Brad Withrow-Robinson, Forestry & Natural Resources Extension agent in Benton, Linn and Polk Counties
Dr. Chris Daly knows weather. And he really likes weather data. Lots and lots of data.
Chris in his office at PRISM Climate Group.
Chris is director of the PRISM Climate Group at Oregon State University which uses vast amounts of weather data, including your OST/CoCoRaHS observations to help predict the future: the weather. Chris is also a senior scientist at the HJ Andrews LTER (Long Term Ecological Research program). Oh, and let’s not forget that Chris is an OST/CoCoRaHS weather observer at home too.
PRISM (Parameter-elevation Regressions on Independent Slopes Model) is a sophisticated computer model that estimates weather and climate variables like precipitation and temperature for areas where there are not actual observations. This is important because while there are thousands of weather stations across the country, there are many, many more locations for which no weather observations exist, and forecasters have to fill in the gaps to know what might be happening in those locations.
PRISM is a valuable tool because it does not just interpolate numbers for areas between actual weather data observations to “connect the dots”, but it simulates how weather and climate varies across the landscape by elevation and aspect, while accounting for temperature inversions, rain shadows and coastal effects. The model has a grid of millions of cells (each measuring only about a ½ mile across), over the entire conterminous US, and fills in the empty grid cells every day, creating a more continuous and accurate image. By filling in these gaps in information, PRISM helps make large global weather models more accurate and relevant at a local scale.
The global weather models are powerful tools which are great at predicting things like the movement of the jet stream, the
development of high pressure ridges and low pressure troughs, which help predict big weather patterns affect our region. But PRISM shows how the big patterns will differ at the small local scale and allow weather and climate forecasters to give different forecasts for Corvallis, Salem and Pacific City. It is PRISM which is telling you to bring a sweater when going to the coast during a Willamette Valley heat wave. PRISM daily data are used in other ways, including the federal crop insurance program, streamflow forecasting, drought assessments, and many more.
This is why your individual OST observations are so valuable. The CoCoRaHS data which you observe and report daily is gathered and incorporated into the long term PRISM data set. It is the nuances of those many observations, from slightly different location on the landscape that help give PRISM its power to make important distinctions in local predictions which are then used by many organizations to develop their daily local forecasts, including the National Weather Service, the Weather Channel, National Drought Mitigation Center, USDA among others.
I recently asked Chris if there is some magic “optimal” number and density of CoCoRaHS observers that we should be trying to attain on the landscape. “No.” he said. “Each site is unique. There is value in a station removed from others, but also value in having a cluster of stations, especially in a complex terrain. A group of neighbors up, down and across a valley in the cascades or in the complex canyons of Eastern Oregon gives us a lot of insight on the weather, and helps improve our model.” His program collects and uses the daily data, and the more data we provide in an area, the better the weather and climate modeling for that area gets.
It is no surprise then that Chris was instrumental in shaping the idea of Oregon Season Trackers program, has been an enthusiastic supporter of both CoCoRaHS and OST, and loves to see the rapidly growing team of OST observers.
Chris and the PRISM model are also a big part of the work at HJ Andrews trying to understand how weather and terrain interact in that mountainous ecosystem. I will talk about that work, and some of what they are discovering another time. But OST observations are likely to make that work more widely applicable across the state.
PRISM produces maps for the entire country.
So next time you see a local weather forecaster predict differences up and down the Valley, know that you are contributing to that forecast each morning when you go out to read your rain gauge. Well done!
Editor’s note: This is one of a series of Observer articles that will introduce some of the key people in OST program: Research scientists, citizen scientists, participating school groups and Extension folks.
