California's Storm

November 30, 2012: Friday

08:19 PST: (Vancouver, BC) On this last day of November, a steady rain falls from a leaden sky. The ground is soaked, street and sidewalks gleaming with wetness. A decent easterly wind shakes the leaf-bare trees in Tisdall Park. I estimate 20-30 km/h at times in gusts. The patio temp is a still warm 10.8ºC, with 80% RH and a still quite low pressure of 29.33".  Vancouver International at 08:00 reported light rain showers and mist with a temp of 9ºC (48ºF), dew point 7ºC (45ºF), wind ESE 22 km/h and pressure 99.34 kPa (29.34" Hg), up 0.4 hPa from a recent pressure minimum at 07:00.

The broad, stacked and semi-permanent 97.0 kPa low still sits over the Pacific off of Vancouver Island. Bands of moisture continue to swing around the base of this low and inland—such as the current rain producer.

Far to the south, this system has produced a decent storm in the San Francisco Bay Area. Strong winds, heavy rain and even thunder have occurred as the trailing cold front interacts with Northern California. The San Francisco Airport reported a maximum gust so far of 87 km/h (47 kt) out of 180º at 02:58. This gust occurred in association with a thunderstorm reported at 03:02. Low pressure also occurred at this time, with an altimeter of 29.77". Short period rainfall reached 6.1 mm (0.24") in the hour ending 04:56, with a total of 29.0 mm (1.14") between 10:56 yesterday and 06:56 this morning. The temp has hovered around 17ºC (63ºF) with a dew point of 16ºC (61ºF) during the main heavy rain episode—a remember those beautifully warm rains. They made for great walks. Winds at Oakland were not as strong, with a peak gust of 54 km/h (29 kt) out of 140º at 03:29. No thunderstorm has been reported there. Low altimeter occurred at 03:10 with a reading of 29.81", probably as the same feature that produced the thunder in San Francisco moved through Oakland. Heavy rain is continuing currently at both stations. Oakland reported 5.6 mm (0.22") in the hour ending 07:53 for the highest so far. However, the same amount, 5.6 mm, has fallen between 07:53 and 08:09, reflecting a very heavy dose of rain. Since 18:53 yesterday, some 36.83 mm (1.45") has fallen at Oakland.

December 1, 2012: Saturday

08:43 PST: The NWP models continue to show a developing cyclone move into Southwest Oregon overnight. The track is too far south for a serious high-wind threat up here. But I plan to follow the low closely. The water vapor satellite loop reveals an enhancing baroclinic leaf inside of 140ºW and along 40ºN currently.

21:07 PST: The expected low is developing well to the south. The 03:00 UTC HPC surface analysis indicated a 99.8 kPa open wave centered near 40ºN 129ºW. The water vapor satellite loop shows an enhanced dry slot and a rapidly ballooning baroclinic leaf in association with the surface low. A very fast jet stream is clearly associated with the cyclone, carrying upper-level cloudiness rapidly to the NE. Barometers all over the west coast seem to be responding to the developing wave, with downward trends even this far north.

Water vapour satellite view showing conditions over the NE Pacific at 20:30 PST 02 Dec 2012.  A marked baroclinic leaf is evident, with a mass of enhanced clouds moving into SW Oregon and NW California. An enhanced dry slot trails right behind the clouds--this is a well-defined an strong weather system. Image courtesy of the National Weather Service.

Crescent City has had some interesting weather over the past few days—not just the Bay Area received a good storm from this persistent system. On 29 Nov, during period with strong S winds gusting up to 67 km/h (16:44), extremely heavy rain arrived. A whopping 21.6 mm (0.85") fell in the hour ending 16:56, followed by 18.3 mm (0.72") in the next. However, the rain intensity reports ceased during that first hour, as of 16:52, with just mist being reported afterward, so this makes the data at lease somewhat suspect to me. Yesterday, 30 Nov, a thunderstorm with heavy rain occurred between 22:52 and 22:59, followed by high winds. The peak occurred at 00:42 this morning with S 67 km/h gusting 85 (36 kt G 46). This is probably the response of the wet and blustery wave that moved through here a few hours later. The thunderstorm dropped 7.4 mm (0.29") of rain in the hour ending 22:56. During the morning of 29 Nov, Arcata received 11.7 mm (0.46") of rain in the hour ending 09:53, but only had light rain during Crescent City's supposed deluge. Winds have not been as strong, with a peak gust of 59 km/h (32 kt) out of 200º at 23:55 yesterday, and a gust to 67 km/h (36 kt) out of 120º at 07:53 on November 28^th. 21:34 PST.

December 2, 2012: Sunday

08:13 PST: (Vancouver, BC) The southwest Oregon low did not quite get fully developed as it moved ashore, remaining an open wave. Northern California has received, and is still receiving in places, a strong storm from this system. Further north, plenty of rain moved through Oregon, Washington and Southwest British Columbia, but winds were significantly slower.

The strong frontal boundary is moving through N California as of the 07:30 PST 02 Dec 2012 time of this water vapour satellite image. The boundary has not yet reached the Bay Area at the time of this image. A large mass of upper-level moisture has moved over Idaho and Montana--the storm is heading into the Intermountain Empire. Strong southerly winds have picked up in the Snake River Plain area in response to the approaching system. Image courtesy of the National Weather Service. 

Here in Vancouver, we had a brief period of moderate rain at 04:00, just ahead of pressure minimum, a quite low 98.73 kPa (29.15" Hg) at 05:00. The low barometric readings are probably the most interesting aspect of this storm up here. Winds have not been much, with a maximum of E 22 km/h gusting 31 (12 kt G 17) at the time of lowest pressure, accompanied by light rain. We recently had a wind shift, to light ESE at 06:22, then S 17 km/h (9 kt) at 07:00, followed by SW 17 km/h at 07:40 and SSW 19 km/h gusting 31 (10 kt G 17) during the most recent observation at 08:00. Looks like the rather weak occluded front moved through. The pressure had climbed to 99.0 kPa (29.23" Hg) as of the latest report, up a strong 1.5 hPa/hr. The temperature hovered around 7ºC (45ºF) for much of the night and is still at this level. The dew point fell a degree to 5ºC (41ºF) by 08:00. Vancouver reported 10.8 mm (0.43") of rain yesterday. Westerly winds are expected to pick up today, but I am not expecting them to be very strong. Our semi-permanent stacked low, now 98.0 kPa and centered right over Haida Gwaii, is currently supporting a SE pressure slope over the area, not the SW slope that is very conducive to westerly surges.

Looking at California, Crescent City reported a peak wind gust of 85 km/h (46 kt) out of 170º at 23:41. During the peak wind phase, where 2-minute speeds ranged from S to SSE 50 to 61 km/h (27 to 33 kt) between 11:22 and 11:52, light to moderate rain fell. Just ahead of the strongest winds, a period of heavy rain brought 7.4 mm (0.29") in the hour ending 09:56. Low pressure occurred at 21:56 with a reading of 99.51 kPa (29.38" alt). Winds shifted to W by midnight and diminished considerably, accompanied by a temperature drop from 14.5ºC (58ºF) at 23:56 to 12ºC (54ºF) at 12:01—just five minutes. Clearly marking frontal passage. A soaking 48.5 mm (1.91") of rain fell in the 24-hr ending 03:56.

Arcata had 56.1 mm (2.21") of rain in the same 24-hr (ending 03:53 in the case of this station). Periods of moderate to heavy rain left as much as 8.6 mm (0.34") in the gauge in the hour ending 01:53. Low pressure of 99.76 kPa (29.45" alt) occurred at 00:53, right at the time of maximum winds: SW 43 km/h gusting 67 (23 kt G 36). Heavy rain immediately followed by 01:06 and winds had shifted to WNW 30 km/h gusting 43 (16 kt G 23). The temp fell from a lofty 15ºC (59ºF) to 12ºC (54ºF) during those same 13 minutes. Frontal passage. Further south, Ukiah had a good dose of heavy rain with 11.7 mm (0.46") in the hour ending 04:56. In the 24-hr ending 03:56, 52.3 mm (2.06") fell. Note that an additional 30.5 mm (1.20") fell after this up to 07:56. The strongest winds occurred during frontal passage with WNW 33 km/h gusting 72 (18 kt G 27) at 04:45. The temp fell from 17ºC (63ºF) to 12.5ºC (53ºF) between 04:26 and 05:56.

Red Bluff reported 17.5 mm (0.69") of rain in the 24-hr period ending 03:54, though the bulk of precipitation associated with the front fell after this time. A soaking 13.2 mm (0.52") fell in the hour ending 05:54, in association with the frontal boundary. Low pressure occurred at 03:54 with a reading of 99.82 kPa (29.48" alt). Ahead of this front, winds climbed to SSE 72 km/h gusting 83 (39 kt G 45). A powerful peak gust of 100 km/h (54 kt) occurred out of 140º at 03:40. Frontal passage happened between 04:54 and 05:54 with the wind shifting from S to SW then WSW and diminishing rapidly. Nearby Redding had 12.2 mm (0.48") of rain in the hour ending 04:53 and wind gusts up to 106 km/h (57 kt) out of 170º at 03:00. Low pressure of 99.49 kPa (29.39" alt) occurred at 03:53. Note the strong 3.3 hPa gradient between the two stations.

The front is just now sweeping through the Bay Area, and I plan on reporting some of the results later. Southerly wind gusts at San Francisco have exceeded 80 km/h (43 kt) at times.
Some other 24-hr rainfall totals for the 24-hr period ending approximately 04:00 include: Eugene 31.5 mm (1.24"), Portland 15.5 mm (0.61"), Olympia 7.4 mm (0.29"), Sea-Tac 8.1 mm (0.32"), Bellingham a mere 1.0 mm (0.04"), Astoria 25.4 mm (1.00"), Hoquiam 33.0 mm (1.30") and Quillayute 24.4 mm (0.96"). 

The sun is shining right now, with much clear sky showing between broken stratus clouds. The yellow low-angle light paints Tisdall Park in a beautiful light. A waning gibbous moon hangs low to the west, a crisp bluish-white orb hanging in the clean blue sky. The wind is calm and the patio temperature 8.5ºC with a 83% RH and pressure of 29.27", rising. 09:04 PST.

Surface analysis overlaid on a satellite photo composite for 04:00 PST 02 Dec 2012. The frontal wave is moving through Oregon at this time, with a strong cold front sweeping into N California. Image courtesy of the Hydrometeorological Prediction Center.

16:45 PST: The frontal boundary and associated wave has moved well inland and to the south now. Even Los Angeles reported some rain early this afternoon as the boundary moved through.

Some of the Bay Area outcomes with this storm include: Heavy rain moved through San Francisco with 7.1 mm (0.28") falling in the hour ending 07:56 this morning. Wind speeds climbed to S 63 km/h gusting 81 (34 kt G 44) at 06:26, with a peak gust of 85 km/h (46 kt) out of 180º at 07:00. Low pressure occurred at 07:56 with 100.80 kPa (29.77" alt). In the 120 hours ending 15:56 this afternoon, San Francisco has had 103.9 mm (4.09") of rain.

Oakland reported 6.6 mm (0.26") of rain in the hour ending 07:53, accompanied by SSW winds of 52 km/h gusting 70 (28 kt G 38) and a mild 16.5ºC (64ºF) temperature. Winds shifted to W by 08:35 and had diminished to 20 km/h (11 kt), with the temp falling to 16ºC (61ºF), all the mark of frontal passage. Oakland had a peak gust of 72 km/h (39 kt) out of 190º at 05:54. In the 120-hrs ending 15:53, this station received 87.9 mm (3.46" of rain).

San Jose had a soaker with 13.2 mm (0.52") in the hour ending 09:53. Maximum winds were not particularly strong with a peak gust of 56 km/h (30 kt) out of 130º at 06:13. Low pressure occurred at 07:53 with a reading of 101.00 kPa (29.83" alt): that makes a decent 2.0 hPa gradient between San Jose and San Francisco at this time. In the 120-hrs ending 03:53, 62.2 mm (2.45") of rain fell at San Jose.

Santa Rosa received a real deluge with 21.3 mm (0.84") of rain in the hour ending 05:53, of which 9.9 mm (0.39") fell in the last 13 minutes. This occurred right at frontal passage, with the wind shifting from S to W and the temp falling from 16ºC (61ºF) to 13ºC (55ºF). Low pressure occurred at 04:53 with a reading of 100.34 kPa (29.65" alt). Winds climbed to a peak of S 48 km/h gusting 74 (26 kt G 35) at the same time. Some 25.7 mm (1.01") of rain fell in the 24-hr ending 03:53, with an additional 37.3 mm (1.47") afterward. Santa Rosa has certainly received a soaking, with a whopping 196.1 mm (7.72") in the past 120-hr ending 03:53. This is 179% of their November normal precipitation (1971-2000) and 171% of the December normal—take your pick, as the past 120 hours occurred in both months. This comparison provides some idea about the magnitude of precipitation in N California.

Ukiah, incidentally, had a little bit more precipitation than Santa Rosa with 202.9 mm (7.99") in the same time period. Arcata received 150.6 mm (5.93") and Crescent City 190.2 mm (7.49").

Looking quickly at Idaho, Pocatello reported a peak gust of 106 km/h (57 kt) out of 160º at 10:35 as the front approached. That about wraps up this storm.

As of the 21:00 UTC HPC surface analysis, the long-lived stacked 98.0 kPa low was centered NW of Haida Gwaii. Seems to be slowly moving away from here. 17:27 PST.