We've all heard how it's been such a hot summer. And you've likely been reading about how the Pacific Northwest is expected to maintain a warmer than normal autumn and winter.
UW Atmospheric Sciences professor Cliff Mass just did an excellent blog post showing why we're expected to be so warm. In a nutshell, Mass says a persistent ridge of high pressure last fall that kept the storms away also keep the ocean from churning very much, which is needed to mix in some cooler water from the depths of the ocean.
Without that mixing, the Pacific has been running warmer than normal off our coast (he referred to it as "the blob" as in a blob of warmer waters) and that has been the culprit of our warmer summer and higher humidity. Models suggest that pattern will maintain through the autumn and winter, helping in turn keep the air mass warmer.
And perhaps making things even warmer is the pending potential for El Nino. Yes, climate forecasters have been gradually trimming their confidence in a developing El Nino this fall and winter, dropping the odds from 80 percent to 65 percent to now in the low 60s percent range and starting a little later, but it's still the odds-on favorite and the prudent bet for this winter. El Nino's usually also bring a mild-to-warm winter around here on its own.
But combine "the Blob" with "El Nino" and you not only get two words that could make an amazing hashtag if combined together the right way (#Blobino? #ElBlobo?), but Mass says it's a recipe for a really mild autumn and winter, and sure enough, he presented some maps that do forecast a much warmer than normal period coming up, both October-December and even warmer for December through February.
Now I've had a few people email me wondering what exactly a warm autumn and winter would entail? I think some people are wondering as hot days well into the 80s persist into September, if we're predicting 70s and 80s to continue right into the heart of the Holidays and into the snow season, and if we'll be wearing shorts on New Year's Day.
No, we're not turning into Phoenix North, so you snow birds don't have to come running back home, but I thought I'd go back into some of our warmest autumns and winters on record to see what kind of weather pushes our boundaries of warmth.
The warmest October through December on record was 1976 with an average temperature of 49.1 degrees – that’s found by taking the high and low and dividing by 2. The average-average is 45.9.
- October had 3 days over 70 degrees, 9 additional days over 65. Average highs start at 65 degrees, dropping to 55 degrees by Halloween. There were 25 days with no measurable rain, including a 12-day dry streak.
- November had 8 days over 60, and only 7 days in the 40s. It was again super dry with 22 days with no measurable rain, including another 10 day dry streak. Only five nights were at or below freezing.
- December had a whopping 19 days over 50 degrees, including seven days warmer than 55 and a 61 degree reading. Highs are normally in the low-mid 40s here. Just two days at or below freezing for lows. And again dry – 20 days with no measurable rain. There was no lowland snow in the period.
Perhaps most telling: The entire winter season amassed just 191 total inches of snowfall at Snoqualmie Pass – the lowest amount on record since the mid 1940s. Average is 439 inches per season.
The second-warmest Oct-Dec was 1965, but that was skewed by a really warm October – 14 days at warmer than 65 degrees with seven of those days at *70* or warmer. And the month had 18 days with no rain. As mentioned, their November and December were fairly normal with actually a significant snow event that spanned 10 days around Christmas. The month would have 510” of snow at Snoqualmie – actually a bit above normal. So 1965 is the outlier.
Third place was 1980, which had six days warmer than 70 in October with one day over 80(!). November ended up normal and then December had a very warm spell to end the year, but it was more tropical warmth courtesy of relentless Pineapple Express-type storms – four days late over 55 degrees and two warmer than 60. Snoqualmie ended up with 219 inches of seasonal snow – third lowest.
But the best year of comparison might be the winter of 1991-92, which had the warmest December-February on record, but also had a very warm winter overall, stretching November through April. Here are their average monthly temperatures and departures from normal:
November 47.3 (+1.9), December 43.8 (+3.2), January 43.9 (+1.9), February 47.3 (+3.9), March 50.3 (+3.8) and April 53.1 (+2.8)
- November: A whopping 23 days were at 50 degrees or warmer, with seven days at 55+ and two days 60-plus.
- December: 13 days 50+, 2 days over 55; only 5 days below normal, no highs under 40, only 4 days of lows at or below freezing.
- January (1992): 14 days 50+, 5 days 55+, 3 days 59+. This month had a lot of rain at the end as we went intense Pineapple Express. A 15-day rain streak brought 6.19" of rain. There were no highs in 30s, only five days of freezing lows.
- February: 20 days 50+, 15 days 55+, 6 days 60+, 3 days 65+! There was only one single solitary low at freezing.
- March: 16 days 60+, 5 days 65+. There were no freezing lows.
So that means from November 1 through March 31, just 10 days with lows at or below freezing.
And as you might imagine, not one lowland snowflake across the winter. Up in the mountains, snow was in short supply, and Snoqualmie Pass tallied its second-lowest seasonal snow total of 211 inches.
Now, that’s not to say that the autumn and winter of 2014-2015 will follow exactly to suit, but it does describe what we might expect if the forecasts hold true: No, there won’t be days in the 70s and 80s in the winter, but there may not be a whole lot of snow either, be it in the lowlands or the mountains.