Under the ‘two-thirds’ rule … forecasters who have entered at least THREE forecasts are included in the interim standings.
Complete interim statistics table and charts at the Contest/s web site here.
Forecaster verification statistics for Winter '16 / '17 contest storms here.
SUMSQ errors for each contest snow storm are normalized with a 'Z-score' ... then averaged to compute the standings. If a forecaster has issued forecasts for more than two-thirds of all snow storm contests ... then Z-scores from their 'best two-thirds' forecasts are used to calculate the Interim and Final standings.
Same idea as dropping the lowest quiz score before computing the final grade.