[Evidence] Yellow cloud coming toward Yokohama on 3/16/2011
[link to fukushima-diary.com]

[snip]

On 3/22/2011, unidentified yellow power was found after rain around in Tokyo. (cf, 2.16 μSv/h from yellow powder [Link])
The Meteorological Agency stated it was pollen, but it had never been seen before even in Spring.

3/16/2011 was the day of full of accidents in Fukushima plant, which are not widely reported.