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Friday, February 19, 2010

Dr. Jeff Master's WunderBlog: Winter Olympics forecast: near-record warmth

Dr. Jeff Masters' WunderBlog 

Winter Olympics forecast: near-record warmth
by JeffMasters,  February 15, 2010
Under sunny skies and warm southwest winds the temperature in Vancouver, British Columbia climbed to 54 °F (12.4 °C) yesterday, just missing the record of 12.9 °C (55 °F) for the date, set in 1991 (records in Vancouver go back to 1937). That was marvelous weather for all the joggers that were out in t-shirts and shorts in Vancouver yesterday, but is lousy weather if you're trying to hold a Winter Olympics. The men's downhill was postponed yesterday and rescheduled for today, because of rain and bad snow. The women's combined, originally scheduled to run Saturday, has been postponed until Thursday. The mountain has been getting snow at the top, a mix of snow and rain along the middle section, and rain at the bottom, making for very difficult skiing conditions. Practice runs have been mostly been canceled. In West Vancouver, where the moguls competition was held yesterday, snow had to be trucked and helicoptered in because there wasn't enough on the ground. The snow-making machines weren't any help, because it was too warm to make snow. Too bad Philadelphia or Washington, DC, didn't make a bid for the Winter Olympics! It's an upside-down winter when Canada has trouble getting snow, and Washington, DC, gets five feet.

As we can see from a plot of the temperature departure from average for the month of January (Figure 1), most of Canada has seen very unusual warmth, with temperatures over 5 °C (9 °F) covering large swathes of the country.

Figure 1. Departure of January temperature from average for the strong to moderate strength El Niño year of 2010 (left), and a composite of the last five years that had a moderate to strong El Niño (right). Note that typically, an El Niño event brings much warmer than average temperatures to Vancouver, and cooler than average conditions to Florida. This year has seen an extreme amplification of this pattern. The impact of the Arctic Oscillation (AO) is evident over eastern Canada and Greenland, where exceptionally warm temperatures were recorded. Image credit: NOAA/ESRL.

Why all the warmth in Vancouver? El Niño partly to blame
So, what's going on? The average high temperature in Vancouver this time of year is typically 8 °C (46 °F). Vancouver has seen above-average temperatures every day this month, and tied one daily record so far. This unusual February warmth follows a record warm month of January, which averaged 3 °C (5.4 °F) above average, beating the previous record set in 2006 by a pretty significant margin, 0.9 °C (1.6 °F). Nearby Seattle, Washington had its warmest January in 120 years of record keeping, and both Oregon and Washington recorded their 4th warmest January. As we can see from a plot of the temperature departure from average for the month of January (Figure 1), most of Canada saw very unusual warmth, with temperature anomalies over 5 °C (9 °F) covering large swathes of the country. Record warm January temperatures were observed not only over British Columbia, but also over Manitoba and over much of Quebec, where half of the province's twelve largest cities experienced their warmest or second warmest January on record. Unusual Canadian warmth is to be expected during a moderate to strong El Niño episode, which is what we've had this winter in the Eastern Pacific Ocean. The pattern we've seen during the previous five moderate to strong El Niños dating back to 1987 (Figure 1, right) shows this trend, and also the trend towards colder than average conditions in Florida. However, the pattern for January 2010 shows an extreme amplification of this El Niño pattern. We had record warmth over much of Canada, and Florida got socked with its 10th coldest January on record. The extreme amplification of the January temperature pattern was due in part to the influence of the Arctic Oscillation/North Atlantic Oscillation, a natural wind pattern over the North Atlantic measured by the difference in pressure between Iceland and ocean areas to the south. That difference in pressure was remarkably small in the first half of January, leading to the weakest Arctic Oscillation pattern in 60 years of record keeping. This allowed cold air to spill southwards into Florida, and helped bring very warm temperatures to Greenland and Eastern Canada. El Niño, combined with the Arctic Oscillation, all superimposed upon exceptionally warm global temperatures, is probably the best explanation for the record January warmth in Canada. Globally, January 2010 was the 4th warmest January on record, with global ocean temperatures the 2nd warmest on record, according to NOAA.

The forecast: near-record warmth for Vancouver
The forecast for Vancouver for the remainder of the week calls for temperatures above 10 °C (50 °F) each day. Today's forecast high of 10 °C (50 °F) will approach the record high for the date of 12.6 °C (55 °F). The long range forecast through the remainder of the Winter Olympics promises continued near-record warmth, as the jet stream is projected to stay in its current El Niño-type pattern. In this configuration, a strong ridge of high pressure stays anchored over the Pacific coast, allowing plenty of warm air from the southwest into British Columbia. Unfortunately for the winter games, I expect that Vancouver will end up experiencing its 1st or 2nd warmest February on record.

No major snowstorms in sight
Today's snowstorm for the mid-Atlantic has shifted northwards, meaning the that the maximum 4-8 inches of snow from this storm will pass north of snow-weary Philadelphia, Washington, DC, and Baltimore. The computer models are showing that this will be the last significant snow storm to affect the eastern half of the U.S. for at least a week, and residents of the Mid-Atlantic can look forward to a slow but steady melting of their huge piles of snow. This is exactly what is needed to avoid a serious flooding situation--a rapid thaw or large rainstorm would have been a major problem.

Next post
I'll have a new post on Wednesday at the latest. I did an interview with the Washington Post weather blog by the "Capital Weather Gang", for those interested.


1 comment:

susan said...

Every picture tells a story, don't it! Although we more or less knew the facts, the graphic is startling. What chance this will be the year the public starts noticing that the propaganda effort has not actually changed reality ...