FOCN45 CWWG 191900

SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM

PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT TUESDAY AUGUST

19 2025.



ALERTS IN EFFECT...HEAT WARNING FOR PORTIONS OF SOUTHERN SASKATCHEWAN

AND SOUTHEASTERN ALBERTA. SPECIAL AIR QUALITY STATEMENT FOR

YELLOWKNIFE AND FORT PROVIDENCE REGIONS IN NT.



SYNOPTIC OVERVIEW...



ALOFT, THE LOW OFF THE PACIFIC BEGINS TO DIG INTO THE CENTRAL BC

COAST VC HAIDA GWAII. SOUTHWESTERLY BC JET VEERS TO WESTERLY OVER THE

PRAIRIES ATOP A BROAD RIDGE CENTRED NEAR THE FOUR CORNER STATES.

JET REMAINS ZONAL RIGHT ON THROUGH TO THE MARITIMES. UP NORTH, AN

EXTREMELY FLAT HEIGHT PATTERN EXISTS OVER THE WESTERN ARCTIC.

MEANWHILE, OVER IN THE EAST, THE LOW JUST EAST OF PRINCE CHARLES

ISLAND CONTINUES TO FILL IN SITU.



AT THE SURFACE, A REMARKABLY FLAT PRESSURE PATTERN CONTINUES OVER THE

PRAIRIES. WEAK TROUGHING OVER CENTRAL SK IS COUPLED WITH AN EQUALLY

WEAK HIGH CENTRE OVER CENTRAL MB. UP NORTH, A RELATIVELY DEEPER LOW

CENTRE LIES JUST EAST OF GREAT SLAVE LAKE. LIKEWISE, A SIMILARILY

STRONG (~1011 MB) LOW CONTINUES TO SPIN OVER SOUTHERN BAFFIN ISLAND.



DISCUSSION...



AB/NORTHERN SK...TRIGGERS ARE LIMITED TODAY WITH THE FLAT PATTERN AND

WILL LIKELY BE TERRAIN LIKE THE SWAN HILLS OR NORTHERN FOOTHILLS NEAR

AND NORTH OF THE JET. BEST POTENTIAL FOR SVR STORMS LOOKS TO BE

BETWEEN DRAYTON VALLEY, SLAVE LAKE, PEACE RIVER AND ROCKY MOUNTAIN

HOUSE WHERE CAPES ARE AROUND 1000 J/KG BUT LIMITED CONFIDENCE.



HEAT WARNING CRITERIA IS EXPECTED TO BE MET FROM TODAY AND WEDNESDAY

FOR THE MEDICINE HAT AND CYPRESS HILLS REGIONS.



SRN SK...CONDITIONAL INSTABILITY REIGNS SUPREME FOR YET ANOTHER DAY.

WITH AN UPPER RIDGE BUILDING IN, MUCH OF EXTREME SOUTHERN SK LOOKS TO

BE CAPPED FROM ANY CONVECTION TUESDAY. KEY WILL BE WATCHING FOR THOSE

'RIDGE (NOT ROUGH) RIDERS' ON THE NORTHERN FLANK OF THE UPPER RIDGE

TO DEVELOP. OF EQUAL IMPORTANCE WILL BE THE SPEED IN WHICH THE FOG/

STRATUS OVER THE EASTERN PRAIRIES CLEARS. YET ANOTHER FACTOR COULD BE

THE RE-INSERTION OF A BIT OF SMOKE ACROSS THE SOUTH FROM USA.

PROGS INDICATE SOME SMOKE COULD ENTER, FURTHER COMPLICATING

CONVECTIVE INITIATION NEAR THE INTERNATIONAL BORDER. HOWEVER,

ASSUMUING THESE FACTORS WILL HAVE MINIMAL EFFECT, THUNDERSTORMS

ROLLING THROUGH THE SK NORTHERN GRAINBELT AND EASTERN REGIONS ABOUT A

WEAK CIRCULATION/TROUGH LINE ARE POSSIBLE. AMPLE MOIST LOLVL

SOUTHERLY/SOUTHEASTERLY FLOW AHEAD OF THE TROUGH LINE IN EASTERN SK

WILL HELP BUOY MLCAPE VALUES UP TOWARDS 1500 J/KG BY 21Z TUESDAY.

BULK SHEAR IS ALSO QUITE ROBUST, 40 KTS OR SO THROUGH EAST-CENTRAL

REGIONS BY MID-AFTERNOON. MLCAPE IS JUST AS GREAT ALONG AND SOUTH OF

THE TRANSCANADA IN SK BUT SHEAR VALUES DO DROP OFF SOMEWHAT.

THIS, COUPLED WITH THE AFOREMENTIONED CAPPING ISSUES MIGHT PRECLUDE

THIS REGION FROM SEEING ANY SEVERE WX TUESDAY. THUS, WITH AMPLE CAPE

AND SHEAR, LARGE HAIL AND STRONG, GUSTY WINDS WILL BE THE MAIN

THREATS FROM ANY STORMS THAT DEVELOP ABOUT THE TROUGH THROUGH THE

GRAINBELT AND POINTS EASTWARD TUESDAY AFTERNOON/EVENING.



STARTING TODAY, PORTIONS OF SOUTHERN SK WILL HIT HEAT WARNING

CRITERIA AS THE AFOREMENTIONED UPPER RIDGE INTENSIFIES OVER THE

REGION. HEAT WARNINGS ISSUED WILL REMAIN IN EFFECT THROUGH EOD

WEDNESDAY WITH COOLER WX PROGGED TO MOVE IN WITH A COLD LOW THAT IS

SLATED TO MOVE ACROSS THE WESTERN PRAIRIES THURSDAY.



MB...FOG DEVELOPED ONCE AGAIN OVER SOUTHWESTERN SECTIONS OF THE

PROVINCE OVERNIGHT. IT IS LIKELY FOG WILL DEVELOP OVER SOUTHERN MB

AGAIN TONIGHT, BUT FURTHER EAST THAN THE PREVIOUS NIGHT.



A FEW NON-SEVERE STORMS WILL DEVELOP ALONG A SEPARATE TROUGH LINE

ACROSS THE NORTH TODAY.



SLIGHT RISK FOR SEVERE STORMS IN INFILTRATE SWAN RIVER AND NORTHERN

INTERLAKE REGIONS OVERNIGHT TONIGHT. STRENGTHENING SOUTHERLY H85 JET

WILL REACH PEAK 40 KTS INTO THE EARLY MORNING HOURS OF WEDNESDAY.

RESULT WILL PROVIDE AMPLE ISENTROPIC LIFT OVER THE WEST-EAST ORIENTED

WARM FRONT VC YQR-YDN-WSZ COME 12Z WEDNESDAY. THIS WILL BE THE

PRECURSOR TO WHAT COULD POTENTIALLY BE A BUSY COUPLE OF SEVERE WX

DAYS ACROSS THE PRAIRIES WEDNESDAY AND THURSDAY.



NT/NU...SMOKE HAS INVADED A FEW COMMUNITIES IN THE NORTHWEST

TERRITORIES, PARTICULARLY YELLOWKNIFE, WHERE A LIGHT WESTERLY FLOW

SEEMS TO BE RESONSIBLE FOR A SHORT AND STEEP DROP IN AIR QUALITY IN

THE REGION THIS MORNING. AIR QUALITY HAS IMPROVED SOMEWHAT BUT A

SPECIAL AIR QUALITY STATEMENT WILL BE IN EFFECT FOR THE REGION UNTIL

AT LEAST THE END OF THIS AFTERNOON WHEN WINDS MAY SHIFT TO BE MORE

SOUTHERLY.



END/SPC-WPG/BATE