Just came across this sigmet today:

WSJP31 RJTD 030330
RJJJ SIGMET A01 VALID 030330/030730 RJTD-
RJJJ FUKUOKA FIR RDOACT CLD FCST WI N3718 E14052 – N3714 E14102 -
N3718 E14112 – N3725 E14115 – N3733 E14112 – N3736 E14102 – N3733
E14052 – N3725 E14048 – N3718 E14052 STNR INTST UNKNOWN=

Yup, that’s right: Radioactive Cloud. Stay away! It’s also being depicted on the SIGWX charts for the region:

Interestingly, yesterday Nav Canada was doing quite a few tests of their systems. They issued test sigmets and test volcanic ash sigmets:

WVCN34 CWUL 022104
SIGMET A1 VALID …