Monday 3 December 2012

Another Strong Storm, This Time Aiming for British Columbia and Washington


December 3, 2012: Monday

15:34 PST: My new weather radio works. Environment Canada issued a wind warning for Metro Vancouver at 10:40 this morning. When I came home, I found the red warning light on, and a high wind warning message scrolling across the screen. Looking at the warning message online, the strongest wind are expected after midnight. This appears to be one of those difficult-to-follow overnight storms.

The latest satellite loops reveal a developing cyclone currently centered approximately 41ºN and 136ºW. The system has a subtropical moisture tap and a well-developed baroclinic leaf. The dry slot is not as enhanced as in some previous storms. Upper-level moisture from the leading warm front is already overriding Southwest British Columbia. Here is the latest visible satellite photo, for 23:00:

Visible satellite photo taken at 15:00 PST 03 Dec 2012. This next frontal system brings with it a large mass of clouds to the southwest of Vancouver Island. Higher clouds are already moving ashore. Image courtesy of the US National Weather Service.
The storm is well to our southwest. Looking at the latest WRF-GFS and MM5-NAM runs from the University of Washington, neither model brings in a full-fledged cyclone, but instead an open wave. It looks like the triple-point is expected to moved across central or southern Vancouver Island. A fairly tight E to SE pressure slope is present over the Strait of Georgia between 01:00 and 13:00 tomorrow. Looks good for 50-60 km/h (30-35 kt) over the water and about half that over land areas. This is not 70-90 km/h as is forecast by Environment Canada. This lowers my confidence in the high-wind forecast for Vancouver. However, EC forecasters seem to expect the strongest winds in the SW part of the warning area, near the water. Also, a cyclone does appear to be "trying" to take shape over the Pacific, and this frontal system certainly bears watching. The National Weather Service, Seattle, has issued a wind advisory for the Northwest Interior. Wind speeds of 20 to 35 mph with gusts to 50 (30 to 55 km/h with gusts to 80). This is not too far off the EC forecast. 16:00 PST.


16:42 PST: Darkness has largely settled over the land, with just the barest blue hint of dusk-light visible. The heavy overcast is probably not helping. The patio thermometer reads a rather mild 9.3ºC, with an 82% RH and a pressure of 29.86" and falling. The wind appears light. Time to look at the 16:00 roundup:

Location WX Temp (ºC) Dew Point (ºC) Wind Spd (km/h) SL Pres (kPa) 1-h tendency (hPa)
Nth Bend OVC 12.8 8.9 14 101.59 -0.7
Astoria OVC 11.1 9.4 24 101.26 -0.5
Hoquiam RABR- 11.1 9.4 24 101.25 -0.4
Quillayute RABR- 8.9 8.3 8 101.00 -0.9
Estevan Pt RA- 8.3 7.2 26 100.65 -1.1
Salem OVC 12.8 6.1 21 101.54 -0.3
Portland OVC 11.1 7.8 16 101.59 -0.3
Olympia RABR- 9.4 8.9 10 101.38 -0.2
Sea-Tac RABR- 8.3 6.7 14 101.47 -0.4
Bellingham BKN 10.0 3.9 13 101.33 -0.6
Abbotsford OVC 7.8 5.0 11 101.34 0.0
Vancouver SHRA- 7.8 6.1 24 101.26 -0.9
Victoria OVC 8.9 7.2 26 101.19 -0.8
Comox SHRA- 7.8 6.1 34 100.96 -1.3
Port Hardy SHRA- 7.2 3.9 26 100.42 -1.4
Average 9.6 7.0 19.4 101.22 -0.65
3-hr Chg
High 12.8 9.4 33.8 101.59 0.0
Low 7.2 3.9 8.1 100.42 -1.4
Spread 5.6 5.6 25.8 1.17 1.4


Rather mild conditions exist over Oregon, with temperatures up to 13ºC (55ºF) at Salem. Further north, where light rain and showers are occurring, the temp is a bit depressed, with the reading of Sea-Tac, 8.5ºC (47ºF), representative. The temperature spread between these stations is a rather modest 5.6ºC (10ºF). Precipitation is currently confined to British Columbia and Washington stations in the list. The barometric pressure is falling most rapidly over the British Columbia section, supporting a track over Vancouver Island. The maximum gradient between any one of the listed locations is 1.17 kPa (11.7 mb), not super-steep. The average wind speed for all these stations, 19.4 km/h (10 kt) is a reflection of this. Interestingly, winds in the Georgia Strait are already blowing rather briskly, with gusts to 50 km/h (27 kt) at Comox, a reflection of a fairly strong SE pressure slope already in place over SW British Columbia. (Note that there is no info in the 3-hr change row because this is the first 3-hr roundup I have taken for this event.) 17:34 PST. The temp spread compared to 16:00 has diminished, in part because Salem has cooled off a tad.


19:00 PST: A steady light rain falls outside, with the temperature on the patio at 9.2ºC. The pressure is now down to 29.82" (101.00 kPa). The satellite loop reveals quite a fast-moving storm on a steady northeast track. The 00:00 UTC HPC surface analysis placed the then 99.7 kPa low at about 42ºN and 135ºW.

Enhanced satellite view with surface analysis overlay for 16:00 PST 03 Dec 2012 by the US Hydrometeorological Prediction Center. The developing wave can be seen due west of the ORCA border, with a 99.7 kPa minimum pressure indicated.
Now for the 19:00 roundup:

Location WX Temp (ºC) Dew Point (ºC) Wind Dir Wind Spd (km/h) SL Pres (kPa) 1-h tendency (hPa)
Nth Bend MM 11.1 8.9 SSE 10 101.22 -3.7
Astoria OVC 10.6 8.9 SSE 13 101.04 -0.9
Hoquiam RABR- 10.6 9.4 SSE 24 101.02 -0.8
Quillayute BR 10.6 10.0 SSE 19 100.71 -1.3
Estevan Pt RA- 9.4 9.4 ESE 32 100.23 -1.5
Salem OVC 11.1 6.1 SE 8 101.19 -1.6
Portland BKN 10.0 7.2 ESE 21 101.31 -1.1
Olympia RA- 9.4 7.8 S 16 101.17 -0.7
Sea-Tac OVC 8.9 6.1 ESE 16 101.25 -0.9
Bellingham OVC 11.1 5.0 SE 24 101.33 -0.6
Abbotsford RA- 7.2 5.0 E 10 101.12 -0.5
Vancouver SHRA- 7.2 5.0 E 19 101.07 0.0
Victoria RA- 8.9 7.8 SSE 13 100.98 -0.8
Comox RA- 7.8 7.2 SE 48 100.65 -1.0
Port Hardy OVC 7.2 3.9 ESE 27 100.02 -1.2
Average 9.4 7.2 20.1 100.95 -1.11
3-hr Chg -0.27 0.33 0.4 -0.26 -0.41
High 11.1 10.0 48.3 101.33 0.0
Low 7.2 3.9 8.1 100.02 -3.7
Spread 3.9 6.1 40.3 1.31 3.7

The barometric pressure has begun to plunge at North Bend, perhaps a reflection of an intensifying wave and the approaching leading warm front. Pressure tendencies over much of the area have picked up considerably, save for around Vancouver. South winds arrived at Quillayute around 17:44, accompanied by intensifying rain and a rise in temperature to 11ºC (52ºF) by 18:27. Estevan Point has also seen an increase in temperature over the past three hours, by 1ºC (~2ºF). Winds appear to be escalating there, with gusts to 56 km/h (30 kt). Some of that warmer air to the south is heading northward. ESE to SE winds have picked up at Bellingham just recently, with gusts up to 44 km/h (24 kt) around 18:51. The temperature is rising in response to this, likely from some downsloping off of the Cascades (look at the T-Td spread). Winds continue to escalate at Comox, marked by an observation at 18:40 of SE 52 km/h gusting 61 (28 kt G 33).

Over the past 3-hr, the average barometric pressure for the above stations has dropped by 0.26 kPa (2.6 mb) and the steepest gradient between any of the stations—in this case North Bend to Port Hardy—has now reached 1.31 kPa (13.1 mb). The 1-hr downward tendency in pressure has increased by 0.4 hPa. The average wind speed among the locations in the table has risen slightly to 20 km/h (11 kt). Indications are pointing toward a deepening and fast-moving system—this is supported by satellite interpretation. Just look at that large area of enhanced clouds (beautiful):

Infrared satellite photo taken on 19:30 PST 03 Dec 2012. A large area of enhanced cloud tops is overtaking the Pacific Northwest and Southwest British Columbia. Image courtesy of the US National Weather Service.

22:00 PST: Steady light rain continues outside. Winds remain rather light here. The patio temp is 9.1ºC with an 83% RH and the pressure is 29.68" (100.51 kPa), falling at a good clip.

The 03:00 UTC HPC surface analysis placed the low center near 44ºN 132ºW, still mostly an open wave but with a hint of an occlusion. The leading warm front had not yet reached the Pacific coast and indeed remained over 100 km off the California coast. The water vapor satellite loop shows a strong dry slot just now reaching 130ºW with just the beginnings of a wraparound band evident. Cyclogenesis appears to be progressing at a steady clip. And the low remains on a NE track.

Water vapour satellite photo taken at 22:30 PST 03 Dec 2012. A mass of cloud wrapping around a strong dry slot is a classic pattern of cyclogenesis. This storm is becoming well organized. Image courtesy of the US National Weather Service.
Now for the 22:00 roundup:

Location WX Temp (ºC) Dew Point (ºC) Wind Dir Wind Spd (km/h) SL Pres (kPa) 1-h tendency (hPa)
Nth Bend RA- 8.9 7.8 SE 13 100.78 -4.4
Astoria RA- 9.4 8.3 ESE 10 100.54 -1.3
Hoquiam RA- 9.4 8.9 E 21 100.58 -1.3
Quillayute RABR 10.0 8.9 SSE 24 100.23 -1.8
Estevan Pt RA- 10.0 10.0 ESE 58 99.68 -1.9
Salem RA- 10.6 5.6 SSE 11 100.82 -1.0
Portland OVC 10.0 7.2 ESE 21 100.78 -1.6
Olympia OVC 8.3 7.2 W 5 100.70 -1.6
Sea-Tac OVC 8.9 5.0 E 10 100.80 -1.9
Bellingham OVC 11.1 5.6 SE 24 100.65 -1.9
Abbotsford RA- 6.1 5.0 NNE 13 100.83 -1.8
Vancouver SHRA- 7.2 6.1 E 27 100.60 -1.7
Victoria OVC 8.9 7.8 SE 27 100.44 -2.0
Comox RA- 7.8 7.2 SE 42 100.16 -1.6
Port Hardy SHRA- 6.1 5.0 ESE 27 99.50 -1.1
Average 8.9 7.0 22.2 100.47 -1.79
3-hr Chg -0.27 0.33 0.4 -0.26 -0.41
High 11.1 10.0 58.0 100.83 -1.0
Low 6.1 5.0 4.8 99.50 -4.4
Spread 5.0 5.0 53.1 1.33 3.4


On the coast, wind has gone offshore, strongly so at Astoria and Hoquiam, a classic pattern for an incoming strong extratropical cyclone. E to ENE at Hoquiam is the typical direction for a storm moving in out of the southwest. Heavy rain has arrived in Quillayute with 6.9 mm (0.27") in the hour ending 21:53. Pressure is falling fast up and down the coast, with the largest changes in the north section and at North Bend. (We just had a brief 1-sec power outage here—and the storm is just barely getting started—22:22—and now we had another.) The strongest pressure falls are concentrated from Estevan Point down to Sea-Tac and then at North Bend. Again, I take the North Bend response to be influenced by the deepening low just offshore and the approaching frontal bands. Like some of the coastal stations, winds have swung offshore at Sea-Tac and Portland as well. SE winds at Bellingham are continuing strong, but show no significant escalation since 19:00. In stark contrast, Abbotsford has light NNE winds, which are bringing significantly cooler air into the area—not very far from Bellingham. East winds at Vancouver have reached their highest level yet this hour and SE winds at Victoria are up a notch. Comox reported a SE gust to 67 km/h (36 kt) at 21:25.

At -1.79 hPa/hr, the average hourly pressure declension (for the 15 stations) is very close to that achieved by the powerful March 12, 2012 windstorm (-2.03 hPa/hr at its most extreme). But the pressure changes have been so uniform over the region that the maximum pressure gradient between the stations is only up slightly at 1.33 kPa (13.3 mb). The average wind speed, however, has climbed to 22 km/h (12 kt), mainly due to increases at the northern stations. Temperatures overall are cooling, largely a reflection of strengthening offshore winds. 22:46 PST.


December 4, 2012: Tuesday

06:45 PST: (Vancouver, BC) The wave occluded and largely shot due north, with the 97.9 kPa low center near Haida Gwaii at 04:00 PST. The cyclone did not become that well-defined on isobaric maps and seemed stuck in an open-wave arrangement. The cloud mass, dry slot and all moved well inland overnight. The end result: Fizzle. At least for the high wind potential in Vancouver Metro. Looking at the last two 3-hourly roundups, with 01:00 PST first:

Location WX Temp (ºC) Dew Point (ºC) Wind Dir Wind Spd (km/h) SL Pres (kPa) 1-h tendency (hPa)
Nth Bend MM 12.8 11.1 S 35 100.58 -2.7
Astoria RABR- 8.3 6.7 ESE 16 99.88 -0.9
Hoquiam RABR- 8.9 7.2 E 29 99.87 -3.1
Quillayute RABR 7.8 6.1 SE 26 99.61 -2.7
Estevan Pt RA 9.4 8.9 ESE 58 99.05 -2.0
Salem RA 8.9 7.8 S 24 100.23 -1.9
Portland RA 8.9 7.8 ESE 21 100.34 -1.9
Olympia RABR 8.3 6.7 S 13 100.14 -2.4
Sea-Tac RA 8.3 5.6 E 13 100.33 -1.2
Bellingham RA- 11.7 5.0 SE 24 100.17 -1.3
Abbotsford RA- 6.1 5.0 NNE 8 100.20 -1.6
Vancouver RA- 7.2 6.1 E 34 100.06 -1.6
Victoria RA- 8.9 7.2 SE 34 99.93 -1.9
Comox RA- 7.8 7.8 SE 47 99.57 -2.1
Port Hardy SHRA- 7.2 5.0 ESE 19 98.83 -2.6
Average 8.7 6.9 26.7 99.92 -1.99
3-hr Chg -0.27 0.33 0.4 -0.26 -0.41
High 12.8 11.1 58.0 100.58 -0.9
Low 6.1 5.0 8.1 98.83 -3.1
Spread 6.7 6.1 49.9 1.75 2.2
North Bend data stopped transmitting at 00:15: This is the observation in the above table. Looks like the warm front had just reached this location, with the temp well up and a strong S breeze. Hoquiam and Astoria still had a good offshore breeze going. Downward pressure tendencies on the coast were quite strong at this time, just head of the incoming front and passing wave. Estevan Point reported a gust to 81 km/h (44 kt) at 23:00. The apparent warm front neared Salem by this time, with winds becoming strong from the S and the temp beginning to rise. Plus, moderate rain to the tune of 5.6 mm (0.22") fell in the hour ending 00:56. Portland also had a decent soaker with 4.6 mm (0.18") in the same hour and Olympia had the same amount. Sea-Tac would end up with 4.8 mm (0.19") in the hour ending 01:53. With strong SE winds blowing up the Georgia Strait, Comox reported a gust to 70 km/h (38 kt) at midnight. Winds were beginning to slow at Port Hardy by 01:00.

And at 04:00 PST:

Location WX Temp (ºC) Dew Point (ºC) Wind Dir Wind Spd (km/h) SL Pres (kPa) 1-h tendency (hPa)
Nth Bend MM 13.3 M S 71 100.67 0.9
Astoria RABR- 12.2 11.7 SW 37 100.21 2.0
Hoquiam BR 11.7 10.6 SSW 39 100.17 1.3
Quillayute RABR- 9.4 8.9 S 26 99.50 1.9
Estevan Pt RA+ 8.3 7.8 SSE 50 99.02 2.0
Salem BR 11.1 10.6 S 27 100.52 0.8
Portland OVC 11.7 10.0 SSE 11 100.51 1.1
Olympia OVC 8.9 7.2 SSW 21 100.07 -0.2
Sea-Tac RABR- 7.8 6.1 SE 13 100.07 -0.2
Bellingham OVC 6.7 5.6 NNE 8 99.83 -1.1
Abbotsford RA- 6.1 5.0 ESE 5 99.84 -1.1
Vancouver RA- 7.2 6.1 ESE 34 99.73 -0.8
Victoria RA- 7.8 6.1 SE 34 99.63 -0.3
Comox RA- 7.8 7.8 SE 52 99.19 -0.8
Port Hardy SHRA- 5.0 3.9 W 11 98.73 1.3
Average 9.0 7.7 29.2 99.85 0.45
3-hr Chg -0.27 0.33 0.4 -0.26 -0.41
High 13.3 11.7 70.9 100.67 2.0
Low 5.0 3.9 4.8 98.73 -1.1
Spread 8.3 7.8 66.0 1.94 3.1
North Bend data is from Cape Arago, a spot favored for high wind readings. Gusts reached 128 km/h (69 kt) at 02:57. A warm front appears to have reached Astoria by 01:55, with the temp jumping from 8ºC (46ºF) at 01:21 to 11ºC (52ºF) by 01:55 and 12ºC (54ºF) by 02:06, accompanied by strong S winds. These winds then shifted to SSW by 02:23 and SW by 03:47. Peak gust 83 km/h (45 kt) out of 210º at 02:28. The warm front reached Hoquiam by 03:23, with winds shifting from E 19 km/h (10 kt) at 03:23 to S 35 km/h gusting 48 (19 kt G 26). The temp jumped from 8.5ºC (47ºF) to 12ºC (54ºF) in that timeframe. Hoquiam's peak gust: 65 km/h (35 kt) out of 200º at 03:52. The warm-frontal arrival at Quillayute occurred just after 04:00, with winds shifting from SSE to S, then SSW and the temp climbing to 11ºC (52ºF) by 04:33. Low pressure occurred at 02:55 with a reading of 99.31 kPa (29.32" alt). The frontal boundary, possibly occluded this far north, had reached Estevan Point by about 04:00, marked by a wind shift to SSE—SW at 05:00—and diminishing winds. Plus a round of heavy rain with 6.6 mm (0.26") in the hour ending 04:00. Peak gust: ESE 91 km/h (59 kt) at 03:00, just shy of high wind criteria; however a maximum wind of SE 67 km/h (36 kt) at 23:00 just edged into high-wind category. 

At Salem, brief heavy rain along with the strongest S winds occurred right around 02:00, clearly marking frontal passage. Peak gust 61 km/h (33 kt) out of 190º at 01:51. Only a modest breeze hit Portland at the time of frontal passage. The front had just reached Olympia at this time and the reported pressure for this station is the storm minimum. The same is true of Sea-Tac, and both stations had the same pressure reading for both hours. Quite interestingly at Bellingham, after a period of light rain that ended after 02:53, the wind shifted to light NNE to NE for a time, bringing with it much cooler air from out of the Fraser Valley and the temp plunged to 6.5ºC (44ºF) by 03:53, from 12.5ºC (53ºF) at 00:53. After this, pressure minimum occurred at 04:53 with a reading of 99.77 kPa (29.44" alt) and strong SSE winds arrived, bringing back the warmer air. All this information points to a passing warm occluded front. Peak gust at Bellingham 63 km/h (39 kt) out of 140º at 05:50. Abbotsford has remained under the influence of NNE to NE winds and a shielding (from strong south winds) cold surface layer.

Unlike Bellingham, Vancouver had a decent period of steady light rain from this front, lasting from 23:00 to 05:00. Low pressure occurred at 05:00 with a reading of 99.69 kPa (29.44" Hg). Winds have shifted to SE as of 07:00, with gusts to 41 km/h (22 kt), accompanied by a temperature rise to 9ºC (48ºF)—with the wind shift and temp increase post-rainfall, this also suggests a warm occlusion. A strong SE breeze blew all night at Victoria. A maximum gust of SSE 61 km/h (33 kt) occurred at 05:00, just after pressure minimum. Winds became SW, with a speed of 33 km/h gusting 46 (18 kt G 25) by 07:16 and the temp climbed to 11ºC (52ºF). The front had moved through. At Comox, pressure minimum of 99.11 kPa (29.26") occurred at 05:00, and maximum winds followed shortly thereafter with a speed of SE 59 km/h gusting 89 (32 kt G 42) at 06:00. By 07:28, the precipitation had stopped and winds had slowed to S 17 km/h (9 kt). The front passed through Port Hardy between 03:00 and 04:00, with the ESE winds shutting down and becoming light westerly. Pressure minimum of 98.60 kPa (29.15" Hg) occurred at 03:00. Pressure is now rising rapidly, with a jump from 99.17 kPa to 07:00 to 99.41 kPa at 08:00. Pressure tendencies at Comox are similar.

The storm has clearly moved through much of the region, and it appears any high wind threat for Vancouver and surrounds is now over. With a peak gust of E 46 km/h (25 kt) at Vancouver International around 05:40, winds did not come close to the forecast. It looks like the Oregon coast received the brunt of the winds.

The satellite photo loops reveal that another wave has developed on the baroclinic band. This feature appears to be targeting Oregon. 08:24 PST.

Water vapour satellite photo for 07:00 PST 04 Dec 2012. The centre of the first wave is skirting east of Hadia Gwaii. A second wave is evident offshore of Oregon. More rain on the way. Image courtesy of the US National Weather Service.
08:35 PST: We are now getting some strong WSW winds, whistling around the window frames and producing some readings on the patio-locked anemometer: 1.8 km/h. Onshore flow has arrived in earnest. The sun paints a beautiful yellow light on Tisdall Park. The sky is a clean powder blue. The storm has passed. 08:36 PST.





2 comments:

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    1. Thank you much. This kind of reporting takes much effort. Good to get some positive feedback.

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