664
FOCN45 CWWG 181900
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT WEDNESDAY JUNE
18 2025.
ALERTS IN EFFECT...SEVERE THUNDERSTORM WATCHES/WARNINGS FOR MUCH OF
ALBERTA, PORTIONS OF SOUTHEAST SASKATCHEWAN AND SOUTHWEST MANITOBA.
SYNOPTIC OVERVIEW...ALOFT TODAY, A HIGH OVER LOW BLOCK CONTINUES TO
SIT IN THE WEST WITH AN UPPER LOW OFF THE COAST OF BRITISH COLUMBIA
AND AN UPPER HIGH OVER NORTHERN ALASKA. EAST OF THIS, AN UPPER LOW
SITS OVER THE CANADIAN ARCTIC ARCHIPELAGO, A DOWNSTREAM UPPER RIDGE
EXTENDS FROM EASTERN NORTHWEST TERRITORIES AND WESTERN MAINLAND
NUNAVUT NORTHEAST TO NORTHERN BAFFIN ISLAND. AN UPPER LOW SITS NEAR
SOUTHAMPTON ISLAND IN HUDSON BAY WITH A LONG-WAVE TROUGH THAT ARCS
OVER SOUTHERN BAFFIN ISLAND AND DAVIS STRAIT TO A WEAK UPPER LOW NEAR
SOUTHERN GREENLAND AND ANOTHER LONG-WAVE TROUGH THAT SWEEPS SOUTHWEST
INTO THE NORTHERN PRAIRIES.
AT THE SURFACE, A 1005 MB LOW SITS WEST OF HAIDA GWAII WITH TROUGHING
INTO SOUTHERN YUKON. TO THE NORTH, A 1013 MB LOW SITS OVER ALASKA, A
1012 MB HIGH SITS OVER THE SOUTHERN ARCTIC OCEAN WITH RIDGING SOUTH
INTO YUKON THAT CURLS SOUTHEAST ACROSS SOUTHERN NORTHWEST TERRITORIES
TO A 1017 MB HIGH THAT SITS ALONG THE NORTHWEST TERRITORIES/
SASKATCHEWAN BORDER. A RIDGE OF HIGH PRESSURE EXTENDS FROM THIS HIGH
SOUTHEAST ACROSS NORTHERN MANITOBA INTO NW ONTARIO. EAST OF THE IS, A
990 MB LOW SITS ON THE COAST OF UNGAVA PENINSULA WITH AN OCCLUDED
FRONTAL WAVE TO ITS EAST. THIS FRONTAL WAVE HAS APEX OVER EASTERN
UNGAVA PENINSULA WITH A WARM FRONT EAST AND A COLD FRONT THAT SWEEPS
SOUTHWEST ACROSS JAMES BAY INTO CENTRAL MANITOBA, THEN CURLS
NORTHWEST ACROSS THE PRAIRIES AND INTO THE NORTHWEST TERRITORIES.
A WARM SECTOR TROUGH SITS SOUTH OF THIS, EXTENDING PROMINENTLY FROM
JAMES BAY WEST-SOUTHWEST ACROSS SOUTHERN MANITOBA INTO SOUTHERN
SASKATCHEWAN. SOUTHEAST OF THE UNGAVA PENINSULA LOW IS ANOTHER POTENT
987 MB LOW NEAR THE QUEBEC/LABRADOR BORDER WITH A COLD FRONT
SOUTH-SOUTHWEST AND A WARM FRONT SOUTHEAST.
DISCUSSION...
AB...THUNDERSTORMS ARE DEVELOPING OVER MUCH OF ALBERTA. IN THE SOUTH,
A DEVELOPING LOW WILL FOCUS THUNDERSTORM ACTIVITY THIS AFTERNOON.
THE MAIN FEATURE WILL BE DEVELOPING LOW AND ASSOCIATED TROUGH ALIGNED
ALONG THE FOOTHILLS. IN ADDITION, A DRY LINE WILL DEVELOP ALONG THE
SOUTHERN FOOTHILLS AND BULGE EASTWARD SOUTH OF CALGARY, ROUGHLY
TOWARD MEDICINE HAT BY MID-AFTERNOON. MLCAPE VALUES EXCEEDING 1500 J/
KG AND 0-6 KM SHEAR OF AROUND 40 KT WILL LEAD TO A FAVOURABLE
ENVIRONMENT FOR SUPERCELLS. LARGE HAIL WILL BE THE MAIN THREAT WITH
THESE STORMS, BUT WITH THE DRY LINE, A TORNADO IS POSSIBLE.
INITIATION WILL BE IN THE EARLY AFTERNOON ALONG THE FOOTHILLS, NORTH
OF CALGARY, WITH SLIGHTLY LOWER VALUES OF MLCAPE AND 0-6 KM SHEAR.
SUPERCELLS ARE ALSO EXPECTED TO FORM HERE AND TRACK EASTWARD WITH
HAIL BEING THE MAIN THREAT. THERE IS ALSO A CHANCE THAT ONE OF THESE
CELLS PRODUCES A TORNADO. THUNDERSTORMS WILL ALSO DEVELOP ALONG A
DEFORMATION ZONE STRETCHING FROM THE PEACE COUNTRY TO LLOYDMINSTER.
THESE WILL BE PULSE STORMS, BUT A SURFACE TROUGH NORTHEAST OF
EDMONTON TO THE PEACE WILL MEAN THE POSSIBILITY OF FUNNEL CLOUDS IN
THESE AREAS. THERE IS A CHANCE THAT A FUNNEL CLOUD BRIEFLY TOUCHES
THE GROUND AS A LANDSPOUT TORNADO.
SK/MB...FOCUS FOR CONVECTION TODAY SLUMPS INTO SOUTHERN SASKATCHEWAN
AND MANITOBA AS THE COLD FRONT AND WARM-SECTOR TROUGH CONTINUE TO
TRACK SOUTHWARD. MOISTURE CONVERGENCE WILL HELP DEW POINTS CLIMB INTO
THE LOW TO MID-TEENS ACROSS THE REGION AS THE WARM-SECTOR TROUGH AND
COLD FRONT PROVIDE FOCUS FOR CONVECTIVE INITIATION. H500 WIND SPEEDS
WILL SIT IN THE 25 TO 35 KNOT RANGE AND THERE MAY BE A SLIGHT
ENHANCEMENT OF THE SYNOPTIC LIFT THROUGH JET COUPLING IF THE LEFT
EXIT OF THE SOUTHERN JET ALONG THE BORDER CAN PHASE WITH THE RIGHT
ENTRANCE OF A JET DIPPING THROUGH MANITOBA. LASTLY, A WEAK LOW
PRESSURE CENTRE WILL LIKELY DEVELOP IN SOUTHERN SASKATCHEWAN TODAY
AND TRACK EAST ALONG THE INTERNATIONAL BORDER THROUGH THE DAY,
PROVIDING ANOTHER CONVECTIVE FOCUS. MLCAPE VALUES WILL CLIMB UP TO
AROUND 1,000 J/KG WITH AROUND 25 TO 30 KNOTS OF UNIDIRECTIONAL BULK
SHEAR.
SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP AROUND ALL THESE
FEATURES TODAY WITH A RISK OF ISOLATED SEVERE THUNDERSTORMS. PRIMARY
THREATS FROM TODAY WOULD BE MARGINALLY SEVERE HAIL AND A RISK OF
DAMAGING WIND GUSTS. PWAT VALUES WILL CLIMB INTO THE 25 TO 30 MM
RANGE, BUT STORM MOTIONS OF 15 TO 25 KNOTS WILL LIMIT POTENTIAL
RAINFALL ACCUMULATIONS.
A FEW SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE INTO THE OVERNIGHT
PERIOD WITH A MARGINAL RISK OF AN ISOLATED SEVERE THUNDERSTORM
OVERNIGHT IN SASKATCHEWAN AS THE COLD FRONT IN THE REGION REBOUNDS
NORTH AHEAD OF THE NEXT LOW TRACKING OUT OF ALBERTA.
A HIGHER END SEVERE THREAT APPEARS TO BE TAKING SHAPE OVER EASTERN
SASKATCHEWAN INTO SOUTHWESTERN MANITOBA ON THURSDAY. A SURFACE LOW
WILL EJECT EAST OUT OF ALBERTA WEDENSDAY NIGHT INTO THURSDAY MORNING
AND IS PROGGED TO LIE SOMEWHERE BETWEEN REGINA AND SASKATOON BY MID
DAY. MODEST MOISTURE ADVECTION/POOLING AHEAD OF THE LOW WILL OCCUR
OVER EASTERN SASKATCHEWAN YIELDING MID TO UPPER TEENS DEW POINTS.
A 50 TO 60 KNOT H5 JET STREAK WILL LIE OVER EASTERN SASKATCHEWAN BY
00Z. THE ENVIRONMENT WILL BE CHARACTERIZED BY 1500 TO 2000 MLCAPE AND
50 TO 60 KNOTS OF EFFECTIVE BWD. PRIMARY THREATS WILL BE HAIL LARGER
THAN GOLF BALLS AND WIND GUSTS IN EXCESS OF 100 KM/H. A TORNADO OR
TWO ALSO APPEARS LIKELY, ESPECIALLY IN THE CORRIDOR FROM YORKTON, SK
TO VIRDEN, MB NEAR THE SURFACE WARM FRONT WHERE ENHANCED LOW LEVEL
WIND FIELDS WILL BE MORE CONDUCIVE TO TORNADOGENESIS. MOST CAM
GUIDANCE IS IN AGREEMENT ON A FEW ISOLATED STORMS INITIATING BY LATE
AFTERNOON. A HIGH (ORANGE/3 OUT OF 4) RISK WILL BE INCLUDED ON THE
DAY 2 THUNDERSTORM OUTLOOK TO ACCOUNT FOR THIS HIGHER END SEVERE
THREAT. LOW STORM COVERAGE, MODEST/MEAGRE LOW LEVEL WINDS AND A H7
WARM NOSE PRECLUDES A HIGHER RISK CATEGORY AT PRESENT TIME.
REGARDING AIR QUALITY, SAT PIX LATE TUESDAY REVEALED RENEWED SMOKE
PRODUCTION FROM THE NOPIMING PROVINCIAL PARK WILDFIRE IN SOUTHEAST
MANITOBA. AS THE COLD FRONT SLUMPS SOUTH THROUGH THE REGION, PLUMES
OF SMOKE FROM THE WILDFIRES NEAR ISLAND LAKE ON THE ONTARIO SIDE OF
THE BORDER AND PLUMES FROM THE NOPOMING WILDFIRES WILL SPREAD
SOUTH-SOUTHWEST INTO THE PROVINCE, THEN SHIFT BACK NORTH AS A RETURN
FLOW DEVELOPS OVER THE PROVINCE. DEGRADED AIR QUALITY WILL BE
POSSIBLE EAST OF LAKE WINNIPEG, SOUTHEAST MANITOBA, THE RED RIVER
VALLEY, AND THE INTERLAKE REGIONS. THE RISK FOR DEGRADED AIR QUALITY
WILL BEGIN LATER WEDNESDAY AND PERSIST INTO THURSDAY. EASTERLY WINDS
ACROSS CENTRAL MANITOBA ON THURSDAY WILL LIKELY BRING DEGRADED AIR
QUALITY TO ISLAND LAKE AND NORWAY HOUSE AREAS.
NWT...A RIDGE OVER THE NWT WILL KEEP THINGS QUIET TODAY. NEARBY
WILDFIRES WILL CONTINUE TO PERDIODICALLY BRING SMOKE INTO FORT LIARD.
NU...LITTLE CHANGE EXPECTED FOR THE PRECIPITATION MOVING INTO BAFFIN
ISLAND. SNOW HAS MOVED INTO THE REGION OVERNIGHT AS EXPECTED AND WILL
TRANSITION TO RAIN EARLY MORNING FOR KIMMIRUT AND LATER IN THE DAY
FOR KINNGAIT. IQALUIT IS A MORE CHALLENGING FORECAST AS MULTIPLE
GUIDANCE SOURCES SUGGEST LOW-LEVEL TEMPERATURES WILL STAY COOLER THAN
FORECAST; THIS INCREASES THE CHANCE THAT PRECIPITATION WILL STAY AS
SNOW THROUGH THE DAY TODAY. EXPECT PREDOMINANT PRECIPITATION TYPE TO
SHIFT TO (WET) SNOW WITH A CHANCE OF RAIN MIXED IN AT TIMES.
OTHERWISE, THE FORECAST REMAINS SIMILAR. PRECIPITATION WILL TAPER OFF
LATER TODAY INTO THURSDAY. GUSTY SOUTHEASTERLY WINDS ARE ALSO
FORECAST WITH THIS SYSTEM OVER SOUTHERN BAFFIN ISLAND. GUSTS TO
80 KM/H WERE ADDED TO THE FORECASTS FOR IQALUIT AND KIMMIRUT.
NEXT PRECIPITATION CHANCE FOR THE KIVALLIQ WILL DEVELOP WEDNESDAY
NIGHT INTO THURSDAY AS A LOW PRESSURE SYSTEM DROPS SOUTH OUT OF THE
HIGH ARCTIC. RAIN SHOWERS WILL SPREAD INTO THE MAINLAND KIVALLIQ
REGION INTO THURSDAY, THEN PRECIPITATION WILL WEAKEN BUT SPREAD OUT
BROADLY ACROSS THE REGION AS THIS LOW AND THE BAFFIN ISLAND LOW MERGE
AND A NEW VORTEX FORMS OVER THE EASTERN ARCTIC.
END/STAMMERS/GRIFFITH
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