Bismarck Situational Awareness

The Arctic Oscillation (AO) is compares 1000 mb height anomalies pole of 20N to those across the middle latitudes.

• A positive AO suggests a stronger polar vortex with lower pressures near the pole, allowing the middle latitude jet stream to blow strongly and consistently from west to east, keeping colder air locked in the polar region.
• A negative AO suggests higher pressures in the polar region, weaker zonal winds and the potential for acrtic air to move south into the middle latitudes. (1998 David WJ Thompson and John Michael Wallace)

The positive phase of the NAO reflects below-normal heights and pressure across the high latitudes of the North Atlantic and above-normal heights and pressure over the central North Atlantic, the eastern United States and western Europe. The negative phase reflects an opposite pattern of height and pressure anomalies over these regions.

Strong positive phases of the NAO tend to be associated with above-average temperatures in the eastern United States and across northern Europe and below-average temperatures in Greenland and oftentimes across southern Europe and the Middle East. They are also associated with above-average precipitation over northern Europe and Scandinavia in winter, and below-average precipitation over southern and central Europe.

The positive phase of the PNA pattern features above-average heights in the vicinity of Hawaii and over the intermountain region of North America, and below-average heights located south of the Aleutian Islands and over the southeastern United States. The PNA pattern is associated with strong fluctuations in the strength and location of the East Asian jet stream. 

The positive phase of the PNA pattern is associated with above-average temperatures over western Canada and the extreme western United States, and below-average temperatures across the south-central and southeastern U.S. The associated precipitation anomalies include above-average totals in the Gulf of Alaska extending into the Pacific Northwestern United States, and below-average totals over the upper Midwestern United States.