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Comment by jordanb | Hacker News Reader

I do some offshore but mostly on the great lakes.

I don't use GFS just by looking at the wind layer though. Wind layer forecasts do not include terrain or local effects as you noted. But the necessary info is in the forecast and is accurate.

For instance, in the great lakes we tend to have large diurnal temperature swings and therefore strong sea/shore breezes. If the model is forecasting big temperature changes and an anticyclone with low wind-layer forecast, this is ripe for strong sea/shore breezes.

The biggest hazard we have in the great lakes is convective storms (squalls). They do not show up in forecasts because convective cells are very small. However, The GFS gribs do have pressure forecasts, and perception, and most importantly CAPE and CIN forecast layers. Combined with WPC synaptic charts you have the info needed to determine if 1) convective storms are likely to occur and 2) if they do occur, the probability that they will be severe.

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The GFS is a coarser model which covers the entire globe, so while the overall situation at the synoptic scale will tend be modeled quite well (at least inside of a few days into the future), the resolution of smaller-scale weather phenomena taking into account local factors just isn't going to be there.

For something maybe more useful on the local scale, you can also look at a model like the HRRR (which I believe does take into account the terrain and other local effects from things like larger bodies of water). While this model only really covers the conterminous United States and southern Canada, I've generally found it good for showing the shorter-term, local weather details, including forecasting convective storms and winds on and around the Great Lakes.

Thanks, I think I need to spend some more time studying meteorology so I can also better interpret how the data predicts actual hazards, as you are doing. I'm not even familiar with many of the acronyms you mention. I am simply comparing how well the predicted wind speeds are reflected in real life, in specific places where I am potentially in the wind shadow of relatively small hills, islands, etc. It is the flow around these objects that requires a high resolution model, as small shifts in wind direction make the wind shadows shift and change in size a lot. The actual overall prevailing conditions are so identical here from day to day in Northern California, there is hardly a need for large scale models unless the rare storm comes through.

I have noticed that where I am, the inland/offshore temperature differential is alone a pretty good predictor of overall wind speeds near the coast, not accounting for geography.

The best weather book for sailors I've ever read is Modern Marine Weather by David Burch

Thanks, I'll check it out! I've read "High Performance Sailing" by Frank Bethwaite, who was a sailing meteorologist and covers some things- but it is more focused on extreme micro-prediction.

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