Issued: Thursday, July 22, 2010.

FXCN01 CWTO 221011
 
...SPECIAL WEATHER DISCUSSION FOR UPCOMING SEVERE WEATHER POTENTIAL..
 
1. SYNOPTIC PATTERN..A BROAD UPPER TROUGH OVER NORTHEASTERN ONTARIO 
ON WEDNESDAY WILL PUSH EAST ALLOWING A BROAD MID-CONTINENT TROUGH TO 
EXPAND EAST OVER THE NEXT FEW DAYS. THIS WILL ALLOW A DEVELOPING LOW 
OVER THE PLAINS STATES TO EMERGE FROM IOWA TODAY AND TRACK TOWARDS 
THE UPPER GREAT LAKES AND DEEPEN VERY SLIGHTLY ON FRIDAY. AN 
ATTENDANT WARM FRONT WILL PROGRESS ACROSS THE LOWER GREAT LAKES 
TONIGHT AND FRIDAY. 
 
2. TONIGHT..AS THE WARM FRONT TRACKS ACROSS LOWER MICHIGAN AND 
EVENTUALLY SOUTHWESTERN ONTARIO..MODELS ARE IN AGREEMENT ON A 
PROGRESSIVE CONVECTIVE COMPLEX JUST AHEAD OF THE ADVANCING FRONT. 
HOWEVER, THERE IS MARKED DISPARITY IN ITS LOCATION..THE NAM AND GEM 
REGIONAL TOO FAR NORTH (NAM SUGGESTS EXTREME NORTHERN LOWER MICHIGAN 
LATE TONIGHT TO MONTREAL LATE FRIDAY)..THE GLOBAL MODELS (GFS AND 
CMC GLOBAL) FARTHER SOUTH (CENTRAL LOWER MICHIGAN TONIGHT TO WESTERN 
NY ON FRIDAY). ALL ARE SIMILAR IN THE AXIS OF GREATEST INSTABILITY 
SHIFTING EASTWARDS INTO SOUTHERN HALF OF LOWER MICHIGAN TONIGHT THEN 
EXPANDING INTO SOUTHERN ONTARIO ON FRIDAY. THE MCS WILL TRACK ALONG 
THE NOSE OF THE FORECAST 50 KT LOW LEVEL JET (FORECAST TO TRACK 
ACROSS CENTRAL LAKE MIGHIGAN TONIGHT AND TOWARDS SOUTHWESTERN 
ONTARIO BY FRIDAY MORNING). WE BELIEVE THE MCS WILL TRACK AFTER 
MIDNIGHT FROM ROUGHLY MUSKEGON TO THE FLINT/MICHIGAN THUMB THEN EAST 
ACROSS SOUTHERN LAKE HURON AND SOUTHWESTERN ONTARIO..THEN 
HAMILTON/NIAGARA FRIDAY MORNING. THE SEVERE WEATHER THREAT WILL 
MAINLY BE HEAVY RAINFALL POTENTIAL AS PRECIPITABLE WATER IS AROUND 
55 MM. ISOLATED LARGE HAIL AND BRIEF DAMAGING WINDS CANNOT BE RULED 
OUT. A GRADUAL WEAKENING ACROSS ONTARIO IS LIKELY AS INSTABILITY IS 
DEPLETED ON ITS EASTWARD JOURNEY FRIDAY MORNING. BUT UNTIL THEN, A 
SPECTACULAR LIGHTNING SHOW IS POSSIBLE MAINLY ACROSS SOUTHWESTERN 
ONTARIO.
 
3. FRIDAY..A POST-MCS BOUNDARY WILL LIKELY BE SET UP ACROSS 
SOUTHWESTERN ONTARIO, AND STRONG SUSTAINED WEST-SOUTHWEST LOW LEVEL 
JET ACROSS SOUTHERN ONTARIO WILL SUPPORT CONSIDERABLE AIRMASS 
RECOVERY FRIDAY AFTERNOON. THE SREF INDICATES AMPLE MLCAPES OF 1500 
TO 2500 J/KG FROM THE SOUTHWEST TOWARDS THE GOLDEN HORSESHOE. THE 
GEM REGIONAL MAINTAINS EVEN MORE ROBUST MLCAPES OF 3000 ACCOMPANIED 
BY SHEARS IN THE 0-3 KM LAYER OF 30 TO 40 KTS. BELIEVE A SECONDARY 
RISK FOR SEVERE STORMS EXISTS FRIDAY AFTERNOON (POST-RECOVERY) WITH 
LINE SEGMENTS AND SOME SUPERCELLS ACCOMPANIED BY THE WHOLE SUITE OF 
RISKS FROM LARGE HAIL OF 3 CM, STRONG DAMAGING WIND GUSTS, 
TORRENTIAL RAINFALL TO AN ISOLATED RISK OF A TORNADO. THE MAIN AREA 
IS SOUTHWESTERN ONTARIO TO NIAGARA.
 
4. SATURDAY..A MORE POTENT UPPER TROUGH APPROACHES WITH FALLING 
(LATE-DAY) HEIGHTS, AN AN ATTENDANT SURFACE LOW MOVING TOWARDS THE 
SOO. ECMWF AND GLOBAL ARE MOST PROMINENT WITH THIS FEATURE. SREF 
ALSO INDICATES POTENTIAL FOR ENHANCED SHEARS AND SUFFICIENTLY LARGE 
CAPE FOR SIGNIFICANT STORMS. GLOBAL SOUNDINGS SUGGEST THE SEVERE 
THREAT WILL EXPAND FARTHER NORTH THAN FRIDAY'S RISK AREA. BUT THAT 
REMAINS TO BE SEEN AS SO MANY PIECES MUST FALL INTO PLACE FIRST.
 
END/ASHTON/OSPC
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