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Iowa Forecast Contest
2011-12 Contest Rules

  1. Forecast Calendar

    The contest will consist of 20 two-week and one-week periods over a year, with the final period as the year-end tournament. Each two-week period will consist of 4 forecasts per week (Monday through Thursday), for a total of 8 forecasts per period. Each one-week period will consist of 8 forecasts per week (two each day Monday through Thursday).

    Forecasters must complete at least 12 of the 20 regular-season periods to have their cumulative score count in the final standings. Forecasters' top 15 period scores will count toward the final overall score, so forecasters who participate in more than 15 periods will have some of their worst scores dropped from cosideration. Tournament eligibility for forecasters who complete fewer than 12 periods will be determined by the chairperson.

    In each period, forecasters must submit at least 6 of the 8 forecasts in the period to have their forecasts counted for that period. In a two-week period, this would require forecasts on 6 of the 8 days. In a one-week period, forecasters must submit a forecast on at least 3 of the 4 days in the period.

  2. Forecast Horizon and Interval

    The forecast day will consist of a different forecast horizon, ranging from Day 1 to Day 7, that will change from period to period and potentially from day to day within a period. Temperature and precipitation forecasts will consist of a daytime period and a nighttime period. Aviation forecasts will cover only a single period.

    • For precipitation forecasts, the nighttime interval runs from 0000 to 1200 UTC. The daytime interval runs from 1200 to 0000 UTC.

    • For temperature forecasts, the nighttime interval will consist of the minimum temperature between 0100 and 1400 UTC. The daytime interval will consist of the maximum temperature between 1300 and 0100 UTC.

    • For aviation forecasts, the forecast interval will run from 0300 to 1800 UTC.

  3. Elements of the Forecast

    The forecast will consist of two distinct types of forecast elements. The majority of forecasts will be made for the basic public elements of temperature and precipitation. A minority of forecasts will be made for the basic aviation elements of wind, ceiling height, and visibility.

    For the public forecast, depending on the time period the forecast is for, the following elements may be forecast:

    • The nighttime minimum and daytime maximum temperatures to the nearest whole degree Fahrenheit

    • The categorized probability of precipitation (POP)
      POP categories are
      Category Probability Category Probability
      0 0% to 4% 6 55% to 64%
      1 5% to 14% 7 65% to 74%
      2 15% to 24% 8 75% to 84%
      3 25% to 34% 9 85% to 94%
      4 35% to 44% 10 95% to 100%
      5 45% to 54%

    • The categorized quantitative precipitation forecast (QPF)
      QPF categories are:
      Category Precipitation Category Precipitation
      0 0.00 in. or trace 4 0.50 in. to 0.99 in.
      1 0.01 in. to 0.09 in. 5 1.00 in. to 1.99 in.
      2 0.10 in. to 0.24 in. 6 ≥ 2.00 in.
      3 0.25 in. to 0.49 in.

    • The categorized amount of quantitative snowfall forecast (QSF).
      QSF categories are:
      Category Snowfall Category Snowfall
      0 0.0 in. or trace 3 4.0 in. to 5.9 in.
      1 0.1 in. to 1.9 in. 4 6.0 in. to 7.9 in.
      2 2.1 in. to 3.9 in. 5 ≥ 8.0 in.

    For the aviation forecast, the following elements will be forecast:
    • The categorized highest sustained wind speed (HWS)
      HWS categories are:
      Category Wind Speed Category Wind Speed
      1 0 kt. to 3 kt. 5 16 kt. to 19 kt.
      2 4 kt. to 7 kt. 6 20 kt. to 23 kt.
      3 8 kt. to 11 kt. 7 24 kt. to 27 kt.
      4 12 kt. to 15 kt. 8 ≥ 28 kt.

    • The categorized lowest reported prevailing ceiling (LRC)
      LRC categories are:
      Category Ceiling Category Ceiling
      1 < 200 ft. 5 2000 ft. to 3000 ft.
      2 200 ft. to 400 ft. 6 3100 ft. to 6500 ft.
      3 500 ft. to 900 ft. 7 6600 ft. to 12000 ft.
      4 1000 ft. to 1900 ft. 8 > 12000 ft. or no ceiling

    • The categorized lowest reported prevailing visibility (LRV)
      LRV categories are:
      Category Visibility Category Visibility
      1 < 0.5 mi. 5 3.0 mi. to 5.4 mi.
      2 0.5 mi. to 0.9 mi. 6 5.5 mi. to 6.4 mi.
      3 1.0 mi. to 1.9 mi. 7 ≥ 6.5 mi.
      4 2.0 mi. to 2.9 mi.

  4. Submission of Forecasts

    Forecasts must be submitted to the chairperson by 2330 UTC using the form on the contest website or email. There is a five-minute grace period for forecasts submitted by email after the deadline. Forecasts submitted after 2335 UTC will be accepted at the discretion of the chairperson.

  5. Failure to Forecast

    Forecasters who do not make a forecast will be assigned consensus MOS values and will be charged with absences as outlined in Rule 1.

  6. Occasional Planned Absences

    If a forecaster knows in advance that he or she cannot forecast for the next day (or days), two options are available:

    1. The forecaster may do nothing, and take consensus MOS as a forecast.

    2. The forecaster may make a planned guidance-based forecast. This option requires an email to the chairperson, stating which numerical guidance (or combination) to use and for which days the guidance will be used.

    Either option will count toward the absence total for the period, and eligibility for the period will be evaluated according to Rule 1.

  7. Computer Model Guidance Forecasters

    Values for relevant model output statistics from the latest runs will be entered by the chairperson or designee. The guidance that will be used includes

    • GFS MOS (MAV)
    • GFS Extended MOS (MEX)
    • Consensus GFS Ensemble MOS (MEC)
    • Eta MOS (MET)
    • Consensus MOS (CMO)

    Since the MOS output may not directly correspond with the forecast horizon and/or forecast elements for some periods, the MOS will be required to opt-out of certain periods.

    MAV and MET will forecast in all periods through day 2.5. The MEX and MEC will not forecast in the aviation forecast periods.

    CMO will be the average of all eligible MOS forecasts rounded to the same precision.

  8. National Weather Service Forecaster

    The NWS official forecasts issued through 2340 UTC will be entered by the chairperson or designee. The Point Forecast Matrix (PFM) will be used for the temperature, POP, QPF, and QSF elements. The Terminal Aerodrome Forecast (TAF) will be used for LRC and LRV elements. The highest wind speed value in either the PFM or TAF will be used for the HWS element.

  9. Average Forecast

    The average of all human and guidance forecasts for each day, interval, and element will be computed to the same precision as the individual forecasts. This average forecast will serve as the baseline for scoring, as outlined in Rule 11.

  10. Verification

    All elements (except for snowfall) will be verified using the official METAR reports produced at the forecast site. For snowfall, National Weather Service cooperative observations for the site will be used.

    Temperatures will be verified based on the six-hour maximum and minimum temperature reported at standard synoptic observation times. Since the forecast interval does not exactly match the 6 hour blocks, the chairperson shall make a reasonable judgment based on hourly observations and six-hour reports as necessary.

    POP will be verified as either 0% or 100%. If at least 0.01 in. of precipitation falls during the forecast interval, 100% POP will verify. For both automated and manual sites, the 6 hour precipitation and snowfall accumulation at standard synoptic observation times will be used for QPF and QSF.

    Both POP and QPF will be verified using the automated report during rainfall events. When snow and/or sleet is reported at anytime by the automated weather identifier during the time period, the NWS cooperative observer site for will be used.

    The HWS will be verified from the highest sustained wind speed reported in the forecast interval. This does not apply to wind gusts or the peak wind gust. Both hourly and special observations will be used for verification.

    The LRC and LRV will be verified based on any observations (hourly or special) reported in the forecast interval. However, if a variable ceiling or visibility is reported in remarks, and this value is lower than any non-variable ceiling or visibility, the variable range will not be used. Only the prevailing lowest reported ceiling or visibility will be used.

    In the event of failure with any of the automated equipment, maintenance performed on the site sensors, any missing observations, or any value deemed unrepresentative of what actually occurred, the chairperson shall perform a reasonable decision regarding the parameter in question based on the nearest weather data available. Questionable parameters will be discussed via email with forecast participants, along with the reasoning that necessitated the change. Any objection to a change should be voiced or written via email to the chairperson.

  11. Scoring of Daily Forecasts

    Raw forecast scores will be computed as the square of the difference between a forecast and the verification value for each element and forecast interval. Temperature errors will be capped at 15°. The sum of these raw square errors will be tabulated for each combination of element and interval for each period. The raw scores for each element and interval will be normalized according to Rule 12.

  12. Normalized Scores

    An attempt will be made to adjust for any differences in difficulty between different periods and elements by obtaining normalized scores. A normalized score will be computed for each combination of forecast element and interval. The normalization procedure is

    1. The standard deviation s of the raw squared errors of all forecasters is computed.

    2. A forecaster's normalized score Z is computed according to the formula

      where X is the forecaster's raw squared error, Avg is the raw squared error for the Average forecast, as defined in Rule 9, and S is the standard deviation of all squared errors.

    Each forecaster's normalized scores within a period are averaged to give the normalized score for the period. The average of the period averages gives the overall normalized score for the contest.

  13. Year-End Tournament

    The year-end tournament will follow the final (20th) period of the contest. The tournament will consist of head-to-head battles between two forecasters. The winner will be determined by the better normalized score during the round. Seeding is based on the final regular season cumulative normalized score. The bracket and schedule will be drawn once the final list of eligible forecasters is available.