Last
night I turned up the thermostat for the first time this fall. In another week or so I will light the stove
and it will burn until April.
The
question now is, how cold will this winter be, and how much wood will I need?
Predicting
the weather over a long period has always been tricky, since there are so many
variables that change from hour to hour.
Climate change makes it more difficult as the rules are now
changing.
I
checked the reports from NASA and NOAA, the two government agencies that study
the weather, to see what trends they are seeing.
One
indicator is the ENSO, the El Niño-Southern
Oscillation. Normally the winds
in the tropics blow from east to west – the easterly trade winds. This pushes tropical warm ocean water away
from the west coast of the US, allowing cooler water from the ocean bottom to
well up along the coast. The result is
the cool, dry, weather and the great fishing of southern California. (It also blows hurricanes from Africa to North America.)
If during an El Niño the winds slow down, the warmer water sloshes back towards California. This warmth and resulting low pressure will pull the jet stream southward, giving wetter weather in the south and drier weather in the north.
If the trade winds speed up and push the warm ocean water further from North America, a phenomenon called La Niña, the opposite occurs. The jet stream will be pushed up by the high pressure over the colder water, bringing wetter, warmer weather up to the north.
Currently it appears that the El Niño winds are slowing down, but with a only small chance of a full La Niña (stronger trade winds) developing. NOAA thinks that there is only a 62 percent chance of La Niña development during November-January 2017-18. The official outlook indicates a likely return to ENSO neutral conditions by next spring. Based on that, there are some long-range predictions that might be made.
With
a slowing of the El Niño
winds, the average temperatures in the US could be slightly warmer than
normal. The precipitation (as of today)
is expected to be normal. Unfortunately
that combination could mean more sleet and ice.
Remember that ENSO is only a part of the prediction, but as of right now
it looks like pretty much like slightly warmer and slightly wetter than normal
this winter in New England.
Then
there is the polar vortex. There are
several high-speed winds that circle the earth;
you have probably heard of the jet stream. These upper atmosphere winds are caused by the
difference in temperatures between the equator and the poles.
Normally
the polar vortex traps the coldest air at the north and south poles. But (as formally denied by the best
politicians that money can buy) as the earth’s atmosphere heats up, and the
poles are warming at a faster rate than the equator, there is less and less
difference in temperatures and the polar vortex weakens. The cold arctic air is not being contained at
the dark north pole as the vortex slows down.
It comes down to visit us.
As
of right now there are no specific warnings about the polar vortex for this
winter, so my prediction remains at very slightly warmer and wetter than
average for New England.