{"id":21238,"date":"2021-02-23T21:27:16","date_gmt":"2021-02-24T02:27:16","guid":{"rendered":"https:\/\/site.extension.uga.edu\/climate\/?p=21238"},"modified":"2021-02-23T21:28:22","modified_gmt":"2021-02-24T02:28:22","slug":"why-seasonal-climate-forecasts-arent-always-accurate","status":"publish","type":"post","link":"https:\/\/site.extension.uga.edu\/climate\/2021\/02\/why-seasonal-climate-forecasts-arent-always-accurate\/","title":{"rendered":"Why seasonal climate forecasts aren\u2019t always accurate"},"content":{"rendered":"\n

Do you use predictions of seasonal climate to plan your farm work? Or are you frustrated because they don\u2019t seem to be very useful? I\u2019ve been getting a lot of complaints this year about how bad the climate forecast for winter was because what we have seen so far has not matched the predictions in many parts of the country. Let me take a few minutes to explain how they are made and what you can learn from them.<\/p>\n\n\n\n

First, let me specify that I am not talking about long-range climate forecasts for 50 years down the road. Nor am I talking about weather forecasts for the next week. I am talking about the forecasts that cover the period from about 15 days to 3 months, which climatologists call the \u201cseasonal to sub-seasonal forecasts\u201d. These are the kinds of forecasts that say \u201cWinter is likely to be warmer and drier than normal\u201d or \u201cGet ready for a big warm-up in the next month.\u201d They can be useful in planning field work a few weeks ahead, but they come with caveats.<\/p>\n\n\n\n

\"\"
“Glory of the Snow” in the snow. Taken by User:Ruhrfisch April 2006, Commons Wikimedia.<\/figcaption><\/figure>\n\n\n\n

Unlike weather forecasts, there are only a few models that predict climate in the monthly to seasonal time period. That is because we can\u2019t just run the weather models out four to twelve weeks and expect to get anything like real weather. The weather models are built to handle short time steps and detailed information about temperatures, rainfall, and all the other factors that make up your daily weather, and to do it fast enough that you can actually use the forecast to decide when to wear your raincoat. They are useful out to about a week, but then their accuracy starts to break down because there are too many things going on around the globe to capture accurately over time, and so the short-term models tend to drift away from reality the farther from \u201cnow\u201d you get. Models for monthly to seasonal climate tend to be based not on dynamical atmospheres like weather models but on statistics. <\/p>\n\n\n\n

\"\"
La Nina causes the jet stream to move northward and to weaken over the eastern Pacific. During La Nina winters, the South sees warmer and drier conditions than usual. The North and Canada tend to be wetter and colder. Source: https:\/\/oceanservice.noaa.gov\/facts\/ninonina.html)<\/figcaption><\/figure>\n\n\n\n

NOAA\u2019s Climate Prediction Center (https:\/\/www.cpc.ncep.noaa.gov\/<\/a>) is the biggest provider of seasonal forecasts, although there are a few others out there. This year we are in a La Ni\u00f1a, and so most of the seasonal forecasts have been based on that affecting our climate this winter. I won\u2019t discuss La Ni\u00f1a here today (that is a topic for a future post, perhaps) but you can read a good general description at https:\/\/oceanservice.noaa.gov\/facts\/ninonina.html<\/a>. The basic patterns of La Ni\u00f1a affect the temperature and precipitation across the United States in fairly predictable ways, and you can use statistics to show these patterns. You can see some examples of how La Ni\u00f1a has affected past winters at https:\/\/www.weather.gov\/mhx\/ensoninaanomalies<\/a>. This year, the primary predictors of the winter climate have been the La Ni\u00f1a and the persistent trend that we are seeing towards warming temperatures due to greenhouse warming. From a statistical standpoint, it made great sense to predict that this winter would be warmer and drier than normal in the southern US and colder and wetter than normal in the north, because that is statistically the most likely pattern to expect in a La Ni\u00f1a winter, even when the climate is trending warmer over time.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

So why did it not work this year? Because statistics can\u2019t account for rare events that don\u2019t follow the expected patterns. At the end of 2020 the atmosphere over the North Pole experienced a Sudden Stratospheric Warming (SSW), which means that the atmosphere about 10 miles above the North Pole suddenly got much warmer than usual. That messed up the usual distribution of temperatures in the Northern Hemisphere and helped push the really cold air to the south. It also pushed the winter storm track far south of where it usually occurs, making this a very wet winter in the Southeast, which is not what we expected! My farmers are not happy, but at least it means less likelihood of drought this summer. You can read more about the SSW at https:\/\/climate.gov\/news-features\/blogs\/enso\/sudden-stratospheric-warming-and-polar-vortex-early-2021<\/a>. It might happen only once every ten years, or the cold air might just get pushed in a different direction next time, missing you and your winter garden altogether. Since the models are based on statistics, they will always show the most likely pattern, and instead we might experience winter that happens just once in ten years. Not so different that being the lucky person who gets rained on when the National Weather Service predicts just a 10 percent chance of precipitation!<\/p>\n\n\n\n

\"\"
90-day temperature departure from normal. Source: https:\/\/hprcc.unl.edu\/maps.php?map=ACISClimateMaps<\/figcaption><\/figure>\n\n\n\n

The good news is that we are getting better at these sub-seasonal to seasonal predictions, and we can expect to see improvements in the future as computers become more powerful and we have more experience looking at these periods. But for now, statistical models will continue to control the predictions at these intermediate periods, and we will continue to see the occasional miss when an unusual weather event occurs.<\/p>\n\n\n\n

Also published in the Garden Professors blog<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Do you use predictions of seasonal climate to plan your farm work? Or are you frustrated because they don\u2019t seem to be very useful? I\u2019ve been getting a lot of complaints this year about how bad the climate forecast for winter was because what we have seen so far has not matched the predictions in […]<\/p>\n","protected":false},"author":58,"featured_media":21205,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-21238","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-climate-science"],"_links":{"self":[{"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/posts\/21238","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/users\/58"}],"replies":[{"embeddable":true,"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/comments?post=21238"}],"version-history":[{"count":3,"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/posts\/21238\/revisions"}],"predecessor-version":[{"id":21241,"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/posts\/21238\/revisions\/21241"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/media\/21205"}],"wp:attachment":[{"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/media?parent=21238"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/categories?post=21238"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/site.extension.uga.edu\/climate\/wp-json\/wp\/v2\/tags?post=21238"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}