Polar/Tropical Climate Interaction Leads to 87F Northwest Russia

Sudden Emergence of -NAO Pattern
05/05/2019, 11:47 am EDT
Adverse Climate for the Central U.S. Continues
05/19/2019, 11:11 am EDT
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87F in northwest Russia May 12

Cause is interaction between polar and tropical climate

Record CO2 level a symptom (not a cause) of the event

Discussion: A large stretch (from the Dateline to tropical Africa) of tropical convection associated with the Madden Julian oscillation (Fig. 1) coupled with high latitude high pressure blocking (negative arctic oscillation) have combined to produce more extreme weather events. Included is a record 87F observed in Northwest Russia this past Sunday. The stormy middle latitude pattern propelled by –AO has frequently entrained tropical warmth and moisture from the MJO-inspired tropical convection to produce extreme precipitation in the U.S. and Europe and anomalous warmth released from those convective rains this time convening on Northwest Russia (Fig. 2). Reports of record CO2 levels over Northwest Russia during this anomalous warm event were not the cause but a symptom of the interaction between the polar and tropical climate.

Fig. 1: Easily the strongest MJO signature of 2019 as identified by a large swath of tropical convection from the Dateline to Africa. The stormy mid-latitude pattern driven by a strong –AO regime is entrain the tropical moisture vaulting heavy precipitation and warmth into the middle/northern latitudes.

Fig. 2: A blocking pattern of high pressure over the North Pole emerged this past week causing the polar vortex to split and shift south into 4 centers. The lower latitude upper troughs entrained much warmer tropical moisture from the south where MJO-inspired convection is plentiful. The interaction between the polar and tropical climate caused the amplified upper ridge over Northwest Russia causing the record warmth.