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CONFIDENCE GRIDS : A METHODOLOGY FOR EFFICIENT THREAT ASSESSMENT IN THE GFE ERA

CONFIDENCE GRIDS : A METHODOLOGY FOR EFFICIENT THREAT ASSESSMENT IN THE GFE ERA Jeffrey D. Fournier, Paul Duval, & Andrew I. Watson NOAA/National Weather Service Tallahassee, FL. NEED TO FOCUS ON “HIGH IMPACT” EVENTS -MOS “ good” guidance for routine forecasts ( MaxT , PoP , Sky, etc.)

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CONFIDENCE GRIDS : A METHODOLOGY FOR EFFICIENT THREAT ASSESSMENT IN THE GFE ERA

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  1. CONFIDENCE GRIDS: A METHODOLOGY FOR EFFICIENT THREAT ASSESSMENT IN THE GFE ERA Jeffrey D. Fournier, Paul Duval, & Andrew I. Watson NOAA/National Weather Service Tallahassee, FL

  2. NEED TO FOCUS ON “HIGH IMPACT” EVENTS -MOS “good” guidance for routine forecasts (MaxT, PoP, Sky, etc.) -High Impact events more likely to affect lives & property -More value can be added to forecasting such events -potential impacts, timing, likelihood -High Impact events strain our resources -phone calls, webinars, media interviews, more products -valuable decision-making time limited -need to plan in advance for staffing adjustments

  3. Should we spend so much time & resources making nearly imperceptible improvements to the numerical guidance? Max/Min Temperature verification for entire NWS 2004 – 2009 (Courtesy of NWS Performance Management website)

  4. Managing hundreds of GFE grids is unwieldy & time consuming

  5. Time pressure Maintain continuous Wx watch NWP analysis Forecasters need a time-saving tool to help determine the potential for upcoming “significant” weather events Coordinate with other offices to maintain NDFD Data analysis Customer phone calls

  6. Conundrum: One must “know” ahead of time if, when, & where high impact weather events will occur in order to effectively adjust time & resources to better forecast & describe such events. “If you haven’t anticipated it, you probably won’t recognize it when it happens” -Charles Doswell

  7. One possible solution being tested by WFO Tallahassee: “Confidence Grids” Local warning criteria are considered to be “high impact” weather events. We use various NWP guidance to compute the probability of these events occurring. TAE Issues a Small Craft Advisory Probability of 20 KT winds from 18 UTC – 00 UTC

  8. Models (GFS, NAM, WRF, GEM ECMWF) GFE Procedure & Smart tools MOS (MAV & MET) Confidence Grids Other (Gridded MOS, bias-corrected model output) TAE has been using “Confidence Grids” internally for almost 3 years. A GFE procedure & smart tools compute the probabilities of specific weather elements or hazards occurring

  9. GFE display showing just some of its hundreds of grids: GFE Confidence Grids Confidence Grids allow one to quickly assess upcoming threats by examining a relatively small grid set Confidence Grids Display

  10. METHODOLOGY: -Most Confidence Grids are uncorrected excedance probabilities -inspired by SREF products available on SPC website -Incorporate as much commonly-used NWP guidance as possible -Probabilities are displayed in 6-hour blocks out through 72 hours -Grids are computed before grid population process begins -forecasters can pre-determine which fields to focus more attention -Confidence Grids can be displayed in webinars -EMs can see threat areas AND the likelihood of the event occurring

  11. Percentage of numerical guidance with Min RH below 35% (NAM12BC MinRH_yes + GFS40BC MinRH_yes + MET MinRH_yes + WRF MinRH_yes + MAV MinRH_yes + ECMWF_MinRH_yes) / 6

  12. How do we use the “Confidence Grids” in our daily operations? How easy is it to settle into a routine on shift ?? “Hi Homer. Anything going on?” “No Lenny…nothing but high pressure.” But…

  13. What about the period of Small Craft Advisory conditions tomorrow? Probability of surface wind speeds > 20 Knots

  14. What can be done with this foreknowledge? -Spend MORE time on Wind & WaveHeight forecast -forecast soundings (BUFKIT momentum transfer) -coordinate with adjacent coastal WFOs and TAFB -apply local knowledge -run local guidance like the SWAN & WRF -use persistence, climo, recent verification -situational awareness -time of week or year? (more boaters) -special events? (like fishing tournaments) -Spend LESS time on other weather elements (T, Td, etc) -remembering our ability to improve upon MOS

  15. Confidence Grids can also be used in the watch/warning/advisory decision process, in a manner similar to how NHC/SPC uses their probabilities to issue watches & warnings. Perhaps we could use the 50% probability line (of Min RH < 35%) to define our Fire Weather Watch boundary for Florida

  16. Another advantage of Confidence Grids…the ability to quantitatively express confidence in a forecast to our customers & partners “How sure are you that the winds will stay below 15 MPH today?”

  17. The Confidence Grids for tornadoes and severe thunderstorms are not quite as simple Probability of Severe Thunderstorms Within 25 miles of a point

  18. COOL SEASON SIGNIFICANT (F2-F5) TORNADOES IN THE GULF COAST STATES Jared L. Guyer and David A. Imy NOAA/NWS Storm Prediction Center, Norman, Oklahoma Much of what goes into our Tornado & Severe Storm Confidence Grids is based on this publication, as well as local verification & calibration with the SPC subjective probability graphics

  19. SPC Day1 Convective Outlook (top) & Storm Reports (bottom) Confidence Grid for severe storms- showing a large area of 15-20% (yellow) for WFO TAE’s area this afternoon

  20. Tornado/Severe Storm Confidence Grids can be used in conjunction with the SPC probabilities. -Our grids provide 6-hour temporal resolution of threat -useful for populating Weather grids and for briefing details -Our grids can be run out through 72 hours with each new model cycle -and still distinguish between tornado and severe storm threat -Our grids are tailored to local climatology -heavy emphasis on cool season (low CAPE/high shear) So far these Confidence Grids often match well with SPC, but tend to be a bit “noisier”

  21. CONFIDENCE GRIDS ADVANTAGES: 1) Forecasters can quickly assess potential high impact weather events within the next 72 hours 2)Greater time & resources can be devoted to the unfolding event (model/data analysis, weather briefings, extra staffing, inter-office coordination, etc.) during the forecast process 3) The probabilities can be used to help decide if, when, & where to issue advisories/watches/warnings 4) Forecasters can give an explicit expression of confidence in an event occurring, instead of using vague terms like possible or chance

  22. Thank you for your time. Any Questions? CONFIDENCE GRIDS: A METHODOLOGY FOR EFFICIENT THREAT ASSESSMENT IN THE GFE ERA Jeffrey D. Fournier, William Paul Duval, and Andrew I. Watson NOAA/National Weather Service Tallahassee, FL jeff.fournier@noaa.gov

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