Fall Transition 2012: Deep Cyclone Skirts Haida Gwaii

The fall transition of 2012 occurred during the period of 12-14 Oct 2012, just after the 50th anniversary of the Columbus Day Storm (AKA Typhoon Freda), with the arrival of two moist frontal systems, followed by a strong extratropical cyclone after the weekend closed:

15 Oct 2012: Monday

1540 PDT: A short-term forecast issued by the National Weather Service, Seattle, at 1533 indicates thunderstorms moving east into the Olympics, Strait of Juan de Fuca and the Chehalis Valley. They expect the thunderstorms to reach Seattle within an hour. Small hail, heavy rain and gusty winds may accompany these showers. Environment Canada indicates the possibility of thunderstorms here in Vancouver this evening, so it appears we are under the lightning gun as the vigorous cold front moves ashore. There is also a wind warning for Victoria, for strong SE winds shifting to W after frontal passage, with the possibility of gusts to 90 km/h, perhaps even up to 100 km/h. Here in Vancouver, SE winds are expected to reach 60 km/h at times, before shifting to west 50-70 km/h.

Based on the latest Water Vapor (WV) satellite loop, the low pressure center is just south of the southern tip of Haida Gwaii, with the leading front now coming ashore on Vancouver Island. The most enhanced cloud-tops, which have a granular, almost ropy structure, indicate the presence of numerous convective cells reaching down the coast from Vancouver Island to Southern Oregon.

Visible satellite photo of the developing extratropical cyclone, center just south of Haida Gwaii. Time 22:30 UTC on 15 Oct 2012. Image courtesy of the National Weather Service.

Quillayute reported a thunderstorm with heavy rain at 15:18, and some 5.3 mm (0.21") of precipitation fell between 1453 and 1537. Winds were not particularly strong during the thunderstorm, with gusts to 29 km/h (16 kt). Hoquiam has not reported a thunderstorm, but heavy rain occurred around 14:50, after which a wind shift occurred: from ESE 16 km/h (9 kt) at 14:53 to SSE 34 km/h (18 kt) by 15:01. Gusts climbed to SSE 53 km/h (29 kt) by 1539. A thunderstorm with light rain struck Astoria around 1509, followed by S gusts to 69 km/h (37 kt) by 1509.

This infrared image from the same time as the visible photo above reveals strongly enhanced cloud tops, stretching SE over Cascadia like giant fingers, associated with deep convection (about 10 km, or 35,000 feet) ahead of the extratropical cyclone's cold front. Most of the thunderstorm activity was confined to the coast, though heavy showers did strike some inland stations. For example, both Eugene and Salem reported heavy rain, with hourly totals around 5-6 mm (0.20-0.25"). Image courtesy of the National Weather Service.

We have a dark gray sky with light rain falling right now, with a patio temp of 13.8ºC, RH 83%, unsettled winds perhaps up to 15-20 km/h at times and a pressure of 29.63" (100.34 kPa), falling at a decent clip. Vancouver International began reporting light rain showers around 1345, with E winds of 16 km/h gusting 27 (9 kt G 15). The 1500 report indicated light rain showers with temp 13ºC (55ºF), dew point 11ºC (52ºF), wind ENE 11 km/h (6 kt) and pressure 100.63 kPa (29.72" Hg), falling 1.9 hPa/hr. Victoria at 1500 reported moderate rain and mist, with temp 12ºC (54ºF), dew point 11ºC (52ºF), wind NNE 10 km/h (5 kt) and pressure 100.55 kPa (29.69"), falling 1.9 hPa/hr.

The 2100 UTC HPC surface analysis indicated a 98.0 kPa central pressure for the extratropical cyclone, with a position almost due south of Haida Gwaii at latitude 51ºN. The weather situation is evolving rapidly. 1605 PDT.

1902 PDT: Not a whole lot of excitement happening here so far. Just a steady light rain outside, with somewhat unsettled winds. The patio temp is 13.2ºC. The most exciting thing, perhaps, is the pressure fall, which has been fairly fast at times.

Vancouver International reported a drop of 2.7 hPa to 100.13 kPa (29.57" Hg) in the hour ending 1700, followed by an additional 1.8 hPa in the next hour. East winds picked up to 24 km/h gusting 34 at 1800 (13 kt G 18). Moderate rain occurred at 1748, dropping back to light by 18:00. It appears that the threat of a thunderstorm is probably over, with the more enhanced cloud tops off to the east, based on the WV satellite loop.

The extratropical cyclone center has passed the southern end of Haida Gwaii and is now racing ENE toward the mainland. Buoy 46147, near Haida Gwaii's Khungit Island, reported a wind shift in the past few hours, from SE 58 km/h (31 kt) at 1500 Alaska Daylight Time to W 47 km/h gusting 87  (25 kt G 47) by 1600 and then WNW 67 km/h gusting 90 (36.5 kt G 49) by 1700, with a pressure jump from 97.15 kPa (lowest pressure; 28.69" Hg) to 97.65 kPa (28.84" Hg), or 5.0 hPa, in the hour ending 17:00. Out in the Hecate Strait, buoy 46185 reported SE winds of 76 km/h gusting 101 (41 kt G 55) at 1700 Pacific Daylight Time, followed by SE 72 km/h gusting 93 (39 kt G 50) by 1800. The pressure continued to show a falling trend, down 3.1 hPa/hr to 97.28 kPa (28.73" Hg), as of the most recent observation, 1800. Note the SE winds as well: The low center has not yet passed north of Buoy 46185.

Sandspit had winds shifting from NNE around 1737-1807 to N by 1815 and then NNW by 1832 finally to NW by 1900 as the low tracked south of the station. Wind speeds have generally been in the 40-50 km/h (22-27 kt) range, with gusts as high as 66 km/h (36 kt). A steady heavy rain fell during the entire wind shift, with the temp slowly falling from 11ºC (52ºF) to 9ºC (48ºF). 1928 PDT.

16 Oct 2012: Tuesday

0823 PDT: (Vancouver, BC) Buoy 46185 had a classic bent-back attack after my last entry yesterday. At 1900 PDT, wind became SSE 50 km/h gusting 67 (27 kt G 36.5), with the temperature climbing to 12ºC (54ºF) from 11ºC (52ºF). The pressure reached its minimum of 97.14 kPa (28.69" Hg), quite low. Then, by 2000, the wind had shifted to W, with a speed of 72 km/h gusting 96 (39 kt G 52). The temp dropped back to 11ºC (52ºF) and would fall further in the next hour to 10.5ºC (51ºF). More importantly, the pressure jumped 3.5 hPa to 98.17 kPa (28.79" Hg) in the hour ending 2000, to be followed by an even stronger climb of 6.8 hPa to 98.77 kPa (28.99" Hg) in the next hour. Winds tapered off after the initial surge. This is a classic pattern for a station that falls under the tip of a extratropical cyclone's bent-back occlusion. Sometimes a city like Victoria or Vancouver is on the receiving end of a strong wraparound band. For many stations, the strongest wind speeds on record have occurred in association with this feature. Here is the wind, gust and sea-level pressure plot for 46185:

Wind speed in knots (blue line), gust (red line) and sea-level pressure in inches (green line) for Buoy 46185. The signature of the 15-16 Oc 2012 extratropical cyclone is quite evident in the sharp wind and pressure response on the right-hand side of the chart. The first escalation in wind occurred out of the SE as the low center approached the station. The second surge, not quite as dramatic, arrived out of the W and is associated with the storm's strong bent-back front. Extremely fast pressure rises accompanied this feature, resulting in a V-shaped pressure trace that is reminiscent of a hurricane. Chart courtesy of the National Data Buoy Center.

1040 PDT: Looking locally, the storm did not quite meet forecast expectations. At Vancouver International, peak winds reached W 47 km/h gusting 56 (25 kt G 30) at 0700, with a maximum gust of 58 km/h (31 kt) reported at 0600. The westerly surge arrived around 0300, and slowly escalated. These wind speeds were not even close to the maximum 61 km/h gusting 74 (33 kt G 40) that occurred after a dry upper trough moved through overnight on 01-02 Oct 2012.

Victoria International reported maximum winds of W 34 km/h gusting 45 (18 kt G 24) at 03:00, nothing like the forecast 90 km/h (even 100 km/h in one warning). Even wind-favored Gonzales Heights only managed WSW 52 km/h gusting 69 (28 kt G 37) at 2300 with a peak gust of 76 km/h (41 kt) at midnight.

Abbotsford reported peak winds of SSW 34 km/h (18 kt) at 0500, with a maximum gust of 40 km/h (22 kt) at 0500 and 0700.

Bellingham reported SSE 39 km/h gusting 52 (21 kt G 28) at 2053, with a maximum gust to 58 km/h (36 kt) at 2019.

Nothing really spectacular happened rainfall-wise with this storm. Bellingham reported 5.6 mm (0.22") in the 24 hours ending 0453. Vancouver had 3.6 mm (0.14") yesterday, with Victoria reporting 10.1 mm (0.40") and Abbotsford a soaking 17.0 mm (0.67"). Quillayute had 25.9 mm (1.02") in the 24 hours ending 0453, a good soaker but still far from any record. Sea-Tac had 7.9 mm (0.31") in the same time period, and Portland 11.2 mm (0.44").

The 15-16 Oct 2012 extratropical cyclone, though it did not bring a big storm to the major population-centers of Cascadia, nevertheless made for an interesting opening to the 2012-13 storm season. 1104 PDT.    

The Classic Windstorm: Perhaps More Likely This Autumn?

The track of the 1962 Columbus Day Storm is an excellent example of the "Classic Path."

A classic path windstorm is one that develops in the lower midlatitudes, say south of approximately 42.5ºN. Maybe this number could be pinned at 40ºN, or perhaps 45ºN. The exact location is not particularly set. As the low deepens and crosses the 130ºW line, it then tracks nearly due north off the Pacific Coast of North America. Ultimately, the extratropical cyclone lands on Vancouver Island. These northward-trending lows, staying offshore, tend to retain their strength since the centers do not strongly interact with rough terrain until the final encounter with The Island. As the weather system sweeps northward, strong and damaging winds, primarily in the southeast quadrant of the storm, sweep the entire coast and inland region from Northern California to Southwest British Columbia, causing widespread damage and affecting millions of people.

As of the time of this writing, the last true "classic path" windstorm occurred on 16 Jan 2000. This cyclone seems relegated to a lesser position—in other words is often forgotten—than events like 14 Nov 1981 and 12 Oct 1962 (AKA Freda or the Columbus Day Storm). I believe the tendency to forget the tempest of 2000 is mainly because the central pressure did not get as fantastically deep, roughly 98 kPa vs 96 kPa, and strong winds did not quite cover as large a region. However, peak wind speed and gust during the 16 Jan 2000 storm at many Willamette Valley locations from about Salem north were comparable to 14 Nov 1981.

Therefore, it has been about twelve years since the last significant classic path event.

Since 16 Jan 2000, big Cascadia windstorms have often tracked more ENE to NE than NNE to N. This includes the major Hanukkah Eve storm of 2006. That event produced the strongest wind and gust speeds yet recorded at Sea-Tac (records go back to 1944), and caused phenomenal tree damage to parts of Vancouver, BC. The late-season 02 Apr 2010 windstorm ultimately did hook on a nearly due north track, but after it had tracked NE, landed on central Vancouver Island and then filled rapidly. The strong 03 Mar 1999 windstorm also fits into the NE-tracking category of event. And the 14 Dec 2001 cyclone tracked just north of due east. NE tracks appear to be far more common than N tracks.

It seems like what is required for a strong classic path event is a narrow upper-level (50 kPa, or approximately 5 km up in the atmosphere) trough situated between 130ºW and 140ºW. Ideally, the trough is slow moving. If the upper trough moves rapidly, developing cyclones are often thrown ashore before they can hook on a more northward track up the trough's east side--in other words, faster upper-level troughs tend to support E to NE tracks, whereas slow-moving troughs tend to support lows that eventually move on a more northward trajectory. There are some other variables at play, such as the breadth of the trough, but motion is a key one.

We had just such a slow-moving trough on 12 Mar 2012. Over the course of 24 hours, as the surface cyclone spun up and deepened at a rate in excess of 1 Bergeron (central pressure dropping ~24 hPa in 24 hours, a phenomenon known as explosive cyclogenesis), the upper trough only shifted 5º further east. The cyclone quickly ran up the east side while still over the ocean, with decent jet support up to nearly the point of landfall at Solander Island on the north shore of Vancouver Island. This low, incidentally, took on numerous characteristics of the Columbus Day Storm, including extreme pressure gradients near the center and highly unusual wind speeds at locations near the track.

Because slow-moving troughs are an important ingredient, major global blocking events have the potential to support the development of classic windstorms. We had a significant blocking event earlier this month, one that contributed to extremely unusual warmth in parts of Eastern North America, and appears to have influenced the slow-moving trough that supported the northward-trending 12 Mar 2012 windstorm on Vancouver Island. If a similar blocking event returns this fall, in essence a long-term persistence forecast, then, indeed Cascadia could be under the gun for a major classic event.

Another phenomenon supporting the possibility of a classic windstorm in the fall of 2012 is that the El Nino Southern Oscillation (ENSO) appears to be shifting from a La Nina (cold-phase) pattern to an El Nino (warm-phase). Models suggest that ENSO may be in a neutral state by the fall. It has been noted by some meteorologists, such as Cliff Mass in his book "The Weather of the Pacific Northwest" (2008), that available evidence suggests that many of the biggest Cascadia windstorms have occurred during an ENSO neutral state.

It appears that conditions may be in place this fall that supports a greater likelihood of a major classic windstorm event. An extreme windstorm, of course, is not certain, but conditions may make one somewhat more likely.

The period from October to December is a key time for major windstorms. Pacific sea-surface temperatures still tend to be warm, relatively speaking. The Columbus Day Storm, for example, developed in the vicinity of 21ºC (70ºF) water off of Northern California. Extratropical cyclones, being storms formed via baroclinicity (strong temperature contrasts), do "feed" off the latent heat in our oceans, and a good source of warm water can help significantly energize a storm. Even in December, with the shortest sun-up times in the northern hemisphere, the Pacific still retains some of the heat from the high sun of the previous summer. On land, people experience this Pacific warmth in part via strong cyclonic warm sectors, with temps climbing to and exceeding 15ºC (60ºF) at times after the leading warm front has moved through. Given such warm air, static stability tends to be low, supporting the presence of downdrafts. These downward currents help mix down momentum from the upper-level airflow, making warm sectors ripe for strong wind readings. The rare Autumn windstorm can bring temps in excess of 18ºC (64ºF) while a gale is raging outside. Later in the storm season, say January through April, Pacific sea-surface temperatures have cooled considerably, and surface warm advection fields also tend to be cooler in response, though a strong storm with deep tropical feed can still bring some strikingly warm air. Colder temps in the north help provide continued baroclinicity to keep cyclones going, a much colder form of storm, with warm sectors that may not have the same degree of instability exhibited during Autumn storms, potentially reducing high-wind potential.

These are all general thoughts. Exceptions abound--one of the key reasons why Nature is so interesting.

To me, the Fall storms are often the most spectacular. This is in part because deciduous trees are still leaved, providing much more drag against the wind. Trees have also had a spring and summer of lighter wind speeds in which to accumulate new dead and weakened material. When an Autumn gale strikes, much of the accumulated dead material falls. Leaves, twigs and branches are torn off in droves, making for a spectacular sight, a blizzard of flapping foliage and a hail of dropping woody debris.