The monitoring page of the “October pattern index” (OPI) is presented. The OPI index
represents a analytic synthesis of the October hemispheric pattern at 500 hPa, and shows from
previous studies quite a high correlation (r ≈ 0.9) with the winter mean Arctic Oscillation Index
(DJF AO); this implies that the lower the OPI index is in October (negative values) and the higher
will be the probability to have a weak polar vortex during the following winter. Therefore the OPI
index could be a valid support tool in the seasonal forecasting of the winter season.
The OPI index is calculated through a dedicated software modeling elaborating the 31 daily
hemispheric October at 500 hPa. This monitoring page is updated automatically with every run of
the global forecast model GFS (Global Forecast System), except the 18:00z run. The software
analyzes the previous consolidated daily charts plus 10 forecast charts as given by the GFS model.
For example on the 15th of October, the software calculates the OPI index based on the 15
consolidated daily charts (1-15 October) adding 10 forecast charts as given by the GFS model (16-
25 October). The definitive OPI index will be available only at the end of October, when the
software will be able to elaborate all the 31 daily consolidated charts of the month. During the
month the index will gradually tend to the final value starting to be reliable past the half of the
month, when the consolidated charts number will overtake the forecast charts number.
Finally, at the beginning of November, the official seasonal forecast for the winter 2014-2015
will be released based on the final OPI value and on the recent developments of this research whose
results have been discussed and analyzed so far with Prof. Judah Cohen (Director of Seasonal
Forecasting at AER) and the Italian Air Force Lt. Col. Guido Guidi.
OPI monitoring page link:
http://app.til.it/opi/
