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).