- ZOA CWSU SFO Approach Fog Study
- Models have difficulty resolving fog occurrences at SFO and seem to overforecast occurrences and undeforecast clearing time
- Can cause major impacts to air traffic at SFO
- 6 occurrences in 07/08 and 6 occurrences in 08/09
- Looked at:
- Coldseason days with 12Z H5 heights >= 5700DM and 12Z [SFO-SAC gradient] <= 1.0MB...preconditions that existed on all days with fog
- Clearing times
- 10Z SMB dewpoint temperature
- 12Z OAK 925MB wind direction from 180...with more northerly flow having larger values
- Initial findings for 07-09
- Average clearing time for all fog events was 21:31Z with only one clearing before 19:00Z
- Average 10Z SMB dewpoint for fog events was 46.8 with standard deviation of 2.1
- Average 10Z SMB dewpoint for days without fog was 43.4 with standard deviation of 5.0
- Average wind direction from 180 for fog events was 147 with standard deviation of 35
- Average wind direction from 180 for days without fog was 124 with standard deviation of 45
- Summary
- Once fog forms, don't expect quick clearing...based on past clearing times
- SMB dewpoints below 45 at 10Z will likely not yield fog
- Northerly flow in low-levels likely ushers cooler air from north bay valleys->only direction without downsloping to disrupt fog formation
- Status
- Will continue to add to study during/after each cold season
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