|El Niño-Southern Oscillation||Arctic & North Atlantic Oscillations||Pacific/North American Pattern||Pacific Decadal Oscillation||Interactions||Influences on Snowfall||Current Conditions|
|El Niño-Southern Oscillation|
The most common way of monitoring the El Niño-Southern Oscillation phase is by looking at sea surface temperatures in the equatorial Pacific Ocean. The animated map below shows sea surface temperature anomalies over the past three months. Warm/positive anomalies are associated with the El Niño phase, while cool/negative anomalies are associated with the La Niña phase.
Several climate models also provide ENSO forecasts, again based on sea surface temperatures over a specific region in the equatorial Pacific Ocean. The graph below shows the observed ENSO phase for the previous three-month period (as a black circle near the left side of the image), along with computer model forecasts for the next 12 months. The thick yellow line represents the average forecast of all dynamical models.
(Forecast plume currently unavailable)
In North Carolina, a warm/positive phase (El Niño) event is often associated with cooler, wetter conditions and an increased chance of winter weather. Likewise, a cool/negative phase (La Niña) event often brings North Carolina warmer and drier conditions. The impacts of ENSO on North Carolina are most prominent during the winter.
Because ENSO conditions are generally slow to change, with a frequency on the order of months to seasons, we have some skill at issuing forecasts on a seasonal and even annual basis.
For more information about ENSO, visit our information page or the Climate Prediction Center's page that includes past, current and forecast conditions.
|Arctic & North Atlantic Oscillations|
The closely related AO and NAO are typically measured by comparing atmospheric conditions from locations in the Northern Hemisphere. For the AO, this measurement includes an average of low-level geopotential heights at locations north of 20° latitude. For the NAO, the index is a measurement of the difference between 500 mb heights or sea level pressure readings in the Azores Islands and Iceland, which gives a good indication of the relative strength of the high and low pressure systems in those areas.
The graphs below show the AO index (top) and NAO index (bottom). The black line indicates the observed values, while the red lines indicate forecasts from a set of computer models (known as an ensemble).
The AO and NAO can have significant impacts to North Carolina, especially during the winter. Positive phase AO and NAO events often see warmer weather in NC, while negative phase AO and NAO events are typically associated with cooler weather and an increased chance of winter weather.
Compared to ENSO, both the AO and NAO change on a much shorter timescale, on the order of weeks instead of years. This means skillful forecasts for these oscillations are limited to less than one month in the future.
For more information about the AO and NAO, visit our information page or the Climate Prediction Center's Arctic Oscillation and North Atlantic Oscillation data sources.
|Pacific/North American Oscillation|
The PNA is characterized by large-scale high and low pressure centers at four locations in the Northern Hemisphere. A PNA index can be measured by calculating the difference between the 500 mb geopotential heights at these four locations.
The graph below shows the PNA index, including the observed values (black line) and computer model forecasts (red lines).
A positive phase PNA event is associated with jet stream "dips", or troughs, over the eastern US, leading to cooler temperatures for North Carolina. Negative phase PNA events see the opposite effect -- jet stream ridging -- over the east coast, bringing warmer temperatures to NC.
Like ENSO, the PNA pattern is most prominent in the winter, but like the AO and NAO, its forecasts are limited to about one month into the future.
For more information about the PNA, visit our information page or the Climate Prediction Center's page.