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lefttab Early Return Stratus righttab lefttab SFO Fog righttab lefttab Post-Frontal Cumulus righttab lefttab Sierra Thunderstorms righttab
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  • ZOA CWSU Sierra TS Coverage Study
    • SCT-WDSPR TS coverage over Sierras can cause certain jet routes to be altered...causing large delays if unforecast
    • Models indicate when and if thunderstorms will form but coverage is less accurate
    • If forecasts are accurate enough, ATC planners could implement "swap routes" ahead of time to reduce delays/increase safety
  • Looked at:
    • All summer days regardless of whether thunderstorms occurred or not
    • 06Z NAM and GFS 18hr forecasts for LI and PW
    • BIH 01Z dewpoint
    • Examined SVE data...representative for northern Sierras
    • Examined BIH data...representative for southern Sierras
    • Forecasters subjectively quantified thunderstorm coverage for southern and northern Sierras daily
  • Initial findings for NAM 07-08
    • 0.71 correlation to coverage for combination of BIH 01Z dewpoint and BIH 00Z fcst LI
    • 0.69 correlation to coverage for combination of SVE 00Z fcst PW and SVE fcst 00Z LI
      • Formula for BIH LI/dewpoint combination is: -(LI*2)+(DWPT/2)
        • Average value for SCT coverage: 24.5
        • Average value for ISOL coverage: 15.7
        • Average value for NONE coverage: 7.1
      • Formula for SVE LI/PW combination is: -(LI*2)+(PW*2)
        • Average value for SCT coverage: 3.4
        • Average value for ISOL coverage: 2.3
        • Average value for NONE coverage: -5

  • Decision Aids...Using 091125/0600 NAM BUFKIT Data and Current Observations

    • Southern Sierras(BIH) Thunderstorm Coverage Raw Score: -8.98
      • Northern Sierras(SVE) Thunderstorm Coverage Raw Score: -25.82


    • Normalized Score: 0= None, 1= Isol, >1 = Sct
      • Southern Sierras Thunderstorm Coverage......-0.57984
      Northern Sierras Thunderstorm Coverage......-1.65776


    • Automated TS Coverage Data based on the following latest NAM BUFKIT forecast data:

      • Current BIH DWPT= 15.8
      00Z BIH LI= 8.44

      00Z SVE LI= 13.08
      00Z SVE PW= 0.17


    • Manual Input Calculator for TS Coverage

      • Southern Sierra
      Thunderstorm Coverage
      Enter Model or Real-Time Data for 00Z

      BIH LI:
      BIH DWPT:
      Computed LI/DWPT:
      Coverage Score(0-2):

      Northern Sierra
      Thunderstorm Coverage
      Enter Model or Real-Time Data for 00Z

      SVE LI:
      SVE PW:
      Computed LI/PW:
      Coverage Score(0-2):


  • Summary
    • Combination of 06Z NAM parameters seems to provide some guidance on coverage of afternoon thunderstorms
    • Good analysis of daily dynamics in combination with formula values may yield good coverage results
    • Initial sample size is very small so will have to add to dataset to verify usefulness
  • Status
    • Continue to track coverage of thunderstorms and how it affects air traffic
    • Add to sample size

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Oakland Center Weather Service Unit
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Fremont, CA 94536-6531

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