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How did a negative North Atlantic Oscillation phase affect northern Europe?

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Line graph showing estimated temperature variations from 1000 to 2000 CE for the Northern Hemisphere and central England, with three lines representing different data sources. The chart highlights the medieval warm period around 1100-1300 and the Little Ice Age from about 1500 to 1850, followed by a sharp temperature rise in the late 20th century. Temperature is shown as deviations from the 1961-1990 average. — Little Ice Age Estimates of temperature variations for the Northern Hemisphere and central England from 1000 to 2000 ce.

During the Little Ice Age, the dominance of the negative phase of the North Atlantic Oscillation (NAO) significantly altered the climate of northern Europe.12

In this negative mode, the pressure cells over Iceland and the Azores are weak, which reduces the pressure gradient across the North Atlantic. This weakening slows the pace of the prevailing westerly winds that typically transport warm, moist maritime air into Europe. Consequently, the region experiences the following effects:123

Colder Temperatures: The reduced westerly flow allows cold, dry air to be drawn into northern Europe from the Arctic and northern Russia.12
Drier Conditions: Because the storm track is redirected toward the Mediterranean, northern Europe receives less precipitation than normal during these winters.12
Increased Variability: The shift contributed to the overall climate instability of the period, characterized by long, cold winters and short, wet summers, which frequently led to crop failures and famines across northern and central Europe.2