Synoptic Discussion - March 2021

Note: This Synoptic Discussion describes recent weather events and climate anomalies in relation to the phenomena that cause the weather. These phenomena include the jet stream, fronts and low pressure systems that bring precipitation, high pressure systems that bring dry weather, and the mechanisms which control these features — such as El Niño, La Niña, and other oceanic and atmospheric drivers (PNA, NAO, AO, and others). The report may contain more technical language than other components of the State of the Climate series.


Indices and their agreement with the temperature, precipitation, and upper-level circulation anomaly patterns, by time period (month, week, or other sub-monthly period).
Time Period Key Driver Other Drivers
Month AO+, WPO+ EPO+
March 1-9 AO+, WPO+ MJO, EPO+
March 10-18 AO+, WPO+ EPO+
March 19-31 La Niña AO+

The dominant climate pattern in March was a strongly positive Arctic Oscillation (AO). March 11 was the ninth highest daily AO value since 1950, and the monthly mean was the fifth highest March on record. This signal is particularly noteworthy because February had some of the most negative values on record.

The positive AO was coupled with a strongly positive West Pacific Oscillation (WPO), which shifted the polar vortex towards northeastern Russia with a strong ridge over the North Pacific. This circulation pattern also led to a ridge over the eastern U.S., which contributed to the warm temperatures from the Northern Plains to the Northeast.

The East Pacific Oscillation (EPO) was also positive early in March, which helped extend the ridge towards the southwestern U.S. This pattern weakened later in the month leading to a series of troughs moving across the southern tier. The first of these led to a historic blizzard for the central Rockies and High Plains. The second produce a major tornado outbreak over the Southeast on March 17, which was repeated eight days later by the final trough.

Monthly Mean

Submonthly Evolution

March 1-9

March began with a ridge over the Great Plains that suppressed precipitation across the country. It was also associated with warmer than normal temperatures particularly for the Northern Plains. These anomalies were particularly noteworthy compared with the very cold anomalies from just a few weeks earlier. The ridge was associated with a wavetrain that included a strong ridge over the northwestern Pacific and a trough over the Gulf of Alaska. The northwestern Pacific ridge was part of exceptionally positive AO and WPO signals, while the trough was part of a strongly positive EPO.

March 10-18

During the middle of March, the trough from the Gulf of Alaska shifted southwestward, and the ridge moved from the Plains to the East Coast. The trough over the Southwest led to cold anomalies there. As it moved eastward, it also spawned a strong surface cyclone that led to a historic blizzard for the central Rockies and High Plains. A subsequent trough propagated across the southern tier and led to the first of two significant tornado outbreaks for the Southeast.

March 19-31

The latter part of March featured a more propagating pattern with a series of troughs and ridges moving across North America. On average, the troughs were strongest in the western U.S. and the ridges dominated the Northeast. The last of these troughs led to a second tornado outbreak over the Southeast and flooding to Tennessee.

Atmospheric Drivers

ENSO: El Niño Southern Oscillation

MJO: Madden-Julian Oscillation

  • Description: The MJO is the biggest source of subseasonal (31-90 day) tropical variability. It typically develops as a large envelope of tropical thunderstorms that develops over the Indian Ocean that then moves eastward. Like ENSO, the MJO's effects on tropical rainfall is so strong that it can alter the atmospheric circulation around the globe. The thunderstorms decay when they cross the Pacific, but the associated winds can often continue across the Western Hemisphere to initiate the next MJO in the Indian Ocean. The MJO is episodic, meaning that it is not always active. Most indices for tracking the MJO identify both the MJO's amplitude and the longitude of its strongest rainfall, usually described as one of eight phases.
  • Status: The MJO was active during March. The MJO index began the month in western Pacific (phases 6/7) and propagated smoothly to the Western Hemisphere (phases 8/1) by mid-month. After stalling there for a few days, the MJO continued across the Indian Ocean (phases 2/3) and ended the month over the Maritime Continent (phases 4/5).
  • Teleconnections (influence on weather): The MJO in phase 6 at the start of March was consistent with the warm anomalies observed March 1-9. However, those would usually be followed by cold anomalies in the subsequent weeks, which were not observed.

PNA: Pacific/North American pattern

AO: Arctic Oscillation

NAO: North Atlantic Oscillation

WPO: West Pacific Oscillation

EPO: East Pacific Oscillation

Citing This Report

NOAA National Centers for Environmental Information, State of the Climate: Synoptic Discussion for March 2021, published online April 2021, retrieved on May 9, 2021 from