Latest posts for the topic "Accuracy of J2Ski's Powder Alarms"

Accuracy of J2Ski's Powder Alarms

Sun, 5 Feb 2017 13:13:17 GMT

I used to love it when I got a Powder Alarm from J2Ski about the resorts I was interested in, generally because I was planning a trip there. But over recent years I have come to expect that only half at most of the advised snowfall will actually happen, if any at all. I know that mountain weather is very changeable but even bearing this in mind I have long been in doubt over J2Ski's reports.

I have recently been interested in the forecasts in Obergurgl and had Powder Alarms in my inbox yet now snow fell there. Today I had another alarm saying that 23cm is due over the next 4 days and looking closer they are forecasting much more over the next 14 days. However, Obergurgl's own website and others are nowhere near that optimistic.

The cynic in me is wondering whether this is a tactic used by J2Ski to get people visiting their site. Do others here feel similar to me about the accuracy of J2Ski's forecasting?

UPDATE
A few days have now passed since my original post. J2Ski initially forecast c.32cms I seem to recall, then a day or so later forecast 23cms still to fall, then a day or so later forecast 10cms for the following day. The reality was that only 10cm fell over this period. It should be noted that several other weather forecasts got it right whereas J2Ski had it wrong. As I said originally, I have noticed this trend over a number of years.

Accuracy of J2Ski's Powder Alarms

Sun, 5 Feb 2017 15:29:49 GMT

Furthy34 wrote:Today I had another alarm saying that 23cm is due over the next 4 days and looking closer they are forecasting much more over the next 14 days. However, Obergurgl's own website and others are nowhere near that optimistic.

Well let's see what actually falls? I notice Obergurgl's site appears to have taken down the statement they had earlier that there would be no snow of note for 4 days (I forget the exact wording). If you look at our 48 hour forecast it shows clear skies early doors (today) with snow later.

The skies were clear first thing this morning, but check the webcams; certainly looks like it's about to snow, if it isn't already :- https://www.obergurgl.com/panorama-cams-winter

If you look at the lovely visualizations of the model outputs on Ventusky (go to https://www.ventusky.com/?p=46.9;11.0;5&l=rain-ac&t=20170205/21&m=gem ), and put Obergurgl in as a location, you can see that it's on the edge of the current weather system pushing up from the South but does look likely to get regular light falls of snow over the next few days (as shown in our forecast). Maybe it won't run exactly like that, but it's what the forecast models are going for right now.

As you probably know, there's a lot of snow happening right now. We've sent out a lot of powder alarms but, if anything, it looks as if we've been under-forecasting the snow currently falling across much of The Alps. Here are some examples from my own Inbox of the last few days...

I got powder alarms this morning for Tignes (18cm over 2 days) and Les Deux Alpes (24cm over 2 days).

Looking at the webcams, they both look as if they've had close to - or more than - that already today (with more to come overnight and tomorrow) :-

http://www.les2alpes.com/en/webcams.html

https://tignes.roundshot.com/lac/

I also got an alarm on Friday for Alpe d'Huez (23cm over 2 days), and they're reporting 40cm fresh already by this morning ( https://twitter.com/alpedhuez?ref_src=twsrc%5Etfw ).

We don't claim they're perfect, and we state repeatedly that anything beyond 48 hours is "subject to significant change and variable reliability". That's just the state of the science.

And if you get our daily updates (and not just the powder alarms), you'll regularly see "there is no significant snow in the forecast" when that's the case...

YMMV, and there are some locations the models sometimes struggle with (e.g. Serre Chevalier seems to have a climate all of it's own occasionally) but the locations I monitor don't seem too far off the mark.

Re:Accuracy of J2Ski's Powder Alarms

Sun, 5 Feb 2017 16:35:55 GMT

And from a quick scan of what's going on this evening, and the latest forecasts for tonight (snow), I'd be surprised if places like the Aravis and Portes du Soleil aren't getting close to double what we were forecasting a few days ago.

Re:Accuracy of J2Ski's Powder Alarms

Sun, 5 Feb 2017 17:12:44 GMT

Thank you Admin Man for your informative reply. I am very pleased to note there is a lot of method going into these reports and I will change to daily updates. The Ventusky site looks brilliant.

Re:Accuracy of J2Ski's Powder Alarms

Sun, 5 Feb 2017 22:58:21 GMT

I have been reading J2ski's snow reports for at least 100 years, (is that right Admin?), and they are generally informative. It is weather. It changes.It is a forecast. not the ten o'clock news.

J2ski is a highly regarded site, and any suggestions that snow reports are geared towards attracting users are pretty low level.

I am reminded of the time, as a young instructor, someone asked Franz, our head instructor, when the next snow would arrive. "Wednesday morning, at 10.00 o'clock" (This was the previous Friday)
"Amazing! How do you know?"
"Well earlier this morning, I saw two crows flying upside down, and that told me when it will snow"

Come the following Wednesday, it started to snow, a few minutes after 10 o'clock.

I met with Franz again last summer, now in his 80s, he is still going strong, so he might be available for weather consultation Admin, if only to provide reassurance to some of your more doubtful readers.

Oh, another crow story. Last season, going up a chairlift in Vail, a crow flying towards us, suddenly turned a flew over our heads upside down.
"That crow will probably vote for Donald Trump", says I. Two Americans on the chairlift burst out laughing. The guy next to me got really angry, defending Trump. After a short conversation, it was established that he worked as a manager in a US investment bank.....

Re:Accuracy of J2Ski's Powder Alarms

Mon, 6 Feb 2017 00:49:24 GMT

Some people still ski with their feet together....

Re:Accuracy of J2Ski's Powder Alarms

Mon, 6 Feb 2017 09:23:04 GMT

Furthy34 wrote:Some people still ski with their feet together....

Yes they do, and J2Ski can confidently predict that people who can do things well - and enjoy doing them - will carry on doing them... see swallow-tail snowboards, monoskis, snow-scooters, sportscars without traction control, etc... 8)

No idea what relevance that has to anything TBH, but let's get back on topic...

Obergurgl are reporting they had 10cm overnight (on the mountain) and it's clearly still snowing. Our forecast has revised to 8cm expected today, v.light snow tomorrow and a further fall on Wednesday.

Elsewhere... there's been shedloads of snow all over everywhere! 8)

Re:Accuracy of J2Ski's Powder Alarms

Mon, 6 Feb 2017 11:00:50 GMT

Thanks Admin Man, I am following events in Obergurgl with interest. As I said in my OP I certainly respect that mountain weather is very dynamic and often difficult to predict, but my thoughts on your forecasts have been borne from many trips not just this latest one and my perception is that the amount of snowfall is often over estimated. Nevertheless I find them interesting.

With regards to skiing with feet clamped together..............let's just say it was a rather childish and pathetic attempt to suggest that people who are of the opinion that that is the correct way to ski should not expect their opinion to be taken seriously in other matters.

Re:Accuracy of J2Ski's Powder Alarms

Mon, 6 Feb 2017 12:56:30 GMT

I would say the powder alarms and 24hr forecast undersestimate snow fall in a Chamonix (only one ever look at). Presumably because they take mid mountain estimates. With upto 1500m elevation the top lifts seem to get between 50 and 100% more snow.
Long term j2ski forecasts are often more optimistic that what resort itself is predicting but that is nature of forecast models. No point getting too excited until snow is in the 2-3 day window.

Re:Accuracy of J2Ski's Powder Alarms

Mon, 6 Feb 2017 17:09:41 GMT

J2Ski are currently reporting a forecast of 11cm of snow down to resort level in Obergurgl on Wednesday. Obergurgl get their forecasts from OberlandWetter.at and hence their website forecasts no snow as does Bergfex.com so we will see who is right.

Re:Accuracy of J2Ski's Powder Alarms

Mon, 6 Feb 2017 20:15:46 GMT

The next notable snow forecast for Soldeu el Tarter is 11cm, expected on 6 February, with around 29cm forecast over the next 7 days - and up to 197cm possible the following week.

Yep. We'll see!

Re:Accuracy of J2Ski's Powder Alarms

Mon, 6 Feb 2017 21:08:10 GMT

https://www.grandvalira.com/en/weather-forecast wrote:LAST SNOWFALL
06/02/2017
FALLEN CMS
30 CM

That's 30cm today, out of the 29cm we forecast for this week... long-range will change Brucie; you're a hard man to please! 8)

Re:Accuracy of J2Ski's Powder Alarms

Tue, 7 Feb 2017 07:01:30 GMT

It's just the 10-14 day prospect that is consistently wildly overestimated.
Perhaps the program needs adjusting?

Re:Accuracy of J2Ski's Powder Alarms

Tue, 7 Feb 2017 17:35:57 GMT

Admin wrote:Our forecast has revised to 8cm expected today, v.light snow tomorrow and a further fall on Wednesday.

The above quote was from yesterday; Obergurgl this morning reported 10cm new snow on the mountain (i.e. yesterday), 5cm in resort - we'd forecast 8cm.

No snow so far today, although it had clouded over by dusk and we're forecasting snow overnight and (last update) 10cm for tomorrow.

Re:Accuracy of J2Ski's Powder Alarms

Tue, 7 Feb 2017 21:06:45 GMT

When will it next snow in Soldeu el Tarter?
The next notable snow forecast for Soldeu el Tarter is 3cm, expected on 7 February, with around 19cm forecast over the next 7 days - and up to 179cm possible the following week.

It's the 179cm that's at issue. Why is the 10-14day forecast always so ridiculously high?

Re:Accuracy of J2Ski's Powder Alarms

Wed, 8 Feb 2017 00:43:06 GMT

Brucie, I tried to follow the issue using your connection. I can see the daily depth forecasts. The only reference I can see to 1.79m is 1.71m, whhich refers to the current depth of snow at various heights, this information generally being supplied by the local tourist board.

On your connection, I cannot see a 10-14 day prospect? Can you provide a pointer, please?

Re:Accuracy of J2Ski's Powder Alarms

Wed, 8 Feb 2017 06:37:02 GMT

It's at the bottom of the forecast page. The summary of which is at the top. It has changed to 51 cm today. I have seen it as high as 497cm which is clearly impossible.

But let's not get hung up on this. Snow overnight and a lovely skiing day in prospect!

Re:Accuracy of J2Ski's Powder Alarms

Wed, 8 Feb 2017 23:00:02 GMT

I thought it was common knowledge that all these snowfall forecasts are generated by computer based weather forecasting models, such as the Global Forecast System (GFS), European Centre for Medium-Range Weather Forecasts (ECMWF) etc. I presume that J2Ski uses the precipitation data generated by the GFS as they are not copyrighted and are available for free, whereas the data from the other models has to be paid for. The price for a maximum charge commercial ECMWF licence is 140,000 EUR/Year (+ delivery charges).

Unfortunately the modelling of precipitation is still not very reliable. If you compare the modelled results with observed values you will see that the model is nothing better than a computer generated guess. The GFS model is run in two parts: the first part has a higher resolution and goes out to 180 hours (7 days) in the future, the second part runs from 180 to 384 hours (16 days) at a lower resolution. The resolution of the model varies in each part of the model: horizontally, it divides the surface of the earth into 35 or 70 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 180 hours, after that they are produced for every 12th hour. Because of the low resolution the model can't see the complex terrain of the Alps, Pyrenees. and other mountainous areas very well. The precipitation data has to be multiplied by a factor to get the predicted amount of snowfall which is another source of error.

J2Ski's forecast for Zermatt last Thursday

Reality on Monday

Zermatt claims that there is 20cm of snow at village level! After a personal inspection yesterday I reckon about 10-15cm fell on the slopes over the weekend.

Re:Accuracy of J2Ski's Powder Alarms

Thu, 9 Feb 2017 01:40:48 GMT

Swing Beep you nicely demonstrate that J2Ski forecasted 49cm whereas only 10-15cms fell. This is exactly the type of over forecasting snowfall I have noticed in recent years and hence my original post.

Re:Accuracy of J2Ski's Powder Alarms

Thu, 9 Feb 2017 02:43:28 GMT

Just imagine they under-estimated, you cancelled and went to the beach - disaster. Even though I know the 14 day forecast is effectively a nonsense there is a certain addictive element to looking and seeing an apocalyptic amount of snow might be heading your way.

If I ran my life on a computer model it would probably conclude a high probability of waking up tired, body won't seem very willing = best stay in bed. Skiing is about the small probability that some trips, some days, some runs everything comes together and you get that bottomless bounce feeling and shot blasts. I would conclude this happens less than 5% of days I ski. By that measure as long as the 14 days forecast is no worse that 95% inaccurate I am in.

Re:Accuracy of J2Ski's Powder Alarms

Thu, 9 Feb 2017 14:54:52 GMT

A few days have now passed since my original post. J2Ski initially forecast c.32cms I seem to recall, then a day or so later forecast 23cms still to fall, then a day or so later forecast 10cms for the following Wed. The reality was that only 10cm fell over this period and on the 10cm forecasted day none fell at all. It should be noted that several other weather forecasts got it right for this period whereas J2Ski had it wrong. So it wasn't just a one off, these were 3 or 4 forecasts over a number of days, all of which were wrong.

As I said originally, I have noticed this trend over a number of years i.e. J2Ski not concurring with other forecasting sites.

Re:Accuracy of J2Ski's Powder Alarms

Thu, 9 Feb 2017 16:40:03 GMT

Furthy34 wrote:you nicely demonstrate that J2Ski forecasted 49cm whereas only 10-15cms fell.

I think, in fact, this demonstrates the issue you have. The amount of snow we forecast over 4 days is not the same as the "amount that fell over the weekend" and that amount is not the same as the snow on the ground on Tuesday. Those numbers are not measuring the same thing.

As soon as snow falls, it begins to transform (settles and sinters) and compacts under its own weight and the layers of snow that follow. Anyone who's been out skiing on a powder day will know that light powder can quickly "go off" - it gets denser and compacts, and surprisingly quickly. Sunshine, warm air, temperature gradients in the snow pack and - especially - wind all have a significant effect.

So if you get 2 falls of 10cm of fresh on successive days, you won't - ever - see the base depth increase by 20cm.

Given the complexity, you simply can't "hindcast" and say that "well, there seems to be 10cm fresh on the ground, so that means 10cm fell 2 days ago". It could easily have been double that.

If you'd like to learn more about the subject, then get hold of the book "Snow" by Robert Bolognesi (handbook size and less than GBP10).

Furthy34 wrote:hence my original post.

You titled the post to refer to our powder alarms. I fully accept it's a very small sample but from the ones I checked - that we issued on Thursday/Friday last week - every one appears to have under-stated the snow that followed. I'm sure there were a few "false alarms" but I couldn't find any.

Furthy34 wrote:A few days have now passed since my original post. J2Ski initially forecast c.32cms I seem to recall, then a day or so later forecast 23cms still to fall, then a day or so later forecast 10cms for the following Wed. The reality was that only 10cm fell over this period and on the 10cm forecasted day none fell at all. It should be noted that several other weather forecasts got it right for this period whereas J2Ski had it wrong.

This is just wrong.

When you made your post, Obergurgl's own site (linked in my initial reply) reported depths of 20cm (low) and 100cm (high). Their own forecast, that morning, stated that no significant snow was expected for the next 4 days.

Whilst the snow we forecast for yesterday didn't materialise (it was cloudy all day but never snowed), the reported depths are now at 30cm and 120cm respectively - with the upper depth incrementing by 10cm on Monday and Tuesday mornings IIRC.

Allowing for settling and compaction, they must therefore have had more than 20cm in the two falls that we did forecast correctly.

So that's 2 out of 3 falls happened that we forecast, none of which appeared in the forecast on Obergurgl's website.

Re:Accuracy of J2Ski's Powder Alarms

Thu, 9 Feb 2017 17:54:41 GMT

Admin Man

I am well aware of snow compaction and hence I was viewing how much fresh snow had fallen in Obergurgl every day.

The fact is that nowhere near 32cms fell. Then after the initial fall of about 10cms you forecast 23cms but nowhere near that amount fell, even at the top.

You then forecast 10cms for Wed and none fell. On Tuesday you changed to 5cms on Wed and none fell.

Whilst all of this was going on I was checking other forecasters including the one that Obergurgl and many other resorts use and they were nowhere near as optimistic as you and as it turned out they were right.

As I have already stated, my OP was made having noticed the accuracy of J2Ski's forecasts over several years.

If you are keen to improve the accuracy of your reports I would politely suggest that you consider using other forecasters or weather stations as your source. What do you think of this idea?

You will have noted the current results from the poll on this and it seems I am not alone in my opinion (Btw, I voted "not very much" rather than "none").

Re:Accuracy of J2Ski's Powder Alarms

Thu, 9 Feb 2017 18:14:49 GMT

Forecasts are just a guide so after the 48 hour rule (I personally prefer 24 hours) you simply have to use your common sense it's not rocket science (sometimes not even science at all!!) And you should always look across other sites to get a general picture

Re:Accuracy of J2Ski's Powder Alarms

Fri, 10 Feb 2017 10:44:40 GMT

I really cannot believe that people are getting so exercised about this :roll: .

The reality is that forecasts of mountain weather are notoriously unreliable :x . To make matters more complicated, practically every ski resort claims that it has a special micro climate that means that they get extra snow :shock: . Expecting snow fall forecasts for a particular resort to be near perfectly accurate is completely unreasonable :roll: . The best you can hope for is a reasonable level of accuracy as to conditions over a maximum period of about 3 days (or occasionally a bit longer for settled fine weather). Even then, the best I ever expect is an indication of low, medium or high snowfalls -) .

If any of the sites issuing forecasts are to be faulted in any respect, it is in their folly of publishing specific forecasts down to the nearest centimetre and often for as long as 14 days. I know people crave this type of information but it needs to be highly qualified, even more so given the level of reliability apparently expected/demanded by some people.

Of course, none of this stops any of us from reviewing multiple sites weeks in advance and obviously only believing the one that forecasts the most snow :mrgreen: . We also see nothing wrong in shifting our allegiances between different sites to allow us pin our hopes on the next big dump :mrgreen:

Re:Accuracy of J2Ski's Powder Alarms

Mon, 13 Feb 2017 19:08:57 GMT

Last Friday J2Ski were forecasting 2cms for that day plus 1cm on each of the following 3 days; all the other sites I checked were forecasting no snow for those days and they were correct. Yet more evidence that J2Ski should change the source of their forecasting.

Re:Accuracy of J2Ski's Powder Alarms

Mon, 13 Feb 2017 19:51:01 GMT

No snow forecast for Saint Gervais and none has fallen. Sort it out J2Ski!!

Re:Accuracy of J2Ski's Powder Alarms

Mon, 13 Feb 2017 19:52:15 GMT

I hasten to add, we are having a great time.