Where are all the Monarchs?

Monarch butterflies usually abound in our area, but this year, strangely and disturbingly, I haven't yet seen one.  I plant dozens of butterfly weed, a member of the milkweed family of plants, just for the purpose of attracting monarchs, which lay their eggs on the plants.  The eggs hatch and feast on the plants, and I've had such a marvelous time in past years watching the process and being amazed at it.  This year, however, it's already mid August, and I have yet to see one monarch.  The butterfly weed in my flower beds isn't being devoured by those magnificent, colorful caterpillars as they reach 2" long before chrysalizing into these gorgeous turquoise and gold nuggets suspended all over the place.  I often don't find the chrysalises until they are empty, sometimes the following spring, as they are very well hidden.  When I have found one, I watch it closely as the color deepens over the next 2-3 weeks, and right before the butterfly emerges, the chrysalis turns a dark turquoise, the butterfly clearly visible through its thin shell.
But this year, alas, no monarchs.  I've had many other butterflies, but not one monarch, and I've certainly been home enough and outside enough to have seen them if they were here.  Obviously, something has upset the balance of nature and the monarchs' passage through this area, and I'm concerned about that.  I keep checking the butterfly weed to see if any eggs, small as a grain of salt, have shown up, but nothing to date.  The eggs quickly hatch into tiny caterpillars, and they grow like crazy as they strip the plants of vegetation.  The caterpillars boast "horns" on both ends, totally harmless and entirely for show to look threatening to predators, and the bright greenish/yellow and black stripes make them striking in appearance.

Here is a photo taken previously -- and in the meantime, I'll keep my eyes out for any monarchs.