In the Forecasting chapter of Tim Vasquez’s book, Storm Chasing Handbook, (p.119) there’s mention of “model spinup” time. I’m not sure that I understand the concept since the way I’m interpreting it makes it very counterintuitive to me. Here’s a quote from the book, “within a couple of hours of the model start time, model accuracy is poor due to the effects of ‘model spinup’, the temporary mathematical noise which quickly dampens after the first few hours. This can produce spurious artifacts in the model charts.” It sounds like that a model such as the HRRR is producing more accurate forecasts for a few hours in the future than it is for an hour in the future. Does that mean that the model is doing something different in obtaining an hour 4 forecast than it is an hour 1 forecast? Is the hour 4 forecast based on the model’s hour 3 forecast which is based on the hour 2 forecast which is based on the hour 1 forecast? If so, how does the hour 4 forecast become more accurate than hour 1? Where can I find a beginner level, in-depth explanation of model spin up? Tim’s book was published in 2009. Some resources I found online that mentioned model spin up were from 2011 and 2015. Is model spin up still a factor to consider with the newest versions of weather models?