You often hear local meteorologists refer to ‘a hole in radar coverage’ in southwest Montana. In fact, it is a common problem that has been researched in detail over the years. It is impossible to see the lower portion of the atmosphere using our current radar technology in parts of southwest Montana.
To understand why you really first need to understand what radar is and how it works. You, no doubt, have at least seen a picture of a radar dome. Many compare the iconic round domes to a giant golf ball. Inside that dome is what looks like a radar dish that spins and tilts inside the confines of the dome. A beam of energy is sent out from that dish as a way of sampling the atmosphere. Anything that the beam might hit along the way is reflected back to the radar site and processed.
That energy can bounce off things like water droplets or ice crystals, even the occasional bird or bug. According to Erik Gustafson from the National Weather Service in Great Falls, Montana, it is that reflected energy that we are watching. “That energy gets reflected back to the radar, and through some computer algorithms it does a little processing and gives us a picture based on the intensity of what that energy coming back to us is” Gustafson explained.
This is where the shortfalls in radar coverage begin. The main National Weather Service radar that covers southwest Montana is located in Great Falls. There are three main reasons that meteorologists in the region can have a hard time getting good returns in radar coverage in southwest Montana at times. It comes down to distance, terrain, and the curvature of the Earth.
Distance: Distance is pretty straightforward. The distance from the radar to Bozeman is about 120 miles and nearly the same for Butte. The radar beam becomes weaker as it hits objects like rain or ice and reflects part of the energy back to the radar site. As it travels, there is less energy reflected back to the radar. This makes the radar less effective at accurately getting data back to the radar.
Terrain: The terrain plays a crucial role in radar coverage. That isn’t unique to southwest Montana. In fact, the vast majority of the western United States has the same problem. For example; the Little Belt mountain range and the Bridger separate Bozeman and where the radar is located in Great Falls. The radar beam is blocked by the rugged terrain making it impossible to get a return back to the radar site.
The curvature of the Earth: This is a little more complicated, but still a major factor. The radar sends the radar beam out at different levels starting at 0.5° above the horizon and scanning up from there. This will allow the radar to ‘look’ at the appropriate level of the atmosphere where we would typically see storms. The radar beam will gradually move higher through the atmosphere as it moves away from the radar site.
Between terrain and the curvature of the Earth, the radar that covers southwest Montana will typically scan above a lot of the winter events. According to Gustafson, the beam itself is about 10,000 feet above Bozeman. Keep in mind, that many of our thunderstorms in the region are can tower from 15,000 feet to 40,000 above the Earth’s surface. The radar can miss the early stages of developing thunderstorms and could miss a lot of detail with the larger storms that could be key to detecting rotation, intensity, or hail that the storm could be producing.
One of the common questions asked is why doesn’t the National Weather Service just add another radar to cover the gap? The short answer is that they can’t because there are none left to add. The WSR-88D radar that is currently being used by the National Weather Service was designed and began being implemented in the 1980s with the Great Falls’ radar installed in the summer of 1994. “We are kind of at the end of the WSR-88D availability,” Gustafson said. “I think the last one was installed in Washington to support out near Seattle”
There are other resources other than radar that may help cover the shortfalls in radar coverage. New technology is playing a part in the process. “We integrate some of the new satellite stuff” Gustafson explained, referencing the new GOES-16 satellite launched last year. “There have been instances where offices (NWS) have been able to issue warnings based on what they are seeing on that one-minute imagery”, Gustafson added.
As the internet becomes more widely available in rural areas in Montana, there is more access to web-based cameras, home reporting stations, and reports from the public. This may not completely compensate for the lack or radar in the region, these are a few of the tools available and meteorologists are taking advantage of those resources.
There is also a push to move to new radar technology, like phased-array radar, but it won’t solve the common problems we have with the WSR-88D that is used today, other than the remote possibility that another radar could be placed in a more beneficial location to help with radar coverage in southwest Montana if one was available.
The meteorologist will need to work with the tools at hand. The current system of radars have a good performance record and are very useful according to Gustafson. “It is amazing that a radar that was designed in the 1980s can do as much as it can to this day and age,” he said. “We will see what the future of the technology will be, but certainly it [WSR-88D] is an amazing tool to have right now”