Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
And as for winter fishing I love it any day where the temp is approaching or exceeding 32* will have me itching to fish. I have even been known to fish in air temps that maxed out in the teens forcing me to chip ice from the tip top every 3rd or 4th cast.