXTENDING SOUTHWARD TO NORTHERN CALIFORNIA.  
WEAK RIDGING OVER THE SOUTHERN PRAIRIES. ANOTHER UPPER LOW IS OVER  
SOUTHERN NUNAVUT AND ANOTHER IN THE VICINITY OF CLYDE RIVER.  
 
AT THE SURFACE, THERE IS A RIDGE OVER THE PRAIRIES. A 994 MB LOW IS  
VICINITY ARVIAT WITH A TROWAL WRAPPING AROUND IT, THE MAIN FRONTAL  
WAVE OVER ONTARIO. A WEAK 1004 MB LOW IS OVER DAVIS STRAIT.  
 
DISCUSSION...  
 
WESTERN PRAIRIES...A INTERESTING CONVECTIVE DAY IS ON TAP FOR ALBERTA  
TODAY. THERE ARE TWO MAIN RISK AREAS FOR SEVERE CONVECTION.  
FOR SOUTHERN ALBERTA...A LOW WILL BE DEVELOPING IN EASTERN MONTANA  
THIS AFTERNOON WITH A SURFACE TROUGH ORIENTED NORTHWEST TOWARDS  
EDMONTON. FOR THE SOUTH OF THE PROVINCE WE WILL SEE A SERIES OF JETS  
VEERING WITH HEIGHT LEADING TO STRONG DEEP LAYER SHEAR BETWEEN  
35-50KNOTS FROM 0-6KM. THE SOUTHEASTERLY 850MB JET AND SURFACE FLOW  
WILL ACT TO CONTINUOUSLY PUSH MOISTURE NORTHWEST ALONG THE SURFACE  
TROUGH, THIS FLOW WILL ACT TO FUEL STORMS AS THE THERMAL RIDGE ALOFT  
MOVES OFF INTO SASKATCHEWAN THIS AFTERNOON. UPWARDS OF 1500-2000 J/KG  
OF MLCAPE IS EXPECTED IN THIS REGION. THIS ENVIRONMENT WILL BE  
CONDUCIVE FOR ORGANIZED SEVERE THUNDERSTORMS WITH LARGE HAIL, STRONG  
WINDS, AND A RISK OF A TORNADO.  
 
THE SECOND AREA IS LOCATED FURTHER NORTH ALONG THE TROUGH LINE  
BETWEEN DRUMHELLER AND EDMONTON AND EAST TOWARDS THE AB/SK BORDER.  
HERE WE EXPECT THE FLOW TO BE MUCH WEAKER AND THEREFORE STORM MOTION  
TO BE MUCH SLOWER. THIS REGION IS ALSO BEING DESTABILIZED AS THE  
THERMAL RIDGE MOVES EAST. HIGH DEWPOINTS IN THIS REGION CONTRIBUTE TO  
THE ABUNDANT CONVECTIVE ENERGY WITH MLCAPES NEAR 2000 J/KG, HOWEVER  
DEEP LAYER SHEAR IS WEAK WHICH WILL FAVOUR SEVERE PULSE STORM MODE  
BEING DOMINANT. WITH PLENTIFUL MOISTURE, FREEZING LEVELS NEAR 11000  
FEET, AND FAT CAPE PROFILES LARGE HAIL UP TO 6CM IS POSSIBLE. ALSO AS  
MENTIONED BEFORE THE THUNDERSTORMS ARE EXPECTED TO BE SLOW MOVING  
LEADING TO LOCALLY VERY HIGH RAINFALL BETWEEN 75-100MM SHOULD THE  
STORMS FORM A LINE OR LINGER OVER A PARTICULAR LOCATION FOR A  
PROLONGED PERIOD. FINALLY THERE IS A NON-ZERO TORNADO THREAT IN THIS  
REGION AS WELL, HOWEVER RECENT MODELS ARE TRENDING AWAY FROM THIS  
SOLUTION.  
 
EASTERN PRAIRIES...RATHER BUSY CONVECTIVE DAY SETTING UP FOR  
SOUTHWESTERN SASKATCHEWAN BEGINNING THIS AFTERNOON AND SPREADING INTO  
EASTERN SASKATCHEWAN IN THE EVENING AND SOUTHERN MANITOBA OVERNIGHT.  
THE LONGWAVE TROUGH OVER BC WILL MOVE EASTWARD THROUGH THE DAY,  
AIDING IN THE DESTABILIZATION OF THE ENVIRONMENT AS COLD AIR ALOFT  
ADVECTS EASTWARD. THE EASTWARD PROGRESSION OF THE LONGWAVE TROUGH  
WILL ALSO PUSH THE ACCOMPANYING SOUTHWESTERLY JET INTO SOUTHWESTERN  
SASKATCHEWAN THIS AFTERNOON. AT THE SURFACE, A BROAD AREA OF LOW  
PRESSURE IS OVER IDAHO AND MONTANA. AS A VORT MAX ROUNDS THE BASE OF  
THE TROUGH AND TRACKS NORTHEASTWARD, IT WILL AID IN THE  
INTENSIFICATION OF A LOW OVER MONTANA EARLY THIS AFTERNOON.  
BRISK SOUTHEASTERLIES WILL DEVELOP AHEAD OF THE LOW, ADVECTING WARM,  
MOIST AIR INTO SOUTHWESTERN SASKATCHEWAN. A TROUGH IS PROGGED TO  
EXTEND NORTHWARD FROM THE LOW, INTO SOUTHWESTERN SASKATCHEWAN,  
PROVIDING A TRIGGER FOR CONVECTION. THE ENVIRONMENT IS CHARACTERIZED  
BY MLCAPE VALUES OF 1500-2000 J/KG AND 40 KTS OF 0-6 KM SHEAR.  
WITH THE VEERING PROFILES, DISCRETE SUPERCELLS MAY FORM INITIALLY  
POSING A TORNADO POTENTIAL, BEFORE TRANSITIONING TO A SQUALL LINE  
WITH THE LINEAR FORCING OF THE TROUGH. WITH THE SUPPORT OF THE VORT  
MAX, STORMS WILL BE SUPPORTED THROUGHOUT THE NIGHT.  
 
ON WEDNESDAY, THE LOW BECOMES STACKED AND STALLS OUT OVER CENTRAL  
SASKATCHEWAN BRINGING POTENTIAL FOR A RAIN AND WIND EVENT TO REGIONS  
IN CENTRAL AND SOUTHWESTERN SASKATCHEWAN.  
 
EASTERN ARCTIC...RAIN CONTINUES ALONG A DEFORMATION ZONE STRETCHING  
FROM NAUJAAT THROUGH CAPE DORSET AND IQALUIT WITH TOTAL AMOUNTS IN  
THE 15 TO 25 MM RANGE. OTHERWISE, JUST LOTS OF PATCHY FOG IN ONSHORE  
FLOW.  
 
WESTERN ARCTIC...SHOWERS AND A CHANCE OF NON-SEVERE THUNDERSTORMS  
NEAR FORT LIARD.  
 
END/MOODIE/SMITH  
 
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