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.
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| 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 windy.com. 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.
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| Windy.com 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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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?
This is rad. Thank you much.
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?
I was looking for an answer to the question that “Val” asked in 2019 above, about the meaning of the wind direction symbols. I finally found an FAQ list at https://training.caltopo.com/all_users/getting-started/faq where it explains how to interpret the wind plots:
“Which direction is the wind going in wind plot? From the narrow end to the fat end of the streaks. Think of it like a comet, where the head of the comet is the direction of travel.”
Four of us had similar interpretations of the wind indicators mimicking wind socks, smoke or sand But we all had doubt if we were right since the mapped wind was either blowing in a really good direction or a really bad direction for the fires. The last fire we were on the weather on the ground matched our theories of how the “wind plot” reads like smoke being blown. The long tails and some even changing color mid tail was interpreted as speed or gusts or drying or temperature factor. I think it would be worth while putting a good explanation in the map legend so there’s no question. Oh and there’s the live weather with the wind drop down that has arrows that point in all directions supporting any theory your have. With confirmation bias plentiful even reading this this current page, it would be great if the map legend had a clear graphic explanation of the “wind plot”.
Thanks for the feedback! We do have a more in depth explanation of interpreting the wind plot in our user guide: https://training.caltopo.com/all_users/overlays/overlay-desc#wind.
What is the forecast model and actual data source being used for the wind forecast? I’m a little unclear from this old blog post if it’s NWS or Windy, and what model is being used. From the FAQ I do see it’s surface wind, but it’s unclear how you’re going from NWS point forecasts to pretty directional comet trails like Windy… I love it, just would like to know better what it’s actually based on.
The data for both the Weather Shading and Wind Plot overlays comes from the National Weather Service’s 2.5 km forecast grids. Windy was offered as an additional resource in this blog post.
TY!