862  
FOCN45 CWWG 171900  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT WEDNESDAY JULY  
17 2019.  
 
ALERTS IN EFFECT...SEVERE THUNDERSTORM WATCHES FOR EASTERN SK/WESTERN  
MB. HEAT WARNING FOR PARTS OF THE SOUTHERN NWT. SPECIAL AIR QUALITY  
STATEMENT FOR THE HIGH LEVEL REGION.  
 
SYNOPTIC OVERVIEW... A BROAD UPPER LOW NEAR HAIDA GWAII HAS A SERIES  
OF EMBEDDED SHORTWAVES FROM THE ALEUTIAN ISLANDS TO CENTRAL BC.  
BROAD TROUGHING OVER THE WESTERN STATES WITH A SHORTWAVE TROUGH  
MOVING ACROSS SOUTHERN MANITOBA. DOWNSTREAM RIDGING OVER  
NORTHWESTERN ONTARIO. FAIRLY SHARP UPPER TROUGH OVER NORTHERN AND  
CENTRAL QUEBEC. UPPER LOW NEAR KUGAARUK, NU. ELONGATED UPPER RIDGE  
FROM NORTHERN MANITOBA THROUGH THE MACKENZIE AND NORTHERN ALASKA.  
 
AT THE SURFACE, 995 MB LOW NEAR HAIDA GWAII WITH TROUGH TO THE  
NORTHEAST. LEE TROUGH DEVELOPING OVER WESTERN ALBERTA. WEAK 1005 MB  
LOW NORTHEAST OF YORKTON NEAR MB/SK BORDER TRACKING EASTWARD. 1019  
MB HIGH OVER NORTHEASTERN ONTARIO. 990 MB LOW OVER NORTHERN  
LABRADOR. FRONTAL WAVE NORTHEAST OF BAKER LAKE WITH TROWAL WRAPPING  
NORTHWARD INTO A 990 MB LOW NEAR TALOYOAK.  
 
DISCUSSION...  
 
ALBERTA... TROUGH FROM NORTHWEST TO SOUTHEAST WILL BE THE MAIN FOCUS  
FOR THUNDERSTORMS THIS AFTERNOON. WITH SIMILAR CONDITIONS TO  
PREVIOUS DAYS (MLCAPE IN THE 500-1000 J/KG RANGE WITH UP TO 20 KT  
DEEP LAYER SHEAR) EXPECTING GENERALLY NON-SEVERE PULSE TO MULTICELL  
STORMS WITH SOME SMALL HAIL AND DOWNPOURS THE MAIN THREATS. FUNNEL  
CLOUDS WILL ALSO BE POSSIBLE ALONG THE TROUGH AXIS. A LOW IS  
FORECAST TO PUSH TO THE EAST TO SIT NEAR JAMES BAY BY FRIDAY MORNING  
WITH A TROUGH HANGING BACK ACROSS NORTH-CENTRAL ALBERTA. RAIN WITH  
TOTAL AMOUNTS NEAR 40 MM BY FRIDAY MORNING IS POSSIBLE OVER CENTRAL  
PARTS OF THE PROVINCE. THUNDERSTORMS WILL MAINLY FORM ALONG THE  
NORTHERN EDGE OF THE RAIN BAND. FLOW WILL BE WEAK BUT INSTABILITY  
MAY BE ENOUGH TO CREATE A FEW NEAR SEVERE HAIL STONES OR LOCALLY  
HEAVY DOWNPOURS ON THURSDAY. A FEW THUNDERSTORMS ARE POSSIBLE OVER  
SOUTHEAST ALBERTA ON THE SOUTHERN EDGE OF THE SYSTEM AS WELL, BUT  
STRONG WESTERLY WINDS OVER SOUTHWEST PARTS OF THE PROVINCE SHOULD  
KEEP THINGS DRY THERE.  
 
SASKATCHEWAN AND MANITOBA...WEAK LOW PRESSURE SYSTEM NEAR MB/SK  
BORDER WILL TRACK EAST-NORTHEAST TO THE NORTHERN INTERLAKE AREA THIS  
EVENING. SOUTHEASTERLY FLOW OF RELATIVELY DEEP MOISTURE AHEAD OF THIS  
SYSTEM WITH SOUTHWESTERLIES ALOFT AND AN APPROACHING SHORTWAVE TROUGH  
WILL FUEL THUNDERSTORM DEVELOPMENT THIS AFTERNOON AND EVENING. MLCAPE  
WILL BE A BIT BETTER TODAY THAN YESTERDAY, WITH OVER 1000 J/KG  
EXPECTED IN PARTS OF SOUTHWESTERN MANITOBA ALONG WITH 30 TO 40 KNOTS  
OF DEEP SHEAR. NEAR THE TRACK OF THE LOW, FUNNEL CLOUDS ARE POSSIBLE  
BUT GIVEN THE INSTABILITY SOME BRIEF LANDSPOUTS CANNOT BE RULED OUT.  
IN ADDITION, AS YOU GO SOUTH TOWARDS BRANDON AND KILLARNEY WITH  
BETTER SHEAR AND INSTABILITY, A SUPERCELL TORNADO IS POSSIBLE IN THE  
LATE AFTERNOON OR EARLY EVENING HOURS ALONG WITH LARGE HAIL. SEVERE  
ELEMENTS ARE LIKELY UNTIL THE STORMS REACH THE WHITESHELL BY WHICH  
TIME THEY SHOULD BEGIN WEAKENING.  
 
WESTERN ARCTIC...SURFACE TROUGH/LOW AND MACKENZIE MOUNTAINS WILL BE  
THE MAIN TRIGGER FOR THUNDERSTORMS ACROSS MAINLAND NWT ONCE AGAIN  
TODAY. DEW POINT TEMPERATURES IN THE LOW TEENS COULD BUMP CAPE VALUES  
AROUND 1500 J/KG, WIND SHEAR VALUES SHOULD SUPPORT SOME MULTICELL  
STORMS WITH HEAVY RAIN AND HAIL THE MAIN THREATS. WITH A SURFACE  
HIGH MOVING IN THURSDAY, THUNDERSTORMS ARE EXPECTED TO REMAIN TO THE  
WEST OVER THE TERRAIN.  
 
PLACES ALONG THE UPPER MACKENZIE VALLEY WILL CONTINUE TO EXPERIENCE  
WARM CONDITIONS THIS WEEK WITH HIGHS NEAR 30 DEGREES EXPECTED. THIS  
PROLONGED WARM SPELL IS EXPECTED TO LAST INTO NEXT WEEK. THE HEAT  
WARNING MAY NEED TO BE EXPANDED TO THE SOUTHEAST, INTO NORTHEAST  
ALBERTA AND MAYBE NORTHERN SASKATCHEWAN, FOR SATURDAY.  
 
EASTERN ARCTIC...SOUTHEASTWARD TRACKING FRONTAL WAVE WILL GIVE  
SHOWERS TO NORTHERN KIVALLIQ TODAY WITH AMOUNTS OVER 10 MM IN SOME  
AREAS. ISOLATED THUNDERSTORMS ARE ALSO POSSIBLE DURING THE AFTERNOON  
AND EVENING OVER SOUTHERN KIVALLIQ ALONG THE COLD FRONT.  
 
END/FULTON/ROMBOUGH  
 
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