The temperature did not get so warm at Sea-Tac, a modest 57ºF (13.9ºC), with Vancouver having the coolest maximum at 54ºF (12.2ºC) suggesting that the triple-point passed south of the Puget Lowlands (also indicated in Figure 2.3). The temperature warming at this location, and in Vancouver, BC, is likely the result of the occluded portion of the front mixing out a cooler surface air layer put in place during the offshore flow ahead of the storm. These easterly winds are indicated by sharp dew point depressions in the morning at Sea-Tac, with warming to 54ºF (12.2ºC) due to downsloping off of the Cascade Mountains. Precipitation ahead of the front then caused evaporational cooling before this layer mixed out when the arrival of the occlusion. Dew point depressions increased again as southerly winds escalated, suggesting the occurrence of vertical mixing post-front during peak winds in the Seattle area, just like at Portland but in this case in a post-occlusion environment, not post-warm front. There is a second but more modest escalation of winds at Sea-Tac around midnight, along with a cooler temperature and shallower dew point depression. Though Olympic Mountain lee troughing may have contributed to this wind escalation (see section 4.1 below), it is here suggested that this is more the mark of the bent-back front acting as a weak secondary cold front in the Seattle Area, bringing in cooler, more stable air. In such an eventuality, the relatively warm air put in place post-leading-occlusion can behave as a de-facto warm sector. Note that if the bent-back front did indeed interact with the Seattle area, it was the very edge of the wrap-around band, not even bringing precipitation.
Vancouver, BC, had a clearer passage of the bent-back front, with the arrival time between midnight and 01:00. Light precipitation moved through around midnight, followed by a secondary wind escalation, peaking at 01:00 at CYVR and perhaps a little later in some other parts of the metro area. The rate-of-rise in barometric pressure slowed down (shown in section 5.1 below) as the bent-back front moved in, followed by a fast rise, along with the arrival of cooler temperatures. The bent-back front was not strong by historical standards and is difficult to detect in the surface observations. Satellite photo interpretation also supports the bent-back front reaching Vancouver around 01:00 on the 12th.
Returning to consideration of upper wind conditions, the arrangement of an intense jet stream right over the Willamette Valley with a flow direction nearly parallel to the axis of the surrounding mountains is actually quite rare even among classic windstorms. The January 16, 2000 storm appears to have had a somewhat similar setup, though perhaps not as strong, with a 250 hPa (10.1 km) wind of 72 m/s (140 knots) out of 195º at 04:00 on the 16th, though height 850 winds were a modest 14 m/s (28 knots) out of 215º at this time. Winds increased to at least 26 m/s (50 knots) some 12 hours later, but from an imperfect 225º, and this after the jet stream moved away from the region. The major December 12, 1995 windstorm does not appear to have had such a good setup, this based on a partial sounding taken at Salem around 16:00 on December 12th, and a more complete record from Medford (KMFR) at the same time. Height 350 to 250 wind speeds were much slower than the 2014 extratropical cyclone, and though 32 m/s (63 knot) 850 winds during the 1995 storm were close, they had a not-so-ideal direction of 220º. The powerful November 14, 1981 windstorm also does not appear to have had the same kind of ideal setup seen on December 11, 2014, mainly because the jet stream core had a more zonal orientation that largely remained south of the Willamette Valley. Nevertheless, the 1981 storm brought over Salem intense 49 m/s (96 knot) 850 winds out of a nearly ideal 190º orientation at 04:00 on November 14th, one of the highest readings from this height on record for this location and likely the reflection of a very deep storm system that dominated the lower tropospheric environment over a huge area. Height 300 winds were a relatively modest 40 m/s (78 knots).
To be clear, the near-perfect setup during the 2014 windstorm likely explains the intense wind gusts in the northern Willamette Valley. Had the jet stream not been so favorably aligned, quite likely Valley wind speeds would have been less than they were--maybe peak gusts around 50-55 mph (80-90 km/h).With the jet axis to the east, the north Oregon coast did not have ideal upper support for strong surface winds, likely explaining the relatively low peak wind gusts, resulting in coast and interior peak wind speeds that were roughly the same (see section 3.5 below). Earlier, as the low tracked off the south Oregon coast, the main jet axis sat right over the shore, supporting the stronger wind readings in the southern region.
The narrative of upper-wind influence over Oregon also applied to Washington as the low tracked up the coast and across Vancouver Island over the next 12 hours (Figure 2.4), but is even more pronounced as the jet streak weakened to 55 m/s (125 knots) and moved over the Cascades. Thus, the Puget Lowlands did not have the same magnitude to upper support as the Willamette Valley, likely explaining in part the lower wind speeds in the region. In the north interior, an area that due to geography is prone to strong SE winds as lows approach the coast, the still strong surface pressure gradients (see pressure gradient sections below) supported wind gusts nearly on par with the Willamette Valley despite weaker upper support.
Peak pressure gradients during classic-path windstorms are usually at a time when the orientation--the pressure slope (Lange 1998)--is to the southeast. These events tend to be the most intense examples of the southeaster windstorm pattern, sometimes called "southeast suckers." The surface pressure conditions during these storms favor those locations that are exposed to SE winds. The Willamette Valley and Puget Lowlands, with north-south orientations, are not as ideally setup as Washington's north interior and the Georgia Strait. The latter two regions apparently do not need the same magnitude of upper support for intense winds during classic-path windstorms, though the tendency for southeast winds at lower levels (e.g. 850 hPa) in the northeast quadrant of extratropical cyclones probably does aid SE surface winds as the lows approach, provided some vertical mixing mechanism is present.
Interestingly, for the December 11, 2014 windstorm, the Puget Lowlands apparently had a good surface setup for high winds--perhaps on par with the north interior due to a nearly south pressure slope at the time of peak gradient (see section 3.4 below)--making the lower peak gusts seemingly an aberration. However, for much of the main storm period, the pressure slope had a less-than-ideal 135-155º orientation over the Puget Sound, perhaps a better indication of surface wind support than the single observation at peak gradient. Interestingly, this pattern of relatively lower peak gusts in the Puget Lowlands, especially in the Seattle Area, has shown up for a large proportion of classic path windstorms, including the 1962 Columbus Day Storm.