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Oakland, California
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  • 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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