El Niño is hanging on by a thread. That thread probably breaks off by winter.
I’ve already gotten a surprising number of inquiries about issuing a winter forecast. These seem to come earlier and earlier every year, possibly because some in social media weather offer theirs earlier and earlier every year.
I still say it’s way too early, and each year, I’ve come to value seasonal forecasts less and less, as how our winters are perceived typically hinge on how two or three winter storm setups play out, not the average temperature or total precipitation over the course of the entire winter.
That said, one place we can get at least a hint for what might happen is the state of the El Niño Southern Oscillation, or the sea surface temperatures in a stripe of the Pacific Ocean just north of the equator.
El Niño, the condition in which these temperatures are above normal, is fading after a run that began last fall. Sea surface temperatures in a key region of the equatorial Pacific Ocean over the past three months averaged half a degree Celsius (0.9 degrees Fahrenheit) above normal, the lowest mark at which an El Niño is considered to exist.
This El Niño never got above 0.8 C (1.4 degrees F) above normal, so it was considered a weak El Niño — which is the state it has been in through some of our snowiest winters, as an enhanced southern branch of the jet stream supplies subtropical moisture but isn’t strong enough to overpower cold air masses that slide in from the north.
Other than one historic snowstorm on Dec. 9 that produced the widest coverage of foot-plus snowfall in 23 years across the forecast area overseen by the National Weather Service’s Blacksburg office, the 2018-19 winter didn’t really live up to snow lovers’ hopes or snow haters’ fears of what a weak El Niño winter often produces.
While the wet pattern of southern stream storm systems frequent in El Niño winters presented itself, cold air was never buckled southward into our region for long by high pressure over Greenland. Curiously, this Greenland blocking high has been almost constantly present since late April, but it doesn’t have quite the same impact on our weather in summer as it does in winter.
Our cold air shots last winter tended to be sharp but short, with a couple of troublesome, widely displeasing snow-changing-to-ice events when moisture barely caught up to the cold air before it pulled out.
Which gets us to an important point about the El Niño Southern Oscillation — it is only one card in the deck of what determines a winter weather pattern.
If you get dealt an ace first you have the chance of a strong poker hand if certain other cards end up being dealt to you also. But an ace can be part of a bad hand and a “2” can be part of a great hand, depending on the other cards.
So winter forecasts, especially those far in advance, sometimes overemphasize the importance of an El Niño or its cool-water sibling, La Niña.
This coming winter is expected to have neither of these in effect, but rather “neutral” conditions in the equatorial Pacific, with sea surface temperatures within a half-degree Celsius of normal.
Neutral conditions mean that there may be no strong influence from the central Pacific, and that other various other factors would determine the overall course of the winter, whether it ends up warm or cold, dry or wet, snowy or not.
So the first clue we have to the puzzle several months from now is, as we should expect in early August, inconclusive.
Generally speaking, our mildest and least snowy winters do not occur with ENSO-neutral conditions. These are more common with a moderate to strong La Niña or, occasionally, with a strong El Niño.
A few of our snowiest winters, including the record 1959-60 winter with nearly 63 inches of snow at Roanoke and likely close to 80 at Blacksburg (newspaper accounts filling in for missing official weather data), have occurred with ENSO-neutral conditions. But more of them cluster around the middle.
The state of the equatorial Pacific has importance beyond what may happen months from now, of course.
The demise of El Niño may boost the Atlantic hurricane season over the next couple of months, with less likelihood of strong winds aloft from the Pacific shearing off developing Atlantic tropical systems.
It also is less likely we’ll see a firehose of storm systems with flooding rain come late fall and winter, though other patterns can develop that bring heavy rain.
There is also some chance that the forecast models and experts are wrong, and that El Niño flares back for winter, or La Niña develops.
So it’s too early to say much about how winter will go, but not too early to start peeking at what that first card the global climate patterns deal us may be.
Weather Journal appears on Wednesdays.