Analyses of Cascadia windstorms on The Storm King tend to be focused on what actually happened, as opposed what may have happened, or in other words forecast examinations are rare. Weather forecasting is a tough job. It really is. I had a chance to experience this while taking an intensive operational meteorology course at the Environment Canada (EC) offices in Vancouver, BC. In the Pacific Northwest, extreme wind and snow forecasts are among the toughest to do. So, to all the forecasters who faced the challenges of the Ides Storm, you have my apologies in advance if it seems like any toes get stepped on in this section.
The Ides Storm, being early season, added extra challenges to wind warnings. In mid October, many deciduous trees are still well foliated. Leaf-bearing trees have a higher coefficient of drag compared to denuded trees, meaning that full crowns result in higher loads for the same wind speed. Also, all trees have new growth increment from the previous growing season that generally has not been tested by strong winds. Pathogens may also weaken trees during the warm season. Thus, significant tree damage can occur at lower wind thresholds. I have discussed this at conferences such as the Pacific Northwest Weather Workshop, and it is well known among forecasters at least anecdotally. Thus, a high wind warning may be issued at lower wind speed thresholds than during later months like December and afterward. I note, however, in the case of the Ides storm, earlier windstorms had already swept through the region, including on October 6-7th and again on October 14th.
In order to simplify, focus will be kept to forecasts covering the most populated locations of the study area. The National Weather Service (NWS), Portland, issued for the north and central Willamette Valley a high wind warning for winds S 25 to 35 mph with gusts to 55 mph (40 to 55 km/h gusting 90) at 0430 PDT on October 15, 2016. NWS, Seattle, at 1000 PDT also issued a high wind warning, this one for winds S 20 to 35 mph with local gusts to 60 (35 to 55 km/h gusting 100) and covering the Seattle-Tacoma-Everette area and surrounds (the majority of the Puget Lowlands). At noon, EC issued a wind warning for the Metro Vancouver area and surrounds for expected southerly winds of 90 km/h or higher. This is a wise downgrading from 100 km/h during an earlier forecast posted at 0506 PDT. Of course, at all of the forecast offices there were earlier warnings and these differed somewhat from the ones issued just ahead of the storm. There probably should be a sociological analysis of how the idea that the Ides windstorm would be a major or even catastrophic windstorm--hence it getting named "Ides of October" even before it had developed--originated and then proliferated in the media (I currently have no plans to do this). In any event, a key part of forecasting is constant adjustment as new information becomes available. The latest numerical weather prediction model runs and most recent observational data may tell a different story than earlier information.
How did the October 15, 2016 windstorm measure up to the above forecasts? Comparing the readings on the map it seems clear that the NWS Portland prognostication captured what eventually did happen quite well. Most peak gusts in the north and central Willamette Valley were in the rather narrow range of 51 to 53 mph (81 to 85 km/h). Further north, forecast accuracy breaks down.
Wind speeds in the Puget Lowlands simply did not match the forecast--most especially for gust. While there is an instance of a gust at the upper end of the warning rage, the 61 mph report from West Point in Seattle, this station is among the very well exposed sides discussed above. In most cases, West Point has the highest reading among the key observing sites in the area, and when winds at this location are exceeded at another it is almost always Paine Field, another fairly wind-prone site. This fact invalidates West Point for verification of a wind warning. To do so would be like firing into the side of a barn at point-blank range and claiming a high level of marksmanship. It would be cheating. In fact, the wind climatology at West Point emphasizes a need for wind warnings in the Puget Lowlands and Northern Waters to have a separation between exposed and sheltered locations, as is done for wind forecasts on the Pacific Coast. The shores of the Puget Sound are a marine coastline and it makes sense to treat them as such when providing wind forecasts.
Looking at other long-term stations in the Seattle area, like Boeing Field, Renton and SeaTac, gust speeds did not even reach 40 mph. Ouch. The Ides windstorm underperformed many other events in recent times, and in fact barely rates as being more than a typical blustery cold-season storm, like the Christmas Day event of 2005. Indeed, the precursor windstorm on October 14, 2016 proved to be stronger at many stations, giving it a higher average. Paine Field in Everett, though not as exposed as West Point, is nevertheless a rather favored site for high wind readings as noted above, especially in situations conducive to southeast winds in the North Interior. This station failed to live up to its reputation during the Ides Storm. Even when allowing for a greater potential for tree damage in the Autumn, widespread peak gusts of 35 to 45 mph (55 to 75 km/h) are better placed in the wind advisory category.