undisclosed Mtn retreat
I'm afraid it will probably remain undisclosed in the Podlasian flatlands. Try Sękacz. If you are adventurous, try flaczki, tripe soup, although most women are a bit squeamish about that.
And how shall I dress as thin blooded Arizonan?
Hard to say for late spring, but it shouldn't be cold by then. If you get chilly, you can always buy a sweater in the excellent Alfa and Biała shopping centres/malls. Don't leave without catching an Orthodox mass, preferably at św. Mikołaja Cudotwórcy (Cathedral of St. Nicholas the Wonderworker), which has the best Orthodox choir in Poland, I reckon. If you miss home, Elvis Burger at ul. Białówny 9, just off the main square, serves great burgers.