Today and tomorrow, cold-core thunderstorms will occur with over 1000 j/kg SBCAPE, shortwave energy and a strong upper level-jet streak. Some storms could become severe with large hail. Gusty winds and heavy rain are also possible but will likely not be severe.
In fact, storms could produce significant quantities of hail as WBZ heights slide below 700 mb.
The greatest convective coverage today will be on the Quebec side of the Ottawa Valley towards Montreal and the Eastern Townships. Tomorrow, it will be on the Ontario side of the Ottawa Valley towards Montreal and the Eastern Townships.
Storms are possible during the 1 to 11 pm timeframes on both days.
Forecasted radar reflectivity for 5 pm today from the 12Z 3K NAM. The image is only here to indicate storm coverage, not intensity.
Confessions of some snowlover's 
Strong storms have formed near Cornwall and seem to be producing hail.
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A SWS is up there, plus watches and warnings in adjacent regions of QC.
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A thunderstorm with gusts near 70 km/h just hit me.
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Watches and SWS continue this afternoon for both ON & QC. Looks like another round is possible tomorrow as you pointed out in your post.
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Severe thunderstorm watches are now up for a section of ON again this morning.
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But only for half of Ottawa…
The strongest storms should be from Ottawa into the Richelieu Valley, according to the short-range model consensus. The severe weather hazards will be similar to those outlined in the Ontario watch write-up (the Quebec watch write-ups are very generic and non-descriptive).
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Our text is highlighting the hail potential, on track with your earlier thoughts – http://weather.gc.ca/warnings/index_e.html?prov=son
“Many of the thunderstorms are expected to produce hail, some of which will likely be 1 to 2 centimetres in size. Given the cool temperatures and favourable atmospheric conditions, the hail may be abundant and nearly cover the ground at times. The main concern is damage to tender crops and plants.”
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On another note, significant vertical growth is being observed in the cumulus field in SE Ontario, and storms are developing now. Further strengthening is expected as the ML moistens (we’ve got 1100 j/kg SBCAPE, but only 21 j/kg MLCAPE).
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Watches have been expanded into S QC as cells break out across the region.
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2000 Hydro One customers are without power in the northern GTA.
Some of the storms in eastern Ontario are very strong, with reflectivites over 60 dbz. They are producing hail.
Storms should eventually evolve and organize themselves, especially after 3 pm. That’s when the severe thunderstorm warnings will start flying.
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A few rounds of thunderstorms have swing through here and it looks like another is on the way from the SW now. Some sunny breaks in the interim.
So far no hail here but a good deal of rain and lightning/thunder. Avoiding hail would be nice since it isn’t all that helpful for vegetation.
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I had a heavy thunderless downpour. It will be interesting to see the progression of the squall line approaching us.
Some power outages have occurred with the second squall line affecting Ottawa.
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