OK, so now everyone knows about DXMaps (previously known as DX Sherlock). This lets you know about QSOs that have already taken place. However, there's another site I use that shows the plot from an ionosonde in northern Utah. If the ionosonde data display shows there's an E cloud there, I put my antenna up and point it northeast from the SF Bay area and start calling CQ. Often enough to make it worthwhile, I make a contact.
Here's the URL: http://www.spacenv.com/secblo/BLO/cadi/index.html
If there's an E cloud overhead, the ionosonde will show a horizontal red line just above the 100 km level. If you're located west of the Rockies and DXMaps isn't showing anything, point your antenna toward northern Utah and call CQ. You may find it works for you too.
Now, the ionosonde can tell you something about what's going on in the F layer as well. If I see clear arcs plotted, hf is probably in pretty good shape. However, when the A and K indexes are high, the plot will seem to be little more than random dots.
Check it out. You may find the site as helpful for you as it's been for me.