An SDR recording catch, with an assist by Carrier Sleuth:
http://blackcatsystems.com/software/medium_wave_carrier_display_app.htmlHere's the normal hi-res / zoomed in waterfall from Carrier Sleuth, showing all the carriers present from stations on 1620 AM. A jumbled mess!

Here's an alternate display I am working on for Carrier Sleuth, that only shows the strongest carrier at any time. The red arrow notes when WNRP came up out of the mess, just at the right time for me to hear a weather report and station ID.

The opening was just for a few minutes, but Carrier Sleuth made it easy to find those few minutes.
That very drifty carrier you see on the left is my local-ish pirate WEDG The Wedge. You can see it really starts to drift around 1200z, or 8 AM local time. I assume thermal drift as this is not long after sunrise.