Late Season Cyclone Lands in Northwest Oregon, Bringing Blustery Winds and Moderate to Heavy Rain

As of 1200 UTC (0500 PDT) on 03 May 2012, a fairly strong 99.4 kPa surface low neared the Oregon coast. This storm brought moderate rain to a large swath of Western Oregon and into Southwest Washington. Image courtesy of the NOAA Hydrometeorological Prediction Center.

0815 PDT: A 99.4 kPa extratropical cyclone that developed along 42ºN yesterday is making a somewhat unusual late-season visit to Northwest Oregon this morning. A strong, winter-like, 130-140 kt zonal jet stream supported the development of this cyclone. As of 1200 UTC, the low sat just offshore of Newport, OR, with the associated frontal system stretching southward nearly upon the coast bringing light to moderate rain.

At 0655 PDT, Astoria reported a pressure of 99.95 kPa (29.52" Hg), lowest so far with this event, but not falling particularly fast at 0.5 hPa/hr. Winds remain light and easterly. Further south, at Newport, the altimeter reported a minimum of 29.54" (100.00 kPa) at 0635, with the readings slowly climbing afterward. South winds picked up after the pressure minimum, and had escalated to SSW 44 km/h (24 kt) gusting 63 (34 kt) by 0735. Newport reported a pressure (altimeter) minimum of 29.61" (100.27 kPa) at 0535. Southerlies picked up shortly afterward and climbed to SSW 37 km/h (20 kt) gusting 56 km/h (30 kt) at 0715. Temperatures have been relatively cool with this system, only climbing to 11ºC (52ºF) at North Bend during the onset of the southerly winds, and 10ºC (50ºF) at Newport.

So far, in the Willamette Valley, winds have been rather light, with Salem and Eugene reporting SSE 13-15 km/h (7-8 kt). However, moderate rain in associated with the storm's front swept through the entire Willamette Valley from Eugene to Portland, bringing a good soaking. Eugene reported the heaviest short-duration reading (so far), with 3.0 mm (0.12") in the hour ending 0254.

As of 1430 UTC (0730 PDT), the cloud shield of the extratropical cyclone had reached Southwest British Columbia, bringing light rain northward to the Lower Mainland, South Vancouver Island and the San Juans. At this time, the low centre appears to be onshore over Northwest Oregon. Image courtesy of the National Weather Service.

Update 2250 PDT:

The extratropical cyclone tracked northeast right over Astoria with a 99.8 kPa central pressure around 0900 this morning. After landing, the low slowly progressed inland and gradually filled as it encountered the rough coastal terrain. The path put the low nearly due north of the Willamette Valley during the afternoon. As a result, the pressure slope became nearly due south for a few hours, a perfect orientation to support south winds up the natural wind funnel made by Oregon's Coast Range and the Cascades. Coinciding with the good isobaric alignment, the pressure gradient increased dramatically. The Eugene-Portland (KEUG-KPDX) measure climbed to +7.0 hPa by 1500, a fairly strong reading that is just a few hPa short of many windstorms in history. The graph below shows the sea-level pressure trend in the Willamette Valley for this storm (many thanks to Richard Halter and Steve Pierce for first bringing this information to my attention):

Sea-level pressure trends in the Willamette Valley on 03 May 2012. A +7.0 hPa gradient is quite strong, though short of many historic windstorms. 

     As a result of this good setup for wind, a rare May windstorm developed, whipping trees draped in fresh green spring-time leaves with gale-force gusts.


     Here are some peak wind and gust reports:

Peak Wind and Gust: km/h (knots) For OR and WA Locations Northwest Oregon Cyclone 03 May 2012 (PDT)
Loc	Wind	Dir (º)	Time	Gust	Dir (º)	Time
Eugene	35 (19)	180	0954	52 (28)	240	1134
Corvallis	44 (24)	210	1235	59 (32)	210	1235
Salem	41 (22)	170	0956	65 (35)	230	1344
McMinnville	41 (22)	200	1253	57 (31)	190	1345
Aurora	31 (17)	190	1153	69 (37)	200	1409
Hillsboro	35 (19)	230	1653	61 (33)	230	1545
Portland	41 (22)	240	1753	72 (39)	210	1519
Troutdale	37 (20)	230	1553	65 (35)	240	1548
Vancouver	30 (16)	210	1453	59 (32)	190	1435
North Bend	37 (20)	200	0815	57 (31)	200	0635
Newport	44 (24)	210	1135	63 (34)	200	0735
Tillamook	33 (18)	190	1315	41 (22)	250	1415
Astoria	31 (17)	300	1455	54 (29)	310	1458

     Clearly this event is a minor windstorm, with peak gusts barely making it to gale force at a few stations. The WSW peak gust at Tillamook and NW peak at Astoria reflect the near passage of the low center to these stations. Wind speeds north of the low center, such as at Hoquiam and Olympia, were generally from the NE through NW and typically lighter than the speeds witnessed in the Willamette Valley. It is not uncommon for lows to have an asymmetrical structure with much weaker pressure gradients, and reduced wind speeds, on the north side of the low.

     The timing of peak winds in the Valley appears to have been a few hours after the front moved through. This is probably the result of the pressure slope swinging to a favorable orientation for south winds behind the front as the low slowly tracked to the due north. An easterly pressure slope, not favorable for high winds in the Valley, had set up over the region ahead of the low in the northeast quadrant. This did support some blustery E to ESE winds through the Columbia Gorge and in the Portland Metro area.

A decent, but not exceptionally strong pressure surge occurred throughout Northwest Oregon as the low moved inland. Astoria reported +3.6 hPa/hr at 1600 and 1200, Salem +2.6 hPa/hr at 1500 and Portland 2.7 hPa/hr at 1600. In the Valley, the strongest gusts are decently correlated with the maximum pressure tendencies. The late timing of the pressure surge at Astoria is probably due to the passage of a weakly-defined bent-back front. A rapid wind shift from SSW to WNW between 1412 and 1423, well after the leading frontal system moved through, with precipitation tapering off after 1453, supports this conclusion.

Gust maxima are also well correlated with the peak pressure gradients. The Eugene-Salem measure reached +3.9 hPa around 1300, and the Salem-Portland measure hit +4.1 hPa around 1500, both coinciding closely with the peak gust times for Salem and Portland evident in the table. Pressure gradient verses wind speed for these locations is shown in the two graphs below.

Pressure gradient and associated 2-minute average wind speed (not 3-second average gust) for key Willamette Valley stations. Maximum winds were generally associated with peak gradients. However, at Salem the wind spiked well ahead of the gradient peak. The escalation in wind may have been due to the mixing of upper-air wind momentum down to the surface in downdrafts associated with the leading frontal system. 

Finally, as the low tracked to the north, carrying the associated frontal band through the Willamette Valley, heavy rain visited Portland, with 3.6 mm (0.14") falling in the hour ending 1153.

Spring Interlude

Over the long Easter Weekend, mid to high clouds from a nearly stationary weather system just offshore visited the Cascadia region. Between patches of blue, wispy cirrus, and thicker blankets of cirrostratus drifted overhead, giving the skies a milky cast, such as shown in the above photo, taken at Alice Lake north of Squamish, BC. Though the persistent clouds reduced the intensity of the sunshine at times, temperatures in many areas climbed to their greatest values for the year to date. Photo taken on 08 Apr 2012.

Sunday and Monday turned out rather warm and quite spring-like. At times, altostratus and cirrostratus from the stalled front off the coast obscured the sun. However, with a tendency for offshore flow, and a southerly airflow around the semi-stationary low off of Northern California, the temperature warmed nicely in many locations.

After spending all weekend off of the Northern California coast, a cutoff low still remains offshore today, and appears to now be slowly drifting SE from its former quasi-stationary position. The system is very much weakened, with a 100.2 kPa central pressure as of the 1500 UTC Hydrometeorological Prediction Center surface analysis. The associated weak frontal system has now reached the Pacific Coast, with moisture streaming due north over Cascadia. However, only light precipitation is associated with the band and among somewhat scattered locations.

For the Easter weekend, a quasi-stationary low set up off of Northern California, quite easy to pick out in this visible satellite photo. The associated frontal band virtually stalled just offshore for a number of days, with mid and high clouds streaming over Cascade country. The southerly flow along the front, carrying air from the subtropics, contributed to the warmth. Also, a tendency for offshore surface flow, with E to NE winds, also contributed to warmer temperatures than during the week previous. Image taken on 09 Apr 2012 at 1130 PDT (1830 UTC) and is courtesy of the US National Weather Service.

Despite the frequent presence of clouds similar to those depicted in the Alice Lake photo above, the temperature at the Squamish Airport reached 19.4ºC (67ºF) at 1400 PDT on Sunday, and then bumped up to 20.6ºC (69ºF) on Monday, 09 Apr.

I heard from a local weather observer that his thermometer in Vancouver, BC, north of the airport, reached 20ºC, the highest so far this year. Last year, the first 20ºC reading did not occur until 13 May. So, it appears that this spring will not be quite as cool as that in 2011. Though, one brief warm spell may not be indicative of a longer-term trend.

Vancouver International had much cooler highs temps than places even a short distance from the water, almost certainly due to a tendency for a WNW to NW breeze to set up during the afternoon, at times reaching speeds of 28 km/h (15 kt) on Sunday, and 17 km/h (9 kt) on Monday. The highs were 12ºC (54ºF) and 15ºC (59ºF) respectively.

The thermometer at Abbotsford, however, more closely reflected the temperature that the weather observer reported, with a high of 19ºC (66ºF) on Sunday and 21ºC (70ºF) yesterday. In 2011, the temperature in Abbotsford did not reach or exceed 21ºC until 13 May. Places south, like Sea-Tac and Portland, had highs similar to those at Abbotsford and Squamish this past weekend. The former reported 21ºC (70ºF) yesterday, and the latter 20ºC (68ºF) on Sunday for the toastiest highs of this spring warm spell (so far).

The March Deluge of 2012

A shower drops snow and rain on the North Shore Mountains in the vicinity of Vancouver, BC, while sunshine bathes the lowlands. This is not an uncommon situation. The tendency for convective activity over the nearby mountains, while the valley remains mostly dry, is just one type of orographic phenomenon that contributes greater precipitation to the higher elevations. Vancouverites can enjoy sunshine while witnessing a deluge on nearby slopes. Photo taken from Iona Beach on 06 Apr 2012.

For Cascadia, March proved quite wet. In some regions, soaked is a better term, for new records for total monthly precipitation were set. So many stations set new all-time high totals, including many mountain-based RAWS sites, that it would make a very long list. Instead, focus will be on a few key locations. The persistent rains of March 2012 found much of Western Oregon. Portland Metro, the most populated region in the state, did not escape the deluge. According to the National Weather Service (NWS), Portland office, the Portland International Airport reported 200.4 mm (7.89") of rain in March, the wettest in a period of record that goes back to 1940. Vancouver, Pearson Field, just across the Columbia River, reported 198.4 mm (7.81"), the 3^rd most soaked March since 1890.

Further down the coast, Southwest Oregon received some phenomenal amounts of rain, as reported by NWS Medford. During the previous March (2011), numerous all-time records were set. Amazingly, a number of these fell in 2012.

One of the more amazing reports occurred at a station designated Port Orford 5E. Some 952.5 mm (37.50") of precipitation fell in March of 2012, breaking the all-time monthly record of 795.5 mm (31.32") set just the year before. Keep this in mind: 952.5 mm is fully 30.7 mm (1.20") of rain a day on average.

Sexton Summit, right near I-5 in the Klamath-Siskyou Mountains, reported 350.0 mm (13.78"), breaking the "old" March record of 290.6 mm (11.44") set way back in 2011.

Moving into Northwest California, NWS Eureka indicated that 305.3 mm (12.02") of rain fell at the forecast office. This makes for the wettest March in a record going back to December 1941. This broke the former record, again set in 2011, of 302.0 mm (11.89") by a mere 3.3 mm (0.13"). Still enough to put March 2012 on top, but maybe not with complete confidence when the potential for error in measurement is taken into consideration.

Further south, rainfall totals were not so spectacular. San Francsico reported 120.9 mm (4.76") of rain during March 2012. Though this is 45.7 mm (1.80") above normal, the total is well short of the 229.1 mm (9.02") record set in March 1958. In fact, the value for 2012 ranks 12^th in terms of wettest Marches in San Francisco, going back to July 1945.

California had a fairly dry "wet season," not atypical of La Nina conditions. There is a phenomenon known as the March Miracle in the Golden State. Sometimes during a dry water year, the jet stream dives south right at the end of the wet season in March, bringing in a series of juicy storms before the storm track starts its seasonal northward migration in the spring. A March Miracle can bring much-needed moisture to a parched California before the summer "dry" arrives. It appears that in 2012, California had a a partial March miracle. Oregon and extreme northern California received the bulk of the moisture this time around.

Looking at interior sections east of the Cascades, NWS Spokane indicated that numerous March total precipitation records were set in Eastern Washington and Northern Idaho. This included Spokane, which had 115.8 mm (4.56").

One interesting aspect of the Spokane record is that more precipitation fell at this location than dropped in Vancouver, BC, during March. Indeed, with a 111.6 mm (4.39"), Vancouver (again, the northern one) appears to have been "gypped" in terms of rainfall. Well, not entirely gypped: The total is almost exactly "normal", based on the 1971-2000 record. In any event, Spokane, in the Cascade rain shadow, is typically much drier than Vancouver during the cold season. Not in March 2012. This reality, and with much heavier precipitation totals down in Oregon, reflects the tendency that storms had during March 2012 to track into the Beaver State and head northeast into Eastern Washington.

Precipitation varies widely between locations that may not be particularly far apart, and this situation is no different in Vancouver Metro. Vancouver is partially rain-shadowed by the Olympics and the Vancouver Island ranges. Plus, rainfall tends to pick up in the vicinity of the North Shore Mountains. There is a well-known gradient of average precipitation going from White Rock to North Vancouver, with the latter receiving higher amounts. A friend of mine who has been keeping a long-term climatological record up on the shallow rise to the north of Vancouver International, reported 133.5 mm (5.26") for March 2012, significantly more than at the airport.

Measurement methodology, instrument type and also instrument siting has changed over the years, resulting in some error. This translates to uncertainty in any rankings mentioned above, especially when the values are close. Nevertheless, the takeaway message is that March 2012 brought with it some historical precipitation amounts in many parts of Cascadia. Other locations appear to have had at least a decent soaking with normal to above normal precipitation.

Many thanks to Steve Pierce who brought to my attention some of the March precipitation records.

Pacific Storm Lingers Into A Second Day

A frontal system moves ashore as the parent low slowly weakens in a semi-stationary position off of the Southeast Alaska coast. After passing over the North Vancouver Island coast yesterday morning, the front has finally reached the Vancouver Metro area and surrounds. Visible satellite photo taken at 0900 PDT 03 Apr 2012. Image courtesy of the US National Weather Service.

The frontal boundary has finally moved through the Vancouver Metro area. E winds of 17 km/h (9 kt) at 0800 shifted to NW 35 km/h (19 kt) gusting 46 (25) by 0900. The temp fell from a rather warm reading of 10ºC (50ºF) at 0700 to 6.1ºC (43ºF) by 0900. Steady light rain accompanied this transition, and the barometric pressure began to rise. On my drive in, I observed rain intensity that in my estimation approached moderate at times up on the hill around Queen Elizabeth Park and driving in to the University of British Columbia.

The semi-stationary cyclone is nearly at the same location as this time yesterday morning, perhaps a few degrees further north. Satellite photos taken this morning are quite similar-looking to those of the previous day. The low, however, is much weakened, with a central pressure at 0500 (1200 UTC) of 97.8 kPa (28.88" Hg), according to the HPC surface analysis.

Here are peak wind and gust speeds from this event for selected stations. Most maxima occurred on 02 Apr. However, winds have recently picked up along the frontal boundary in a few places, such as Abbotsford and Bellingham. These peaks are denoted in italics:

Peak Wind and Gust: km/h (knots) Deep Haida Gwaii Cyclone 02-03 Apr 2012 (PDT)
Loc	Wind	Dir	Time	Gust	Dir	Time
Port Hardy	44 (24)	ESE	0800	70 (38)	ESE	0800
Campbell River	59 (32)	ESE	1306	81 (44)	SE	1200
Comox	65 (35)	SE	1200	83 (45)	SE	1400
Victoria	37 (20)	SE	1100	56 (30)	SE	1100
Vancouver	41 (22)	ESE	1100	52 (28)	ESE	1100
Abbotsford	33 (18)	S	0900	44 (24)	S	0900
Bellingham	33 (18)	SE	0953	57 (31)	SSE	0817
Navy, Whidbey	48 (26)	SSE	0856	69 (37)	S	0739
Quillayute	35 (19)	S	1553	74 (40)	SSE	1552
Tofino	56 (30)	SSE	0900	80 (43)	SE	1100
Estevan Pt	69 (37)	ESE	1500	93 (50)	ESE	1400
Solander I	120(65)	ESE	0600	143(77)	ESE	0900

North Vancouver Island received the strongest winds with this storm, both on the coast and in the interior. Comox and Campbell River were hit with significant gusts in excess of 80 km/h (43 kt), but nowhere near the magnitude of the 12 Mar 2012 windstorm. Further south, yesterday morning's wind forecast did not pan out for either Vancouver Metro or Bellingham.

Quite cold air has moved in behind the front. At Quillayute, for example, the temperature fell from 8.3ºC (47ºF) at 0353, with winds S 15 km/h (8 kt), to 2.2ºC (36ºF) at 0653, with winds E 9 km/h (5 kt), this after a period of heavy rain (5.6 mm, or 0.22", in the hour ending 0453) and gusty westerly winds as the front swept inland. The temp fell further to 1.7ºC (35ºF) by 07:53, with light rain continuing. Tofino reported 3.9ºC (39ºF) at 0900.