Notes from the Field

Introducing OLYMPEX, A Ground Validation Field Project in the Pacific NW

November 1st, 2015 by Dr. Lynn McMurdie


I live in Seattle, part of the Pacific Northwest in the NW corner of the continental United States. We have the reputation of being a very rainy place, but it’s nothing compared to the Olympic Peninsula, just to my immediate west. Starting next week, we begin the Olympic Mountain Experiment, or OLYMPEX. It is a NASA-led field campaign, which will take place from November 2015 through February 2016. The goal of the campaign is to collect detailed atmospheric measurements that will be used to evaluate how well rain-observing satellites measure rainfall and snowfall from space. In particular, OLYMPEX will be assessing satellite measurements made by the Global Precipitation Measurement (GPM) mission Core Observatory, a joint mission by NASA and the Japan Aerospace Exploration Agency (JAXA), which launched in 2014.


The Olympic Peninsula is an ideal location to conduct a ground validation field campaign. The Peninsula is home of a temperate rain forest, with old growth trees covered in lichen and moss. Its active winter storm season consists of wet weather systems traveling from the Pacific Ocean, over the coastal region and into the Olympic Mountains. The peninsula reliably receives annual precipitation amounts ranging from over 100 inches (2500 mm) on the coast to about 180 inches (4500 mm) in the forested mountainous interior.


This is Joe Zagrodnik, graduate student at University of Washington, on his way up to install instruments at one of our ground site. That’s some tree.

I am a Senior Research Scientist and Senior Lecture in the Atmospheric Sciences department of University of Washington and Project Manager and one of the lead scientists of OLYMPEX. Together with colleagues here at UW, other universities, Environment Canada and, of course, NASA, we have set up ground instruments including rain gauges, advanced weather radars, and balloon launching sites to monitor incoming storms. Simultaneously, we will collect data from three aircraft flying through and above rain clouds, as well as from the GPM Core Observatory and other rain-observing partner satellites when they pass overhead.

Much of our ground network is in place and collecting data. We are currently experiencing a very wet storm system and the NASA ground instruments measured 24-hr rain amounts ranging from 35 mm (1.3″) on the coast to over 170 mm (6.7″) at a station at 540m elevation. This station is actually not at a terribly high elevation. Mt. Olympus is much higher at almost 2400 m, but 540m of elevation is enough to really affect the storms systems when the air is forced up and over the terrain enhancing the rain producing processes.


This is a map of 24-hr precipitation totals in mm as measured at a variety observing stations, including some installed for the OLYMPEX field project.

As the field campaign ramps up over the next couple of weeks, we will keep everyone posted about the progress of the project, the storms we are sampling and the experiences we’re having as we try to keep up with onslaught of storm systems from the Pacific Ocean.



8 Responses to “Introducing OLYMPEX, A Ground Validation Field Project in the Pacific NW”

  1. Mike Dawson says:

    It’s great to get the attention on the Olympic Peninsula through this project! I am really curious to see how much is learned about the extreme differences here between the wet side and the rainshadow. It’s too bad that last storm system came through before the project had completely started. It seems like the chance of getting a GPM pass right over the Olympics during such an event might be a little tricky?

    • lmcmurdie says:

      Thanks for your comments Mike. We too are really curious to see those extreme differences in precipitation between the wet side and dry side. What’s also really interesting is the variations in the degree of orographic enhancement on the wet side. In the Halloween weekend storm, there was a factor of 4 to 5 difference between rain totals on the coast and the rain totals on the southwestern slopes of the Olympic Mountains. In other cases, there is only 1.5 to 2 times the precipitation on the Olympics versus the coast. We’re not really sure what the processes are that controls those enhancement differences. Yes, too bad the project wasn’t completely ramped up for that storm, but we should be ready for the next one. We typically get GPM overpasses two times a day. However, it’s not critical to coordinate with that. The aircraft that are coming have the same instruments as the satellite, so we can fly the airplanes back and forth simulating the measurements made by GPM.

  2. mashy says:

    Love earth.!!!

  3. mashy says:

    Love earth.!!!

  4. Jon Preston says:

    Thanks to NASA JPL and the team for the tour of the DC8 on Veterans day. These last couple of days have shown the true colors of the windward slopes of the Olympic mountains. I have been collecting data on rainfall and rainwater chemistry in the Hoh valley for quite a few years now. This last event was a pretty fine example of an atmospheric river interaction with the Olympics. From the looks of things, it looks like a pretty good data set was amassed. Those were some impressive numbers! Looks like we will probably be transitioning to a post frontal instability environment for tomorrows satellite pass. Stay safe out there. Keep a pot on the stove. Great weather for hot chocolate.

    • Dr. Lynn McMurdie says:

      Amazing totals indeed! We got a foot of rain in 16 hrs at one of our sites and 6- 10″ at many others all in about 16 hours. Event totals were closer to 15″ in places. We flew both days and are still trying to dig out from the deluge of rain and the deluge of data! Thanks for your support!

  5. Melli says:

    Interesting how terrain affects rainfall totals…don’t have the wherewithal to look historical sat images, but it does appear it came from the South. I note your observation that mid elevation stations got blitzed, yet lowland areas didn’t. And the peaks didn’t see any precip.
    So, is this experiment to calibrate the sat instruments? Curious, by which method they ascertain precipitation data?

    • Dr. Lynn McMurdie says:

      Yes, this storm system had a strong southwesterly flow moving warm moist air straight into the Olympic Peninsula and the Olympic Mountains. You have to be a little careful with the real time rain map we produce every day. The four high elevation stations are SNOTEL sites that don’t update as often as the other stations and sometimes those totals don’t get plotted. It doesn’t mean that they didn’t get precipitation, it’s just we didn’t plot it on the map as it happened. We will go back and fill in those numbers later. They most likely got as much or more than the mid elevation stations. Yes, this experiment is to calibrate the satellite based instruments that measure rainfall. Those satellite instruments are either a radar-type instrument or a passive microwave instrument. You can read more about the satellite and the instruments at: