What we do: We are making sub-seasonal forecasts for time periods of high probability of cold air outbreaks in Eurasia and North America 30-40 days in advance. We issue such forecasts on a weekly basis and this website is updated around Thursday each week.
New Feature: Maps of probability of cold surface temperature anomalies over both North America and Eurasia continents in the vicinity of forecasted stratospheric PULSE events
New Forecast Made on January 14:
No new stratospheric PULSE event is named this week.
Minor warming event (02/07 – 02/10)
We continue to forecast a minor warming event to occur around 02/07 during or immediately after STRAT_F1. This minor SSW event would cause a temporary relocation of the polar stratospheric vortex off the Arctic
We forecast a prolonged cold period (about three weeks long starting around on Jan. 20) associated with the three PULSE events: STRAT_F, STRAT_F1, and to STRAT_G.
Follow up on Forecast Made in the Previous Weeks:
STRAT_D1 (12/24 – 12/31), first forecasted on 11/25 and later revised on 12/03, occurred in the range as we forecasted. STRAT_D1 turns out to be a three-peak cluster event and our forecast did successfully catch the first two peaks. The first peak of STRAT_D1 occurred on 12/26 and the second peak occurred on 12/30, both transported 0.6 trillion tons of air mass per day into the polar stratosphere. The third peak occurred on 01/03 with a strength of almost 0.8 trillion tons per day. As we forecasted, STRAT_D1 mainly affected North America rather than the mid-latitudes of Eurasia. The first two peaks of STRAT_D1 event were associated with the winter storm Fortis, which swept through the North American continent, causing below-normal temperature in the Western United States and bringing heavy snow to New England Area. The third peak of STRAT_D1 is associated with the winter storm Helena, which has already brought snow to the West and Midwest in the last few days, and will continue to bring snow and ice to the Southeast, causing travel to a standstill.
STRAT_E (01/08 – 01/13), first forecasted on 12/03, has happened. It peaked on 01/09/2017 with a peak net mass transport into the polar stratosphere about 1.1 trillion tons per day. The current winter storm Jupiter is associated with our STRAT_E, which is bringing ice storm to parts of the Plains and Midwest through next Monday, causing damages to infrastructures and agriculture, and posing threats to transportation and people’s lives. Meanwhile, the winter storm Egon is bringing chaotic winter weather to Europe. Cold weather hampers Europe’s rail service, continuing to trouble travelers, and causing chaos in many areas in Europe.
STRAT_F (01/23 – 01/28), first forecasted on 12/10 with a 45-day lead. STRAT_F is still expected to occur on time. It looks to be the first peak of a long lasting strong cluster event. We expect the main peak to occur on 01/24, transporting about 1.2 trillion tons per day of air mass into the polar stratosphere. The second peak was forecasted last week as STRAT_F1. Most area of extratropical latitudes of Eurasia (north of 45°N) is expected to experience below-normal temperatures, while North America is anomalously warm at the early stage of STRAT_F. Followed is a remarkable drop in surface temperature over North American continent, especially the western coast, during the last week of January.
STRAT_F1 (02/02 – 02/06), first forecasted on 01/07, is still expected to occur on time right after STRAT_F between 02/02 to 02/06 with a peak on 02/03. STRAT_F1 together with STRAT_F event, forms a cluster of PULSE events. Associated with STRAT_F1 are new round of cold air outbreaks over both continents.
STRAT_G (02/11 – 02/15), first forecasted on 01/07, is still expected to occur on time. We consider STRAT_G as an “aftermath” event that occur after the minor stratospheric sudden warming event during the migration of the polar vortex back to the Arctic. We believe STRAT_G will bring below-normal temperature to both North America and Eurasia continents.
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