My old man was in Nevada for some of the tests. He and a handful of others (mostly) RCAF set up the GND (Ground Nuclear Defense) Section and he was an instructor in the basics of same. He told me some things relating to your questions.

All tests were followed up with weather observations at all altitudes, for long periods. Radiation was measured at all military US, British, French, Spanish... bases daily.

As well, some tests were conducted during specific weather conditions with the intent of measuring high altitude fallout at great distances, particularly eastern US and CA. If you go through the test names you may note that some are names of states or towns. Some tests also had a "sub-name. One was Schooner and the high altitude fallout was specifically "aimed" at Atlantic Canada.

They also used herds of sheep placed at varying distances... I'll stop there... you get the drift.

Just one more... I was fascinated as a wee lad when he told me of the first test he attended. I don't know what distance they were away but the men were told to shield their eyes with their hands and he saw the bones in his hands. Okay... one more... I was even more fascinated by the fact that he could find a rock, no matter where I hid it, with a gieger counter.