I just grabbed this screenshot from the awesome Wind Map - check it out when you have a chance. We are currently getting winds straight out of the gulf coast and will continue to get strong south winds until the cold front passes by, in which case the winds will switch to the north.
These winds have been coming straight out of Texas and the Gulf of Mexico to locations further north for the last two days, and now these winds are blowing straight into southern Ontario. Leamington, Ontario (i.e. Point Pelee) is currently getting hit with strong south winds, gusting up to 75 km/h. It sure feels that strong here at my office too.
While this certainly does not guarantee that all kinds of rare birds will be found in the next few days in Ontario, it does mean that there will probably be higher number of rarities than usual to be found in the province, waiting to be found by birders! Yesterday, Ken Burrell reported a Yellow-throated Warbler at Pelee Island, the first "southern overshoot" of note so far this spring. There is a very good chance that more Yellow-throated Warblers, as well as other early overshoots (Summer Tanager, Henslow's Sparrow, Glossy Ibis, Worm-eating Warbler, Lark Sparrow etc) may make an appearance in coming days. But what everyone looks for is the mega rarity. Again, there is no guarantee that one will be found with this weather, but I would say that the chances are higher for the next few days than they have been at any time in the last 4-5 months.
One theory in regards to bird migration in Ontario is that all of these overshoots (that inevitably show up after strong systems from the southwest move through in the spring) will retrace their steps once they realized that they have flown too far. Southern Ontario is somewhat funnel shaped and it is very possible that these retreating overshoots will bunch up along the lakeshores. In theory, the Swallow-tailed Kite that may be blown up into Ontario today will likely try to vacate the province tomorrow, and in doing so may end up at Point Pelee or Long Point or Hamilton or something!
One more thing - here is a list of some of Ontario's more notable rarities that have shown up between the dates of April 14 and April 20 (the next seven days). This time period is the week before when the birding really starts to go nuts in southern Ontario; the birdlife often has a mid-April feel to it (surprisingly), with many temperate migrants and the first few neotropical migrants.
Brambling (Kenora; April 18, 1994)
Black-headed Grosbeak (Bruce Peninsula; April 14, 1998)
Burrowing Owl (Renfrew County; April 19, 1991)
Garganey (Renfrew County; April 18)
Say's Phoebe (Chatham-Kent; April 18, 1964, two others in last two years)
Smith's Longspur (Long Point; April 20, 1980)
Other rarities that sometimes have arrived in mid April include Ferruginous Hawk, Swainson's Hawk, Bewick's Wren, Cinnamon Teal, Tufted Duck, rare herons (Yellow-crowned Night Heron, Little Blue Heron, Snowy Egret, etc), and Western Grebe.
Only time will tell what will show up - get out there and find the birds!