Summary of major North American large scale weather pattern relationships and trends.

ONI - Oceanic Niño Index (ENSO)

“El Niño and the Southern Oscillation, also known as ENSO is a periodic fluctuation in sea surface temperature (El Niño) and the air pressure of the overlying atmosphere (Southern Oscillation) across the equatorial Pacific Ocean. If the ONI exhibits warm or cool phase conditions for at least five consecutive values, it officially becomes an El Niño or La Niña event.” -

QBO - Quasi-Biennial Oscillation

“The quasi-biennial oscillation (QBO) is a quasi-periodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km (0.6 mi) per month until they are dissipated at the tropical tropopause.” - NCAR

(-) Negative (easterly)

Linked to more frequent -AO, -NAO

(+) Positive (westerly)

PDO - Pacific Decadal Oscillation

“The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean. When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value (Courtesy of Mantua, 1999).” -

(-) Cold Phase PDO

Image from NCSU

(+) Warm Phase PDO

Image from NCSU

AMO - Atlantic Multi-decadal Oscillation

“The Atlantic Multi-decadal Oscillation (AMO) has been identified as a coherent mode of natural variability occurring in the North Atlantic Ocean with an estimated period of 60-80 years.” - NCAR

(-) Cold (Negative)

(+) Warm (Positive)

MJO - Madden-Julian Oscillation

The Madden-Julian Oscillation - "The largest element of the intraseasonal (30- to 90-day) variability in the tropical atmosphere. The Madden–Julian oscillation is a traveling pattern that propagates eastward at approximately 4 to 8 m/s (14 to 29 km/h, 9 to 18 mph), through the atmosphere above the warm parts of the Indian and Pacific oceans. This overall circulation pattern manifests itself most clearly as anomalous rainfall" - Wikipedia

Precipitation and temperature trends by phase change throughout the year.

PNA - Pacific North American (Oscillation)

The Pacific-North America (PNA) pattern is one of the most prominent modes of low-frequency variability in the Northern Hemisphere extratropics, appearing in all months except June and July.The spatial scale of the PNA pattern is most expansive in winter.” - NCDC

(-) Negative

  • Wet Great Lakes

(+) Positive

  • Drier than average Wisconsin.

AO - Arctic Oscillation

“The AO is a climate pattern characterized by winds circulating counterclockwise around the Arctic at around 55°N latitude. When the AO is in its positive phase, a ring of strong winds circulating around the North Pole acts to confine colder air across polar regions. This belt of winds becomes weaker and more distorted in the negative phase of the AO, which allows an easier southward penetration of colder, arctic airmasses and increased storminess into the mid-latitudes.” -

(-) Negative

(+) Positive

NAO - North Atlantic Oscillation

“The North Atlantic Oscillation (NAO) index is based on the surface sea-level pressure difference between the Subtropical (Azores) High and the Subpolar Low. 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. Both phases of the NAO are associated with basin-wide changes in the intensity and location of the North Atlantic jet stream and storm track” - NCDC

(-) Negative

(+) Positive

EPO - Eastern Pacific Oscillation

“As the name implies, the EPO is a variation in the atmospheric flow pattern across the eastern Pacific, as well as Alaska. When the EPO is in a positive phase, mild Pacific air flows straight into the West Coast of North America.when the EPO is in a negative phase, a ridge in the upper levels of the atmosphere is present over the eastern Pacific off the West Coast.” - WDT

(-) Negative

(+) Positive