Why we have had a wacky winterPublished 9:40am Tuesday, February 14, 2012
Column: Pothole Prairie
This winter’s weather has had me reading about worldwide weather patterns.
I’ve always had a passing fancy in how weather works. When I was a kid and there were only four channels — the three major networks and public TV — the weather was my favorite part of a newscast. I recall watching Willard Scott on “Today” tell us what the jet stream was doing. I recall Mike Lozano of WHO-TV in Des Moines, Iowa, describing high pressure systems and low pressure systems. When I was 6, I wrote Lozano a letter, and he sent me a typed letter on yellow paper about weather. I think it was one that he had prepared for sending to all the kids who wrote from time to time, but he actually signed it. I learned about the hot and cool air that meet to produce severe thunderstorms and sometimes spawn tornadoes.
Since then, weather followers have learned terms like Alberta Clipper, Pineapple Express, El Niño, La Niña, the Gulf Stream and Santa Ana Winds. We’ve learned about snow levels, storm surges, wind shear, gustnados and anticyclones. (Flatlanders often don’t know that a snow level is the elevation in the mountains where precipitation turns from rain to snow. It’s not part of our nightly weather reports.)
The mild winter this year has taught me about the Arctic Oscillation. All the reports I read are saying it is the cause.
The Arctic Oscillation refers to the atmospheric pressure over the northern latitudes. It has negative and positive phases, with lower-than-normal pressure over the Arctic Ocean producing a positive phase. When the AO is in a negative phase, we here in the Upper Midwest get a lot of cold and snow and the jet stream cuts across the United States. The jet stream, as you probably have noticed over the years, often acts as a boundary between cold northern air and warmer air to the south.
This winter, the jet stream largely has flowed north of us, up in Canada, because the AO is in a positive oscillation. This has brought loads of snow and bitter cold to Alaska and Canada while bringing warmer-than-usual weather to much of the Lower 48.
With a positive phase, the polar winds are stronger and stay north, keeping the colder air bottled up there.
However, the AO turned negative a few times this winter, but the North Atlantic Oscillation protected North America quite a bit, sending the wintry weather to Europe and Asia. Cold weather still spills our way, but, poof, warm weather returns. For instance, it was cold and snowy Monday, but today the high is forecast to be 37 degrees — above freezing yet again in a season where we usually stay below for weeks on end, with only one or two warm spells.
Apparently, it is difficult to forecast what the AO will do beyond a week, maybe two at times. Weather is a science that we know much more than we did 10 or 20 years ago thanks largely to computer models, but we, surprisingly, still have huge gaps in our knowledge base. Even wind — especially the chaos of turbulence — remains quite confounding.
Of course, we cannot blame the AO for everything. The weather phenomenon that rules our planet more than any other is the warming or cooling of surface temperatures in the Pacific Ocean. It is called the ENSO — or El Niño Southern Oscillation. This is a La Niña year, which is a cooling of the surface, and anyone who reads agricultural journals knows it has brought the drought conditions across many parts of the United States, including ours.
The La Niña cycle is forecast to end this summer. Experts don’t know what the Pacific will do next. Some have said it will enter a neutral phase.
Does that mean weather will return to normal? Let’s hope so.
Tribune Managing Editor Tim Engstrom’s column appears every Tuesday.