MDCJets From United States of America, joined Apr 2001, 175 posts, RR: 1 Posted (12 years 10 months 1 week 3 days 22 hours ago) and read 1473 times:
I flew out of SCJ both this last December and the preceding December. I have flown out (and into) to SCJ many times but both these times in December, the weather was cloudy-not particularly stormy or windy-just cloudy. I have noticed whenever the weather is like this, the takeoff is to the south, as opposed to the regular takeoff to the north. I'm sure there is a very simple reason, however because both these times it was not windy or stormy, I cannot seem to think of one. Perhaps the pattern alters frequently and just by chance, its been a northern takeoff when the weather is cloudy. If anyone has any information I would appreciate it.
N659AA From United States of America, joined Aug 2000, 136 posts, RR: 0
Reply 2, posted (12 years 10 months 1 week 3 days 22 hours ago) and read 1454 times:
I went to school in San Jose (San Jose State), so I am pretty familiar with climate of Silicon Valley. As with any airport, the runway in use depends solely on the direction of the wind. In the South Bay, the silicon valley is oriented in a Northwest through Southeast direction. The prevailing winds are from the Northwest coming off San Francisco Bay down the valley towards Gilroy which is why the common use runways are 31L/31R.
During inclement weather, if Low Pressure systems track along a certain course, the circulation around the low pressure system will cause the wind direction to come from the South, causing the use of runways 12L/12R towards the Southeast.
People in the area associate the use of runway 12 with bad weather. It just so happens that bad weather usually means a change in wind direction. Bad weather does not necessarily mean the use of Runway 12.