FXCN01 CWTO

Issued: Monday, May 23, 2011.

1. TODAY AND TONIGHT..POTENTIALLY A VERY ACTIVE AFTERNOON AND EVENING OVER SRN/ERN ONTARIO AS FAR AS THUNDERSTORMS ARE CONCERNED. STRONG SWLY FLOW OF WARM MOIST AND INCREASINGLY UNSTABLE AIR HAS BECOME ESTABLISHED ACROSS THE DISTRICT IN THE WAKE OF LAST NIGHTS HIT AND MISS WARM FRONTAL THUNDERSTORMS. ANOTHER N-S BAND OF CLOUD AND A FEW EMBEDDED SHOWERS/ISOL TSTMS WILL CROSS SRN ONTARIO THIS MORNING. HOWEVER THERE APPEARS TO BE MORE BREAKS AND LESS COVERAGE IN THE SHOWERS THAN SUGGESTED BY GUIDANCE..SO THIS WILL HELP TO INCREASE DAYTIME HEATING A BIT AND DESTABILIZATION ESPECIALLY SWRN ONTARIO. MLCAPES OF SEVERAL HUNDRED TO NEAR 1000 J/KG, EFFECTIVE SHEARS OF 30-35 KNOTS, AND HELP FROM APPROACHING SHORT WAVE TROUGH AND POSSIBLE LEFT EXIT RGN OF UPPER LEVEL JET MAX FCST TO BE OVER SRN LOWER MICHIGAN BY EVENING ARE ALL SUPPORTIVE AND TSTMS THAT DO DEVELOP SHOULD BE FAST MOVING AND MAY PRODUCE DAMAGING WIND GUSTS OF 100 KM/H GIVEN FAST FLOW ALOFT. SREF AND GEM GUIDANCE ALSO HAVE BEEN FAIRLY CONSISTENTLY SUGGESTING STORM RELATIVE HELICITIES OF 150 M2/S2 OR MORE SWRN ONTARIO THIS AFTERNOON, WITH FORECAST HODOGRAPHS LOOKING QUITE FAVOURABLE INDEED. HENCE THERE SHOULD BE AT LEAST A FEW ROTATING SUPERCELLS WITH MESOCYCLONE SIGNATURES SHOWING UP ON DOPPLER RADAR THIS AFTERNOON. WE HAVE ADDED A SLIGHT RISK OF A TORNADO AS A RESULT SWRN ONTARIO WHERE SOME ADDED EXTRA LOW LEVEL CONVERGENCE FROM POSSIBLE LAKE BREEZES (HIGHLY DEFORMED IN STRONG SWLY FLOW) MAY HELP. MOST OF THE DAMAGING WINDS THOUGH SHOULD BE FROM BOW ECHO TYPE SEGMENTS AS THE SHEAR OUTSIDE OF THE INLAND AREAS OF SWRN ONTARIO MAY BE A BIT MORE UNIDIRECTIONAL. SEVERE THREAT CONTINUES INTO THIS EVENING BEFORE A COMBINATION OF NOCTURNAL COOLING AND COLD FRONT MOVING THROUGH BRING THE THREAT OF THUNDERSTORMS TO AN END BY TOMORROW MORNING.

2. OVER NERN ONTARIO A FEW EMBEDDED NON-SVR TSTMS ARE LIKELY TODAY AND INTO THIS EVENING BEFORE THE COLD FRONT MOVES SE OF THE AREA. MAIN FEATURES HERE WILL BE HEAVY DOWNPOURS FREQUENT LIGHTNING AND GUSTY WINDS. WINTER TRIES TO MAKE A TEMPORARY COMEBACK FAR NRN ONTARIO IN THE WAKE OF AN ARCTIC COLD FRONT WITH ENOUGH FLURRIES TO PERHAPS WHITEN THE GROUND A BIT POSSIBLE IN PLACES LIKE BIG TROUT LAKE AND PEAWANUCK. THE COLD AIR WILL FILTER INTO NWRN ONTARIO AND UNDER CLEARING SKIES TONIGHT, WE CONTINUE TO INDICATE FROST OR A RISK OF FROST IN THE FORECASTS UP THERE. A SPECIAL WEATHER STATEMENT HAS BEEN ISSUED FOR NWRN ONTARIO AS AN EARLY HEADS UP TO FROST WARNINGS WHICH MAY BE REQUIRED LATER TODAY (FROST WARNING SEASON BEGAN ON 21-MAY). 

 
3. TUESDAY..AS IS OFTEN THE CASE AFTER A SEVERE THUNDERSTORM THREAT DAY, WITH THE COLD FRONT WELL SOUTH OF THE GREAT LAKES AND RIDGING BUILDING IN FROM THE NW, LOOKS FOR A MUCH QUIETER DAY PROVINCE-WIDE WITH NO CONVECTION EXPECTED. HOW FAST LINGERING POST COLD FRONTAL LOW CLOUD TAKES TO CLEAR OVER SRN ONTARIO WILL BE A FORECAST PROBLEM, BUT WE DO INDICATE AN IMPROVING TREND IN THE AFTERNOON SRN/ERN ONTARIO THANKS TO THE VERY STRONG MAY SUN. 

 
4. IN THE LONGER RANGE..FRONT REMAINS STALLED SE OF THE LOWER LAKES WEDNESDAY BUT STARTS RETURNING SLOWLY NWD BY EVENING. HENCE MOST AREAS REMAIN SHOWER FREE SRN ONTARIO BUT THEY MAY WORK THEIR WAY BACK INTO THE WINDSOR AREA AND MAYBE NEAR THE NORTH SHORE OF LAKE ERIE BY EVENING. THIS MAY SET THE STAGE FOR A WET AND COOLISH THURSDAY WITH THE FRONT STUCK EITHER OVER OR JUST SOUTH OF THE LOWER LAKES. NRN ONTARIO WILL BE UNDER RIDGING WED-THURSDAY WITH THE RIDGE HOPEFULLY PUSHING INTO SRN/ERN ONTARIO ON FRIDAY. IT WON'T BE AS WARM AS IT HAS BEEN FOR THE PAST COUPLE OF DAYS, WITH TEMPS RUNNING NEAR OR ON THE COOL SIDE OF NORMAL.

 
5. HAVE A GREAT VICTORIA DAY, EH?


END/KUHN/OSPC