989  
FOCN45 CWWG 211900  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT THURSDAY JUNE  
21 2018.  
 
ALERTS IN EFFECT...HEAT WARNINGS FOR PORTIONS OF THE NWT, NORTHERN  
AND CENTRAL PRAIRIES.  
 
SYNOPTIC OVERVIEW...HIGH OVER LOW BLOCK OVER WESTERN CANADA HAS NOW  
BROKEN DOWN AS NEW UPPER LOW HAS DEVELOPED OVER IOWA AND UPPER LOW  
OVER MONTANA SHEARED APART. UPPER RIDGE REMAINS IN PLACE OVER THE  
PRAIRIES WITH A NEW UPPER LOW MAKING IT'S WAY TOWARDS SOUTHERN  
ALBERTA FROM OREGON. THE JET STREAM LIFTS NORTHWARDS THROUGH THE  
EASTERN PACIFIC, ROUNDS THE APEX OF THE UPPER RIDGE THROUGH  
YT/WESTERN NWT THEN HEADS SOUTHEASTWARDS THROUGH THE REST OF THE  
NWT, SOUTHERN NU, SOUTHWESTERN HUDSON BAY INTO NORTHERN ONTARIO. IT  
THEN ROUNDS THE BASE OF A LARGE UPPER TROUGH EXTENDING SOUTHWEST  
FROM AN UPPER LOW COMPLEX OVER THE LABRADOR SEA. FURTHER NORTH, A  
POTENT SHORTWAVE WHICH CROSSED THE BOOTHIA PENINSULA OVERNIGHT IS  
NOW MOVING INTO FOXE BASIN.  
 
AT THE SURFACE, THE PRAIRIES HAVE A VERY SLACK FLOW. A 1021 MB HIGH  
OVER MT HAS RIDGING THAT EXTENDS ACROSS THE SOUTHERN PRAIRIES. A  
1008 MB LOW JUST NORTH OF YIV WITH COLD FRONT WESTWARD FROM LOW  
THROUGH CENTRAL PRAIRIES. IN THE NORTH, THE POTENT SHORTWAVE HAS AN  
ASSOCIATED 992 MB LOW OVER THE NORTHERN FOXE BASIN WITH A SHARP  
OCCLUDED FRONT EXTENDING SOUTH THROUGH HUDSON BAY. 1020 MB  
ARCTIC HIGH CENTRED OVER WESTERN VICTORIA ISLAND.  
 
DISCUSSION...  
 
EASTERN PRAIRIES...HEAT WARNINGS CONTINUE ACROSS THE NORTHERN AND  
CENTRAL PRAIRIES WITH TEMPERATURES AGAIN CLIMBING TO LOW 30'S  
TODAY. WITH COLD FRONT SLUMPING A LITTLE SOUTH TODAY, SHOULD BE  
ABLE TO END HEAT WARNINGS FOR THOMPSON AND LYNN LAKE THIS  
AFTERNOON AS TEMERATURES SHOULD COOL SOMEWHAT TONIGHT WITH  
NORTHERLY WINDS BEHIND FRONT. SOUTHERN MANITOBA CONTINUES TO BE VERY  
CLOSE TO HEAT WARNING CRITERIA, BUT DAYTIME HIGHS ARE FORECAST TO  
REMAIN JUST SHORT OF WARNING CRITERIA AT 31C.  
 
SOME MOISTURE POOLING ALONG COLD FRONT TODAY WITH TDS IN MID  
TEENS. CONVERGENCE ASSOCIATED WITH FRONT COMBINED WITH THE  
STRONG THERMODYNAMICS WILL LEAD TO A FEW THUNDERSTORMS DEVELOPING  
ALONG THE FRONT THIS AFTERNOON AND EVENING. SHEAR IS FAIRLY  
MINIMAL SO NOT EXPECTING MUCH MORE THAN ISOLATED PULSE TYPE NON  
SEVERE CELLS. SLIGHT CHANCE OF AN ISOLATED SHOWER OR THUNDERSTORM  
OVER PARTS OF SOUTHWESTERN SASKATCHEWAN AS WELL. MODEST MID LEVEL  
LAPSE RATES ASSOCIATED WITH UPPER TROUGH UNDERCUTTING THE PRAIRIE  
UPPER RIDGE AS WELL AS A WEAK SURFACE LOW LOCATED NORTH OF  
LETHBRIDGE THIS MORNING WILL LIKELY LEAD TO A FEW NON SEVERE  
THUNDERSTORMS THIS AFTERNOON AND EVENING. COULD BE SOME LOCAL  
ENHANCEMENT WITH OROGRAPHIC LIFT OVER THE CYPRESS HILLS.  
 
WESTERN PRAIRIES...OVER ALBERTA, SCATTERED THUNDERSTORMS ALONG  
WESTERN AND SOUTHERN PORTIONS OF THE PROVINCE ARE EXPECTED TODAY.  
SOUTHEASTERLY FLOW OVER SOUTHERN ALBERTA WILL HELP PUMP MOISTURE  
INTO THE REGION RESULTING IN MLCAPES UPWARDS OF 1000 J/KG. WITH WEAK  
WINDS UNDER THE UPPER RIDGE, VERTICAL SHEARS ARE MINIMAL. AS SUCH,  
THERE SHOULD BE NO SUPERCELL STORMS. THERE MAY BE SOME STATIONARY  
SEVERE PULSE STORMS WITH HEAVY RAIN BEING THE MAIN THREAT. THIS MAY  
LEAD TO THUNDERSTORM WATCHES BEING ISSUED LATER THIS AFTERNOON FOR  
PARTS OF SOUTHERN ALBERTA. LASTLY, GIVEN THE MODERATE MLCAPE VALUES  
AND THE PRESENCE OF SOME VORTICITY IN THE MID AND UPPER LEVELS THERE  
IS A VERY SLIGHT CHANCE OF A LANDSPOUT TORNADO THIS AFTERNOON NEAR A  
DEVELOPING SURFACE LOW IN SOUTHEASTERN ALBERTA. CONFIDENCE IN THIS  
IS LOW AT THIS TIME.  
 
OTHERWISE, HEAT WARNINGS REMAIN IN PLACE FOR NORTHERN AND CENTRAL  
ALBERTA TODAY. WITH COOLER TEMPERATURES EXPECTED TOMORROW SOME OF  
THE HEAT WARNINGS MAY BE ABLE TO BE ENDED OVERNIGHT TONIGHT. THAT  
BEING SAID, ABOVE SEASONAL TEMPERATURES WILL STILL EXIST RIGHT  
THROUGH THE WEEKEND.  
 
WESTERN AND CENTRAL ARCTIC... HEAT WARNINGS CONTINUE OVER THE  
SOUTHERN NT TODAY. MIGHT SEE SOME SLIGHT COOLING TOMORROW BUT THE  
WARM TEMPERATURES LOOK TO CONTINUE THROUGH THE WEEKEND. THUNDERSTORM  
WISE, EXPECT TO SEE DEVELOPMENT ALONG THE MACKENZIE MOUNTAINS TODAY.  
SIMILAR TO THE SITUATION IN AB AND BC, THERE MAY BE SOME SLOW MOVING  
PULSE STORMS WITH HEAVY RAIN AND STRONG GUSTS IN THE FORT LIARD  
REGION THIS AFTERNOON.  
 
EASTERN ARCTIC...STRONG NORTHWEST WINDS OF 50G70 KM/H FOR  
PORTIONS OF THE NORTHERN KIVALLIQ TODAY AND TONIGHT WITH STRONG  
NORTHWEST GRADIENT ON BACKSIDE OF FOXE BASIN LOW. SOME  
SHOWERS IN CYCLONIC FLOW ON BACK SIDE OF LOW MAY SWITCH OVER  
TO WET SNOW AS COLD ADVECTION SWEEPS IN BEHIND LOW FOR  
NORTHERN KIVALLIQ AND 925 MB TEMPS DROP DOWN TO NEAR 0C.  
 
END/MCDONALD/ALBRECHT  
 
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