Tutorial Weather Maps / Weather Terms

Discussion in 'Weather' started by Ian D, Jul 3, 2013.

  1. Ian D

    Ian D Pool Room
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    For a basic introduction to what to look for on a weather map or satellite map that indicates snow you can refer to this page:

    http://ski.com.au/weather/tutorials/index.html


    Please add to this thread with examples of how to read more complicated maps and glossary of terms of jargon used.

    Post away ....
     
    #1 Ian D, Jul 3, 2013
    Last edited by a moderator: May 11, 2015
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  2. Claude Cat

    Claude Cat Gone Fishing
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    Great idea.

    Things I look for on weather charts

    Images may update.

    Thickness
    "Thickness" is simply a measure of the thickness of the air.
    What does "Thickness" mean?


    [​IMG]



    850hPa Temp
    This is the temprature of the air where at a pressure level = 850hPa
    A rough figure of merit is that 850hPa = 1600m, but note pressures do change with weather, so when we have a strong low, then that altitude will be less than 1600m.
    Ideally, <0 C temp for snow [​IMG]



    Freeze level
    Similar to 850hPa, it shows the altitude where the temp is 0C. For obvious reasons.



    Precipitation accumuation
    How much is going to fall.

    GFS will show you 3 hour totals as per
    Or go to WeatherOnline for 3, 6 or 12 hour durations
    Or here for whatever period you like/
    Dial in the dates you you're looking at there it is.
    http://forecasts.bsch.com.au/raincast.html


    500 hPa Tempratures and Thicknesses
    The so called temprature of "uppers".
    The colder it is in the upper atmosphere the better.
     
    #2 Claude Cat, Jul 3, 2013
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  3. Donza

    Donza Pool Room

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    I also look for something such as this.
    The dotted line following the front is an "embedded trough" or area of unstable air.
    Typically after a cold south west change the air will lose its moisture and therefore capability of producing snow. Ie it will dry out.
    Embedded troughs will increase the amount of moisture. When embedded in cold SW stream they are epic.

    [​IMG]
     
    #3 Donza, Jul 3, 2013
    Last edited by a moderator: Nov 12, 2013
  4. Donza

    Donza Pool Room

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    Also re precipitation amounts that CC listed above.
    They shouldn't be treated as gospel in relation to the amount of snow that will fall.
    The the amount of snow that falls is also relative to temperature.
    Ie 10mm of precipitation forecast at -2 at 1700 will probably produce 10cm of snow
    Ie 10mm of precipitation forecast at -8 at 1700 will produce usually 2 to three times that amount.
    I use the freeze level charts vs the precip charts to determine snowfall.

    Its also prudent to take into account the duration a storm will be over the alps.
    A prolonged storm will always produce more snow than anticipated.
     
  5. Claude Cat

    Claude Cat Gone Fishing
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    Also in terms of precipitation, consider the effects of orographic lift. Models can be not that good at allowing for this, so you may well get more over the mountains than is shown on the model.
     
  6. Donza

    Donza Pool Room

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    You might need to explain the concept of orographic lift vs topography.
     
    #6 Donza, Jul 3, 2013
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  7. Claude Cat

    Claude Cat Gone Fishing
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    Wiki can do it a lot better than I.

    http://en.wikipedia.org/wiki/Orographic_lift

    [​IMG]
     
    #7 Claude Cat, Jul 3, 2013
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  8. mick chopps

    mick chopps Pool Room
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    I can decipher the info (or at least recognize what looks good and what doesn't) displayed on most of the charts you guys use and reference and I've managed to find some of them online for myself. My issue is understanding their progression and why you guys might or might not find the model charts to be somewhat fanciful. Accepting that certain models aren't all that reliable the further out they are, are there any indicators in particular that you guys look for to judge whether they're "on crack" as is sometimes suggested? Or is it just experience in watching the sort of weather we actually receive?
     
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  9. Claude Cat

    Claude Cat Gone Fishing
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    [​IMG]
    That's probably something that can only be gained by experience I think.
    Essentially, based on past experience you can usually know what a weather system is going to do.
    If the model starts showing something unexpected, that's when you might consider you've got an outlier (perhaps due to a specific set of inputs the model has been provided).
     
    #9 Claude Cat, Jul 3, 2013
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  10. Donza

    Donza Pool Room

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    Its also personifying models Mick. They get traits...personalities.
    I know PG will disagree .
    Yet you spot trends and behavioral aspects.
    I mentally lay every model over each other, then expand them by each timestamp. Look at the progression and see if it looks logical. Using experience I guess of past outcomes.
    Its good to compare history.
     
  11. Donza

    Donza Pool Room

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    Yeah you have to consider also the rise in altitude offset by the distance the air travels .
    If the rise is gradual the lifting is slow and ineffective.
     
    #11 Donza, Jul 3, 2013
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  12. azzski

    azzski Old And Crusty
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    I realise I'm just dumping a heap of topics of varying lengths together here, but this is some jargon/acronyms from the latest predictions thread that could stand further explanation for the layperson, along with their significance (if any):

    The "Spaghetti" model
    06Z GFS (00Z GFS) 00Z EC and the +84/96 etc that go along with it
    AXS-G/R
    ECL
    EC
    CMC
    JMA
    UKMET
    Access
    LWT

    Some of these are obvious contractions/model names like BoM for Bureau of Meteorology but that doesn't mean that it necessarily means anything to someone who is trying to follow what is being said [​IMG]
     
    #12 azzski, Jul 3, 2013
    Last edited: Jun 19, 2014
  13. Donza

    Donza Pool Room

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    The “Spaghetti†model- its an ensemble model that graphs the height of the 500hpa (therefore the temp) using a "spaghetti plot. In other words it creates a graphical "mean" or average of all the model runs. Its a trend model. rather than specific.
    06Z GFS (00Z GFS) 00Z EC and the +84/96 etc that go along with it Thats just the time stamp of the model run on zulu time.
    AXS-G/R Australian model...G being a lower resolution (models forecast using grids so to speak, the smaller the grid the more calculations) R is a smaller grid yet shorter forecasts
    ECL East coast low..a trough that deepens over the east coast of Australia. usually as a reaction to warm sea surface temps
    EC European model..(ie its from)
    CMC Canada
    JMA Japan
    UKMET UK
    Access (see AXS)
    LWT Long wave trough A measure of the polar vortex.. circles around the poles kinda like a cold lava lamp...spewing forth cold air towards lower latitudes. It has peaks and troughs...much like a swell on a ocean..the peaks are nodes.
    The best is a defined 5 node pattern.
     
    #13 Donza, Jul 3, 2013
    Last edited by a moderator: Dec 13, 2013
  14. Claude Cat

    Claude Cat Gone Fishing
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    ok.
    EC = European Centre for Medium-Range Weather Forecasts
    model runs at 00 UTC and 12 UTC (00Z, 12Z)
    GFS = Global Forecast System - the US main model.
    model runs 4 times per day 00UTC, 06Z, 12Z, 18Z
    CMC = Canadian weather model
    UKMet = United Kingdom met-office model
    JMA = Japan Meteorological Agency model
    Access = Australian BOM's model (various flavours AXS-R (regional) AXS-G (global)
    AXS-R has smaller grid size, but is only 3 days ahead. AXS-G has a larger grid size, but is longer term model (10 days IIRC)
     
  15. Claude Cat

    Claude Cat Gone Fishing
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    Then we should talk about ensembles and "confidence"
     
  16. D_Dog

    D_Dog Active Member

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    The following link has a huge number of definitions and is a good resource to have

    http://www.mountainwatch.com/snow-news/features/20120725/GLOSSARY---The-Grasshopper's-Guide-to-Weather-Definitions
     
  17. cyclopath

    cyclopath Active Member

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    Hi guys,
    Very long time lurker, new poster. This is a great resource thread for relative newbies like me. Much appreciated.
     
  18. Claude Cat

    Claude Cat Gone Fishing
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    Dont forget the weather links thread that shows all the links to models and other resources.

    Weather Links
     
    #18 Claude Cat, Jul 3, 2013
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  19. azzski

    azzski Old And Crusty
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    So that helps with what those acronyms stand for. Of what use are the models from around the world for Australia's weather patterns? Which do the predictors (in their opinion) think most consistently predict the weather patterns?

    For my own interest, what's the significance of the Z on the time periods? [​IMG]

    This is all good stuff and will be great once we've got it all out and rolled up into a single page/post.
     
    #19 azzski, Jul 3, 2013
    Last edited by a moderator: Nov 12, 2013
  20. Claude Cat

    Claude Cat Gone Fishing
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    Z = 0 UTC (the old Greenwich mean time)
    Short for UTZ = Universal Time Zone
     
  21. azzski

    azzski Old And Crusty
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    Cheers [​IMG]

    From the Weather links thread, a Spaghetti plot explanation:

     
    #21 azzski, Jul 3, 2013
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  22. Claude Cat

    Claude Cat Gone Fishing
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    IMO, the european model EC, is by far the most consistent medium range forecast model.
    GFS (US) is very good, but has idiosyncrasies. The classic "all-in" at 144 hours where the model predicts deluges before rapidly backing away "downgrading".
    AXS-R tends to be very good within 3 days.

    It's also worth noting that models behave differently in Summer and Winter. Eg GFS tends to predict thunderstorm activity and precipitation from very well in summer.
    UKmet is very similar to EC - use as a cross-check
    CMC is very similar to GFS - use as a cross-check
     
    #22 Claude Cat, Jul 3, 2013
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  23. 7wombathead

    7wombathead Dedicated Member

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    The Orographic lift effect is a little bit over simplified with respect to a prediction with respect to the main range.

    In a windy storm the snow is dumped then blown off the western side and the peaks (2200m) back to eastern side. Perisher, Thredbo, and Charlotte Pass.

    Often on these types of events the whole main range is stripped of any snow and the resorts are replenished each day with windblown snow.
     
  24. nfip

    nfip Part of the Furniture
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    Thanks all this is excellent. Have been flicking around trying to put a lot of this together and a few times decided the good old BOM 4 day synoptic (Alan Wilke used to point at) is for me. But maybe there's now hope yet.
    Appreciated your time for this. Cheers.
     
  25. Tanuki

    Tanuki Dedicated Member
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    #25 Tanuki, Jul 3, 2013
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  26. 7wombathead

    7wombathead Dedicated Member

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    Yep these days this is the best chart and AXS R.

    That's because the regional synoptic forecast model that BOM has developed is pretty good compared to say 5 years ago, its just a bit short sighted thats all.

    The GFS is the best to keep you thinking about the future ( two weeks) IMO.
     
  27. 7wombathead

    7wombathead Dedicated Member

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    Well its just what happens based on observation of localized conditions.

    Try going up to the main range sometime after a windy blizzard.

    The diagram listed by wiki indicates that no moisture reaches the eastern side of the ranges

    But the topography of the Main range is pretty flat and wider than high on the top.

    So you have to imagine that Orographic lift does not limit snow falls to Perisher or Thredbo too much. Rather it limits precipitation to the Monaro Plains and coast down here in Merimbula.

    That is the correct way to visualize the Orographic lift effect in the Snowy Mountains.

    Thats why we are fortunate here in OZ.

    Bom could and should update AXS R to include the topography better though. [​IMG]
     
    #27 7wombathead, Jul 3, 2013
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  28. Presto

    Presto Active Member

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    Very interested in properly reading this thread when I have some spare time.
     
  29. Rush

    Rush Pool Room
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    Actually what is most likely to happen in the future is that Access G will be further refined (down to 20 km or so) and Access R will be ditched all together. Instead you'll have high resolution models in in the majors urban areas (resolution of < 10 km).
     
    #29 Rush, Jul 3, 2013
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  30. Rush

    Rush Pool Room
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    No I don't. Each model will tend to have its own biases due to parameterisations that work better/worse under certain initial condition. The range of data assimilated will also affect forecast performance. The EC assimilate the most which is arguably the main reason why the are the best.

    This is different to what you said a few weeks ago, implying that models need time to 'bed in' during the early winter. This isn't true, the models have no automatic adaptive tuning or bias corrections over time. They aren't neural networks.

    Of course, the development team may identify biases in the model and alter various settings to give better forecasts but this happens manually, not automatically.
     
    #30 Rush, Jul 3, 2013
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  31. Rush

    Rush Pool Room
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    In any case if you want to understand how the ECMWF forecast systems works, they have lots of documentation available here
     
    #31 Rush, Jul 3, 2013
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  32. Claude Cat

    Claude Cat Gone Fishing
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    mick chopps and cyclopath like this.
  33. mick chopps

    mick chopps Pool Room
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    Brilliant stuff, very informative and helpful!
     
  34. Seafm

    Seafm Dedicated Member
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    This certainly a very informative thread about what actually goes on in predicting the weather. Meteorologists have to look at so many different pieces of information and possible scenarios before they actually tell you whether or not it's going to rain or snow or whatever tomorrow. Fortunately for you guys down south the weather is fairly predictable with cold fronts coming through all the time. Northern Australia is pretty different though even in the wet season. The monsoon trough can be clearly drawn on the synoptic chart and not have drop of rain in it. A common weather forecast heard on local radio here over summer can read "mainly fine with the chance of an afternoon shower of thunderstorm". Wouldn't have a clue? You're dead right, called covering your arse. @Claude Cat I notice that you also run a thread for the cyclone season each year. Something useful to throw in there would be a video update done by a bunch of guys in Townsville called Oz Cyclone Chasers. I've been following their updates for the last 2 years and everything they've said that could possibly happen with a current cyclone event has been spot on using all the information mentioned above along with a couple of others like predicted humidity levels.