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December 14-15, 2006 Windstorm compiled by Wolf Read |
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On December 13, 2006, in the heels of an intense 957 mb (28.26") cyclone that moved into the Queen Charlotte Islands, a cyclone developed in the North Pacific far off the shore of southern Oregon, out beyond 140ºW. Over the course of December 14th, this low traveled ENE at a fairly rapid pace and deepened to about 970 mb (28.64") as it neared the north tip of the Olympic Peninsula. By this time, around 16:00 PST, the low had become very large, with a steep pressure gradient reaching all the way down to the Mendocino Coast of California. Damaging, and in some cases extreme, winds raked the Pacific Coast from CA to Vancouver Island, and surged inland, slamming the Willamette Valley with 48 to 58 mph peak-gusts officially, and the Puget Lowlands with gusts up to 69 mph at Sea-Tac. For Oregon, the highest winds occurred in two phases, with some peak gusts occurring around 16:00 in the warm air advection field post-warm front as the low neared, and some peaks happening around 20:00 with the arrival of the storm's strong cold front. For Washington, many places experienced peak gusts around 01:00 on the 15th, in what some people have begun to call "The Surge," as the cyclone's intense bent-back occlusion swept inland. Wind-wise, this was the most powerful storm for the Seattle Area since the January 20, 1993 Inaugural Day Storm. For the south Willamette Valley this was the most powerful event since the February 7, 2002 gale, and for the greater Portland Metro area, including Aurora, Hillsboro and Troutdale, the December 2006 storm was likely the strongest since January 16, 2000. This powerful storm challenged the old notion that Pacific Northwest windstorms tend to be dry. Intense rainfall accompanied this cyclone as the leading warm front, fed with copious tropical moisture, swept into the Pacific Northwest. Another burst of heavy rain accompanied the cold front in some areas. Areas of Seattle experienced some of the heaviest short-period rainfall on record, with hourly rates reaching around an inch. Flash floods inundated some low-lying areas. All this precipitation fell on top of soil that had been saturated by earlier December storm systems, and one of the wettest Novembers on record for many areas (a weather event worthy of it's own web-page). Saturated soil loses it cohesion, and doesn't hang on to trees' roots very well. Many shallow-rooted Northwest trees, such as the Douglas-fir, simply uprooted in the pummeling wind. The huge trees acted as hammers, smashing through surrounding vegetation, powerlines, homes and other structures--forced amplifiers. The long duration of high winds in many areas probably also exasperated the situation. The effect: For the Willamette Valley, many places experienced tree damage worthy of a windstorm with 65 to 70 mph gusts. For many areas of Washington, trees toppled with disturbing regularity--uprootings, shattered tops, broken trunks. The saturated soil is perhaps an equally significant factor to wind in the damage brought by this storm. Figure 1, below, is courtesy of the Hydrometeorological Prediction Center, and shows the cyclone just off the Washington coast at 16:00 PST on December 14, 2006. In the tight gradient south of the low's center, winds had reached damaging levels in Oregon and parts of Southwest Washington by this time.
Here are my journal notes: |
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Some Further Notes The journal summary above demonstrates a windstorm that struck a particularly large region. Significant tree loss is documented from Corvallis, OR, in the south to Seattle, WA in the north. Based on official wind speeds, and news reports, this kind of damage stretched from about Eugene, OR to Whideby Island, WA, in interior sections, and from Crescent City, CA to southern Vancouver Island on the coast. The February 3-4, 2006 windstorm roared through a similar-sized region, but, in general, the measured windspeeds were generally less, and the damage simply wasn't as frequent. Not since January 16, 2000, has a windstorm caused such widespread disruption in the western Pacific Northwest, and the more recent event appears to have been the bigger one. Granted, heavy rains and saturated soil significantly contributed to the December 14-15, 2006 windstorm's impact. But nature works this way. Disasters tend to be the result of seemingly independent variables coming into phase at similar times. How Deep Was the Low at Landfall? Examination of stations on the Olympic Peninsula and southern Vancouver Island, where the low's center landed, reveal these minimum sea-level pressures;
Offshore, the lowest pressure at Buoy 46005, 46.1N 131.0W, was 977.4 mb (28.87"), Buoy 46036, 48.4N 133.9W, was 989.4 mb (29.22"), and Buoy 46206, 48.8N 126.0W, was 976.5 mb (28.84"). Looks like the low landed with a central pressure of about 977 mb, and there's some question about the actual minimum central pressure offshore--the low may not have been any deeper than 976 mb, though the Hydrometeorological Prediction Center indicates a possible minimum of 970 mb on its 16:00 PST map on December 14th (00:00 UTC 15 Dec 2006). In any event, it appears that the low had reached a mature stage (stopped deepening) many hours before landfall. |
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December 14-15, 2006: Comparative Meteorological Details |
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Storm Track
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Figure 25, above, outlines the storm track for the December 14-15, 2006 windstorm. Positions were based on Hydrometeorological Prediction Center surface maps, and water vapor satellite photos collected from the NWS at the time of the storm. Compared to many past windstorm events, some of which are included in the figure, this cyclone developed at a much higher latitude, and followed a more easterly track. Thus sparing most of California, and parts of Oregon a more serious hit. The close proximity of the storm center during peak development, and its depth, counteracted some of the ameliorating effects of the northern track: Much of the Oregon Coast suffered intensely damaging winds, and the Willamette Valley still suffered a fairly powerful gale. |
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General Storm Data Minimum Pressures and Peak Gradients Table 1, below, lists the lowest sea-level pressures achieved during the December 14-15, 2006 storm for 11 Pacific Northwest locations. For a major storm, pressure minima for the southern stations weren't very low. Arcata's reading is downright summer-like. This is a reflection of extreme pressure gradients associated with this storm, the details of which are discussed below in the caption for Table 2. In parts of Washington, barometric pressures dropped to some fairly extreme lows, but still not approaching the records seen in past storms, such as December 12, 1995 or October 12, 1962. From available data, Tatoosh Island experienced the lowest reading in the state, with a value of 28.86" (977.2 mb) at 22:00 PST. Source: Pressure data is from the National Weather Service, Seattle, METAR. Some data in the above comments are from the National Data Buoy Center. |
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Figure 26, below, depicts the sea-level pressure readings for coastal stations during the December 14-15, 2006 storm. A strong gradient is reflected in the wide separation between trend-lines. Interestingly, Tatoosh Island showed higher pressure than more southern stations for a time ahead of the windstorm--the mark of a low approximately tracking from the southwest to the northeast. The timing of pressure minima for all four of these stations is fairly close, which makes this event somewhat different than, say, the relatively similar March 2-3, 1999 and February 12-13, 1979 storms (see March 2-3, 1999 for coastal SLP graphs for these two storms). Clearly the December 14-15, 2006 storm tracked more eastward than northward compared to many of its predecessors. The cyclone of January 19, 1964 seems to share a similar pattern of closely-timed pressure minima (graph shown below--note the change in scale along the y-axis due to the extreme minimum pressure recorded at Tatoosh Island in 1964), and probably followed track similar to the December 14-15, 2006 storm. But there are also some significant differences. The 1964 storm hardly effected the barometers at North Bend and Arcata. And the sharp V-trace at Astoria and Tatoosh suggest a cyclone arriving rapidly during peak development, whereas the December 14-15, 2006 storm reached peak development offshore and had begun to degrade as it moved inland. |
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Table 2, below, lists the maximum pressure gradients achieved during the December 14-15, 2006 windstorm for 12 Pacific Northwest measures. Despite extensive power disruption in the region, the ASOS stations performed rather well during this major storm event, with only OLM having a significant loss of data during the high-wind period. Thus, unlike many storm events in the ASOS era, there's an excellent record in which to analyze. Many of these readings are of extreme nature, marking a very strong storm. The ACV-TTIW measure of +42.7 mb (+1.26") is the most extreme gradient between those two stations out of any storm documented on this website. For comparison, the December 12, 1995 windstorm peaked at +31.8 mb (+0.94") at 18:00 on the 12th, the November 13-14, 1981 windstorm peaked at +38.7 mb (+1.14") at 08:00 on the 14th (for ACV-UIL--might have been a bit higher ACV-TTIW, but pressure data for Tatoosh Island is missing from this time period), the January 19-20, 1964 windstorm peaked at +38.7 mb (+1.14") at 16:00 on the 19th and the punishing October 12, 1962 storm peaked at +32.3 mb (+0.95") at 22:00 on the 12th. At 22:00 on December 14, 2006, the barometer at Arcata, CA, read a benign 1019.9 mb (30.11") while the pressure at Tatoosh Island, WA, sat at its very low 977.2 mb (28.86") minimum for the storm. This kind of gradient supports the extreme wind velocities measured at coastal stations, especially the stretch north of North Bend. Of interest is the +9.1 mb (+0.27") reading for the Willamette Valley (EUG-PDX). Most major windstorms for the Valley--including the December 12, 1995, November 13-14, 1981 and October 12, 1962 events--tend to push the gradient in the +8.0 to +10.0 mb range, with a few extreme events (usually cyclones that make landfall in the vicinity of AST) like October 2, 1967 above the +10.0 mb threshold. All these extreme events, with their attendant high pressure-gradient, produced wind gusts of 60 to 80 mph on official NWS (formerly the WB) anemometers. In this regard, the December 14-15, 2006 windstorm was a distinct underachiever. Peak gusts at official anemometers in the Willamette Valley ranged from 48 to 58 mph, with most in the mid-50s. The gradient conditions were right, but other factors were not. Due to a more northeasterly track for this storm compared to the northward-tracking big classic events, the upper air flow in Dec 2006 probably didn't effectively support strong south winds. Perhaps a gradient like that seen on October 2, 1967 (+13.7 mb) would have been required for official sensors to show 60 to 80 mph gusts. Over Western Washington, gradients show a very extreme nature. On the coast, the +20.5 mb (+0.61") AST-TTIW reading exceeds the +17.7 mb (+0.52") maximum gradient during the Columbus Day Storm of 1962. The PDX-SEA value of +15.9 mb (+0.47") not only exceeds the Columbus Day Storm's reading of +9.9 mb (+0.29") but also exceeds the peak gradient of +12.9 mb (+0.38") that occurred during the devastating October 21, 1934 gale and the extreme value of +15.3 mb (+0.46") that occurred in the massive December 12, 1995 storm. The December 14-15, 2006 windstorm almost tied the October 21, 1934 event for the number one slot on the PDX-BLI measure, with a reading of +22.3 mb (+0.66") compared to +22.7 mb (+0.67") in 1934. Ultimately, what the maximum pessure gradient data in Table 2 reveal is that the focus of this event was in Western Washington, with the effects diminishing southward. This mirrors a pattern seen with other big storms that have followed the approximate track of the December 14-15, 2006 storm: events like February 12-13, 1979, January 19-20, 1964 and October 21, 1934. |
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Table 2 Notes: [1] Last occurrence. Gradient had same value at 14:00. |
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Figure 27, below, depicts coastal pressure gradient readings for coastal stations during the December 14-15, 2006 storm. The coastal gradient from ACV-TTIW stayed above 40.0 mb for no less than five observation periods, and above 30.0 mb for ten observation periods (nearly ten hours). Gradients along the southern part of the region, reflected in the ACV-OTH values, though strong, weren't at the extreme levels witnessed in the northern part of the afflicted region. This is better depicted in the accompanying graph, which compares shorter gradient measures between stations of approximately (this is a rough approximation) equal distances apart. The gradient between Astoria, OR, and Tatoosh Island, WA, is nearly 6.0 mb higher than the gradient between Arcata, CA, and North Bend, OR (in these graphs, Cape Arago data is used in place of North Bend Airport). Notice the later timing of the northern peak gradient compared to the southern coast. When AST-TTIW reached its maximum of +20.5 mb at 22:00, ACV-OTH had relaxed to a much more gentle +7.6 mb and OTH-AST a modest +12.0 mb. The gale in Oregon was winding down as Washington's pummeling was approaching a crescendo. |
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Pressure Tendencies Table 3, below, lists the maximum hourly pressure falls and rises achieved during the December 14-15, 2006 storm for 11 Pacific Northwest stations. This storm brought with it a strong pressure couplet, especially in Washington. Pressure declensions of -3.3 to -3.8 mb/hr (0.09 to 0.11 in/hr) mark a rapidly deepening storm that also moved toward the coast fairly rapidly. Astoria, Quillayute, Seattle, Bellingham and likely Olympia (who's pressure data was lost during the height of the gale), with intense pressure climbs in the range of +5.1 to +6.9 mb/hr (+0.15 to +0.20 in/hr) appear to have all been zapped by the tip of the cyclone's well-developed bent-back occlusion. Though Bellingham was spared the intense SW to W gale that the other stations received, probably due to the low rapidly filling and weakening by the time the occlusion arrived, places like Astoria and Seattle were subjected to the feature's intense 50 mph gusting 70 winds (65 mph G 80 on parts of the WA coast). The area of peak pressure tendencies (which suggest peak gradient), and highest winds, was fairly narrow, perhaps a belt 50 to 100 miles wide who's southern border appears to have been along an Astoria to Chehalis line. Locations that were outside of the bent-back occlusion's primary zone of influence (marked by weaker pressure tendencies) generally had peak winds in the range of 40 mph gusting 55. The bent-back occlusion is discussed further in the Peak Wind and Gust section below (see especially Fig 28). |
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Table 3 Notes: [1] The -2.0 mb hourly fall is the last of two occurrences. [2] The OLM AWOS stopped reporting after the 23:00 observation. [3] The -3.3 mb hourly fall is the last of two occurrences. |
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Peak Wind and Gust Table 4, below, lists the peak wind and gust for eleven key stations in the Pacific Northwest, their direction, and their time of occurrence. "Peak Wind" is a 2-minute average, and "Peak Gust" is a 5-second average. By my own personal methodology, a wind event rates the term "windstorm" when the average peak gust of these eleven stations reaches 39.0 mph (gale force) or higher. This ranking favors those storms that follow a northward path close to the U.S. Pacific Coast, and for good reason--such storms affect the largest land area, and therefore are potentially the most destructive. The December 14-15, 2006 cyclone did not follow such a path, tracking inland on a ENE-ward path across southern Vancouver Island instead, and the focus of damaging winds was primarily in the northern part of the region under consideration. Even despite an unfavorable track for a high ranking, this cyclone managed to generate a high score. With an average peak gust of 55.2 mph, the December 14-15, 2006 storm just made the "major windstorm" category. Moderate windstorms have an average of 45.0 to 54.9, and major windstorms are those that reach or exceed 55.0. Only a handful of storms have made the majors, including December 12, 1995 with 60.5, November 14, 1981 with 65.9 and October 12, 1962 with 80.5. It should be noted, however, that the peak gust measure for the earlier storms was different. Peak instant gust was noted up to about 1995, with the December 1995 storm's average containing a mixture of instant gusts at some stations and the new ASOS 5-second peak. ASOS hadn't been fully implemented in the Pacific Northwest by December 1995--that took until mid-1996. Peak gusts recorded during the December 14-15, 2006 storm appear to be of the 5-second variety, though the introduction of sonic anemometers at official stations may have changed this--I believe that a 3-second gust is the new standard with these sensitive anemometers. There's a difference between peak instant gust of the past and the 5-second peak of the modern era (and even the 3-second gust). A 5-second average could contain a peak instant reading that is significantly higher--maybe even by a factor of 1.2 (20%), depending on the amount of turbulence at the site. Multiplying the 55.2 average peak gust for the December 14-15, 2006 storm by 1.2 yields 66.2, which would put the 2006 storm deeply into the major windstorm category. The disparity probably isn't this strong--an adjustment of 1.05 to 1.10 (5 to 10%) is probably more realistic, as airport-based anemometers tend to be subjected to fairly steady winds due to their typically good exposures. These lower adjustments would put the December 14-15, 2006 storm in the range of 58.0 to 61.0 for comparison to events like the Columbus Day Storm and November 14, 1981. December 1995 is more tricky, due to the mix of measures--it's probably in the range of 62.0 to 65.0 when adjusted for the difference in peak gust measure. In any event, the December 14-15, 2006 windstorm is the first event to reach major status since December 12, 1995 without an adjustment for 5-second gust, marking a truly significant storm. When past windstorms are adjusted for 5-second gust, the December 14-15, 2006 gale appears to be the first major to afflict the region since the January 16, 2000 classic event. It is unfortunate that various ASOS stations suffered outages during the December 14-15, 2006 gale. Large blocks of wind data are missing for North Bend, Astoria and Olympia during critical points in the storm, and actual maximum velocities at these stations could have been higher than indicated. For more details, reading the notes for Table 3, which appear below the table, is encouraged. |
| Location |
Peak |
Direction |
Obs Time of |
Peak |
Direction |
Obs Time of |
| California: | ||||||
| Arcata |
21 |
180º |
20:26 HRS, 14th |
36 |
210º |
20:32 HRS, 14th |
| Oregon: | ||||||
| North Bend [1] |
62 |
229º |
19:00 HRS, 14th |
97 |
189º |
16:36 HRS, 14th |
| Astoria [2] |
39 |
200º |
13:39 HRS, 14th |
69 |
200º |
15:34 HRS, 14th |
| Medford |
28 |
200º |
14:53 HRS, 14th |
47 |
200º |
15:01 HRS, 14th |
| Eugene [3] |
31 |
210º |
18:54 HRS, 14th |
54 |
250º |
19:30 HRS, 14th |
| Salem |
35 |
220º |
20:56 HRS, 14th |
53 |
220º |
19:37 HRS, 14th |
| Portland [4] |
38 |
230º |
19:55 HRS, 14th |
53 |
220º |
20:07 HRS, 14th |
| Washington: | ||||||
| Quillayute |
29 |
280º |
23:53 HRS, 14th |
59 |
290º |
00:15 HRS, 15th |
| Olympia [5] |
36 |
190º |
23:54 HRS, 14th |
53 |
190º |
23:53 HRS, 14th |
| Sea-Tac [6] |
46 |
230º |
00:53 HRS, 15th |
69 |
220º |
00:44 HRS, 15th |
| Bellingham |
40 |
170º |
23:53 HRS, 14th |
55 |
160º |
23:49 HRS, 14th |
| AVERAGE |
34.8 |
213º |
55.2 |
214º |
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Table 4 Notes: [1] North Bend's (OTH) last report was at 16:15 on the 14th, before being shut down by the storm for the next 16 hours. Cape Arago (CARO3) data are used to substitute for data loss at the height of the storm. Note the timing of the peak gust for CARO3. Based on the continuous winds data for CARO3, sudden surge of very high winds struck the coast, representing an increase in 2-minute velocities of around 45-mph-gusting-70 to 55-mph-gusting-95 around 16:30, and apparently this escalation silenced OTH. Compared to the airport station, CARO3 is highly favored for very fast wind readings. Based on a quick and very rough comparison, peak wind velocities at OTH were probably in the 40-45 mph gusting 55-60 range during the height of the storm, which raged from 16:30 to about 20:00. The CARO3 values are not included in the 11-station average. Instead, 40 G 60 is substituted. [2] Peak gust is the last of two occurrences, with the other happening at 14:15 out of 190º. Likely due to storm-related failure, wind data is missing between 15:38 on the 14th and 03:55 on the 15th, which includes part of the height of the gale, so peak wind and gust could have been higher. [3] Peak 2-minute wind was 44 mph from 240º according to the Preliminary Local Climatological Data report for Dec 2006. Peak 2-minute winds listed in the above table are those gleaned from the regular and special METAR. [4] Peak gust is the last of three occurrences. Gusts of 53 mph were also reported at 17:14 and 19:51. Peak 2-minute wind was 43 mph from 240º according to the Preliminary Local Climatological Data report for Dec 2006. Peak 2-minute winds listed in the above table are those gleaned from the regular and special METAR. [5] Olympia AWOS down between 23:54 on the 14th and 17:54 on the 15th. This failure occurred during the initial wind escalation phase of the storm, and, based on data from other stations such as SEA and TCM, likely OLM's peak wind and gust were higher than the values reported in the table. [6] Peak 2-minute wind was 52 mph from 220º according to the Preliminary Local Climatological Data report for Dec 2006. This is perhaps the highest 2-minute wind speed ever recorded at the Sea-Tac Airport. Peak 2-minute winds listed in the above table are those gleaned from the regular and special METAR. |
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Examination of Some Peak Gust Details The winds at Sea-Tac are particularly noteworthy, given that they represent some of the highest velocities ever attained at this station. From available data, the peak gust of 69 mph is only exceeded by a gust to 75 mph recorded on January 15, 1951 storm and 71 mph on January 9, 1953. However, note again that peak gust records from the 1950s were generally of the "instant" (1-second) variety. A 5-second gust of 69 mph could easily have contained instant velocities as high as 75 mph, and maybe as high as 80 mph. Given the damage that occurred in the vicinity of Sea-Tac Airport, and in some areas to the east and northeast, such extreme values are supported. Official wind measurements during the November 3, 1958 windstorm provide evidence for peak instant wind gusts around 80 mph at the Sea-Tac Airport in 2006. As the 1958 storm's bent-back occlusion tore through Hoquiam, peak 1-minute winds reached 52 mph with a gust to 81. At Olympia, peak 1-minute winds reached 60 mph with a gust to 76. And at The Dalles, peak 1-minute winds also reached 60 mph with a max gust to 81. According to the Local Climatological Data, Dec 2006, publication for SEA, the maximum 2-minute wind in the early morning of December 15, 2006, reached 52 mph (the final value in the daily and monthly summaries typically differs from the max 2-minute wind gleaned from the METAR reports--see Table 4 notes). Maximum 1-minute winds are usually a few percent higher than 2-minute winds, say by a factor of 1.05. Therefore, perhaps SEA had 55 mph maximum 1-minute winds. According to the information from the 1958 storm, peak instant gusts could have been as high as 81 mph (as per HOQ). If this is the case, likely, the December 14-15, 2006 windstorm was the strongest at Sea-Tac for the 1948-present era, and perhaps the strongest since the great October 21, 1934 gale. It is interesting that peak gusts at the Renton Airport, 51 mph, Boeing Field, 56 mph, and at the University of Washington, 55 mph, are far below those measured at the Sea-Tac Airport. Sea-Tac is exposed upon a hill left over from glacial times with the waters of Puget Sound not too distant to the west, and both the Renton Airport and Boeing Field are down in narrow valleys with a north-south trend. Given the direction of the peak gust at SEA, 220º, which is counter to the north-south orientation of the valleys, it appears that the lowland stations were sheltered from the most damaging aspects of this storm. This idea may not work so well in explaining the UW's lower wind speeds. A peak gust of 70 mph at West Point in Seattle, which has much open water to the southwest, suggests that Sea-Tac bore the brunt of this storm in a fashion similar to locations right on the Puget Sound shoreline. The Dalles, OR, experienced a peak gust of 63 mph out of the southwest. Due to generally favorable pressure gradient orientations and better upper-air support, Storms that track more easterly than northerly tend to favor the west-east trending Columbia River Gorge, and December 14-15, 2006 was no exception. Classic storms such as October 12, 1962, following their more northerly-directed tracks, tend to yield much lower wind speeds at The Dalles. In the case of 1962, the peak gust at The Dalles was a mere 29 mph, this while gusts of 106 mph were recorded approximately 60 miles to the west at Troutdale. The intense eastward-tracking low of November 3, 1958 offers an example of a worst-case scenario for The Dalles. The Willamette Valley: Official vs. Spotter and Unofficial Readings Peak gusts measured at official stations throughout the Willamette Valley ranged from 48 mph at Corvallis to 58 mph at Troutdale, with the other stations falling between these values. The consistency of peak gusts among the official stations, with most ranging between 53 and 55 mph, speaks loudly to the soundness of these measurements. Plus, given past wind behavior in the Valley during storms of similar track and intensity, the official wind speeds are also consistent. Even if many stations peaked just a few mph below high-wind criteria, Troutdale's peak gust verifies the high-wind warning issued by the NWS, Portland, ahead of the storm in anticipation of possible gusts of 65 mph (gusts to 58 mph are the minimum for high-wind criteria). Interestingly, there were a number of spotter reports that were much higher than the official readings in the Valley. Some of these strong unofficial readings were in higher terrain, like the West Hills of Portland (G 65 mph), and this likely explains the difference. However, an 80 mph gust was recorded 5 miles NNE of Salem, and gusts as high as 70 mph were reported in the vicinity of Forest Grove. Given these very high readings relative to the official numbers, it would be interesting to know the site conditions of these wind sensors. Local terrain features, and/or, the sensor placement relative to nearby structures may have had a bearing in these higher speeds. One key meteorological detail in support of these high unofficial readings: the +9.1 mb EUG-PDX pressure gradient, which matches many storms that have produced wind gusts of 65 to 80 mph at official stations. |
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Figure 28, below, depicts 2-minute wind speeds recorded at Destruction Island, WA, during the December 14-15, 2006 windstorm. Sample rate is 10 minutes. This data shows very-well the arrival of the cyclone's bent-back occlusion, a feature that was discussed above, in the section on the storm's pressure tendencies. After about 18:00 UTC on the 14th, winds switch from northeasterly to southeasterly and escalate. With a gradual shift to southerly, winds reach 50 to 60 mph at times as the low passes just to the north of this station's location. Then, after a brief period of moderate southwesterly winds, a sudden surge arrives out of the west, and for nearly an hour, wind speeds average 58 to 66 mph, with gusts as high as 80. This marks the arrival of a well-defined and strong bent-back occlusion. After the initial surge, the winds gradually decayed as the low moved steadily inland. |
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Peak Gusts in the Seattle Area: 15 Dec 2006 Strongest since at least 20 Jan 1993 Table 5, below, lists Seattle-area peak gusts, in mph, for recent storms (those that have struck since ASOS was fully implemented). The data reveal that, for the greater Seattle area, the December 14-15, 2006 windstorm outclasses all events since the damaging March 3-4, 1999 gale. Likely, the December 2006 storm was stronger than March of 1999. Almost certainly, on official anemometers, the December 2006 windstorm outclasses the far-reaching and powerful December 12, 1995 event. The January 20, 1993 Inaugural Day storm seems like a close match, but the earlier storm may have been more intense in the immediate Seattle area than December 15, 2006. The December 14-15, 2006 gale appears to be in the storm-of-the-decade category. |
| Storm |
Tacoma McChord
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SeaTac Airport
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Renton Airport
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Boeing Field
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West Point
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U of W ATG
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Everett Paine
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Average
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| 15DEC2006 |
69
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69
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51
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56
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70
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55
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66
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62.3
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| 04FEB2006 |
47
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47
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44
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47
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66
|
48
|
52
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50.1
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| 01JAN2006 |
41
|
49
|
40
|
40
|
54
|
40
|
45
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44.1
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| 25DEC2005 |
40
|
38
|
38
|
35
|
48
|
35
|
48
|
40.3
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| 27DEC2002 |
51
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52
|
49
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48
|
59
|
56
|
58
|
53.3
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| 16JAN2000 |
60
|
52
|
53
|
54
|
69
|
55
|
60
|
57.6
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| 03MAR1999 |
55
|
60
|
51
|
52
|
68
|
MM
|
57
|
57.2
|
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More Scenes From the December 14-15, 2006 Windstorm |
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Last Modified: September 23, 2007 You can reach Wolf via e-mail by clicking here. | Back | |
