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.