Watch as a weather instrument

[Arthur]

I have a Suunto Ambit 3. First question. If I understand it correctly and this seems to be the pattern, the sea level barometric pressure on the watch is compensated by the gps altitude and will be steady as the altitude in hiking changes as long as the weather does not change. Correct? Second question. Therefore, it should be a good weather indicator of approaching storms if the pressure reading drops. Third question. Does this barometric prediction method even work in the typical pop up afternoon thunderstorms so common in the mountain west? It would seem to work well in a lot of the country where fronts move thru, but that less common in the mountains where pop ups are the rule there. Thoughts?

[Todd T]

The watch has a pressure sensor that has to be calibrated.  My Suunto Core lets you do that by either setting the known (adjusted-to-sea-level) barometric pressure or the known elevation.  I’ve found setting the baro a much better way to go.

I don’t know if the Ambit has the same “auto” setting as my Core, but if so I highly recommend using it.  Calibrate while you’ve got access to a local weather report, then let the auto do it’s thing.  It watches the rate of change in the pressure to intuit whether you’re moving or not, and adjusts either the baro setting or the elevation setting in response.

If you don’t have that auto feature, you have to just recalibrate as needed.  The smart money is on (a) not going nuts recalibrating at every pass or lake (i.e., let the small weather changes average out) and (b) not expecting accuracy to more than a couple hundred feet.

[Bruce Tolley]

The manual  is on the Suunto website,

From the Ambit3 manual:

“The weather trend indicator is comprised of two lines forming an arrow. Each line represents a 3-hour period. A change in barometric pressure greater than 2 hPa (0.59 inHg) over three hours triggers a change the direction of the arrow.”

You also have a storm warning:

“Storm alarm A significant drop in barometric pressure typically means a storm is coming and you should take cover. When the storm alarm is active, Suunto Ambit3 Peak sounds an alarm and flashes a storm symbol when the pressure drops 4 hPa (0.12 inHg) or more during a 3-hour period.”

I am no weather expert but I would posit that even a very local storm front causes a drop in barometric pressure.  I occasionally use the weather indicator on my Suunto Vector but I find that the Mike Clelland LATS method works just as well for backpacking and does not require the manual calibration the Vector requires. LATS = look at the sky.

[David Thomas]

With an old-school mechanical altimeter, if you gained elevation “for free”, (like the altimeter said you were higher in the morning than you were the previous night, or you’d previously set the altimeter at a known elevation and now it shows too high and has to be readjusted down), that’s like cheating and cheating is bad and forecast bad weather.  That was my mnemonic device:

Unearned (apparent) gain in elevation = cheating = bad = bad weather ahead.

And Bruce is right, air pressure under a thunderstorm is lower than in the surrounding area.

[Matthew / BPL]

I have found the weather trend indicator and storm alarm to be effective predictors of stormy weather in my home town.

Unfortunately I haven’t spent much time at significant and varying altitude since I picked up the watch so I can’t speak to how well it works for predicting storms in the mountains. I have been slightly disappointed to discover the watch seems to need occasional altitude calibrations. This puzzles me given that it’s hitting GPS satellites every minute.

edit: Ambit 3 Peak

[SIMULACRA]

Fenix5X is random in effectiveness. More often than not, I get the alert after it’s been raining hard for a bit. Then sometimes way before nothing happens. I’ve messed around with changing the measurement increments in the allotted timeframe. Re-calibrating every so often at sea level or otherwise. Overall it’s okay. Maybe a ‘meh.

[Ian]

I don’t own the OP’s watch but I own a Pathfinder ABC watch.

It has a setting where I can track barometric pressure trends on a graph from the main screan.

Anecdotally I’ve watched the graph take a nose dive as storms have rolled in.   That information could be useful when sorting out the best time to cross over an exposed pass.

Off topic but Doug subscribed to something with his InReach that gives weather updates.   We found this to be useful in the Sawtooths to avoid the high ground during a storm that wasn’t on our forecast when we left the trailhead

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