Autumn Quarter 2009 Atmospheric Sciences 101 Forecast Competition

NOTE: The first date on which a forecast can be made is Tuesday October 20, 2009.
Prior to entering you must first register a pseudonym.

Introduction:

Forecasting is optional and for extra credit. Students who do well on their forecasts, and submit at least 30 forecasts, are eligible for up to 9 additional points of extra credit on the final.

You will be entering your forecast for maximum and minimum temperature and precipitation (measurable/trace/none) at Seattle-Tacoma Airport. Observations are taken over a grassy runway, with an elevation of 137.8 metres (452 feet) above mean sea level.

The time period for which you are forecasting is a 24 hour period beginning at 08 UTC. This is equivalent to midnight PST during standard time, or 1:00am PDT during daylight savings time, on the following day. For example, a forecast entered at 8:30pm on 30 July, will be verified against observations made between midnight 31 July and 11:59 pm 31 July. The maximum temperature often occurs an hour or two before sunset and the minimum temperature often occurs near dawn. Remember, however, that frontal systems and changing weather can result in the maximum and minimum temperatures occurring at any time during the day. For instance, it is possible for the maximum temperature to occur at night and the minimum to be reached at mid-day due to the passage of warm and cold fronts. This type of occurrence is infrequent in the Pacific Northwest but occurs more often than one might expect in other parts of the nation.

Before you begin forecasting, you need to sign up for the competition (see link on the forecasting front page). When you do this, you will provide your name, student identification number, a pseudonym (nickname, alphanumeric characters only (a-z, 0-9) and a password. This will allow you to enter forecasts anonymously and prevent other people from entering forecasts for you. It also allows everyone to check each other's progress without revealing true identities.

In addition to the forecasts of your fellow students, forecasts from the National Weather Service (NWS), computer-based forecast models, the class consensus (average), persistence (todays's weather used as tomorrow's forecast) and climatological values will also be entered. These should provide a benchmark for how you are doing.

The forecasts from computer models are labelled as MOS (Model Output Statistics). GFS-MOS is based on a global model that runs around 7:00pm PDT each night.  We are entering values from the forecast generated the evening before the day you forecast, so the forecast is usually about 36 hours old for the minimum and 48 hours old for the maximum temperature. On average the GFS-MOS should be the worst model forecast. The NGM-MOS is a local area model run around 7:00am PDT, so it provides a more up-to-date forecast. The forecasts from the NWS are from the mid-afternoon update usually issued around 4:00pm local time.

Rules:

  1. Forecasts are for the 24 hour period beginning at midnight the next day and must be entered by 10:00pm.   If you enter a forecast after 10:00pm it will be submitted as your forecast for the following forecast day.   The clock on the entry form is used to determine the forecast day.   It updates every minute.

  2. The first forecast will be for Wednesday, 21 October 2009 and can be made on Tuesday, 20 October 2009 before 10:00pm.

  3. The last forecast is for Thursday, 10 December 2009 (entered before 10:00pm on Wednesday, 09 December 2009), so the final results will be available prior to the last day of class.

  4. You are forecasting maximum and minimum temperatures and precipitation for Seattle-Tacoma airport (Station ID is KSEA).

  5. Temperature is forecast in degrees Fahrenheit.

  6. Precipitation is forecast as None, Trace or Measurable. "None" means that no rain falls during the forecast period. "Trace" means that rain fell but there was not enough to measure. "Measurable" means that measurable precipitation (over 0.01 inches) fell.

  7. The rules for snowfall are the same as those for rain; the precipitation is considered as measurable if over 0.01 inches of liquid water equivalent (melted snow) fall.   As a general approximation 1" water equivalent equals 10" snow.

  8. You may re-enter your forecast as many times as you like until the 10:00pm cut-off. Only the last forecast you enter will actually be scored.

  9. You may forecast for any days you choose and you may enter more than the required number of forecasts.

  10. On days you do not forecast, you will automatically receive an additional 30 points added to your score.

  11. Please ensure that decorum is used when selecting your pseudonym.

  12. You are responsible for remembering your own pseudonym and password. Forgotten passwords will result in a 100 point penalty which will be added to your precipitation score. If you forget your password, contact the TA or instructor and he or she will remove your password from the file to allow you to enter a new one or assign you a new one.

Scoring:

The objective is to have the lowest overall score. Your score will only count toward extra credit if you have entered at least 30 forecasts by the end of the contest.

In the beginning, all forecaster's scores appear on a yellow background. Once forecasters have entered the required minimum number of forecasts to obtain extra credit on the final (30), their scores appear on a green background. If a forecaster is unable to achieve the minimum number of forecasts (based on days remaining in contest), their scores will appear on a red background. Forecasts can still be entered, but no bonus will be awarded at the contest end.

At the end of each forecast day, the forecasts are automatically verified against actual observations and scored as described below. Very occasionally the data feed to the observing network is lost and this automatic scoring may fail. If the automatic verification looks wrong contact your instructor as soon as possible so that the forecast can be verified by hand.

Submissions are scored as follows:

  1. Temperature: (Actual Temperature - Forecast Temperature)2 to a maximum of 100 points per field.   Note that the difference is squared.

  2. Precipitation:

Example: Cassidy forecasts a maximum temperature of 56oF and a minimum of 34oF. She also predicts that there will be no rain. Charlie forecasts a maximum temperature of 62oF and a minimum of 53oF. He also predicts that there will be a trace of rain. Observations for Seatac the following day yield a maximum temperature of 54oF and a minimum of 45oF and indicate a trace of rain.

Cassidy scores as follows:    

  • 4 points for maximum temperature: (56 - 54)2 = 4.
    •    
  • 100 points for minimum temperature: (34 - 45)2 = 121; however, the maximum per day is 100.
    •     
  • 10 points for precipitation. (34)2
    •
          For a total of 114. (34)2

    Charlie scores as follows:    

  • 64 points for maximum temperature: (62 - 54)2 = 64.
    •    
  • 64 points for minimum temperature: (53 - 45)2 = 64.
    •     
  • 0 points for precipitation. (34)2
    •
          For a total of 128. (34)2

    How much extra credit will you receive?

    Amongst those with 30 or more entries, extra credit points awarded will be the largest of the following:

  • 2 points for beating the climatology forecast (relatively easy).

  • 3 points for beating the persistence forecast (still fairly easy).

  • 5 points for beating the consensus average of all participants.

  • 9 points for beating the GFS-MOS forecast.

  • 9 points for beating the National Weather Service forecast.