CE, don't worry about that big cat-tail, let it get real big and then Sissy can come give you a hand with her little red tractor and pull it out! Ha ha ha. But seriously, large cattails only do good when "cut Loose", they don't grow well when contained in small container, but a big container could be fine. I would bet that cattail clump is stunning with the cat-kins and long slender leaves blowing gently in the wind.... cut too small and that will read "blow over in the wind" ha ha ha! But! You can cut pieces from around the edges and trim some of the rhizomes back, little at a time, without disturbing the plant too bad.
Yes CE ... your "weather blip" must have got here last night, currently at 50 degrees right now, that's a good 10 degree drop since this morning, think its "sputtering out" ha ha ha!