GardenSMART :: What Does Lack of El Nino, La Nina Mean For Winter
What Does Lack of El NiÑo, La NiÑa Mean For Winter
By Linda Lam, The Weather Channel/weather.com
Photographs courtesy of The Weather Channel
Neither El Niño nor La Niña is expected through winter. The so-called neutral conditions still offer clues on what winter could bring.
This neutral phase means there is no push in the atmosphere in either direction from the equatorial Pacific water. This lack of forcing can make it more difficult to predict the weather pattern in the months ahead, and there are many other elements to consider.
NOAA indicates that the polar jet stream may be shifted farther south and have more of a tendency to allow colder-than-average air into portions of the Midwest and Northeast during a neutral winter.
Meanwhile, much of the southern tier of the U.S. may end up with a warmer-than-average winter overall.
In addition, the subtropical jet stream may shift the track of storms to bring an overall wet winter to much of the South. The Pacific storm track may also result in low-pressure systems moving more into the Northwest versus California compared to a typical El Niño winter.
However, it is important to note that this is just an overall trend of the season from December through February as a whole. Individual cold fronts and low-pressure systems will deviate from this at times.
Sea surface temperature differences compared to average in degrees Celsius. Area in red box highlights where sea surface temperatures are monitored for possible El Niño or La Niña conditions.
When sea-surface temperatures are warmer than average in the eastern and central equatorial Pacific by at least 0.5 degrees Celsius for at least three months along with consistent atmospheric indications, an El Niño is considered to be in place. When sea-surface temperatures are colder than average by at least 0.5 degrees over that same period, a La Niña is in effect.
The latest NOAA update indicates a 55 percent chance of neutral conditions continuing through this winter.
Potential winter weather pattern when El Niño and La Niña are absent.
Impacts on Hurricane Season, Fall From a Neutral Phase
Neutral conditions have been factored into this fall's temperature forecast, with most of the contiguous U.S. likely to see near-to-above-average temperatures. The exception is the Pacific Northwest where near-to-slightly-below-average conditions are currently anticipated through fall.
A lack of El Niño conditions has already played a role in the Atlantic hurricane season forecast.
El Niño can result in widespread and hostile upper-level winds in the Atlantic Basin, which inhibits the formation of tropical cyclones. Without the unfavorable winds that El Niño was expected to bring, there is a higher chance for a more active Atlantic hurricane season than previously forecasted.
El Niño and La Niña are different phases of the El Niño-Southern Oscillation (ENSO) pattern. ENSO refers to the fluctuations in temperature between the ocean and atmosphere in the eastern and central equatorial Pacific that can shift back and forth irregularly every two to seven years.
Each phase of ENSO can trigger some notable changes in temperature, precipitation and winds in the equatorial Pacific. These changes can then disrupt large-scale air movement in the tropics and consequently weather across the globe.
ENSO conditions are just one piece of a large puzzle in determining the weather in a given season or month.
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By Justin Hancock, Monrovia Horticultural Craftsman
Photographs courtesy of Monrovia
Labor Day may represent summer’s unofficial close but now is a perfect opportunity to add late-summer perennials that will continue to beautify your landcare until fall arrives. click here for an article that identifies 9 perennials for late summer.
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