First stratospheric warming/arctic air generation event of season
Discussion: In the stratosphere a large area of warming over East-central Asia is occurring now and will expand westward across Southern Russia this weekend into early next week (Fig. 1). As the stratosphere warms and expands the troposphere below contracts and cools and causes higher pressure due to the (more) weighty troposphere at ground level which is the recipe for artic air development.
Fig. 1: Stratospheric warming is indicated in the 10 MB temperature anomaly forecast by the ECM ENS.
Central and southern Russia turns very cold and snow cover increases in both the day 1-5/day 6-10 period (Fig. 2-3). The tendency is for the core of the arctic air to ease southward. Snow cover increase could hold this air in-place for a while as dislodging cold air masses from this region can be difficult due to no exposure of maritime warming.
Fig. 2-3: The ECMWF OP day 1-5/day 6-10 temperature anomaly forecast across the Middle East to Russia.