Wednesday, December 2, 2015

What Will It Be?

Check out the wind forecast for Chapin for tomorrow:
The pictures shows two computer model predictions: the NAM model on the left, and the GFS on the right. The interesting time is around 1 pm. NAM predicts 19 mph. GFS predicts 29 mph, which would be fantastic. Which will it be?

The NAM model is intended to be more accurate - it calculates the weather at a higher resolution than the GFS model. Let's check the forecast map for tomorrow at 1 pm. Here is the NAM map from
There's a "low wind bubble" where Cape Cod extends out into the ocean. The GFS model does not have this bubble:
Does it matter which model is right? Sure it does! Many reasons:
  • 19 mph is barely worth rigging; any less, and we'd need huge sails; but 29 mph is prefect
  • We can't wait until 4 pm, when both models predict wind - it gets dark at 3:30.
  • It will be warm (50ºF, 10ºC) and sunny tomorrow after noon.
  • It has not been windy for a while.
So, which model will turn out to be right? Often when we see such discrepancies, the GFS model is closer to the truth, especially in the fall. Sometimes, the wind comes in even stronger than the GFS model predicts. But sometimes, the "light wind bubble" that the NAM model predicts actually happens. For tomorrow, my bet is on the GFS - but windsurfers have to be optimists. So watch the meters!

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