La Niņa and the 1998-99 Winter Forecast
Charlie A. Liles
Q&A
What are "La Niņa" winters like in New Mexico? Historically, La Niņa's produce drier than normal weather in New Mexico. Over the course of this century, precipitation has only averaged 50 to 70 percent of normal during La Niņa winters.
What is the forecast for the (1998-99) winter in New Mexico? For several months now, the Climate Prediction Center's Forecasts has indicated the likelihood of a winter with below normal precipitation and above normal temperatures. This forecast is very strongly influenced by atmospheric models forecasting the strengthening of a La Niņa.
Speaking of long-range forecasts, was the El Niņo forecast for last winter a dud? One can look at the 1997-98 winter precipitation forecast that was issued in the fall of 1997 and compare it to what actually happened. When you look at the entire country, the forecast looks amazingly accurate. However, the forecast didn't work out well at all in a few areas such as central Nebraska, Southwest Texas, extreme northern Wyoming and parts of northern Arizona and northern New Mexico. In New Mexico, the forecast was for a wetter than normal winter. If one takes the entire state and computes the average precipitation for the 1997-98 winter, they find the state average was 120 percent of normal. However, in typical fashion, the range of precipitation across the state was huge. Some locations between Chama and Taos only received about 50 to 60 percent of the normal precipitation, while areas of the Eastern Plains between Clines Corners and Portales collected 200 to over 300 percent of the normal precipitation. If you were stuck in the winter blizzards that hit the Eastern Plains, you were left with the impression that El Niņo did a number on you. If you were around El Rito or Ghost Ranch, you probably thought the whole "El Niņo" thing was just a bunch of hype.
So, what does this mean for the spring's snowmelt runoff? We have to realize that forecast for above and below normal precipitation are for large areas, not specific locations in the state. Consider a winter in which precipitation in New Mexico is 100 percent of normal. It would be normal in such a winter to have some areas of the state receive only 50 percent of the normal precipitation, while other areas received 150 percent. We even have winters in New Mexico when some areas receive as little as 20 percent of the normal precipitation while others get dumped on by 300 percent of the normal precipitation. This kind of disparity is...NORMAL! During a La Niņa winter, when precipitation averages only 50 to 70 percent of normal, some areas of the state will likely see only 20 to 30 percent of the normal precipitation, while other areas receive 120 to 150 percent. NO one can forecast where those areas are going to be.
Does La Niņa mean we won't have to deal with major storms such as the ones that hit the Plains of New Mexico in December 1997? Whether we are in the middle of an El Niņo or a La Niņa, winter storms affect New Mexico every winter. During any winter, some storms will dump from one to three or four feet of snow somewhere in New Mexico. During a La Niņa winter, New Mexico tends to have periods (longer than normal) of tranquil weather interrupted by winter storms.
What happened in New Mexico during the last strong La Niņa? The last strong La Niņa (not that the present La Niņa is considered strong) affected New Mexico the winter of 1988-89. True to form, when you look at the entire winter for the entire state, it was a dry winter. However, the first week of February 1989 was anything but dry for northern New Mexico. One of the more intense storms of the century hit during that week, depositing about 80 inches of snow at Red River in five days and higher amounts of snow in the nearby mountains. This is a good reminder that major winter storms hit New Mexico from time to time, regardless of whether we are in an El Niņo, La Niņa, or neither!
How certain is it that the 1998-99 winter precipitation will be below normal? Even though the signals are pretty strong that La Niņa produces drier than normal winters in New Mexico, we only have about ten La Niņas to draw experience from. Additionally, we have to remember that long range forecasting is in its infancy. Consequently, it would not be wise to bet one's life savings on a long range forecast! Because of La Niņa, it is likely the average 1998-99 winter precipitation in New Mexico will be below normal, but it's not a certainty.
If long range forecasts can't be relied upon with a great amount of certainty, why even have them? One can consider all the ramifications of an accurate long range forecast and the answer becomes obvious. Just consider the value of an accurate winter forecast for the utility companies, the trucking companies, or those who need to plan next year's water dispersion from mountain snowfall runoff. Once you get to thinking about it, the ways in which the weather impacts the entire economy of the country soon produces a very long list. Accurate weather forecasts (long and short range) are a tremendous aid to the country's commerce. This is all the more reason to continue long range forecasts but make them much better. Just realize that as we approach the end of the century, long range forecasts are in the "toddler" stage.