Forecasting is optional and for extra credit. Students who submit a minimum of 18 forecasts will have 4 extra credit points added to their final. Students who do well on their forecasts, and submit at least 18 forecasts, are eligible for up to 9 additional points of extra credit on the final (total possible extra credit is 13 points added to an 80-point final).

You will be entering your forecast for maximum and minimum temperature and precipitation 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 May, will be verified against observations made between midnight 31 May and 11:59 pm 31 May. 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.

Before you begin forecasting, you need to sign up for the competition. When you do this, you will provide your name, student identification number, a pseudonym (nickname) 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 classmates, 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 forecasts from the NWS are from the mid-afternoon update usually issued around 4:00pm local time.

The objective is to have the lowest overall score. Your score will only count toward extra credit if you have entered at least 18 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 (18) to obtain extra credit on the final, 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.