You’ve been there. You're checking the Hobart weather radar, seeing a massive blob of blue and yellow heading straight for the CBD, and you decide to cancel the BBQ. Ten minutes later? Nothing. Not a drop. Or maybe it's the opposite—you're getting drenched while the Bureau of Meteorology (BoM) app shows a perfectly clear sky over Sandy Bay. It’s frustrating. But honestly, it isn't usually a "glitch" in the system.
The Hobart weather radar, specifically the high-tech rig sitting atop Mt Koonya, is an incredible piece of kit, but it’s fighting a constant battle against Tasmania’s wild, vertical geography. Understanding how it actually works—and why it sometimes "lies" to you—is the only way to really stay dry in this city.
The Giant on the Peninsula: Mt Koonya
Most people think the radar is right in the city or maybe up on kunanyi / Mt Wellington. It’s not. The primary "Hobart" radar is actually located at Mt Koonya on the Tasman Peninsula, about 46 kilometers east-south-east of the city.
Why put it all the way out there? Basically, it’s about perspective. If you put a radar in the middle of a valley, it can’t see over the next hill. By sitting 478 meters above sea level on the peninsula, the Mt Koonya radar (a Wurrung-2502C C-band model, for the nerds out there) gets a relatively clear line of sight across Storm Bay and into the Derwent Valley.
It’s got the tallest radar tower in Australia—a 36.6-meter beast—just to make sure it can peer over the local scrub.
Why kunanyi ruins everything (for the radar)
Here is the problem. While Mt Koonya is great for seeing stuff coming in from the Tasman Sea, Hobart’s weather often comes from the west or northwest. To see those rain bands, the radar beam has to travel across the water and then smack right into the massive rock wall that is the Wellington Range.
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Because the radar beam travels in a straight line but the Earth is curved, and because the beam has to be angled slightly upward to avoid hitting every single tree on the peninsula, it often "overshoots" the low-level rain.
When you see "clear" on the radar but you're getting drizzled on in South Hobart, it’s likely because the clouds are tucked in low against the mountain, beneath the radar's "gaze." The beam is literally screaming right over the top of the rain.
Doppler and the "Ghost" Rain
The Mt Koonya site is a Doppler radar. This is the gold standard. Unlike old-school radars that just show where rain is, Doppler measures how fast the rain is moving toward or away from the dish. This is how forecasters spot wind shear or those nasty squalls that flip boats on the Derwent.
But even with Doppler, you get "ghosts." You’ve probably seen weird, stationary speckles on the Hobart weather radar that never seem to move. That’s usually ground clutter.
Even though the BoM uses clever algorithms to filter out echoes from land, the sheer ruggedness of the Tasman Peninsula and the Hartz Mountains means some "noise" always slips through. On cold, clear nights, you might even see "AP" (Anomalous Propagation). This happens when a layer of warm air traps the radar beam and bends it back toward the ground, making it look like a massive storm is brewing over Fredrick Henry Bay when it’s actually just the radar looking at the ocean surface.
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The Backup: Hobart Airport Radar
Wait, isn't there a radar at the airport? Sort of.
The installation at Hobart Airport is primarily a "windfinding" radar. It’s a WF100 C-Band, and while it can do weather watch, its coverage is pretty poor compared to Mt Koonya. It’s surrounded by hills in almost every direction. It’s great for making sure planes don't land in a microburst, but if you’re trying to see if it’s going to rain in Glenorchy, stick to the Mt Koonya feed.
How to read the Hobart weather radar like a local
To actually get value out of the radar, you have to stop looking at the "now" and start looking at the "loop."
- Check the 128km Loop: This is the "sweet spot." Anything further out (like the 256km or 512km views) is often looking so high in the atmosphere—sometimes 3 or 4 kilometers up—that the rain it sees might evaporate before it ever hits the ground. That’s called virga.
- Watch the Movement, Not the Color: In Hobart, rain often "breaks up" as it passes over the Highlands. If you see a solid red block over Lake St Clair, don't assume it’ll stay red by the time it reaches Brighton. The mountains literal-mindedly "squeeze" the moisture out of the air.
- The Cone of Silence: Remember that the radar can’t see directly above itself. If a storm is sitting right on top of the Tasman Peninsula, the radar at Mt Koonya will show a "hole" in the middle of the rain. It’s not a dry patch; it’s just the radar’s blind spot.
Real-world accuracy and the "Drizzle Problem"
Honestly, the biggest weakness of the Hobart weather radar is drizzle.
C-band radars, like the ones used in Tassie, use a wavelength that is great for piercing through heavy rain but not so great at "seeing" tiny, misty droplets. This is why Hobart winters feel so much wetter than the radar suggests. Those grey, misty days where you need your wipers on "intermittent" often won't show up as anything more than a faint grey haze on the screen, if they show up at all.
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It’s also worth noting that Hobart is one of the driest capital cities in Australia (second only to Adelaide!), but our rain is "efficient." When it does rain, it's often associated with cold fronts that have a lot of vertical structure. This is where the Mt Koonya radar shines—it can see those tall, icy clouds from a hundred miles away.
What to do next
Next time you’re planning a trip to the Salamanca Market or a hike up the mountain, don't just glance at the static image. Open the BoM Hobart weather radar loop and set it to the last 30 minutes.
Look at the speed of the echoes. If they’re hauling mail from the west, that "clear" gap might close faster than you think. Also, cross-reference the radar with the kunanyi / Mt Wellington webcam. If the mountain is "cloaked" in white but the radar is clear, you’re looking at low-level cloud that the radar is overshooting.
Stop relying on the "percentage chance of rain" on your phone app. That’s just a statistical average. The radar is the only "live" truth you’ve got—as long as you know its blind spots.
To get the most accurate local picture, always check the latest warnings page on the BoM website alongside the radar. If there’s a "Severe Weather Warning" for damaging winds, the radar might look clear, but the Doppler wind data is telling a much scarier story. Always trust the warnings over a pretty picture of rain.