FOCN45 CWWG 271200
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 7:00 AM CDT THURSDAY JUNE
27 2024.

ALERTS IN EFFECT...HEAT WARNING FOR PARTS OF THE MACKENZIE DELTA.
RAINFALL WARNING FOR PARTS OF WESTERN ALBERTA AND PARTS OF CENTRAL
SASKATCHEWAN.

SYNOPTIC OVERVIEW...ALOFT THIS MORNING, AN UPPER TROUGH LIES OVER THE
BC COAST WITH A LARGE UPPER LOW OVER VANCOUVER ISLAND AND THE LOWER
MAINLAND. AN UPPER RIDGE IS BREAKING DOWN OVER THE AB/SK BORDER WITH
AN UPPER HIGH OVER ALASKA AND THE YUKON. AN UPPER LOW SPINS OVER
SOUTHERN BAFFIN ISLAND WITH NUMEROUS SHORTWAVES ROTATING ABOUT IT.
ONE SUCH UPPER TROUGH LIES ACROSS THE KIVALLIQ/MB BORDER.

AT THE SURFACE, A RIDGE LIES OVER SOUTHEASTERN SASKATCHEWAN AND
SOUTHERN MANITOBA. A 1005 MB DEVELOPING LOW IS OVER SOUTHERN AB WITH
A WARM FRONT ARCING SOUTHEASTWARDS INTO MT AND A COLD FRONT EXTENDING
SOUTHWESTWARDS THROUGH ID INTO OR. A WEAK TROUGH LIES ACROSS THE
EASTERN ARCTIC STRETCHING FROM SOUTHERN BAFFIN ISLAND TO THE
KIVALLIQ. WEAK AREAS OF LOW PRESSURE LIE WITHIN THIS TROUGH NEAR
SOUTHAMPTON ISLAND AND IQALUIT. FINALLY, A 1021 MB HIGH LIES NEAR
BANKS ISLAND WITH A RIDGE SOUTHWARD THROUGH THE NWT.

DISCUSSION...

ALBERTA...AN UPPER LOW OVER BC WILL GRADUALLY MOVE EASTWARD TODAY.
AHEAD OF IT, WIDESPREAD SHOWERS AND EMBEDDED THUNDERSTORMS ARE
EXPECTED TO DEVELOP IN CENTRAL ALBERTA BY THIS EVENING. THE HEAVIEST
RAIN IS FORECAST ALONG AN AXIS ROUGHLY FROM GRANDE CACHE TO ROCKY
MOUNTAIN HOUSE OVER THE NEXT 36-48 HOURS. EVENT TOTALS IN THE RANGE
OF 50-80 MM ARE EXPECTED BEFORE RAIN TAPERS OFF ON FRIDAY.
ADDITIONALLY, LOCALLY HIGHER RAINFALL TOTALS ARE POSSIBLE IN THIS
AREA, AS ANY THUNDERSTORMS THAT DEVELOP THIS AFTERNOON AND TONIGHT
WILL BE QUITE SLOW-MOVING. ELSEWHERE DOWN THE FOOTHILLS AND EASTWARD
THROUGH THE EDMONTON AREA, 30 TO 50 MM IS EXPECTED BY THE WEEKEND.

THERE IS ALSO THUNDERSTORM POTENTIAL THURSDAY ASSOCIATED WITH A
SURFACE LOW AND FRONTAL WAVE DEVELOPING IN SOUTHERN ALBERTA. MLCAPE
VALUES UPWARDS OF 1200 J/KG ARE EXPECTED BY LATE AFTERNOON, ALONG
WITH EFFECTIVE SHEAR VALUES OF 20-30 KT. THE AREA TO WATCH WILL
LIKELY BE NEAR THE SURFACE LOW, WHERE LOCALLY ENHANCED EFFECTIVE
SHEAR VALUES IN EXCESS OF 30 KT ARE POSSIBLE, ALONG WITH VEERING WIND
PROFILES. CONSIDERABLE UNCERTAINTY STILL EXISTS AS TO THE TIMING AND
PLACEMENT OF THIS DEVELOPING SYSTEM AND THE RESULTING SEVERE WEATHER
THREAT. HOWEVER, AT THIS STAGE ALL MODES OF SEVERE WEATHER LOOK TO BE
ON THE TABLE. THE ULTIMATE OUTCOME OF THIS SCENARIO WILL HINGE ON
AREAS NEAR THE SURFACE LOW CLEARING OUT AND ALLOWING FOR ROBUST
DAYTIME HEATING IN THE ZONE OF HIGHEST VORTICITY.

MANITOBA/SASKATCHEWAN...ATTENTION QUICKLY TURNS TO THE LARGE UPPER
TROUGH WITH EMBEDDED LOW MOVING INLAND OVER SOUTHERN BC WHICH WILL
BRING A SWIFT RETURN TO UNSETTLED CONDITIONS ACROSS THE PRAIRIES.
LEE CYCLOGENESIS IS WELL UNDERWAY THIS MORNING, WITH A PAIR OF LOWS
HAVING BEGUN TO DEVELOP; ONE OVER SOUTHERN ALBERTA AND ANOTHER OVER
EASTERN MONTANA. THE DEVELOPING LOWS WILL INDUCE A RAPID NORTHWARD
SURGE OF GULF MOISTURE WITH ITS APEX NEAR THE MONTANA-NORTH
DAKOTA-SASKATCHEWAN BORDER.

HERE, MLCAPE VALUES WILL RISE TO THE 1000 J/KG MARK WITH BULK WIND
SHEAR IN THE NEIGHBORHOOD OF 50 KNOTS. ADDITIONALLY, THE FOCUS OF A
WARM SECTOR TROUGH WOULD ELONGATE HODOGRAPH CURVES, INCREASING THE
EFFECTIVE HELICITY FOR ANY THUNDERSTORMS THAT MANAGE TO GET THEIR ACT
TOGETHER IN PROXIMITY. THIS COULD SUPPORT SUPERCELLULAR THUNDERSTORMS
BRIEFLY - BUT THERE IS SIGNIFICANT UNCERTAINTY ALSO. MAIN UPPER LEVEL
SUPPORT IS STILL WELL WEST; WITH UPPER RIDGING STILL OVER SOUTHERN
SASKATCHEWAN, RESULTING PROFILES LOOK NICE DYNAMICALLY BUT WITH
SKINNY CAPE VALUES RESULTING IN UPDRAFTS THAT WILL BE SUBJECT TO DRY
AIR ENTRAINMENT FROM THE RELATIVELY DRY AIR MASS UNDER THE RIDGE.
ANOTHER ISSUE WILL BE HOW FAR NORTH THE WARM FRONT REACHES WITH
PLENTY OF SHOWERS AND RAIN COOLED OUTFLOW PUSHING SOUTH OUT OF
CENTRAL SASKATCHEWAN. AND FINALLY, PERHAPS MOST CRITICALLY, IS THE
LIKELIHOOD OF LARGER SCALE DEVELOPMENT IMMEDIATELY SOUTH IN MONTANA -
WHICH WILL QUICKLY ROB MORE NORTHERLY AREAS OF INCOMING MOISTURE AND
INSTABILITY AND PULL THE CONVECTIVE FOCUS ENTIRELY INTO THE UNITED
STATES. MOST LIKELY, A LARGE UPSCALE LINE WILL DEVELOP IN EASTERN
MONTANA LATE DAY AND PROGRESS EASTWARD INTO THE NIGHT.ALL THIS TO
SAY, IT REMAINS TO BE SEEN WHETHER EXTREME SOUTHERN SASKATCHEWAN HAS
ANY SURFACE BASED THUNDERSTORM THREAT OR IF SEVERE WEATHER REMAINS
STATESIDE. THERE WILL BE A BRIEF WINDOW IN THE LATE AFTERNOON WHERE
PARAMETERS MAY ALIGN AND ALL MODES OF SEVERE WEATHER ARE POSSIBLE
OVER EXTREME SOUTHERN SASKATCHEWAN.

REGARDLESS OF THE HIGHLY CONDITIONAL CONVECTIVE SEVERE WEATHER
THREAT, LARGER SCALE HEAVY RAINS ARE LIKELY TO THE NORTH OF THE LOW
TRACK OVER SOUTHERN SASKATCHEWAN AND SOUTHERN MANITOBA WITH TOTAL QPF
POTENTIALLY EXCEEDING 50 MM FOR SOME AREAS. THE DEVELOPMENT OF THIS
SYSTEM IS QUITE COMPLEX IN NATURE DUE TO THE BIMODAL AND CONDITIONAL
PARAMETERS AND MAKES FOR QUITE A DIFFICULT FORECAST. HOWEVER THAT MAY
BE, CONFIDENCE IS INCREASING IN A CORRIDOR OF INCREASED RAINFALL
ACCUMULATION BETWEEN KINDERSLEY AND THE YELLOWHEAD AND EXTENDS
EASTWARD TOWARDS WATROUS. LARGE-SCALE ASCENT DUE TO THE DEVELOPING
LOW PRESSURE AND FALLING HEIGHTS, IN ADDITION TO FORECAST PWAT VALUES
IN EXCESS OF 1.25", INDICATE RAINFALL WARNING VALUES IN THESE AREAS.
THE CONDITIONAL MOISTURE SOURCE IS LESS OF A CONCERN FARTHER NORTH AS
THERE IS EXISTING MOISTURE IN PLACE, REQUIRING LESS MOISTURE
TRANSPORT AS AREAS FARTHER SOUTH. GENERAL AMOUNTS IN THIS AREA WILL
LIKELY BE ON THE ORDER OF 40 TO 60 MM, HOWEVER, ANY AREAS THAT
RECEIVE A CONVECTIVE SHOWER COULD SEE IN EXCESS OF 80 MM OF RAIN BY
STORMS END. A RAINFALL WARNING WILL BE ISSUED FOR PARTS OF CENTRAL SK
THIS MORNING AND MAY BE EXTENDED AS NEED BE.

AS THE LOW RAMPS UP AND MOVES EAST, PRESSURE GRADIENT PACKING WILL
RESULT IN STRONG SYNOPTIC WINDS OVER PARTS OF SOUTHERN SASKATCHEWAN
OVERNIGHT AND THROUGH THE DAY ON FRIDAY. WINDS COULD POSSIBLY GUST IN
EXCESS OF 70 KM/H.

NWT...A HEAT WARNING REMAINS IN PLACE FOR PORTIONS OF THE MACKENZIE
DELTA AND IS EXPECTED TO CONTINUE INTO THIS WEEKEND. IT MAY NEED TO
BE EXPANDED TO COVER PAULATUK FOR LATER IN THE WEEK.

SMOKE FROM THE FIRE NEAR FORT GOOD HOPE IS LIKELY TO AFFECT THE
COMMUNITY OFF AND ON FOR THE NEAR TERM.

NUNAVUT...SEASONAL WEATHER EXPECTED WITH AN ABUNDANCE OF LOW CLOUD,
SHOWERS, DRIZZLE AND FOG IN ONSHORE FLOW.

END/SPC-YWG/VAN LOCHEM