Solar Flares and Geomagnetic storms have a great deal to do with the propagation of shortwave radio.  When this activity is high, radio signals get weakened and interference increases.  This is particularly true for shortwave radio, which uses the ionosphere to bounce the radio waves across the globe.

Solar weather is monitored and predicted by the powers that be and can be accessed up to the minute on the net.  Here's where you can access NASA's solar forecast .  Also, we've included the latest images of the sun at the right hand side of this page.  When a big flare happens you will see the explosions on these pictures.  The first image is a simple meter of activity.  If the line is in the BLUE than activity is low and radio waves are likely to perform their best.