609  
FOCN45 CWWG 221900  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT TUESDAY AUGUST  
22 2017.  
 
ALERTS IN EFFECT...NONE.  
 
SYNOPTIC OVERVIEW...UPPER RIDGE OVER WESTERN CANADA WITH NORTH TO  
SOUTH SURFACE RIDGE OVER EASTERN SK. WEAK VORT MAX EMBEDDED IN THE  
THE RIDGE NEAR LAKE ATHABASCA. NEARLY VERTICAL LOW JUST SOUTHWEST OF  
JAMES BAY WITH SURFACE TROUGH WESTWARD FROM LOW. STACKED LOW OVER  
BAFFIN BAY, WITH TROF EXTENDING SOUTHWESTWARD INTO NORTHERN HUDSON  
BAY. STACKED LOW MAKING LANDFALL IN THE ALASKA PANHANDLE.  
 
DISCUSSION...  
 
PRAIRIES...VORTMAX OVER LAKE ATHABASCA WILL TRIGGER THUNDERSTORMS  
OVER NORTHERN SK. LOOKS LIKE A PRETTY GOOD SETUP FOR FUNNEL CLOUDS IN  
THE REGION AS SURFACE WINDS REMAIN LIGHT AND SUFFICIENT LOW LEVEL  
VORTICITY WITH THE VORT MAX. A FEW NON-SEVERE THUNDERSTORMS ARE  
POSSIBLE THIS AFTERNOON ALONG THE ALBERTA FOOTHILLS WITH  
DIFFERENTIAL HEATING. COLD AIR ALOFT OVER SOUTHERN MB WITH 500 MB  
TEMPS BELOW -20C AND WITH CONVERGENCE ALONG TROUGH WILL SEE  
CONSIDERABLE CU/TCU OVER MUCH OF MB TODAY AND MAY SEE SOME LOW  
TOPPED CB'S OVER SOUTHEAST MB WHERE SLIGHTLY BETTER THERMODYNAMICS  
EXIST AS WELL AS ENHANCED CONVERGENCE WITH LAKES CONVERGENE.  
CONVECTION SHOULD DISSIPATE RATHER QUICKLY THIS EVENING WITH LOSS OF  
DAYTIME HEATING.  
 
WEDNESDAY SHOULD SEE A RETURN OF MORE SUBSTANTIAL THUNDERSTORMS IN  
ALBERTA FROM CALGARY TO GRANDE PRAIRIE. DEPENDING ON MOISTURE  
AVAILABILITY, MLCAPE OF 1000 TO 2000 J/KG AND DEEP-LAYER SHEAR OF 40  
KNOTS WILL LEAD TO A FEW SUPERCELLS CAPABLE OF LARGE HAIL AND  
DAMAGING WINDS.  
 
ARCTIC...NORTHERLY FLOW OVER JONES SOUND GIVES POTENTIAL FOR GUSTY  
WINDS POSSIBLY UP TO 80 KM/H LATER THIS AFTERNOON AND TONIGHT IN  
GRISE FIORD ALTHOUGH INVERSION MAY BE A BIT HIGH. OTHERWISE, SOME  
COASTAL FOG ALONG ARCTIC COASTLINE AND BAFFIN ISLAND EAST COAST  
ESPECIALLY TONIGHT AND WEDNESDAY MORNING.  
 
END/MCDONALD/NISKA-ARO  
 
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