New Zealand Local Weather Forum

FOCN45 CWWG 311200  
SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM  
PREDICTION CENTRE OF ENVIRONMENT CANADA AT 7:00 AM CDT THURSDAY MAY  
31 2018.  
  
ALERTS IN EFFECT...WIND WARNING FOR CAPE DORSET.  
  
SYNOPTIC OVERVIEW...GENERALLY A SOUTHWESTERLY FLOW ALOFT OVER MUCH OF  
THE PRAIRIES. RELATIVELY STRONG SHORTWAVE TROUGH OVER NORTHWESTERN  
ONTARIO EXTENDING SOUTHWESTWARD INTO THE AMERICAN MIDWEST TRACKING  
EASTWARD. ANOTHER UPPER TROUGH IMPINGING UPON THE WEST COAST OF THE  
UNITED STATES. LARGE UPPER LOW CIRCULATION COVERS THE CENTRAL AND  
EASTERN ARCTIC, WITH THREE CENTRES, THE STRONGEST OF WHICH IS OVER  
FOXE BASIN THIS MORNING.  
  
AT THE SURFACE, 982 MB LOW OVER FOXE BASIN. RIDGE OF HIGH PRESSURE  
EXTENDING FROM THE CWESTERN ARCTIC ARCHIPELAGO SOUTHEASTWARD ACROSS  
SOUTHERN KIVALLIQ. FRONTAL BOUNDARY THAT STADDLES NORTHWEST TO  
SOUTHEAST ACROSS NORTHERN ONTARIO INTO THE DAKOTAS AND MONTANA.  
  
DISCUSSION...  
  
WESTERN PRAIRIES...A BOUT OF PROLONGED SOAKING RAINS WILL OCCUR OVER  
THE SOUTHERN THIRD OF THE PROVINCE DURING THIS FORECAST PERIOD.  
RAIN WILL BEGIN THIS AFTERNOON AND CONTINUE UNTIL FRIDAY EVENING, AS  
THE PROVINCE EXPERIENCES THE COLD SIDE OF THE UPPER JET.  
TOTAL 48-HOUR AMOUNTS SHOULD BE IN THE 20 TO 40 MM RANGE, BUT REGIONS  
SOUTH OF A PINCHER CREEK-OYEN LINE MAY SEE UP TO 60 MM BEFORE RAIN  
ENDS, ESPECIALLY WITH ANY LEFTOVER/REMNANT CONVECTION THAT SPILLS  
INTO THE PROVINCE FROM SASKATCHEWAN AND MONTANA.  
  
EASTERN PRAIRIES...EXTREME SOUTHERN SASKATCHEWAN INTO SOUTHWESTERN  
MANITOBA...  
  
SOUTH OF THE INTERNATIONAL BORDER IN MONTANA AND NORTH DAKOTA,  
EXCELLENT DYNAMICS AND THERMODYNAMICS ARE SETTING UP FOR TODAY WITH  
THE POSSIBILITY OF ALL SEVERE WEATHER TYPES THERE INCLUDING TORNADO  
POTENTIAL. THE PRIMARY FORECAST UNCERTAINTY AT THIS TIME IS THE  
PLACEMENT OF A WARM FRONT, CURRENTLY FORECAST ENTIRELY ON THE  
AMERICAN SIDE IN NORTHEASTERN MT INTO NORTHWESTERN ND - SHOULD THIS  
BEGIN TO LIFT NORTHWARD INTO EXTREME SOUTHEASTERN SK/SOUTHWESTERN MB  
UPGRADED THREAT LEVELS AND HAZARDS WILL BE NEEDED FOR THE REGION.  
BUT SO FAR JUST NORTH ON THE CANADIAN SIDE, COOLER AND DRIER  
NORTHERLIES ARE OCCURRING AT THE SURFACE AND LOOK TO ABRUPTLY  
DIMINISH THE AVAILABLE MOISTURE AND INSTABILITY FOR SEVERE  
THUNDERSTORM SUPPORT. WITH LIMITED INSTABILITY, WEAK TROUGHING NEAR  
THE CYPRESS HILLS AND SOME TERRAIN INTERACTIONS COULD PROVIDE  
SUFFICIENT TRIGGER THERE FOR AFTERNOON THUNDERSTORM DEVELOPMENT.  
FARTHER EAST FOR EXTREME SOUTHEASTERN SASKATCHEWAN AND SOUTHWESTERN  
MANITOBA, SLIGHTLY HIGHER DEWPOINTS REMAIN BUT WITH EITHER FLAT OR  
SLIGHT WARM AIR ADVECTION IN THE LOWER LEVELS; SURFACE-BASED  
DEVELOPMENT HERE IS POSSIBLE BUT STILL SOMEWHAT UNLIKELY DESPITE  
BETTER INSTABILITY. HOWEVER, THE UPPER LEVEL JET STREAM OVER THE  
ENTIRE AREA REMAINS STRONG - 80 KNOTS FROM THE SOUTHWEST - AND WILL  
PERMIT STRONGER STORMS TO CROSS THE BORDER AS THEY DEVELOP DOWN SOUTH  
IN THE AFTERNOON. EVEN WITHOUT CONTINUED INSTABILITY TO FUEL THE  
THUNDERSTORMS, ALREADY DEVELOPED CELLS WILL PRESENT A THREAT OF  
STRONG WIND GUSTS ESPECIALLY AS THEY BEGIN TO COLLAPSE. MARGINALLY  
SEVERE HAIL IS ALSO POSSIBLE. THIS SEVERE WEATHER POTENTIAL WILL  
CONTINUE THROUGH THE NIGHT AS THE FAVOURABLE JET DYNAMICS REMAIN IN  
PLACE AND CONVECTION BECOMES ELEVATED. GENERAL NON-SEVERE  
THUNDERSTORM ACTIVITY WILL ALSO BEGIN TO EXPAND NORTHWARD TOWARDS  
CENTRAL SASKATCHEWAN AND THE REMAINDER OF SOUTHERN MANITOBA THROUGH  
THE NIGHT AS BOTH STORM MOTION INCREASES AND THE UPPER FLOW TURNS  
MORE NORTHWARD.  
  
EASTERN ARCTIC...STRONG WEST/NORTHWESTERLY FLOW IS NOW IN PLACE ON  
THE BACKSIDE OF THE FOXE BASIN LOW OVER WESTRN QIKIQTAALUK AND  
NORTHERN KIVALLIQ. ALTHOUGH BLIZZARD/NEAR BLIZZARD CONDITIONS WERE  
REPORTED OVERNIGHT AT HALL BEACH WEB CAMS AT THE AIRPORT INDICATE  
BETTER VSBYS THAN WHAT THE AUTO STATION IS REPORTING. THERE ARE  
ADVANTAGES TO HAVING 24 HOURS OF DAYLIGHT. WILL HAVE TO WAIT FOR THE  
MANNED OBSERVATION TO SEE IF THIS IS ALSO THE CASE IN NAUJAAT.  
  
WIND WARNING REMAINS IN EFFECT FOR THE CAPE DORSET AREA. 925 MB WINDS  
TOP OUT NEAR 50 KTS NEAR MIDDAY THEN DIMINISH IN THE AFTERNOON.  
  
SNOWFALL AMOUNTS AT BOTH PANGNIRTUNG AND CLYDE RIVER HAVE BEEN NUDGED  
DOWNWARDS AS WE SUSPECT SNOWFALL AMOUNTS IN SCRIBE ARE BEING  
INFLUENCED BY UPSLOPE TERRAIN ENHANCEMENT.  
  
END/RUSSO/CARLSEN