Friday, October 13, 2017

Wind Forecast Layer

When I added the weather forecast layer this summer, I mentioned my frustrations with the way the NWS requires you to bring up endless point forecasts to get an accurate picture of local precipitation amounts.  With the Northern California fires, I'm running into the same issue with wind - I'll read about a forecasted red flag warning, but the Napa and Santa Rosa forecasts barely hit double digits.  I'll admit that I had no idea wind speeds were so locally variant - or at least, no idea that the NWS forecast grid captured such small-scale variations.

24hr wind gust plot.  From 15mph in St Helena to 50mph on Mount Hood just 3 miles away.

Fortunately I already had wind speed mapping on the back burner - it didn't get deployed along with the earlier temperature and precipitation work, but most of that code was reusable.  I can't show wind direction - even if I were to render directional arrows on the map, frequent direction changes make it impossible to show a single meaningful 24hr or 36hr wind direction.  However peak forecasted wind speeds and gusts are shown for 1hr, 6hr, 12hr, 24hr and 36hr intervals, using the same green-yellow-orange-red-purple-blue-black gradient scale as the temperature layer.

One option that does provide wind direction is the crowd favorite  However, windy does not reflect the small-scale variations in the NWS forecast grid (see below).  As with temperature and precipitation, it's an open question as to how accurate the NWS grid variations are, but I like to provide as much raw data as possible and let users draw their own conclusions. plot of the same location
The wind layer is a checkbox option alongside temp and precip:

The forecast grid option immediately below will also show point speeds (remember, the point is simply the center of a grid square, and the forecast applies to the entire square), and clicking on a point will bring up the hourly weather chart.

I feel like I've pretty much run through the backlog of fire-related items I had sitting around, so I think this will be the last major layer change in response to the Northern California fires.

Update: there are now two wind layers, the "max wind speed" layer as described above, and a "wind plot" that provides forecasted directions and speeds for specific points in times, at 3 hour intervals to 12 hours, and then 6 hour intervals to 36 hours.  The same color chart is used for speed, with short lines tracing direction.  The length of the lines has no meaning.


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  3. Great to see that Caltopo can become a useful tool on so many different levels. Question: is there any way to make Caltopo "remember me" so I don't have to log in every single time I open it up?

  4. Ok - which way is upwind and which way is downwind on the little windplot lines? E.g. are they windsocks or arrows, and if arrows, are they pointing to the direction of the incoming wind?

    1. I'm not sure if this will make sense, but what I am seeing is that the narrow end of the wind plot lines indicates the direction the wind is coming from and the heavy end of the line is the direction the wind is going. NOAA forecasts will show the compass direction the wind is coming from (eg W 3km - out of the west at 3 kilometers/hour). I think that is correct. If I am mistaken, please correct me. THanks,

    2. I have the same question - could someone from CalTopo give a *definitive* answer about which end of the wind indicators show the wind direction?

    3. DEFINITIVE: Hope this helps.

      The same color chart as the Max Wind Speed overlay is used to indicate speed with short lines tracing direction (the thicker end of the short line indicates which direction the prevailing wind is blowing). The length of the lines has no meaning.