I would say there is little doubt that there will be a new surge of migrants and vagrants into SW Ontario tonight and Friday night, before things get cold again for a few days... Check out the weather maps if you don't believe me!
For tonight (18th) at midnight, with the warm front pulling into the SW....
Here's a link to a broader nexrad radar if you want to watch the birds "light up" tonight after the sun goes down:
This would be roughly the third sizable surge of warm air + birds already this year... Considering we rarely have 1 by this date, it seems fairly clear that this year isn't normal - and no doubt there are several more rarities to be found right now than is typical for the time of year..
As I'm quite happy to already eat crow on my comments on "lack of CMF's" pre Apr 24th in Ontario, and have decided to get my Dad back to Pelee for the next few days to take in some more early birding
Heck, just look at what the Chicago area has had over the past few days:
Lark + Henslow's + LeContes + Nelson's Sparrows
+ Glossy Ibis (4) and Cinnamon Teal not too far away from the city as well....
Pretty sweet considering they're on the Great Lakes (and maybe a bit advanced in migration) but not really that far from SW Ontario... Heck, Wisconsin is to the north and they've had White-faced Ibis, Marbled Godwit(s), Hudsonian Godwit, Summer Tanager, Yellow-throated Warbler etc - just in the last 3 days...
For fun, here's a documentation video of a Blue-headed Vireo (mine and Ken's FOY) from Pelee a few days ago, eating a freshly arrived Question Mark in the butterfly invasion...