Forecasts made on October 21, 2014

• As we forecasted consistently since September 22, 2014, our latest forecasts still call for, with a higher confidence, a great possibility of cold air outbreaks in mid-latitudes across the two major continents around the week of Halloween. As indicated by the model forecasts for the stratospheric mass transport index, we still expect that the STRAT_B event would take place between 10/28 and 11/02, which has been forecasted several weeks ago by the model. Latest model forecasts for the cold air branch of the mass circulation started to indicate a stronger equatorward mass transport, as large as 9 trillion tons per day, out of the polar region during the week of Halloween. This assures our forecasts for cold air outbreaks based on STRAT_B forecasts.

• As we first forecasted on October 9, we still forecast the STRAT_C event  will take place during 11/07-11/11. The model forecasts for cold air transport catches a glimpse of this stronger mass transport event, although the forecasts are less decisive. Therefore, we are continuing to forecast STRAT_C and its potential for cold air outbreaks in the week around 11/07-11/11.

• Looking further into the future, there is a possibility of strong mass transport into polar stratosphere in the last week of November and first week of December. We will monitor it to see if it would be STRAT_D event. If so, we will expect a cluster of cold air waves circulating the NH mid-latitudes in the weeks before and after Thanksgiving, which may interrupt holiday travels.

• A more confident forecast than the Thanksgiving one is a strong mass circulation into the stratosphere around December 12-15. Due to its extra long lead time (almost 2 months from today), which is somewhat beyond the model's prediction ability even for the stratospheric events, we will continue to watch for this signal to persist in later forecasts before issuing our official forecasts for it.