Featured How To Forecast the Snow: Part 1

Discussion in 'General Skiing' started by Jellybeans1000, Oct 30, 2017.

  1. Jellybeans1000

    Jellybeans1000 Resident Weatherman Industry Insider

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    I am a powder lover; I bet you are, too. But how do you know when the powder is coming? By using weather forecasting maps. Whether you are going on a backcountry trip looking for some sun or just looking for a powder dump, knowing how to read weather charts can help you find where the snow is going to fall.

    Of the many concepts in the science of meteorology, most are not crucial for snow forecasting. We are mainly interested in air temperature and pressure, snow level, snow accumulation, and precipitation. First, let’s talk about temperature and pressure.

    A key concept is the snow level, which is the minimum elevation at which snow falls. You may find maps for the freezing level, which is the elevation where positive temperatures meet negative ones. The snow level is below the freezing level because snow doesn't melt as soon as it goes into positive temperatures; it falls for a few hundred meters until it melts.

    Let's look at this surface air temperature map (“2 meter” in this context means “surface”). The temperature scale on the right-hand side lists temperatures in Fahrenheit; they are shown as both numbers and colors. In this map, blue coloring inside the red lines means below freezing temperature (32°F). Therefore, all areas colored in blue can receive snow if there is enough moisture.
    [​IMG]
    There are many other types of temperature charts, such as the 850hPa and 700hPa charts, which show the temperatures at approximately 5,000 and 10,000 ft, respectively.

    You may be wondering what hPa is. It is the measurement of air pressure, which is another important part of weather forecasting. Millibars (mb) and hectopascals (hPa) are used interchangeably as the units for air pressure. The mean pressure on Earth's surface is 1013 hPa: any area of surface pressure above that is called a high, and any area of surface pressure below it is called a low. In North America, lows are the driving force behind most snow events.
    [​IMG]
    Above is a 500hPa heights and MSLP map. 500hPa heights are on the scale on the right. The dam (or decameters, where 1 dam = 10 m) in this situation is the measurement between 500 and 1,000 mb. You don't really need to understand the full science behind it, but the lower the 500hPa height, the colder it will be. For example, a dam of 582 (orange) is going to be much warmer than a dam of 540 (light blue). A dam of 540 or below can lead to low-level snow (> 1,000 ft). Dams below 564 are generally needed to get snow below 12,000 ft or so.

    The other concept in there is MSLP, or mean sea level pressure. The L’s and H’s signify lows and highs, respectively, with their MSLP numbers. The lower the pressure, the deeper the low becomes. A deep low is generally associated with cold air. The lines around the lows and highs signify the direction of the wind, with winds around lows being counterclockwise and winds around highs clockwise.

    Thank you for reading this explanation into temperature and pressure weather charts. I hope you learned something. Next, I will explain precipitation and moisture maps. Until then, enjoy the remaining snow!

    [All weather forecast charts are created by Levi Cowan, a PhD graduate student at Florida State University. Link here: http://www.tropicaltidbits.com/analysis/models/]

    I also need to acknowledge the assistance of @SBrown for editing this article, and @Tricia and @Philpug for helping me to make this happen. Thanks all.
     
    Last edited: Nov 10, 2017
  2. dbostedo

    dbostedo Asst. Gathermeister--Utah Team Gathermeister

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    Is there any resource that shows places where there is a snow chance based on elevation? I.e. places that might not be blue (in your first map) but might still get snow at higher elevations?

    I know OpenSnow will predict where the rain/snow line is, which can be very nice to know. Is there a way to see that over a larger area?
     
  3. Phelmut

    Phelmut German for Northeasterner Skier

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    Too cool. That stuff is Greek to me, but maybe after a few more lessons I'll have a basic understanding of reading the radar/maps. Thanks.
     
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  4. karlo

    karlo Getting off the lift Skier

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    Thank you!

    Question. If the hPa chart is sufficient to indicate snow at a particular elevation, then what is the purpose of looking at the surface temperature map? Thanks.
     
  5. Jellybeans1000

    Jellybeans1000 Resident Weatherman Industry Insider

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    1. That would be shown by a snow accumulation map or a snow probability map. The former will be discussed in Part 2, the latter is a highly exclusive product.

    2. There are only freezing level predictions, not snow level predictions. I have bunch of them on my paid source, but they are for free here kinda. https://www.windy.com/?deg0,45.460,-137.109,2
     
  6. Jellybeans1000

    Jellybeans1000 Resident Weatherman Industry Insider

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    hPa charts are a guide for elevations, not exact though. Temperature charts give you feeling of what the temperature is going to be like at your resort/city/region.
     
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  7. PTskier

    PTskier Been goin' downhill for years.... Skier

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    I can predict the weather with 100% accuracy. When I go skiing, the snow stops.

    The most common words I hear about weather are, "You should have been here last week."
     
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  8. SSSdave

    SSSdave Putting on skis Skier

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    A wise hobby for Tahoe region powder enthusiasts without engaging more deeply into weather models, is daily reading the Reno NWS technical forecast discussion:

    http://www.wrh.noaa.gov/total_forecast/getprod.php?prod=RNOAFDREV&wfo=mtr&version=0

    While also viewing what the corresponding infrared and water vapor satellite images look like:

    http://www.wrh.noaa.gov/satellite/?wfo=mtr

    When one reads a term one does not understand go here:

    http://w1.weather.gov/glossary/

    And during storms, watching precipitation patterns on radar is also educating. Gradually one will become more knowledgeable without having to resort to much else to understand what may be approaching.

    David
     
  9. stan51

    stan51 Booting up Skier

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    I agree with the recommendation for reading the forecast discussions. They have served me well for both general weather understanding and for offshore sailboat racing. In short, while the weather bureau has to put out a forecast, the discussion lets you know how confident they are with that forecast.
     
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  10. Jellybeans1000

    Jellybeans1000 Resident Weatherman Industry Insider

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    Fair enough, but understanding the weather maps allows you to not rely on the NWS. They are the best weather source.
     
  11. Tricia

    Tricia The Velvet Hammer Admin Pugski Ski Tester

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    I was just watching my local weather forecast and thought about this thread.
    Thanks for giving us some insight on this part of our world.
     
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  12. mdf

    mdf back to being an ordinary Gatheree Skier

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    If you go into www.weather.gov and drill down to a "point forecast" does that adjust for ground altitude? I thought it did.
    I believe snowforecast.com or snow-forecast.com (I forget which is which) does something similar to what you are describing, applying aviation weather products to adjust for altitude. I know they show contours of freezing altitude on their maps.

    No substitute for local knowledge, though, to remember spots where the standard models and analysis over or under promise consistently, and which are most reliable for your reason. That's why I'm an OpenSnow subscriber (and yes, their local guys are better in some regions than others).
     
  13. SBrown

    SBrown Steve Admin Pugski Ski Tester

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    Yes, it does. It's helpful around here, since the weather at 9K and the weather at 12K can be very different, even though it's within a mile or two.
     
  14. AJP

    AJP At the base lodge Skier

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    NOAA is very useful through point forecasts and forecast discussion for specific topography. Regarding models , wx.graphics is a good site which gives you a good amount of access to the ECMWF model which you would typically have to pay for on most sites. It is run by Dr. Ryan Maue who helped form weatherbell.com(paid site) which also coverts model data into forecast maps.

    The forecast for the next 10 days looks great for the tetons on northward! Grand Targhee might be 90-100% on opening day next friday. Winter is here!
     
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  15. Jellybeans1000

    Jellybeans1000 Resident Weatherman Industry Insider

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    Pictures from OP were down for a bit, now they are back.
    This ^^ Yes it does take into account ground elevation. snow-forecast.com apparently applies a "1km digital elevation model". It's basically dressed up GFS. That's how they work out the freezing level, not the snow level which matters much more.

    I probably should summarise the models like GFS and how to pick the best one in a more detailed post, because they are the basis to all forecasts around the world.

    I will quote a knowledgeable European forumite from Snowheads...
    I am not criticising your statement, locals will definitely be able to tell you what part of the mountain gets more snow by looking at the wind forecast, and show you the best powder spots. But locals aren't as better than any other forecaster. That's why a Aussie like me, can predict things with the exact same accuracy, as local meterologists, Opensnow forecasters, etc. But what I can't tell you, and what they can tell you, is what ski resort to go to, etc. This is because I don't their areas as well as them.

    If that's a good reason to subscribe to Opensnow (plus their sweet meteograms and analysis products), go right ahead. I do. But any weather enthusiast (and observer of the NWS forecast) can tell you the forecast. I try and show the modelling and give more complex detail. But someone like BA in Tahoe could say for example, skip Squaw and go to Kirkwood, depending on the wind direction, radar, snow accum, etc. That's why you should subscribe, not because he is some magic genie.... as I can tell you out of hard experience that isn't possible ;)
     
  16. Jellybeans1000

    Jellybeans1000 Resident Weatherman Industry Insider

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    Yes, I use Maue's new site frequently. I would have used them for this tutorial, but the tutorial has been in the works since May, long before he released the free EC data. It's kinda of a revolution.
     
  17. jack97

    jack97 Booting up Skier

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    GFS and ECMWF are the us and euro models respectively, they usually converge to each other 3 to 4 days in. Both have been know go wild further out in time. Some of the local forecasters who use both knows the strength and weakness of each model. They will look at current and past measurements to make adjustments to the model's forecast.

    IMO, both still has room for improvement in term of skill, I recall the time then we had the super el Nino and it threw both models off, storm tracks to NE.and East coast never followed the models. That said, I remember a time when a 5 day forecast in the summer was unheard off but is currently status quo.
     
  18. jack97

    jack97 Booting up Skier

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    btw, I use to follow Ryan Maue comings and goings base since his phd research. Currently is spending his efforts on other ventures. His latest tweet captures the essence of what I posted. Make America's Models Great Again!

    [​IMG]
     
  19. Jellybeans1000

    Jellybeans1000 Resident Weatherman Industry Insider

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    EC is better than GFS. Some forecasters do know the bias of each models, like I do with it's longer term indicators. EC is a very good model with fewer bias and errors, compared to GFS.

    Ryan can't really make America's models great again, only NOAA can do that, and that won't be happening..... His free model interpretations are awesome, but he can't increase skill in the models, just show a broad range of counter models.
     
  20. jack97

    jack97 Booting up Skier

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    Updates to the models are always in the pipeline, these updates and development are dependent on the country's funding. Ryan has been involved in the field long enuf to know when and which model updates will kick in.
     

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