Our near-term weather in Southwest Virginia is fairly simple, as the nor’easter pulls away along the Northeast coast (several inches of snow from New Jersey to Maine). We’ll have several dry, mostly sunny days through the weekend, gradually warming — 50s on Thursday, some 60s by Friday-Sunday, wouldn’t rule out a few low 70s. Then a cold front arrives near the middle of next week with a chance of rain and some cooler temperatures again. Some chance of a larger storm system beyond that, but we’ll leave that for the future now. I will focus on a few other even longer-term things today.
The time to submit entries for the snowfall prediction contest closes out Thursday at midnight — I must have your entry emailed to email@example.com by then for it to count. IMPORTANT NOTE: I screwed up on Wednesday’s column in the paper, the period of the contest runs from Nov. 15 to March 31 — 16 days longer than I said in Wednesday’s column. This column from October 17 has the correct dates, entry guidelines listed at the bottom of the column.
I want to dig a little deeper into the historical winter analysis I conducted in Wednesday’s column, linked here (contest closing date information also now corrected). The analysis was based entirely on Roanoke’s snowfall history during winters in which there was either a weak El Nino (warming of equatorial Pacific sea surface temperatures) or neutral conditions leaning a little warm but not enough to be considered an El Nino. This winter appears likely to be on the cusp between those two as of now. If you’ve read here before, you know that I consider El Nino highly overrated as a singular factor in predicting a winter — however, it does have the advantage of being a constant, slowly changing factor, unlike the whims and fancies of the North Atlantic Oscillation and Pacific-North America pattern that can change week to week, even within a few days, whatever the overall trend of a season may be. So I thought it was worth taking a look to see if there was a discernible pattern for our winters based on similar El Nino phases in the past.
The weak El Nino winters I studied, with total snowfall in parentheses, were 1953-54 (10.7 inches), 1969-70 (26.8 inches), 1976-77 (19.2 inches), 1977-78 (37.3 inches) and 2004-05 (16.1 inches). The “almost El Nino” winters were 1979-80 (31 inches), 1989-90 (16. 1 inches), 1990-91 (1.2 inch), 1992-93 (28 inches), 1993-94 (16.3 inches) and 2003-04 (21.9 inches). As you can see, 1990-91 was the only one of these winters under 10 inches of snowfall, and it and 1953-54 were the only two under 16 inches. That seems to be a fairly significant pattern leaning strongly to near-normal and above-normal snowfall winters, if we consider 17 inches or so the norm for Roanoke (which I do, not the old 22-24 inch figures you may have seen or heard, for 3 major reasons I explain in the column).
A few other things I noted:
* Four winters of the 11 studied also had a similar pattern to this year of predominant North Atlantic Oscillation-positive pattern (no blocking high near Greenland) switching to predominantly NAO-negative (blocking high near Greenland, forcing the jet stream south, bringing cooler air) from the first half of the year to the latter part of the year — 1969-70, 1976-77, 1977-98, and 2004-05. Those winters averaged nearly 25 inches of snow. My pick for Roanoke snowfall this winter was 26 inches (31 for Blacksburg).
* Only 2 of the 11 winters studied included a snowstorm of more than 12 inches: Christmas Day 1969 and the March 1993 Superstorm.
* The one low-snowfall exception on the list, 1990-91, seems to be well explained by its being the only one of the 11 winters to exhibit an extremely strong positive phase of the NAO. All of the almost-El Nino winters went predominantly positive on the NAO, however, while all but one of the weak-El Nino winters tilted NAO-negative.
* Total precipitation was within an inch of normal in 19 of the 33 months, and rarely extreme in the above or below-normal months. Temperatures skewed cold in 3 of the 5 weak-El Nino winters, while averaging near normal in the almost-El Nino winters.
So, boiling down all of this down, and considering the tendency for northern latitude blocking patterns we’ve seen forcing the jet stream south (possibly linked to record summer Arctic ice melt, according to some studies) and the rapid growth of snowfall over Eurasia and Canada, I’m leaning to a winter of frequent periods of cold — interrupted by some unseasonable warmth in between — and occasional light to moderate snow events, with perhaps one event of the 6-12-inch nature. I’m leaning against a “big’un” type snow of 12-plus, but would give it perhaps 1 in 3 odds of occurring — much better odds than a year ago. I think there may be 2 or 3 setups this winter that could develop into that if the details line up right.
I said 26 inches for Roanoke, 31 for Blacksburg and Dec. 15 for first 1-inch snow at each site.
So there’s one idea of how things will go. Somewhat educated guesswork at best.