Ok guys, I'm going to go with St. Anne's Park for this Sunday. Just checked the weather forecast and there's a 20% chance of precipitation, but a temp. of 17 degrees.. so hopefully will be nice. If not, there are bandstands and places to take shelter. Also, Clontarf is a stroll away, which is another opportunity for sketching in itself.
We will meet at 1pm, at the entrance on the corner of James Larkin Road and Mount Prospect Avenue. (see map in link)
St. Anne's Park is amazing, here is a link to a layout plan of it - showing the walled gardens, different arboreteums, the red stables, a model car track and much more!!
The Park should have a nice atmosphere too with the Vampire Cloak race which Stephen pointed out!
Hope to make it out, happy sketching!!