PASPC Thunderstorm Outlook Day 1

The Thunderstorm Outlook has ended for the season. Please continue to http://www.weather.gc.ca/ for any of your weather needs.

FOCN45 CWWG 211900

SIGNIFICANT WEATHER DISCUSSION ISSUED BY THE PRAIRIE AND ARCTIC STORM PREDICTION CENTRE OF ENVIRONMENT CANADA AT 2:00 PM CDT SATURDAY OCTOBER 21 2017.

ALERTS IN EFFECT...SNOWFALL WARNING FOR BAKER LAKE AND NAUJAAT, SPECIAL WEATHER STATEMENT FOR CHESTERFIELD AND RANKIN INLETS, ARVIAT AND CORAL HARBOUR. WINTER STORM WATCH FOR HALL BEACH AND IGLOOLIK. WIND WARNINGS FOR THE SOUTHERN ALBERTA FOOTHILLS TO LETHBRIDGE.

SYNOPTIC OVERVIEW...ALOFT AS OF EARLY THIS AFTERNOON, A SIGNIFICANT NORTH-SOUTH TROF EXTENDS THROUGH THE CENTRAL PRAIRIES. RIDGING THROUGH ONTARIO AND HUDSON BAY, TROUGHING OVER BAFFIN BAY. AT THE SURFACE, A 987 MB SURFACE LOW JUST NORTH OF THE MANITOBA LAKES WITH A WARM FRONT RUNNING EASTWARD AND A COLD FRONT DIVING DUE SOUTHWARD, HAVING PASSED THROUGH WINNIPEG LATE THIS MORNING. BROAD TROUGHING EXTENDS NORTHWESTWARD FROM THE LOW THROUGH GREAT SLAVE LAKE AND ALONG THE MACKENZIE. HIGH PRESSURE OVER NORTHERN QUEBEC AND BAFFIN ISLAND AND TROUGHING ALONG THE GREENLAND COAST.

DISCUSSION...

WESTERN PRAIRIES...FOG THAT WAS IN NORTHERN SECTIONS THIS MORNING IS LIKELY TO RETURN TONIGHT. A WEAK LOW WILL DEVELOP OVER WESTERN ALBERTA TONIGHT TRACKING TO THE SOUTHEAST AND BRINGING A SLIGHT CHANCE OF FREEZING RAIN TO THE ELBOW REGIONS SUNDAY MORNING. OVER SOUTHERN ALBERTA A STRONG WESTERLY FLOW SETS UP SUNDAY. WARNING-LEVEL WINDS, SOME REACHING POSSIBLY 120 KM/H, ARE EXPECTED ALONG THE SOUTHERN FOOTHILLS AND AS FAR EAST AS LETHBRIDGE. THE POTENTIAL FOR EXPANSION TOWARDS CYPRESS HILLS STILL EXISTS, BUT UNCERTAINTY IS HIGH. DIFFICULT FORECAST FOR THE MOUNTAINS TONIGHT AS THE WESTERLY FLOW DEVELOPS AND MODELS BUILD SIGNIFICANT PRECIPITATION ALONG THE ROCKIES. SOME OF THAT LOOKS TO MAKE ITS WAY INTO THE ICEFIELDS PARKWAY AND POSSIBLY TO LAKE LOUISE BUT BANFF SHOULDN'T SEE SIGNIFICANT AMOUNTS. THE SNOWFALL WARNING IS FOR HIGHER ELEVATIONS ALONG THE ROADWAYS.

EASTERN PRAIRIES...COLD FRONT CONTINUES TO WORK ITS WAY THROUGH SOUTHERN MANITOBA. NOT A SHARPLY DEFINED FRONT, BUT WIND SHIFT ALONG WITH A DROP IN DEWPOINT SUGGESTS FRONTAL PASSAGE OCCURRED BETWEEN 16-17 UTC IN WINNIPEG. SIGNIFICANT COOLING DOESN'T OCCUR UNTIL SOME DISTANCE BEHIND THIS FEATURE, SO AREAS FROM THE RED RIVER VALLEY EASTWARD WILL CONTINUE TO ENJOY A REMARKABLE SATURDAY AFTERNOON, WHEREAS WEST OF THIS TEMPERATURES WILL BEGIN TO DROP SHARPLY AS COLDER AIR MOVES IN. IT'S POSSIBLE FOR A FEW THUNDERSTORMS ALONG THE FRONT JUST BEFORE IT PUSHES INTO ONTARIO THIS AFTERNOON. ADDITIONALLY, NOCTURNAL CONVECTION IS PROBABLE IN THE WARM SECTOR OVER NORTHEASTERN MANITOBA TONIGHT. OTHERWISE PATCHY SHOWERS WILL WRAP AROUND THE LOW TODAY OVER THE EASTERN PRAIRIES. TONIGHT AS THE LOW GETS ITSELF ORGANIZED SHOWERS WILL CHANGE TO CONTINUOUS RAIN AND THEN SNOW OVER NORTHERN MANITOBA AS COLD AIR WRAPS BEHIND THE LOW. SNOWFALL ACCUMULATIONS SHOULD REMAIN UNDER 5 CM.

WIND WARNINGS ARE ONCE AGAIN A POSSIBILITY FOR SOUTHERN SK ON SUNDAY AS A WEAK LOW WILL RAPIDLY TRACK THROUGH THE PRAIRIES. BEST FORECAST AT THE MOMENT IS FOR WESTERLY WINDS OF 60G80 KM/H, JUST SHY OF WARNING CRITERIA.

EASTERN ARCTIC...GUIDANCE SHOWING LOTS OF PRECIPITATION RIDING THE WARM CONVEYER BELT INTO THE KIVALLIQ REGION, BUT WHETHER OR NOT THIS IS ACTUALLY OCCURRING IS IN SOME DOUBT. CYBK STARTED OFF ON TRACK WITH HEAVY SNOW THIS MORNING, BUT THIS HAS NOW TAPERED OFF WITH A GENEROUS ESTIMATE OF 4 CM HAVING FALLEN, AND MOST OF THAT HAVING BLOWN AWAY. CALL TO THE OBSERVER AT 18Z ESTIMATED 1-2 CM SNOW DEPTH IN PLACES WITH SLUSHY WET SNOW AND LOTS OF PATCHES OF GROUND SHOWING. 18Z SYNO OB OF 16 MM SEEMS IN ERROR - SOMETHING ABOUT NOT CHECKING THE GAUGE LAST NIGHT DUE TO A WOLVERINE SIGHTING. THERE IS A SECOND SHOT OF SNOW THAT SHOULD COME IN TONIGHT WITH ANOTHER 5 CM OR SO ON TAP. INITIAL ESTIMATES WERE FOR 20-25 CM BY SUNDAY EVENING, BUT THIS IS NOW IN SERIOUS DOUBT. THIS HAS REPERCUSSIONS SUNDAY EVENING AS THE SYSTEM MOVES OVER HUDSON BAY AND INTENSIFIES, BRINGING NORTHWEST WINDS UP TO 80 GUSTING 110 KM/H OVER MUCH OF THE KIVALLIQ. COASTAL AREAS WHICH ARE SEEING MAINLY RAIN SHOULD REMAIN BLIZZARD-FREE, AND EVEN BAKER LAKE WILL LIKELY NOT SEE A BLIZZARD UNLESS THERE IS SIGNIFICANTLY MORE SNOW IN THE INTERVENING TIME. REGARDLESS, VERY STRONG NORTHWEST WINDS WILL AFFECT MUCH OF THE KIVALLIQ REGION SUNDAY NIGHT.

HEAVY SNOW ALSO EXPECTED THROUGH NAUJAAT THEN INTO HALL BEACH AND IGLOOLIK, ALTHOUGH CONFIDENCE IS NOW SOMEWHAT LOWER GIVEN THE LACK OF SNOW AT CYBK.

RAIN AND STRONG SOUTHERLIES AS THE SYSTEM APPROACHES WILL SPREAD INTO SOUTHERN BAFFIN ISLAND SUNDAY NIGHT. FREEZING RAIN IS POSSIBLE, BUT GIVEN WINDS WILL BE ONSHORE FOR MOST COMMUNITIES AND THE ICE PACK HAS NOT YET DEVELOPED IT SHOULD REMAIN LIMITED IN DURATION.

WESTERN ARCTIC...FOG IN THE MACKENZIE IS LIKELY AGAIN TOMORROW MORNING. MAIN CHALLENGE WILL BE THE KIVALLIQ LOW TRACK. KUGAARUK IS NEAR THE SNOW EDGE AND COULD SEE 30 CM OR SO IF THE TRACK DEVIATES SLIGHTLY WESTWARDS. THEY WILL GET AN INITIAL IMPULSE TONIGHT WHICH HAS BEEN PRETTY CONSISTENTLY FORECAST BETWEEN 5 AND 10 CM. LATE SUNDAY EASTERLY WINDS WILL DEVELOP IN GRISE FIORD AND RESOLUTE WITH POTENTIAL FOR WARNING CRITERIA WINDS MONDAY.

END/FULTON/CARLSEN