510  
FOCN45 CWWG 181200  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 7:00 AM CDT SATURDAY  
AUGUST 18 2018.  
 
ALERTS IN EFFECT...SPECIAL AIR QUALITY STATEMENT IN EFFECT FOR ALL  
AREAS OF THE PRAIRIE PROVINCES.  
 
SYNOPTIC OVERVIEW...ALOFT, PRAIRIES IN A MODERATE ZONAL FLOW WITH  
DIGGING UPPER TROUGH OVER NORTHERN ALBERTA WHICH WILL CONTINUE TO  
DIG SOUTHEASTWARDS INTO SASKATCHEWAN TODAY. MAIN UPPER LOW IN THE  
ARCTIC IS ANCHORED NEAR BANKS ISLAND AND HAS AN UPPER TROUGH  
EXTENDING SOUTHEASTWARDS TO BAFFIN ISLAND.  
 
AT THE SURFACE, 993 MB SURFACE LOW OVER DAVIS STRAIT GRADUALLY  
FILLING TODAY. 984 MB LOW OVER MELVILLE ISLAND WITH WARM FRONT  
EXTENDING TO THE SOUTHEAST AND COLD FRONT STRETCHING TO THE  
SOUTHWEST ACROSS THE NWT. 1004 MB LOW WEST OF ARVIAT WITH COLD FRONT  
DRAPING ACROSS NORTHERN MANITOBA AND SASKATCHEWAN AND THROUGH  
CENTRAL ALBERTA, SURFACE TROUGH ASSOCIATED WITH LOW EXTENDS TO THE  
SOUTH.  
 
DISCUSSION.  
 
SMOKE WITH POOR AIR QUALITY CONTINUES TO BE THE MAIN STORY FOR  
ALBERTA TODAY. A PLUME OF VERY THICK SMOKE HAS PLUNGED SOUTHWARD  
ACROSS ALBERTA OVERNIGHT AND WILL CONTINUE TO DRIVE SOUTHWARD  
TOWARDS MEDICINE HAT AND LETHBRIDGE THIS MORNING BRINGING THE  
MAJORITY OF THE PROVINCE UP TO THE VERY HIGH RISK CATEGORY. LATER  
TODAY, THE UPPER FLOW WILL BECOME MORE NORTHWESTERLY WHICH WILL HELP  
TO CLEAR OUT NORTHERN REGIONS OF THE PROVINCE AND HOPEFULLY BRING  
SOME RELIEF TO AREAS NORTH OF RED DEER BY THIS EVENING. HOWEVER,  
THIS FLOW IS UNLIKELY TO CLEAR THE SMOKE OUT OF AREAS AROUND CALGARY  
AND TO THEIR SOUTH ANYTIME SOON.  
 
WITH THE SMOKE SUPPRESSING THE DAYTIME TEMPERATURES, THUNDERSTORMS  
HAVE BEEN STRUGGLING TO DEVELOP. THUNDERSTORMS TODAY ARE FORECAST TO  
DEVELOP ALONG THE EXTREME SOUTHERN FOOTHILLS THIS AFTERNOON, AS A  
WEAK COLD FRONT PUSHES SOUTHWARD AND GETS HUNG UP ALONG THE TERRAIN.  
MLCAPE VALUES OF AROUND 500 J/KG WITH MODERATE SHEAR OF 20-35KTS  
WILL LIKELY ONLY PRODUCE WEAK NON-SEVERE THUNDERSTORMS. IN ADDITION,  
FOREST FIRE SMOKE COULD GREATLY REDUCE THE POTENTIAL FOR ANY STORMS  
BY REDUCING DAYTIME HEATING AND THUS REDUCING THE AMOUNT OF ENERGY  
AVAILABLE FOR THESE STORMS TO DEVELOP.  
 
OVER NORTHERN SASKATCHEWAN, A SHORTWAVE TROUGH, CURRENTLY JUST TO  
THE NORTH OF URANIUM CITY, WILL TRACK INTO NORTHERN SASKATCHEWAN  
THIS MORNING. A FEW ISOLATED NON-SEVERE THUNDERSTORMS ARE ALSO  
POSSIBLE WITH THIS SYSTEM THROUGHOUT THE DAY TODAY.  
 
EASTERN PRAIRIES...  
COULD BE AN INTERESTING CONVECTIVE DAY IN SOUTHERN MANITOBA. LATEST  
RUN OF THE FIREWORK MODEL INDICATING SMOKE TO BE THINNING OVER  
SOUTHERN MANITOBA TODAY. THIS IS SUPPORTED BY SATELLITE IMAGERY FROM  
YESTERDAY EVENING WHICH INDICATED AN AREA OF LESS DENSE SMOKE OVER  
SOUTHERN SASKATCHEWAN THAT WAS DRIFTING SLOWLY EASTWARD. WITH THE  
THINNING SMOKE, TEMPERATURES COULD REACH LOW 30S IN SOUTHERN  
MANITOBA WITH DEWPOINTS POTENTIALLY IN THE MID-TEENS, LEADING TO  
MLCAPE VALUES OF 1750 J/KG. WITH 25 KTS OF 0-6 KM BULK SHEAR AND  
A SURFACE TROUGH MOVING THROUGH SOUTHERN MANITOBA IN THE AFTERNOON,  
THERE IS A POTENTIAL FOR SEVERE THUNDERSTORM DEVELOPMENT. HOWEVER,  
RDPS PROG SOUNDINGS ARE INDICATING A STRONG CAP IN PLACE TODAY WITH  
15 DEGREE TEMPERATURES NEAR 750 MB, WHICH COULD INHIBIT ANY SEVERE  
THUNDERSTORM DEVELOPMENT.  
 
LATE YESTERDAY EVENING THUNDERSTORMS DEVELOPED ALONG THE COLD FRONT  
SOUTH OF EDMONTON AND CONTINUED LATE INTO THE EVENING HOURS. THIS  
COLD FRONT IS PROGGED TO TRACK SOUTHEASTWARD ACROSS THE PRAIRIES  
TODAY AND PASS THROUGH SOUTHEASTERN SASKATCHEWAN AND SOUTHWESTERN  
MANITOBA LATE THIS EVENING GIVING A SECONDARY AREA OF POSSIBLE  
THUNDERSTORM DEVELOPMENT, ALBEIT, NON-SEVERE IN THIS AREA.  
 
AS THE TROUGH AND COLD FRONT TRAVERSE ACROSS THE PRAIRIES, A  
NORTHWESTERLY FLOW WILL BE LEFT IN THEIR WAKE. THIS NORTHWESTERLY  
FLOW WILL AID IN CLEARING OUT THE SMOKE. BUT, SMOKE WILL LIKELY POOL  
ALONG THE COLD FRONT, AS HAS BEEN SEEN IN PREVIOUS DAYS. THAT IS TO  
SAY, EXPECT CONDITIONS TO GET WORSE BEFORE THEY GET BETTER. TODAY,  
NORTH-CENTRAL MANITOBA AND SOUTHERN SASKATCHEWAN COULD SEE REDUCED  
VISIBILITIES AND ELEVATED AQHI VALUES WHICH WILL THEN SPREAD INTO  
SOUTHERN MANITOBA OVERNIGHT BEFORE CLEARING SUNDAY AFTERNOON. THE  
CURRENT GDPS RUN IS INDICATING A NORTHWESTERLY FLOW FOR THE NEXT  
SEVERAL DAYS, WHICH WILL GIVE A WELCOME REPRIEVE FROM THE SMOKE.  
 
EASTERN ARCTIC...COLD FRONT TRACKING THROUGH KIVALLIQ TODAY WILL  
BRING SHOWERS TO REGIONS THERE AS WELL AS NORTHERN BAFFIN ISLAND.  
STRONG NORTHWESTERLY WINDS BEHIND FRONT WILL GIVE NORTHWEST WINDS OF  
50 GUSTING TO 70 KM/H TO COMMUNITIES IN SOUTHERN KIVALLIQ OVERNIGHT.  
 
WESTERN ARCTIC...A LOW TRACKING SLOWLY EASTWARD TOWARDS RESOLUTE  
WILL BRING STRONG SOUTHEASTERLY WINDS AND SOME LIGHT SNOW TO THE  
AREA OVERNIGHT TONIGHT. WINDS ARE EXPECTED TO REMAIN BELOW WARNING  
CRITERIA WITH WIND GUSTS TO 70 KM/H. THESE WINDS ARE UNLIKELY TO  
REACH WARNING CRITERIA BUT WILL HAVE TO BE MONITORED CLOSELY.  
 
END/MOODIE/GREENHOUGH  
 
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