741
FOCN45 CWWG 281900
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT WEDNESDAY JUNE
28 2017.
ALERTS IN EFFECT...NONE.
SYNOPTIC OVERVIEW...DOMINANT UPPER FEATURE TODAY IS A REX BLOCK
FORMED BY A RIDGE CENTERED OVER THE WESTERN KITIKMEOT, AND A COLD LOW
OVER CENTRAL AB. THIS COLD LOW WILL MEANDER THROUGH THE PRAIRIES OVER
THE REMAINDER OF THE WEEK PUSHING INTO MB ON FRIDAY. OTHERWISE
RIDGING OVER B.C., A SHORTWAVE TROF PUSHING THROUGH THE PAULATUK
AREA, AND A FILLING UPPER LOW OFF THE COAST OF LABRADOR.
AT THE SURFACE, A TRIPLET OF LOWS IN EAST-CENTRAL AB, THE MANITOBA
INTERLAKE, AND WESTERN MINNESOTA CONNECTED BY A SHARP TROUGH OF LOW
PRESSURE. ANOTHER LOW VICINITY PAULATUK SLOWLY MOVING EAST. A FINAL
LOW WAS ANALYZED WITH THE 12Z MAP VICINITY SK/AB/MT BORDER
INTERSECTION. THE DOMINANT BAROCLINICITY LIES WITH THE MINNESOTA LOW
GRADUALLY TRACKING EASTWARD TOWARDS THE GREAT LAKES. OTHERWISE, A
1021 MB HIGH NEAR KUGAARUK BUILDS SOUTHWARDS, AND WEAK TROUGHING
CONTINUES OVER EASTERN BAFFIN BAY.
DISCUSSION...
ALBERTA...UPPER LOW AND ASSOCIATED SHOWERS SLUMPING SOUTHWARDS.
GOOD VORTICITY OVER EASTERN ALBERTA TODAY WITH THE UPPER LOW AND
SURFACE TROUGH MAY BRING FUNNEL CLOUDS. THUNDERSTORMS FORECAST
THROUGH SOUTHERN ALBERTA WITH THE FOCUS NEAR A SURFACE TROUGH RUNNING
FROM ROUGHLY CLARESHOLM TO OYEN. POCKETS OF MLCAPE NEAR 1000 J/KG AND
SHEARS NEAR 30 KNOTS EARLY IN THE AFTERNOON. AS THE DAY PROGRESSES
SHEARS DROP OFF TO 20. SLIGHT CHANCE OF SEVERE GUSTS BUT MOSTLY
NON-SEVERE STORMS. IN NORTHEASTERN SASKATCHEWAN SOME AREAS MAY
APPROACH RAINFALL CRITERIA. AN AREA OF THUNDERSTORMS GAVE A QUICK 30
MM TO FLIN FLON OVERNIGHT AND SIMILAR COULD OCCUR THROUGH PELICAN
NARROWS TOWARDS LA LOCHE.
MANITOBA...SHOWERS CONTINUE ALONG THE TROWAL (WHICH HAS NOW MOVED
EAST OF WINNIPEG) AS OF EARLY THIS AFTERNOON WITH 5-15 MM OF RAIN
FORECAST BY THURSDAY MORNING AND LOCALLY 25+ MM POSSIBLE IN
THUNDERSTORMS. THIS SYSTEM IS VERY SLOW MOVING AND ISOLATED
THUNDERSTORMS MAY REDEVELOP THIS AFTERNOON, BUT THE PRECIPITATION
SHOULD MOVE ENTIRELY OUT OF SOUTHERN MANITOBA TONIGHT.
SASKATCHEWAN...SURFACE BASED CONVECTION IS FORECAST TO DEVELOP IN SK
UNDER THE UPPER LOW. WITH CAPES GENERALLY IN THE 400 TO 1000 J/KG
RANGE, AND 0 TO 6 KM BULK SHEAR VALUES OF 20 TO 30 KNOTS, SEVERE
THUNDERSTORMS ARE UNLIKELY. THAT SAID, FUNNEL CLOUDS ARE POSSIBLE IF
NOT LIKELY UNDER THE UPPER LOW AS IT DRIFTS INTO WEST CENTRAL
SASKATCHEWAN THIS AFTERNOON. ALSO OF CONCERN IS A SMALL DISTURBANCE
MOST READILY IDENTIFIED ON SATELLITE IMAGERY ALONG THE SK/MT BORDER.
AREA OF MID-LEVEL INSTABILITY AS EVIDENCED BY MORNING ACC (FROM
SATELLITE/WEBCAMS) FROM ROUGHLY CYYN-CYMJ-CYQR-WAQ. ALTHOUGH SURFACE
DEWPOINTS ARE LOW, WEAK CYCLOGENISIS LIKELY FROM SK/AB/MT LOW SEEMS
TO ADVECT LOW-LEVEL MOISTURE INTO THIS AREA THIS AFTERNOON. SUBTLE
SHORT WAVE IN MT DRIFTING NE COMBINED WITH FALLING HEIGHTS FROM
APPROACH OF AB UPPER LOW TRIGGERING A FEW THUNDERSTORMS IN THIS AREA
AT THE MOMENT, AND THESE STORMS HAVE THE POTENTIAL TO INCREASE IN
SEVERITY AS THE DAY WEARS ON AND SHEAR VALUES INCREASE. CONDITIONAL
RISK OF SEVERE THUNDERSTORMS WILL EXIST IN THIS AREA THIS AFTERNOON,
DEPENDENT UPON HOW THE SITUATION EVOLVES.
MB/SK THURSDAY...A SIMILAR SITUATION IS EXPECTED ON THURSDAY WITH THE
UPPER LOW TRIGGERING SURFACE BASED CONVECTION OVER SOUTHEAST
SASKATCHEWAN AND SOUTHERN MANITOBA. FUNNEL CLOUDS WILL ONCE AGAIN BE
A POSSIBILITY THURSDAY OVER EXTREME SOUTHEASTERN SK AND SOUTHWESTERN
MB. CAPE VALUES ARE EXPECTED TO APPROACH 1500 J/KG IN THAT AREA,
HOWEVER LOW LEVEL SHEAR IS EXPECTED TO BE A LIMITING FACTOR FOR
SEVERE CONVECTION, HOWEVER BRIEF LANDSPOUT TORNADOES MAY BE A
POSSIBILITY. SHOWERS WILL CONTINUE ON THURSDAY ALONG THE TROWAL
EXTENDING THROUGH CENTRAL MB INTO WEST CENTRAL SK.
CANADA DAY OUTLOOK...IT LOOKS LIKE MAINLY SUNNY SKIES IN STORE FOR
SASKATCHEWAN AND WESTERN MANITOBA AS THE UPPER RIDGE BUILDS INTO THE
WESTERN PRAIRIES. THERE IS A FAIR AMOUNT OF DISAGREEMENT BETWEEN THE
MODELS WITH REGARDS TO THE POSITION OF THE UPPER TROUGH ON SATURDAY,
HOWEVER A SHOWERY COOL DAY OVER EASTERN MANITOBA REMAINS A
POSSIBILITY. LATE DAY SHOWERS OR THUNDERSTORMS APPEAR LIKELY FOR
ALBERTA. STAY TUNED...
WESTERN ARCTIC...RISK OF THUNDERSTORMS IN THE CENTRAL MACKENZIE.
EASTERN ARCTIC...NIL SIG WX.
END/FULTON/MACKAY
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