CKAT has more than likely been on 10000 watts Day power and pattern for a long time. I suspect that it started because they were upset about WTVN 610 IBOC sidebands. Now it interferes with WSNL 600 (formerly WTAC, the station once owned by the Chess Brothers before they sold it and bought WVON and WLUP) all the time, and makes their de facto NIF way above the decent 6.7 mV/m it's supposed to be.
Somebody built a cell tower too close to WMT 600, and they have been on STA off and on, and they are most likely also radiating more to the East, more than the 1 kW equivalent toward originally WICC 600, et. al., the pattern they are still supposed to have.
Would WTVN's IBOC sidebands have mattered that far north though? I don't remember them ever being in IBOC at night, and that's the only time WTVN would make it that far. That signal definitely travels very well to the north at night, so I am sure it can be heard in North Bay if not for CKAT slop.