I found 5 dead pond frogs over a period of about two months. February and March. We have had unusual weather with some warm days and freezing nights. The frogs came out of my backyard pond to sun themselves during the warm days and then I found dead frogs in the water. The goldfish have been unchanged and the water quality is the same as ever. The pond was not frozen over and anyway I keep a small heater to maintain an opening. One frog remains and seems completely normal now in April. Could the extreme weather have killed the others?
Yes, the weather extremes could have been a contributing factor in this case. Frogs also are susceptible to habitat pollution, pesticide exposures, and diseases (chytridiomycosis). Since you are in Montgomery County, you might be interested in this reference and the local 'FrogWatch' program. https://www.montgomerycountymd.gov/water/streams/frogs-and-toads.html
The Maryland Department of Natural Resources also is a good resource for information about frogs.