The mathematical models used to make predictions on the nowcast are based on measurements of environmental and water-quality variables known to influence E. coli levels. These are called "explanatory variables" and include measurements of rainfall, wave height, and water clarity.
During 2011, two models will be used at Huntington, three models will be used at Edgewater, and three models at Maumee Bay State Park. Which model is used is based on the date; that is, a different model is used at the beginning of the season than at the end of the season. Using different mathematical formulas and different variables in the models for different times of the year minimizes the percentage of incorrect predictions. The models for Huntington and Edgewater were developed with radar rainfall, obtained from the National Weather Service through a series of data transfers. In the event the radar data are not transmitted successfully, a model for each beach was developed as a backup using rainfall data obtained from the National Weather Service site at Hopkins International Airport.
At Huntington, the variables used in the models for the 2011 nowcast are as follows:
Subseason 1 (May 18−July 23): (1) log turbidity (the logarithm of the measured water clarity) plus the wave height (2) radar rainfall from six 4-km grids surrounding the beach during the previous 48 hours, and (3) day of the year. The threshold probability for issuing an advisory using this model is 21 percent.
Subseason 2 (July 24−Sept 7): (1) log turbidity plus the wave height and (2) radar rainfall from six 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight, and (3) instantaneous wind code x wind speed. Wind code is 0.1 for no wind, 1 for winds 91 to 269° (SE, S, SW), and 2 for winds in winds 270 to 90° (W, NW, N, NE, E) at the time of sampling. The threshold probability for issuing an advisory using this model is 30 percent.
Backup model with airport rainfall (entire season): (1) log turbidity plus the wave height, (2) airport rainfall from the previous 48 hours with the most recent rainfall receiving the most weight, (3) day of the year, and (4) instantaneous wind code x wind speed (as described above). The threshold probability for issuing an advisory using this model is 25 percent.
Subseason 1 (May 1−June 15): (1) log turbidity (the logarithm of the measured water clarity) plus the wave height and (2) radar rainfall from two 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight. The threshold probability for issuing an advisory using this model is 28 percent.
Subseason 2 (June 16−Aug 10): (1) log turbidity plus the wave height, (2) radar rainfall from two 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight, and (3) day of the year. The threshold probability for issuing an advisory using this model is 32 percent.
Subseason 3 (Aug 11−Sept 15): (1) log turbidity, (2) radar rainfall from two 4-km grids surrounding the beach during the previous 48 hours with the most recent rainfall receiving the most weight, and (3) instantaneous wind code x wind speed. Wind code is 2 for 270 to 359° (W to NW), 1 for 360 and >0 to 90° (N, NE, and E), and 0.1 for other wind directions (S, SE, SW) or no wind, at the time of sampling.
Backup model with airport rainfall (entire season): (1) log turbidity plus the wave height and (2) airport rainfall during the previous 48 hours with the most recent rainfall receiving the most weight, and (3) day of the year. The threshold probability for issuing an advisory using this model is 30 percent.
Subseason 1 (May and June): (1) solar radiation for the previous day, (2) change in lake level over the previous 24 hours, (3) wind code summed for the previous 4 hours x turbidity, and (4) rainfall in the previous 24 hrs at Toledo Metcalf Airport. The threshold probability for issuing an advisory using this model is 19 percent.
Subseason 2 (July): (1) turbidity, (2) change in lake level over the previous 24 hours, and (3) wind code summed for the previous 6 hours, The threshold probability for issuing an advisory using this model is 25 percent.
Subseason 3 (August): (1) solar radiation for the previous day and (2) instantaneous wind code x turbidity.
For all models: wind code (2 categories) is based on wind direction from Toledo Metcalf Airport—N to E winds (360º or 0º to 90º) are coded as “1” and all other wind directions and no wind are coded as “0.1”.
