Courtesy Reuters Buffalo New York THE WINTER OF 2013-2014 JUST HOW WEIRD WAS IT EXACTLY? Eyad Atallah and John Gyakum McGill University
Some Headlines Certainly for large portions of southern Canada and the northern USA, the story of the winter was unusually cold weather resulting in scenes like this from Niagara Falls. (March 2, 2014 High temp -13C, low -19C.
Some Headlines In fact, The Great Lakes showed the largest amount of Ice Cover in over 35 years with only Lake Ontario remaining largely ice free
Meanwhile on the other side of the Atlantic The United Kingdom was unusually warm with wide swaths where the temperature was over 2 C above normal. And at the same time precipitation amounts were generally 150-200% above normal
A case of extremes An examination of Climate Division Rankings shows that parts of the Midwest had a top 5 coldest winter while parts of the Southwest had the warmest cool season ever Climate Division Data
The extremes were not a local phenomena, but the cold was An examination of the 1000-500 hpa Thickness relative to a 66 year climatology shows a small area of -3C near Hudson Bay and corresponding +3C anomalies in the North Pacific and Eastern Europe
The extremes were not a local phenomena, but the cold was The previous picture becomes a little more stark when you consider the ranks of the thickness over the 66 Year period since 1949
Hemispheric Average Thickness The negative anomalies from this winter are particularly impressive when you consider the background state of the atmosphere is warming. 5540 5520 5500 5480 5460 5440 Northern Hemisphere Area Weighted Thickness Ave Min-Ave 4990 4970 4950 4930 4910 4890 5420 4870 5400 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 4850 In fact 2014 had the 4 th warmest average thickness and the coldest average thickness value is also the 4 th t
Latitude Band Average Thickness In fact, Polar latitudes experienced the highest average thickness on record consistent with the southern displacemen t of the Polar Vortex 5450 5400 5350 5300 5250 5200 5150 5100 5050 5000 4950 Area Weighted Average 1000-500 hpa Thickness 45-60N 75-90N 15-30N Linear (45-60N) Linear (75-90N) Linear (15-30N) y = 0.2355x + 5666.7 R² = 0.3489 y = 0.2657x + 5233.6 R² = 0.286 y = 0.6023x + 4979.9 R² = 0.4433 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 5700 5650 5600 5550 5500 5450 5400 5350 5300 5250 5200
Specific Thickness Thresholds (<480 dam)
Specific Thickness Thresholds (<498 dam)
Specific Thickness Thresholds (<510 dam)
Specific Thickness Thresholds The story behind the thickness thresholds indicates that it really wasn t the quality or intensity of the cold air that was at issue, instead it really was the persistence of the pattern.
So why so persistent?
Persistence The reason for the persistence is somewhat unclear. A popular perception is that weakening zonal winds result in slower propagation/ more blocking.
Persistence However, another possibility is the warm pool in the eastern North Pacific. This warm pool ranks as the 1 st ranked warm anomaly relative to an 1981-2014 climatology for the 5 month period.
Persistence Interestingly, a global view of the SST anomalies from ESRL suggests that the North Pacific warm pool is THE anomaly globally.
Finding Analogues The problem with finding analogues for the winter is the overall trend in thickness, particularly at higher latitudes Area Weighted Average 1000-500 hpa Thickness 45-60N 75-90N 15-30N Linear (45-60N) Linear (75-90N) Linear (15-30N) 5450 5400 5350 5300 5250 5200 5150 5100 5050 5000 4950 y = 0.2355x + 5666.7 R² = 0.3489 y = 0.2657x + 5233.6 R² = 0.286 y = 0.6023x + 4979.9 R² = 0.4433 5700 5650 5600 5550 5500 5450 5400 5350 5300 5250 5200
Finding Analogues Analogues are based on the correlations of the thickness anomaly pattern relative to the pattern that we see in 2014
Finding analogues However, doing so results in all of the 7 best analogues (outside of 1990) occurring in the past 15 years because of the ubiquitous warm anomalies in Polar Regions. To get around this problem a linear trend in the thickness is calculated at every grid point leading to a detrended anomaly pattern.
Detrended Anomaly Basic Anomaly Detrended Anomaly
Analogues Detrended Thickness Anomaly SST Anomalies
Persistence A similar global pattern of SST anomalies is again found for 1990
Persistence SST anomalies for the five best analogues to 2014. An inspection of each of the analogues indicates a North Pacific warm pool...
But surely this winter will be different
Notable points 4 th Warmest Hemispherically Juxtaposition of Coldest and Warmest average thicknesses in 66 years over the North Atlantic Warmest ever average thickness in the Arctic Air not exceptionally cold/warm, but pattern exceptionally persistent Analogues all show significant North Pacific Warm Pool