Over the years I have had people ask me to prepare a weather forecast for their wedding that is coming up in a year. There is a very simple answer to that request. There is no way I can give you an accurate weather forecast that far in advance. I always follow that up with the explanation that they could contact me a week or so before the event and I could start with the seven day outlook and then count them down day-to-day as to the kind of weather they should expect.
It has been my experience that our forecasts for days one, two, and three are quite accurate but once we get past those days and see days four through seven, the confidence level drops a bit each day. The National Weather Service can forecast out fifteen days and any farther out is more of a trend rather that a specific forecast. As I have discussed before I have lived all over the country and each place where I lived posed a different set of complications to accurately forecasting the weather.
There are times, here in the Pacific Northwest, when things change so quickly that the forecast can’t keep up with the changes fast enough. Take for example when I lived in Eau Claire, Wisconsin back in the mid 1970s. By the time most of the winter storms were approaching our area the storm had what I call a “personality.” Let’s say in moved onshore at the Pacific coast. The storm would then push eastward past the Coast Range mountains, the Willamette Valley, the Cascades, Eastern Oregon, the Rocky Mountains, and then the Plains before striking Wisconsin.
With that history the forecaster has a better handle on what the storm might do next by following what it had already done. You add in the satellite and surface weather station data and plug that information into a computer program and there is your forecast. The National Weather Service has depended on geostationary satellites to see the clouds and storm structure over the globe. Geostationary satellites stay in one spot above the earth so they can look at a one area of the Earth over period of time.
Now, here we are in Oregon. What history do we know about a storm that is steaming across the Pacific Ocean and poised to change our weather? Not as much, I say. We do have a battery of satellites orbiting the earth and some which are stationary that can look down at weather systems and see, not only visibly, but also with infrared technology to collect as much data as possible to make a forecast. What really complicates things is the terrain these storms must traverse once they move over land. The Coast Range and its various passes can have a various amount of effects on a storm which can change in a moments notice. There are also some weather reports from ships out on the Pacific Ocean, but that data doesn’t come near to the amount of information that can come from following a storm’s life as it moves across much larger distances.
Why do I bring this up? Simple, I ran into an article in the Bulletin of the American Meteorological Society titled “What is the Predictability Limit of Midlatitude Weather?” The authors of the paper discussed in the Journal are Fuqing Zhang and Y. Quiang Sun from the Department of Meteorology and Atmospheric Science, and Center for Advanced Data Assimilation and Predictability Techniques, The Pennsylvania State University, University Park, Pennsylvania.
Quoting the introduction to their paper “Weather forecasting has improved dramatically since the introduction of numerical weather prediction (MWP) nearly 6 decades ago (Bauer et al. 2015). This has been accomplished through ever-increasing computing power, improved models running at ever-increasing resolution with more accurate representation of atmospheric processes, and more sophisticated four-dimensional data assimilating algorithyms that can better injest ever-increasing volumes and quality of in situ and remotely acquired observations (WMO 2015).” That is a brief history of the growth of weather prediction.
From their abstract: “Understanding the predictability limit of day-to-day weather phenomena such as midlattitude winter storms and summer monsoonal rainstorms is crucial to numerical weather prediction (NWP).” The predictability limit is studied by using high-resolution global models with ensemble experiments of the European Centre for Medium-Range Weather Forecasts (ECMWF; 9 km. operational model) and identical twin experiments of the U. S. Next-Generation Global Prediction System (NGGPS; 3km).
Thirty years ago the extended outlook could only reach out to seven days. Now the forecast window goes out to 10 days. Using the newest techniques available they hope to be able to extend the forecasts past that 10-day threshold. However, they feel that there will be a limit as to just how far past the 10-days an accurate weather forecast can pushed.
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