Strong Extratropical Cyclone Now Developing Over The Northeast Pacific

07:49 PST: (Vancouver, BC) The anticipated cyclone is developing over the Pacific and moving rather quickly eastward. At 12:00 UTC, the HPC analyzed the low center near 47ºN 142ºW with a 99.0 kPa central pressure. Since that time, the low has moved inside of 140ºW, based on satellite loop interpretation. The storm is already analyzed as occluded, unlike 13-14 Dec 2001 event which remained an open wave as is tracked inland. There is a robust warm front associated with today's cyclone, a feature that will likely move inland ahead of the low and bring unstable air that will likely contribute to strong winds on the Oregon coast and inland. Further north, the leading front is expected to arrive occluded, but winds could still be quite strong in the vicinity of the occlusion.

Figure 1: Water vapor satellite photo for 16:30 UTC (08:30 PST) 16 Dec 2012. The developing cyclone is marked by a strong dry slot and baroclinic leaf in the vicinity of 47-48ºN and 136-138ºW. The storm appears to be moving rapidly east at this point, but may slow down as it nears land. Image courtesy of the US National Weather Service.

According to NWS Seattle and Portland the models are suggesting a track even further south than yesterday's runs, perhaps even over Puget Sound. Past events that followed such a track include the intense 03 Nov 1958 windstorm and the strong 15 Dec 1977 cyclone. This southern track does not favor high southeast winds for Vancouver or Victoria, BC, though the potential for strong westerlies is still supported. The 1958 event brought W gusts to 78 km/h (42 kt) to Vancouver. Strong westerlies blowing through the Strait of Juan de Fuca can still afflict parts of Victoria and Whidbey Island. South of the low's track, strong southerlies are expected to pick up as the low moves inland, with the potential for gusts of 80 km/h (43 kt) in the Willamette Valley and over interior SW Washington. High winds are expected on the Oregon and Washington coasts.

Here is the 07:00 roundup:

Location	WX	Temp (ºC)	Dew Point (ºC)	Wind Dir	Wind Spd (km/h)	SL Pres (kPa)	1-h tendency (hPa)
Nth Bend	RA-	7.2	M	SSE	13	101.19	-0.3
Astoria	RA-	5.6	3.9	E	5	100.72	-0.4
Hoquiam	RA-	3.9	2.8	ENE	10	100.70	-0.2
Quillayute	BR	1.7	1.7	E	8	100.52	0.0
Estevan Pt	RA-	2.2	2.2	ENE	13	100.22	-0.6
Salem	RA-	5.0	3.9	S	19	100.99	-0.4
Portland	RA-	5.6	3.9	SSW	16	100.99	-0.3
Olympia	RA-	2.8	2.2	S	14	100.80	-0.2
Sea-Tac	BKN	3.9	1.1	S	21	100.81	0.4
Bellingham	OVC	3.9	2.2	SSE	23	100.62	0.3
Abbotsford	OVC	2.8	1.1	S	23	100.52	-0.2
Vancouver	BKN	1.1	0.0	E	13	100.46	0.1
Victoria	BKN	3.9	0.0	SSW	19	100.51	0.2
Comox	BKN	0.0	-1.1	SW	3	100.29	-0.1
Port Hardy	OVC	1.1	0.0	CLM	0	100.06	-0.3

The calm before the storm. Light rain is falling over much of the coast, this from a band of cloud ahead of the cyclone. Rather cold air is in place, especially in the northern sections. Light offshore winds are already occurring at many stations, a typical response to strong incoming extratropical cyclones. The incoming warm front could raise temperatures along the Oregon coast by a full 5-8ºC (~10-15ºF) later today. Looking at overall pressure trends, the highest readings between yesterday's system and today's incoming storm appear to have occurred this morning or are occurring right now. The last vestiges of the front yesterday are still affecting parts of the northern interior, with SSE winds at Bellingham, SSW at Victoria and S winds at Abbotsford. Winds, however, have already gone offshore at Vancouver. Rather cold air is in place at the BC stations, with some reporting freezing conditions. Frost developed at my home in Vancouver.

Currently, the maximum pressure gradient between the listed stations is 1.13 kPa (11.3 mb). This is between North Bend and Port Hardy. In response to the relatively modest gradient, the average of all the reported wind speeds is 13.3 km/h (7.2 kt). The temperature spread is 7.2ºC (13ºF). I anticipated this to increase as the warm sector air invades the southern region—namely Oregon—while cold air remains trapped in places like Vancouver and Abbotsford until the westerly winds arrive. 08:37 PST.

10:51 PST: The developing cyclone continues to progress rapidly eastward, with the center apparently near 135ºW and 47.5ºN based on water vapor satellite interpretation. The 15:00 UTC (07:00 PST) HPC surface analysis placed the low center near 47ºN and 138ºW. The central pressure of 98.6 kPa points toward a deepening of 1.3 hPa/hr, which, if carried out for 24-h would qualify for cyclogenic bomb status. The warm front is indicated crossing 130ºW off of the Southwest Oregon coast.

Figure 2: Water vapor satellite photo for 19:00 UTC (11:00 PST) 16 Dec 2012. The low centre appears in the vicinity of 47ªN 135ºW and is tracking fairly quickly eastward. US National Weather Service.

Figure 3: The 15:00 UTC HPC surface analysis, overlaid onto an enhanced satellite image, indicated a 98.6 kPa central pressure for the developing system. Courtesy of the US Hydrometeorological Prediction Center.

Here is the 10:00 roundup:

Location	WX	Temp (ºC)	Dew Point (ºC)	Wind Dir	Wind Spd (km/h)	SL Pres (kPa)	1-h tendency (hPa)
Nth Bend	RA-	7.8	M	S	16	101.02	-0.7
Astoria	RABR-	4.4	3.3	ESE	10	100.48	-0.8
Hoquiam	RA-	4.4	2.8	E	21	100.52	-0.7
Quillayute	BR	3.3	1.7	ESE	8	100.29	-0.7
Estevan Pt	RA-	3.3	3.3	E	13	99.97	-0.8
Salem	RA-	5.6	4.4	SSE	19	100.81	-0.8
Portland	RA-	6.1	3.9	SSE	13	100.83	-0.6
Olympia	RABR-	2.8	2.2	S	13	100.68	-0.3
Sea-Tac	RA-	3.3	1.1	S	16	100.73	-0.6
Bellingham	RA-	4.4	2.2	SSE	11	100.59	-0.6
Abbotsford	RA-	2.8	2.2	SW	14	100.55	-0.2
Vancouver	OVC	5.0	2.2	SE	13	100.43	-0.5
Victoria	BKN	5.0	2.2	SSE	5	100.40	-0.8
Comox	BKN	1.1	0.0	SW	3	100.20	-0.3
Port Hardy	SHRA-	2.2	1.1	SE	10	99.81	-1.0
Average		4.1	2.3		12.3	100.49	-0.63
3-hr Chg		-0.27	0.33		0.4	-0.26	-0.41
High		7.8	4.4		20.9	101.02	-0.2
Low		1.1	0.0		3.2	99.81	-1.0
Spread		6.7	4.4		17.7	1.21	0.8

Atmospheric pressure is decidedly falling across the region now, with the strongest rates generally along the coast. The average for all stations is -0.63 hPa/hr, compared to a mere -0.14 hPa/hr at 07:00. The lowest pressures remain in the north section—as are the strongest pressure falls at this point. Of course Port Hardy and Estevan Point, being the furthest west, are closest to the storm center at this point. Winds are also generally offshore throughout the region, save for southerlies at North Bend and in some of the interior sections. The incoming warm front is still offshore. Light rain continues to fall at many locations from moisture streaming inland ahead of the low—likely warm-front-related.

The average wind speed has diminished somewhat, down to 12.3 km/h (6.7 kt), this despite a slight steepening of the maximum pressure gradient between stations to 1.21 kPa (12.1 mb). The temperature spread has decreased slightly largely due to some diurnal warming at northern stations. 11:25 PST.

11:37 PST: The latest model runs are putting an intense pressure gradient over Northwest Oregon and Southwest Washington as the low tracks inland. The pressure gradient magnitude depicted on NWP maps suggests the possibility of 100-110 km/h gusts (55-60 kt) in parts of the Willamette Valley and Southwest Washington interior. This bears watching. However, keep in mind yesterday's discussion on the upper wind support, which is not ideal for extreme S winds at the time of peak gradient. My expectation is that this storm may underachieve with respect to pressure gradient magnitude and that peak wind gusts may be more like 80-90 km/h (45-50 kt) in the Valley, which is borderline high-wind criteria (if the storm follows the forecast track). I also add that Nature has a tendency to surprise. 11:45 PST.

13:10 PST: The 18:00 UTC (10:00 PST) HPC surface analysis puts the then 98.2 kPa low center near 47ºN 135ºW. The system had deepened another 4 hPa over the previous 3 hr. The warm front just touched the southwest tip of Oregon. Interpretation of the current water vapor satellite loop indicates that the low has tracked to about 131ºW up to 20:30 UTC (12:30 PST). The low is moving decidedly east and if it holds this direction it would land in the vicinity of Hoquiam. A track very close to the 03 Nov 1958 windstorm. For those south of this track, it is time to prepare for potentially damaging gusts.

Figure 4: Water vapor satellite photo for 21:30 UTC (13:30 PST) 16 Dec 2012. The low centre appears in the vicinity of 47ªN 131ºW and is tracking fairly quickly eastward. Image courtesy of the US National Weather Service.

Figure 5: The visible satellite view for the same time as in Figure 4. The storm has a nice comma-shape. Image courtesy of the US National Weather Service.

Here is the 13:00 roundup:

Location	WX	Temp (ºC)	Dew Point (ºC)	Wind Dir	Wind Spd (km/h)	SL Pres (kPa)	1-h tendency (hPa)
Nth Bend	RA-	7.8	M	SSE	16	100.44	-2.0
Astoria	RA-	4.4	2.8	ESE	16	100.17	-1.9
Hoquiam	RA-	3.3	2.8	ENE	24	99.94	-2.8
Quillayute	RABR-	3.3	2.2	ESE	10	99.66	-3.2
Estevan Pt	RA-	3.9	3.9	E	23	99.39	-2.0
Salem	RA-	6.1	4.4	SSE	19	100.26	-2.3
Portland	RA-	6.1	4.4	ESE	13	100.36	-2.1
Olympia	RA-	3.9	2.8	S	16	100.13	-2.4
Sea-Tac	RABR-	3.9	1.7	ESE	10	100.27	-2.4
Bellingham	BKN	5.6	1.7	SE	24	100.17	-2.2
Abbotsford	OVC	5.0	2.2	NE	8	100.16	-1.8
Vancouver	OVC	5.0	2.8	E	24	100.06	-2.0
Victoria	OVC	6.1	2.8	SE	29	99.94	-2.5
Comox	OVC	5.0	2.2	ESE	40	99.78	-2.2
Port Hardy	OVC	3.9	1.1	ESE	26	99.38	-1.8
Average		4.9	2.7		19.9	100.01	-2.24
3-hr Chg		-0.27	0.33		0.4	-0.26	-1.62
High		7.8	4.4		40.3	100.44	-1.8
Low		3.3	1.1		8.1	99.38	-3.2
Spread		4.4	3.3		32.2	1.06	1.4

Pressure tendencies on the coast are now in the rapid declension category, with the strongest in the Hoquiam-Quillayute area. This seems to be the region that the cyclone is currently targeting. Offshore winds at some of the coastal stations have picked up at notch. There is still little evidence of the arrival of a surface warm front, even down in North Bend. In any event, the low is clearly progressing fairly rapidly in both movement and development and conditions will likely deteriorate rapidly from this point onward. Pressure tendencies at interior stations are also following suit, with strong downward trends everywhere. SE winds at Victoria continue to pick up, with a gust to 50 km/h (27 kt) at 13:32. They have also picked up noticeably at Comox and Port Hardy. Easterly winds at Vancouver have begun to ramp up as well. The entire region is clearly under the influence of the incoming cyclone at this point.

The average pressure declension among the stations is now a very high -2.24 hPa/hr, reflecting the encroaching storm. This is higher than the -2.03 hPa/hr maximum for the 12 Mar 2012 windstorm. Even with the pressure falling, the maximum gradient between stations has relaxed some to 1.06 kPa (10.6 mb), a reflection of the low center approaching the middle of the region (the Olympic Peninsula) and evening out a pressure field that has had a tendency to be lower to the north. However, wind speeds have picked up in response to a strengthening offshore gradient, with the average up to 19.9 km/h (10.7 kt). The temperature spread has continued to diminish, now down to 4.4ºC (8ºF), mostly in response to diurnal warming to the north and the lack of a strong warm frontal passage up to the 13:00 PST at any of these stations—I am expecting it to show up at North Bend first. 13:54 PST. 

15:59 PST: The 21:00 UTC (13:00 PST) HPC surface analysis indiated the low near 47.5ºN and 132ºW, with a central pressure of 98.1 kPa. If this pressure is close to accurate, it suggests that the rate of deepening slowed significantly between 18:00 and 21:00, and this might indicate a cyclone that is perhaps moving away from the best upper support and nearing maximum depth already. Since there is often significant error in these central pressure estimates, the 00:00 analysis will provide a better sense on the overall deepening rate. The satellite photo loops up to 23:30 UTC (15:30 PST) indicate that the low center has likely crossed 130ºW and is still on an easterly track.

Figure 6: Water vapor satellite photo for 00:00 UTC (16:00 PST 16 Dec) 17 Dec 2012. The low centre appears in the vicinity of 47.5ªN 130ºW and is tracking fairly quickly eastward. Image courtesy of the US National Weather Service.

Figure 7: The 21:00 UTC (13:00 PST) HPC surface analysis, overlaid onto an enhanced satellite image, indicated a 98.1 kPa central pressure for the developing system. This suggests that the rate of deepening had slowed around this time. Courtesy of the US Hydrometeorological Prediction Center.

The 16:00 roundup:

Location	WX	Temp (ºC)	Dew Point (ºC)	Wind Dir	Wind Spd (km/h)	SL Pres (kPa)	1-h tendency (hPa)
Nth Bend	OVC	12.2	10.0	S	35	99.86	-1.0
Astoria	RABR-	7.2	5.6	SE	13	98.82	-2.8
Hoquiam	RABR-	3.9	2.8	ENE	34	98.83	-3.9
Quillayute	RABR-	2.8	2.2	E	19	98.52	-4.6
Estevan Pt	RA-	3.9	3.9	E	18	98.35	-3.3
Salem	OVC	8.3	5.0	S	45	99.36	-2.4
Portland	RA-	5.6	5.0	ESE	26	99.46	-2.6
Olympia	RABR-	3.9	2.8	NNE	10	99.20	-2.8
Sea-Tac	RA	4.4	2.2	E	16	99.36	-3.2
Bellingham	RA-	3.9	1.7	NNE	13	99.50	-2.6
Abbotsford	SHRA-	2.8	2.2	ENE	5	99.52	-2.6
Vancouver	RA-	3.9	1.1	E	34	99.32	-3.7
Victoria	RA-	3.9	2.2	E	29	99.19	-3.3
Comox	RA-	2.8	2.2	SE	40	99.14	-2.5
Port Hardy	OVC	3.9	1.1	E	37	98.85	-1.3
Average		4.9	3.3		24.9	99.15	-2.84
3-hr Chg		-0.27	0.33		0.4	-0.26	-0.60
High		12.2	10.0		45.1	99.86	-1.0
Low		2.8	1.1		4.8	98.35	-4.6
Spread		9.4	8.9		40.3	1.51	3.6

The warm front finally arrived at North Bend around 13:55, marked by a temperature jump from 9ºC to 11ºC (48ºF to 52ºF) and a shift from SSE to S winds. Rates of pressure fall also slowed when the boundary went through. Winds at Astoria have shifted more to the SE and are beginning to accelerate. The pressure drop over the past three hours has been phenomenal: -10.6 hPa. With the temperature also warming, I suspect the warm front is nearing Astoria. Rates of pressure fall are favoring a landfall more toward Quillayute at this time and may suggest a somewhat more northerly track than expected. That 1-hr declension rate of -4.6 hPa is, well, phenomenal. Estevan Point still has the lowest pressure, with a reading approaching 29" even. Looking at the interior, winds at Salem have definitely picked up, with gale-force gusts being reported this hour. The temp is also climbing, a mark of the approaching warm front. The Columbia Gorge is seeing to continued ESE winds at Portland, and cooler temperatures. At Bellingham, SE winds shifted to NNE between 13:53 and 14:53—this is typical of lows more southwest than west of this station and is an interesting response. The temp has fallen there as cooler interior air from the Fraser Valley moves into Bellingham on that northerly wind. In essence, B'ham has joined Abbotsford in cool offshore flow. That cooler air is also sweeping through Vancouver on an increasing E wind and is moving across the Georgia Strait into Victoria. A cold rain is falling through that chilly air.

The average pressure declension at 16:00 had increased to -2.84 hPa/hr, indicating very fast pressure falls throughout the region. The average pressure is down to 99.15 kPa (29.28" Hg), quite low. The maximum pressure gradient between the stations has increased to 1.51 kPa (15.1 mb), an indication that the storm center is nearing. The average wind speed has continued escalating, now to 24.9 km/h (13.4 kt). And the temperature spread has widened considerably (as anticipated), now to 9.4ºC (17ºF), given the arrival of the warm front in Oregon and the cooler air spilling across the Lower Mainland.

This is clearly an intense storm that is now in control of the surface weather conditions throughout Cascadia. 16:49 PST.

18:52 PST: The La Crosse barometer reads 29.06", the R. E. White aneroid barometer 29.10" and the Davis 98.43 kPa (29.07" Hg), making for an average of 29.08" Hg or 984.8 kPa. It has been a long time since I have seen a pressure this low here in Vancouver, and the trend remains downward. By the way, the aneroid barometer indicated a 4.3 hPa pressure drop between 16:00 and 17:00.

A steady rain pours outside—mixed with snow, and in some cases large flakes. The patio temp is 4.8ºC with an 81% RH. A gusty wind shakes the trees, but it is difficult to see how much in the dark.

The 00:00 UTC (16:00 PST) HPC surface analysis indicated a 97.2 kPa central pressure for the low, a value that suggests that the 21:00 UTC central pressure estimate was too high. (Or maybe this one is a bit low.) The cyclone center had moved to 47.5ºN 129.5ºW by the time of the surface analysis, with the warm front indicated nearly upon Astoria and past Salem. Strong winds were lashing much of Oregon west of the Cascades by this time. Examination of satellite loops suggests that the low center is near 127ºW at this time, perhaps at 47.5ºN.

Figure 8: Water vapor satellite photo for 03:30 UTC (19:30 PST 16 Dec) 17 Dec 2012. The low centre appears to be in the vicinity of 47.5ªN (maybe even 48ºN) 127ºW and is tracking steadily eastward. Image courtesy of the US National Weather Service.

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	RA-	12.2	12.2	SSW	45	99.53	-1.0
Astoria	OVC	10.0	7.8	SSW	23	98.46	1.3
Hoquiam	RABR	3.9	3.3	NE	16	98.21	-1.2
Quillayute	RABR-	5.6	4.4	SE	16	97.82	-1.5
Estevan Pt	RA-	3.3	3.3	N	19	97.81	-1.5
Salem	BR	9.4	7.8	S	45	98.83	-2.2
Portland	RABR-	10.0	8.9	S	35	98.73	-2.7
Olympia	RABR	6.7	5.0	SSW	23	98.37	-2.0
Sea-Tac	RA-	5.0	2.8	ESE	13	98.46	-2.0
Bellingham	RA-	2.8	1.7	NNE	26	98.46	-3.4
Abbotsford	RA-	2.8	1.1	NE	21	98.57	-3.0
Vancouver	RA	2.2	1.1	E	29	98.43	-2.7
Victoria	RA	3.9	2.8	E	34	98.36	-1.8
Comox	RASN-	2.2	1.1	NE	14	98.52	-1.5
Port Hardy	OVC	3.9	-1.1	E	19	98.52	-0.9
Average		5.6	4.1		25.2	98.47	-1.74
3-hr Chg		0.7	0.8		0.3	-0.68	1.10
High		12.2	12.2		45.1	99.53	1.3
Low		2.2	-1.1		12.9	97.81	-3.4
Spread		10.0	13.3		32.2	1.72	4.7

[Note: Some of the calculations in the previous tables, mainly the 3-hr change, are bogus. Just caught them now and do not have the time to change the numbers. The calcs in the 19:00 table appear to be good.]

Winds at North Bend have been blowing quite strongly, but not at high-wind criteria. A peak gust so far of S 80 km/h (43 kt) occurred around 16:55. The warm front has definitely passed through Astoria, with the temp jumping from 8ºC (46ºF) at 16:04 to 11ºC (52ºF) by 16:36 while accompanied by a surge of southerly winds that reached 80 km/h (43 kt) in gusts out of 210º at 17:46 and again out of 240º at 18:05. After reaching a low of 98.33 kPa (29.04" alt) at 17:55, the pressure jumped to 98.46 kPa (29.08" alt) by 17:55, another indication of frontal passage. The pressure is likely to begin falling again, or stay roughly flat, as the low center approaches the coast. Newport reported maximum winds so far of SSW 67 km/h gusting 104 (36 kt G 56) at 16:55. Winds at Hoquiam remain NE and light, with much cooler temperatures—the warm front has not reached this part of the coast. Quillayute also remains in the colder air amid offshore flow. This station is also neck-in-neck with Estevan Point for lowest pressure this hour. The northerly winds at the latter station suggest that the low is nearly due south of this location, and the satellite photos support this. Again, it looks like the low is tracking right for the region around Quillayute, maybe even further north: Tatoosh Island reported a 97.71 kPa (28.85" Hg) pressure at 19:00, accompanied by roaring E winds up to 83 km/h (45 kt) in gusts. The pressure is lower than Quillayute—however, Tatoosh seems to report somewhat lower pressures that surrounding stations, so it might be considered equivalent to the more southern station.

For the interior stations, Salem continues to report strong S winds, with a gust to 70 km/h (38 kt) at 19:08. The warm front has definitely gone through Salem, and has also reached Portland recently, with a temp jump from 5ºC (41ºF) to 9ºC (48ºF) between 17:53 and 18:41, accompanied by a surge of S winds. The warm front appears to be nearing Olympia where the temperature has begun to rise and winds have shifted to SSW. Sea-Tac reported east wind gusts to 41 km/h (22 kt) around 16:44, not atypical of incoming strong lows. NNE to NE winds at Bellingham and Abbotsford have become rather strong—it is almost looking like a Fraser outflow event, but the temp is relatively warm compared to a decent winter weather outbreak. Moderate rain has reached Vancouver, accompanied by strong east winds and a cold 2ºC (36ºF) temp. Flirting with snow, as the rain/snow mix at my home indicates. Victoria has similar conditions to Vancouver. As of 19:22 at Comox, pure snow is falling, with light NNE winds. Signs of the low's track south of the region.

The La Crosse now reads 29.00", with the aneroid at 29.04" and the Davis at 98.22 kPa (29.00"), resulting in an average of 29.01" Hg or 982.4 kPa, a drop of 2.4 hPa in nearly an hour (19:46 PST).

The average hourly pressure declension among the stations has slowed considerably to -1.74 hPa/hr. The average pressure among the stations is a low 98.47 kPa (29.08" Hg). The pressure gradient has climbed a bit, but is still well short of many storms even from earlier this year at 1.72 kPa (17.2 mb). This is due to the fact that the cyclone has depressed the pressure over a wide region—a roughly uniform pressure fall that has prevented a super-steep gradient from developing. Plus, the low is moving right into the middle of the region. The indicated gradient is effectively Newport to Quillayute. Strong, but not at major levels as of yet. The average wind speed has escalated slightly to 25.2 km/h (13.6 kt). Reduced winds in the far north have offset increased winds in the south. The temperature spread has increased a little to 10ºC (18ºF) in response to slowly cooling air up north. 20:03 PST.

22:00 PST: The Davis indicated a minimum pressure  so far of 981.2 kPa (28.97" Hg) at 21:00, with the aneroid down to 29.02" and the La Crosse at 28.97", for an average of 28.99", or 98.16 kPa. The pressure has trended up slightly since then, say by 0.01". My minimum agrees well with Vancouver International, which reported 98.18 kPa (28.99" Hg) at 21:00.

Rain/snow mix continues with a patio temp of 5.0ºC and relative humidity of 82%. Winds are still gusty.

The 03:00 UTC (19:00 PST) HPC surface analysis had the low center position almost unchanged from the 00:00 location. Though the forward progress has slowed, I am not convinced by that much. The surface low center appears near 47.5ºN 127.5ºW in the infrared satellite loop, tracking east, if not a bit ENE at a slower pace than before. My earlier interpretation had the low center too far east. The HOC analyzed the 03:00 UTC central pressure at 97.2 kPa, unchanged over the past 3 hr.

Figure 9: Infrared satellite photo for 07:00 UTC (23:00 PST 16 Dec) 17 Dec 2012. The low centre appears to be in the vicinity of 47.5ªN (maybe even 48ºN) 127.5ºW and is tracking slowly eastward, perhaps somewhat ENE toward the Olympic Peninsula. Image courtesy of the US National Weather Service.

Figure 10: The 03:00 UTC (19:00 PST) HPC surface analysis, overlaid onto an enhanced satellite image, indicated a 97.2 kPa central pressure for the system, unchanged from 00:00 UT. The position is only changed slightly, reflecting a slowdown of the forward momentum of the system. Image courtesy of the US Hydrometeorological Prediction Center.

Here is 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	OVC	12.2	8.9	SW	47	99.70	-0.3
Astoria	RABR	10.0	7.8	SW	45	98.26	-1.1
Hoquiam	RA-	8.9	7.2	S	23	98.05	-1.6
Quillayute	BR	8.3	7.2	VRB	10	97.76	-0.4
Estevan Pt	RA-	2.8	2.8	NNW	23	97.97	1.2
Salem	RA	10.0	6.1	SSW	48	98.98	-0.2
Portland	BKN	10.0	7.2	SSW	26	98.75	-1.0
Olympia	RA-	7.2	6.1	S	24	98.30	-0.8
Sea-Tac	BKN	6.7	3.9	SSE	24	98.40	0.0
Bellingham	RA-	3.3	2.8	N	13	98.23	-0.4
Abbotsford	RA-	2.2	1.1	ENE	13	98.28	-0.4
Vancouver	RA-	2.8	1.1	ENE	39	98.16	-0.2
Victoria	RABR-	5.0	2.8	SSE	26	98.02	-0.6
Comox	SN-	0.0	0.0	W	5	98.21	-0.7
Port Hardy	OVC	3.9	0.0	ENE	10	98.44	0.0
Average		6.2	4.3		24.9	98.37	-0.44
3-hr Chg		0.6	0.2		-0.3	-0.10	1.31
High		12.2	8.9		48.3	99.70	1.2
Low		0.0	0.0		4.8	97.76	-1.6
Spread		12.2	8.9		43.5	1.94	2.8

North Bend appears to have been slammed by an apparent cold front around 19:35 when wind gusts reached 96 km/h (52 kt) out of the WSW. The temp fell 1ºC to 11ºC (52ºF), but has since rebounded. The pressure jumped as well, but appears to be falling again. Heavy rain with 8.1 mm (0.32") falling in the hour ending 19:55 also accompanied the wind. Seems like a front, but not backed with strongly cold air relative to the warm advection field. Winds have picked up at Astoria along with the arrival of moderate rain and the pressure is falling again, likely a response to the incoming cold front. The warm front has finally moved through Hoquiam, though in weaker form compared to places south. The temp elevation and wind speeds have not been as high. This is also the case for Quillayute where there has been a clear spike in the temp, to 8.5ºC (47ºF), but not as sharply as places south, and with minimal winds. Perhaps this far north, the front is a warm occlusion. Heavy rain accompanied the band, with 10.2 mm (0.40") in the hour ending 20:53. Tatoosh Island reported a pressure of 97.62 kPa (28.83") at 22:00, along with SSE winds of 37 km/h gusting 48 (20 kt G 26). With that wind direction, it does not seem like the low is on a track south of Tatoosh, though the leading front could be modifying local winds.

In the interior, wind and rain have both picked up at Salem, along with a down-tick of the barometric pressure. This may be a response to the incoming cold front that hit North Bend and appears to be very near Astoria. Salem has a new maximum gust of 74 km/h (40 kt) out of 210º at 21:55. Winds have slowed in Portland, but the incoming front may provide another kicker over the next couple of hours. As with the Washington coast, Olympia appears to have a weak warm frontal signature that may in fact mark a warm occlusion. South winds briefly hit 43 km/h (23 kt) in gusts around 20:33, just after the temp jumped from 4.5ºC (40ºF) to 7ºC (45ºF) between 17:54 and 19:54, accompanied by moderate rain. In the past couple of hours, Sea-Tac had a similar response, with SSE winds picking up to 46 km/h (25 kt) in gusts around 20:53 and the temp rising to 6.5ºC (44ºF) from 5ºC (41ºF) at 18:53. Winds are now due north at Bellingham and at Abbotsford ENE. Light rain/snow mix fell at the latter location around 21:00 and has resumed in moderate form at 22:32. Winds are also ENE at Vancouver and going at a good clip, with light rain and the temp at a chilly 3ºC (37ºF). Like with Tatoosh, Victoria has had an interesting wind shift from NE 30 km/h (16 kt) at 20:00 to SSE 26 km/h by 22:00 that may be an early indication that the low center is tracking a bit further north than expected. The very low pressure of 98.02 kPa (28.94" Hg) is another indicator. This wind shift occurred after a period of heavy rain around 20:00 that suggests a frontally-related situation. Winds were S 19 km/h gusting 37 (10 kt G 20) at 22:37. Pure light snow continues to fall at Comox and has been since 19:22, with moderate intensity at times. Not much going on at Port Hardy save a rather low barometric pressure and a chilly temp.

Average 1-hr pressure tendencies have slacked to -0.44 hPa/hr, likely reflecting the slow-down of the low's forward movement and the stall in the deepening of the storm. The average pressure has fallen to 98.37 kPa (29.05" Hg). The maximum pressure gradient between the stations, essentially that between North Bend and Quillayute in the case of this storm, has increased to 1.94 kPa (19.4 mb). Average wind speed has held about steady at 24.9 km/h (13.4 kt) with a tendency for the strongest winds to be in the southern section, as expected given the storm's track. The temperature spread has increased to a fairly large 12.2ºC (22ºF) due to the warm air in place over Oregon and the freezing temperature at Comox. In essence, a decent baroclinic zone is in place over the region.

My barometers are indicating a lower pressure now, with the Davis showing 98.08 kPa (28.96" Hg), the La Crosse 28.96" and the aneroid 29.00". The average is 28.97" Hg or 98.11 kPa. 23:13 PST.