Figure 1.1 above Peak gusts (mph and km/h) for the March 13, 2016 windstorm. Wind speeds are largely from long-term surface airways weather observation sites, data buoys, lighthouses and C-MAN stations, with limited data from other networks (e.g. RAWS). Stations with long histories are preferred because of the research focus on intercomparison of historic storms. Numbers preceded by a tilde (~) represent the highest gust report in a dataset that has been interrupted at the height of the storm--usually data loss is from power outages. Values in italics are gusts estimated from peak wind, usually 2-minute or 5-minute, using a 1.3 gust factor. Stations with high-wind criteria gusts (58 mph or 93 km/h) are denoted with white-filled circles. Isotachs depicting ≥60 mph (~100 km/h) gusts are included to highlight the regions that had concentrations of the indicated magnitudes. The track of the extratropical cyclone center is shown (yellow arrow). Click on the map to see a larger version. Here is a map listing the station names.

Figure 2.1 above Storm track estimation largely based on surface maps provided by the US. NOAA Weather Prediction Center and satellite photo interpretation. Date and time in PST and central pressure in hPa (mb).

The extratropical cyclone intensified far to the south off of the southern Oregon coast (Figure 2.1) and initially moved east, followed by northeast to inside 130ºW at about 43ºN. The low continued tracking northeast to just off of the southwest Washington coast, deepening rapidly from 990 hPa (29.23" Hg) to 981 hPa (28.97" Hg) in just nine hours, marking a strong system. At this point, the low changed direction to nearly due north and tracked just off the Washington coast until landing in the vicinity of Quillayute. The system remained very strong, with some deepening up to the point of landfall. There, the storm moved over the tip of the Olympic Peninsula, then across the Strait of Juan de Fuca and through southern Vancouver Island before crossing the Georgia Strait and entering the British Columbia Mainland. As the extratropical cyclone moved onto land and interacted with the steep and complex terrain of the region, the storm began to weaken in classic fashion, gaining 10 hPa (0.30" Hg) in six hours. This likely reduced the wind impact in much of British Columbia.

This windstorm is a marginal classic-path event. A track inside 130ºW south of 45ºN, then recurving to the tip of the Olympic Peninsula followed by a nearly meridional track across southern Vancouver Island. Is just enough to put the storm in the category, though it might be considered a marginal case since the center remained quite far from much of the Oregon coast.

Figure 2.2 above Satellite photo composite of: a) four km resolution visible; b) four km water vapor; c) four km enhanced infrared; and d) one km visible images for 1630 UTC (0830 PST) on March 13, 2016 for the first three and 1645 UTC (0845 PST) for the 1 km visible.

Figure 2.3 above Satellite photo composite showing four km resolution water vapor images for: a) 0400 UTC (2000 PST) on March 13, 2016; b) 0600 UTC; c) 1430 UTC; and d) 1630 UTC. Images a and b depict the incipient cyclone developing in the base of a Gulf of Alaska low. Frames c and d show the extratropical cyclone at peak intensity, with an enhanced dry slot, well-defined bent-back front and classic comma shape.

Table 3.1 above For 24 key stations in the study region, peak wind and gust (knots, mph and km/h), with direction (º) and time of occurrence (PST). Regional and overall maximums, minimums and averages are provided, along with the legacy 11-station average. Average gust ratios (average wind/average gust), or AGR, are also included. Wind direction average is based on vector components.

Figure 3.1 above Peak wind (mph), peak gust and peak wind direction (º) for coastal stations arranged by latitude.

Figure 3.2 above Peak wind (mph), peak gust and peak wind direction (º) for interior stations arranged by latitude.

Figure 3.3 above Peak wind (mph) and peak wind direction (º) for coastal and interior stations arranged by latitude.

With a 24-station average peak wind of 30.8 mph (50 km/h) and average peak gust of 46.0 mph (74 km/h) from the S, the March 13, 2016 windstorm performed about average for this class of windstorm (Table 3.1). The legacy 11-station averages were not much different from the 24-station averages, a common outcome (the 24-station and 11-station averages are usually within one mph of each other), suggesting that this smaller list of stations traditionally used on The Storm King was sufficient to classify windstorm magnitude. In comparison to the March 13, 2016 event, the 1983 Thanksgiving Day storm had an 11-station average peak wind of 29.9 mph (48 km/h) with average gust to 49.9 mph (80 km/h) out of the SSW, the gusts being somewhat stronger on average than during the 2016 windstorm--this includes 60 mph (96 km/h) at Olympia and 62 mph (100 km/h) at Sea-Tac. The December 21, 1982 produced an average peak wind of 29.3 mph (47 km/h) with gust to 45.4 mph (73 km/h) out of the S, almost a match though the fastest interior gusts were not quite as strong as seen in 2016. The 1993 Inauguration Day Storm produced a strong 31.9 mph (51 km/h) average peak wind with gust to 52.4 mph (84 km/h) from the SSW, markedly stronger, with intense coastal gusts and strong interior gusts including 64 mph (102 km/h) at the Sea-Tac Airport.

There are, of course, differences in wind measurement methodology between the storms. During the abovementioned storms from 1982-1993, the wind was measured on analog cup-based anemometers with wind (sometimes called sustained wind) being a 1-minute average and gust being an instantaneous (~1-sec) reading. Digital sonic anemometers were in operation during the March 13, 2016 windstorm, with wind a 2-minute average and gust being a 3-second moving average. The longer period averages used in the present day would tend to favor lower readings for the same run of wind, though by how much is unclear because sonic anemometers are very sensitive to sudden changes in winds speed as they do not have the inertial response issues of cup-based anemometers. This means that the 2016 windstorm might have been closer to the 1993 Inaugural Day Storm than it at first appears, though the difference in damage outcomes suggests something less.

The peak gust at Vancouver International Airport of 43 mph (69 km/h) occurred out of 70º as the low-pressure center approached from the south-southwest. While 43 mph is not particularly fast for a windstorm, this is one of the strongest gusts out of the northeast quadrant ever recorded at Vancouver. Indeed, it is the highest since a gust of 47 mph occurred out of 90º on March 14, 1995--21 years nearly to the day.

The March 13, 2016 windstorm's narrow focus of strongest winds is somewhat evident on the coast between the latitudes of 46ºN and 48ºN (Figure 3.1). The interior surface wind response has a much more pronounced peak than the coast. This maximum is shifted a degree of latitude further north than the coastal peak, between 47ºN and 49ºN (Figure 3.2), the distribution reflecting the north-northeast track of the low-pressure center. Interestingly, the strongest winds missed both the Victoria and Vancouver International Airports while lashing nearby locations, resulting in the jagged trend-line at the north end of the interior station plot.

On average, the coast had higher peak gusts than the interior, though locally this pattern reversed dramatically north of 47ºN (Figure 3.3). Peak gust directions were roughly the same between the coast and interior, S to SW, though some stations that ended up in the low's northwest quadrant had peaks out of the E while under the wraparound cloud shield of the low, a classic response under the circumstances.

Figure 3.4 above One-minute samples of average wind (WND) and gust (GST) in mph, with wind direction in degrees (WDIR), for March 13, 2016. Times are in UTC (-7/-8 hours for PDT/PST). Data are from the University of Washington Department of Atmospheric Sciences rooftop sensor.

Figure 3.5 above One-minute samples of average wind (WND) and gust (GST) in mph, with sea-level pressure in hPa (PRES), for March 13, 2016. Times are in UTC (-7/-8 hours for PDT/PST). Data are from the University of Washington Department of Atmospheric Sciences rooftop sensor.

In the Seattle Area, the onset of the March 13, 2016 windstorm's strongest winds was quite sudden (Figure 3.4). The heavy gusts arrived right after the wind direction went through a rapid shift from E to SE then S. The strongest gusts occurred within about a half hour of the S wind arrival--to be matched later on but not exceeded. Much of the damage from this windstorm occurred during this early period.

This kind of sharp wind attack has been observed before during Pacific Northwest windstorms, including in the Seattle Area. Perhaps the strongest such example happened during the October 21, 1934 windstorm. For extratropical cyclones with a strong meridional track (i.e. north-northeast to north), southerly winds tend to ramp up very quickly when the pressure slope (i.e. pressure gradient orientation) shifts above 90º, or approximately when the low-pressure center has moved north of the latitude of the station of interest.

An added complication with the March 13, 2016 windstorm is that the leading occluded front arrived at nearly the same time that the low reached the latitude of Seattle (Figure 3.5). This is evidenced by the sharp pressure minimum just ahead of the strongest winds. Once the front moved through, the rain ceased and the temperature warmed to about 52ºF (11ºC) (not shown) along with the arrival of the strongest winds--this lasted from about 2030 to 2130 UTC. After an initial jump, the barometric pressure climbed steadily during this strong wind phase of the storm. After a modest lull that lasted about an hour, the winds picked back up around 2220, along with a more rapid pressure rise and falling temperature. This likely marks the passage of the bent-back front. With this feature, wind speeds matched those of the initial wind escalation, before fading after 2300. Overall, wind gusts of 40 mph (65 km/h) and above occurred from 2038 to 2254, or about 2.25 hours.

The March 13, 2016 extratropical cyclone developed in the base of a deep Gulf of Alaska low--a secondary spinup situation--and followed a classic track for a Seattle Area and North Interior windstorm. Other storms with similar tracks and peak wind and gust outcomes include December 21, 1982 and the 1983 Thanksgiving Day Storm. The measured wind speeds put the March 13, 2016 windstorm about on par with the two 1980s storms. The January 20, 1993 Inaugural Day Storm is a more intense windstorm example from this track type.

Because the extratropical cyclone developed and tracked into a region with relatively low pressure overall, the March 13, 2016 windstorm appears to have behaved like a classic 985 to 990 hPa (29.09" to 29.23" Hg) low, despite having a 979 hPa (28.92" Hg) central pressure at landfall. One outcome of this is that the March 13, 2016 windstorm had a compact core. High winds only affected a fairly focused region, and indeed the strongest gusts skirted just north of much of Seattle. Minor deviations of track could have altered peak wind outcomes significantly. A little further south and Seattle may have been hit with the 60-70 mph gust that occurred in the North Interior.

Figure 5.1 above Southerly wind gusts of 45-55 mph (70-90 km/h) swept the Lake Washington Shores around Seward Park, bringing down trees and branches. This Douglas-fir broke near the base and then crashed into nearby pines, breaking several large branches as the tree plunged to the ground, its top shattering over a walkway. The Douglas-fir clearly had some heartwood rot and this may have contributed to a greater vulnerability to breakage. Near to where this tree fell, another windthrown bole crushed a car, killing one person.

Figure 5.2 above Emergency response after a large tree fell and crushed a car in Seward Park, killing the driver. The rescue of a second passenger, a toddler, continued as the winds raged.

Figure 5.3 above As if on a routine day, a person runs past a snapped tree as gale-force wind gusts continue to pummel Seward Park and emergency responders attend to a tree-related fatality.

Figure 5.4 above Along South Genesee Street in Seattle, a fence had been blown out by the wind. Solid wooden fences like this are a routine damage feature during windstorms.

Figure 5.5 above This tree at the University of Washington grazed a light pole on its way down and reached a sidewalk. As measured from the rooftop of the Atmospheric Sciences Building, wind gusts reached 49 mph (80 km/h) on campus. This tree had lost much of its heartwood to rot that probably compromised its ability to withstand heavy wind loads.

Figure 5.6 above A healthy red alder snapped under the force of the gale and nearly struck a utility pole. The top crashed across a sidewalk along Sand Point Way NE in Seattle.

Figure 5.7 above Large birch branches dropped onto this sidewalk along NE 65th St in Seattle.

Figure 5.8 above During the windstorm, power outages left traffic signals dark, here on NE 65th in Seattle, turning many intersections into four-way stops. Heavy gusts, the leftovers from earlier stronger winds, cased the lights to sway as the photo was taken.

Figure 5.9 above A broken branch is left suspended in this cedar tree. This is a common long-term hazard after windstorms. Branches captured in the canopy can eventually be shaken loose by following storms, including ones of moderate intensity. Photo by Charlie Phillips.

Figure 5.10 above This windthrown black cottonwood, growing right on the Lake Washington shore, buried a path with numerous limbs. The tree seemed to have poor anchorage and may have had some fungal damage. But as with all wind-shattered trees that have pathologies, one is left asking questions like why did this tree not fall during the August 29 or November 17, 2015 windstorms, when it almost certainly still had many of its leaves (offering more resistance to the wind)? Perhaps the cottonwood was better sheltered by the leafy crowns of its neighbors in the summer/autumn. Photo by Charlie Phillips.

Figure 5.11 above Post-storm cleanup near E Pine Street in Seattle. These days, the buzz of chainsaws and chippers is the sound of an abating tempest. Photo by Charlie Phillips.