This question already has an answer here:
[I do not believe this question duplicates a previous question, which involves different conditions and circumstances]
I'm interested in the airline's response to a query of mine about why a flight was cancelled due to weather when destination airport had visibility of at least 12 SM. I asked them and the airline wrote back, attaching relevant METAR and TAF reports.
The destination airport was Victoria International (CYYJ) which is not category III (maybe cat II?). All METAR reports indicated 12SM visibility with the lowest ceiling FEW170. The airline acknowledges that the actual conditions were clear. The flight was scheduled to depart 0716 ZULU, 33 min. duration, 2 alternates with CAT III available at 16 min (Vancouver, CYVR) and 33 min (Seattle, KSEA) flying time.
The aircraft was a Dash 8. A competing airline flew the same route with a CRJ 15 minutes before the scheduled departure without incident. This was the only cancellation at YYJ that evening (there were perhaps a dozen arrivals, mostly Dash 8s or Q400s but there was an A320 and at least one 737).
The airline claims a TEMPO condition of 1/4SM made it illegal to dispatch. But the TAF at 335Z said TEMPO 1 1/2SM BR SCT002, not 1/4SM. The bases prediction was P6SM SCT250 but there was also a PROB40 for 1/4SM and fog (FG).
Is a PROB40 for fog and 1/4 SM visibility enough to cancel? Is the airline required to cancel at that point? The 335Z TAF also had RMK next forecast by 0600Z, 1 hour before departure.
The new TAF issued at 538Z did not have TEMPO but had PROB30 (I can't find PROB30 in my TAF/METAR definition list, as PROB40 is supposed to be 30-50%, right?) for 1/4SM and fog (FG) again with what appears to be a main prediction of P6SM FEW150 SCT250. Was this enough to reasonably cancel? Was the airline legally required to cancel on this basis?
Update: a poster asked me if I could post the full set of TAF and METAR reports, as received from the airline. Here they are (assuming no typos on my part because I received these hard-copy not electronic):
Scheduled flight departure from SEA Zulu 7:16 Flight duration: 33 min. Arrival YYJ
METARS for YYJ:
0700Z 27004KT 12SM FEW170 BKN250 01/01 A3043
0600Z 27004KT 12SM SCT250 M01/M01 A3041
0500z 27004KT 15SM FEW250 00/M00 A3041
TAFs for YYJ:
CYYJ 1005338Z 1006/1106 VR03KT P6SM FEW150 SCT250
PROB30 1006/1016 1/4SDM FG VV002 FM101800 29008KT P6SM FEW004 SCT100
FM102000 35005KT P6SM SKC RMK NXT FCST BY 101200Z
CYYJ 100335Z 1003/1024 VRB03KT P6SM SCT250
TEMPO 1003/10-18 1 1/2SM BR SCT002
PROB40 1005/1016 1/4 SM FG VV002 FM101800 29008KT P6SM
FEW004 RMK NXT FCST BY 100600Z