What’s Behind the Cold, Snowy Winters Like Those of the 1960s & 1970sJanuary 13th, 2011 at 9:06 pm by Chad Evans under Chad's WLFI Weather Blog
This winter is not necessarily a surprise. It has looked like a cold & snowy one since September. The winters of the early 1960s & 1970s have returned. Since the 2009-10 winter, the consistent snow & cold is commonplace.
However, I have found that the cold & snow in the past two winters is more unusual due to consistency than extreme, extreme bouts of cold & heavy, heavy snow/blizzard here.
Arctic Oscillation & Strong La Nina in Cahoots:
One of the key factors in this cold, snowy winter is the Arctic Oscillation & a strong La Nina. It is that La Nina, whose warm waters in the western Pacific, has brought Australian & Hawaiian floods. This moisture can energize the “Pineapple Express” or subtropical jet & brings floods to the West Coast. Since the warming is more central Pacific (La Nina Modoki), it focuses the flooding more on California, than Washington & Oregon. Normal La Ninas bring floods to Washington & Oregon.
What is the Arctic Oscillation?
The difference between the upper level pressures of Greenland/North Atlantic & Hudson Bay give you an index. The higher the pressure over Greenland/North Atlantic & the lower the pressure over Hudson Bay, the bigger the numerical difference & the more negative the AO.
Reason for Very Negative Arctic Oscillation (Negative = Cold Here):
The lack of Arctic sea ice & lack of snow cover in the Arctic, specifically in Alaska & Greenland has created a surface high, which has built upward through the winter due to the positive feedback of the brown ground. This is how drought-producing & heat wave-producing upper ridges develop in the eastern U.S. It starts with a dry, dry ground, this is a positive feedback to produce a stagnant high with no rainfall, then the heat & dryness build upward, way up into the troposphere. With time, the heating disrupts the upper-level westerlies & a strong, strong, stagnant ridge forms.
This summer, it was in the southeast U.S. & on the periphery, we had the “Ring of Fire” with severe storm complexes here. This winter, it is every Asian snowstorm moving up & over the ridge, dropping southward as an Alberta clipper, bringing us minor snow event after minor snow event.
This winter these have gelled with that subtropical jet filled with Hawaiian, Indonesian & chunks of Australian moisture to blow up huge southern & northeastern U.S. winter storms. It has been the same thing in Europe with heavy snow, ice & extreme cold. The unusual rains have greened up the northern African Sahara. In fact, northern Africa has not seen this much rainfall since the late 1970s after years & years of drought.
A warming Arctic melting all the sea ice has likely contributed to this pattern, which has brought about theories on a global warming connection. I have seen this pattern before in the 1960s, 1970s, 1984-85, 1989 & 2009, 2010, 2011. Even back in May 2006, we had a massive blocking ridge in eastern Canada with 80s in northern Quebec & 40s in Indiana with a cold, drizzly rain that combined to wipe out a good chunk of Indiana’s newly-planted tomato & watermelon crop from cold & fungal infection.
Are ridges getting stronger due to warming? It is too, too hard to say. I have seen similar patterns before & I do not think this is an extreme anomaly. Think about the extreme, extreme upper ridge over the U.S. in 1936 with the heat & drought. That similar ridge over Alaska that winter produced temperatures of -22 degrees here.
However, what is so, so different is the degree of warming underneath those ridges. In parts of the Arctic (Alaska & in Greenland), it has been some of the most consistent mild winter weather of the last 500 years.
Is it Global Warming?
Well, it depends on who you ask. Alaskans & Yukons would tell you “YES, YES, YES! THIS IS CRAZY WEATHER!” U.S. citizens, Europeans & Chinese, as well as the Korean people would tell you, “THERE IS NO WAY!”. Even Hawaiians, who have snow on their mountain tops & have seen readings on the Coast dip to record cold readings in the lower to middle 50s would tell you, “NO WAY!”.
Climatologists take all temperature readings from around the world & average them out. If the Arctic warmth outruns (numerically-speaking) the cold waves of the Northern Hemisphere, then it is a warm winter. It is all about averaged numbers & where each climate station is placed. All readings are getting warmer, but how many of these stations are placed in urban centers? We only have so many weather stations worldwide. What role does the urban heat island over weather stations in big cities have? With more ocean buoys are we just being able to access warmer temperatures. Ideally, a dataset of climate over 1000, 500, even 300 years is essential, but modern data only dates back to 1895 & really, really good upper air data & solid, dense data sets have only existed since the 1950s.
I do not believe we are in the warmest weather of the last 10,000 years in the world. I think the warmest time period was during Medieval times & during another warm, dry period thereafter. The warmest period of the last 80,000 years likely in the Northern Hemisphere was the Sangamon interglacial, which was a period of very mild weather sandwiched between the Illinoian & Wisconsinan glacial episodes in Indiana.
If the frequency of extreme upper ridges continues & unusual stratospheric warming events continue over decades & decades, then the alarm will need to be sounded.
In Coming Posts: Unusually Warm & Dry Periods Over the Past 80,000 Years In Our Region:
Over the coming weeks we will examine these anomalous warm periods in Indiana’s weather history & how they affect our region.
The Winter 2010-11 Pattern: