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Methods for Forecasting TS in the TAFs

Methods for Forecasting TS in the TAFs. NWS WFO and CWSU Chicago. Definitions. CB Only used with TS/VCTS VCTS prevailing TS in the 5-10 mile donut around the terminal

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Methods for Forecasting TS in the TAFs

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  1. Methods for Forecasting TS in the TAFs NWS WFO and CWSU Chicago

  2. Definitions • CB • Only used with TS/VCTS • VCTS • prevailing TS in the 5-10 mile donut around the terminal • used when coverage is scattered/or storms skirting by and there is uncertainty that the terminal will be directly affected

  3. Steps • What is the forcing mechanism? • How much coverage is typical? • How long does TS usually last with this type of setup? • How confident are you that TS will occur? (what mitigating factors are there?) • What is the most likely time window for occurrence?

  4. What is the forcing mechanism? • Cold fronts • Warm fronts (overrunning, LLJ…) • Stationary fronts • MCS’s • Upper cold pool/trough/daytime heating

  5. How much coverage is typical?

  6. How long does TS usually last with this type of setup?

  7. How confident are you that TS will occur? • Forcing mechanism • Magnitude of forcing • Magnitude of instability/moisture • Magnitude of inhibition • Timing consistency

  8. What is the most likely time window for occurrence? • Apply the typical duration of thunder to the time window that you think is most likely • Timing uncertainty can be conveyed in AFD • Timing adjustments made with AMD’s • Can establish a trend/show confidence

  9. How soon to include thunder? • Anytime…but consider: • Confidence dependent (see previous slide) • Think about the typical conditions associated with the forcing mechanisms • May not have enough confidence to add TS beyond 6-10 hours • Highlight low confidence and/or low probability in AFD’s and briefing calls

  10. What type of thunder should I include?

  11. TEMPO and PROB30 • Confidence and mode dependent • What to do with PROB30 at the 9 hr mark? • can establish a trend • show confidence

  12. Cigs and Vsby • Cigs • MVFR or VFR • Multiple MCS’s – progressively lower w/ each (3500ft 1st round, 2500ft 2nd, 1500ft 3rd) (8/23 event) • Vsby • Mainly MVFR/VFR but <= IFR for short periods

  13. Important Guidelines • Amend when needed • don’t wait til the next 2/3 hr update • Add detail as the event nears, especially if storms are on the scope • narrow time window • carry prevailing TS • Wind gusts? Hail? **Wind details following convection

  14. Important Guidelines • Communicate • WFO/CWSU • within the WFO • Brief the facilities • Heads up in the morning • Heads up 1 to 2 hours prior to arrival (TRACON boundary is beyond the airport) • Heads up if timing changes within the first 3 hours

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