With the Climate Prediction Center issuing a La Nina watch for this upcoming winter, the Nebraska State Climate Office would like you to be aware of a suite of products that may help you understand how temperature and precipitation reacted to La Nina and El Nino episodes since the 1950’s. The uniqueness of these data products is that agricultural producers can now match up their yield records with past events to see how their local area production matches up individual events.
Figures 1 (top) shows El Nino patterns for December to February. Figure 2 (bottom) show La Nina patterns for December to February.
La Nina and El Nino events form in the eastern through central Equatorial Pacific. This natural phenomenon occurs on average every 3 to 5 years, with El Nino events having a slightly higher frequency of occurrence in the historical data base. A typical La Nina or El Nina event will begin developing in the late summer and peak in late December before weakening and/or ending prior to or during the onset of the northern hemisphere growing season.
Agricultural Impacts are greater in the southern hemisphere because the peak of La Nina and El Nino occurs during their summer (our winter). The graphics in figure 1 and 2 (Global La Nina, El Nino December to February responses) indicate that some of the typical responses are centered over southeastern Brazil (soybeans), northern Argentina (corn, wheat), northeast South Africa (corn), and northwestern Australia (wheat).
For North America, La Nina patterns favor colder and wetter-than-normal conditions across the Pacific Northwest, wetter-than-normal conditions across the eastern Corn Belt, while warmer- and drier-than-normal condtions are favored across the southern third of the United States.
The CPC has categorized all La Nina and El Nino responses to precipitation and precipitation by ranking each event from weakest to strongest. Each individual year is presented with mean temperature and precipitation departures across the continental U.S. and is an excellent resource for referencing the impacts of the individual events and allowing producers to examine the role these conditions may have potentially had on the following growing season (Four graphics: two La Nina; and two El Nino precipitation and temperature U.S. winter responses).
You will notice from these La Nina and El Nino graphics that several events were multi-year in nature. On average, just over one of every three events will hold together during the spring and summer months, then strengthen during the fall period. This makes understanding spring weather patterns considerably more difficult when summarizing them into useful statistics, since over half of the events have faded into obscurity prior to the heart of the growing season.
The CPC has put together a useful tool that separates severe weather development by El Nino and La Nina events. These severe weather statistics are most pertinent when the event is still ongoing, so they are not as useful in during a spring season when conditions in the Equatorial Pacific return to normal and La Nina or El Nino advisories have ended.
For the central Plains (including Nebraska), severe weather is elevated during Spring when La Nina conditions are still ongoing. El Nino’s generally bring weaker severe weather conditions to the central U.S. You will notice that the area of Oklahoma, northeast Texas, and southeastern Kansas have the strongest responses to La Nina and El Nino conditions.
During El Nino events, the southern jet (subtropical jet) is more active than the northern jet, thus reducing the spin in the atmosphere and available cold air aloft to support thunderstorm development. When La Nina conditions are present, the northern jet stream is usually stronger than in a normal year, which provides the spin and cold air in the upper atmosphere to support and sustain severe thunderstorm development.
The maps show the influence of the El Niño (left) and La Nina (right) on the frequency of tornadoes (top) and hailstroms (bottom).
Source: Allen, J.T., Tippett, M.K., Sobel, A.H. (2015). Influence of the El Niño/Southern Oscillation on tornado and hail frequency in the United States. Nature Geoscience 8, 278–283.
|Winter temperature patterns during strong, moderate and weak El Nino events since 1950.||Winter precipitation patterns during strong, moderate and weak El Nino event since 1950.|
Winter temperature patterns during strong, moderate and weak La Nina events since 1950.
Winter precipitation patterns during strong, moderate and weak La Nina events since 1950.