Sunday, August 6, 2017

Forecasting Local Winds with Meteograms

This is just a printed note of a method described in more detail in the video link at the end. It is one way to study local wind forecasts, and especially the use of the US WRF model, whose high-quality data are otherwise only available to us as rather large scale graphic images, with wind speeds presented on a color scale.

In short, this note is a quick way to decide if you want to sit through a 11-minute video!

We use the UW WRF model, one of the best for this region of Puget Sound (though typically older forecasts than we want on race day), but nevertheless very good for planning the day before.

The meteograms are at this link:

The page looks like this:

Choose latest run, 1.3 km resolution, click the point of interest to load the lat-lon, then reset the elevation to 0. The 3 marks here are about the places we tested here.

It takes a minute or so to get each picture back, but there is a warning about this in red.

The data look like this:

The video discusses these in more detail. For now we care only about the second panel of wind speed and direction.

The three regions in study were then cut from this type of picture and pasted into one graphic.

The 0 h here is the run time at UW, that was 12 aug 8, or 5 am PDT. Then the time scale goes from there.

The video first points out that this is not best example, as there is not much wind in this case, not to mention we have a layer of smoke over the Sound at the moment, which is bound to affect any forecast.  Nevertheless,  we proceed while the method is fresh in the mind.  It is also explained that the apparent chaotic wind directions are just an artifact of how they are plotted. We still see clearly veering and backing, and pretty well by how much. the scale is not optimum for this.

If interested, the details are below:

The next step will be to get hi-res CONUS NDFD data and load it into a program like Expedition which offers the option to build a meteogram at any point from the stored data. Quick checks shows it all works as intended, but the ultimate role of the meteograms is not clear. 

For example, below is a 4-min video looking at these same WRF winds discussed above but in the conventional way using the graphic images.  We see a lot from the graphic presentation, so it could be the meteograms might best serve as simply a way to more precise or digital values.  We have a convenient link to this graphic WRF data from UW at  in the model forecast section.  (To clarify a question that comes up in the video, it appears the 1.3km WRF model is run every 12h and generates 1h forecasts out to 72h.)

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