On November 9th 2017, NOAA declared that 2017/18 winter in North America will be a weak La Nina Winter.
Today, NOAA has FINALLY shared snowfall maps that show us EXACTLY what we’ve been waiting for: Maps that show us exactly who has gotten above average snowfall during La Nina winters in North America.
According to these La Nina snowfall maps, you’ll want to spend 2017/18 at:
- Crystal Mountain, WA
- Mt. Baker, WA
- Mt. Bachelor, OR
- Mt. Hood, OR
- Grand Targhee, WY
- Jackson Hole, WY
- Copper Mountain, CO
- Sun Valley, ID
- Revelstoke, B.C.
- Whistler, B.C.
NOAA has placed the bullseye on Mt. Rainier & Crystal Mountain Ski Resort in Washington. According to the maps above Crystal Mountain is where you’ve got the best chances to see above average snow in a La Nina year.
NOAA just published this article about where the skiing is forecast to be best this La Nina winter 2017/18.
NOAA is calling for above average snowfall and below average temps for the Northern US this winter.
La Niña = Skiers Delight over the Northern United States
by meteorologist Dr. Stephan Baxter/NOAA
In a nutshell, La Niña is associated with a retracted jet stream over the North Pacific Ocean. The retreat of the jet stream results in more blocking high pressure systems that allow colder air to spill into western and central Canada and parts of the northern contiguous U.S. At the same time, storm track activity across the southern tier of the U.S. is diminished under upper-level high pressure, which also favors milder-than-normal temperatures. The storm track is in turn shifted northward across parts of the Ohio Valley and Great Lakes (2).
Based on climate analysis (3) from this new snow dataset, we see that La Niña favors increased snowfall over the Northwest and northern Rockies, as well as in the upper Midwest Great Lakes region. Reduced snowfall is observed over parts of the central-southern Plains, Southwest, and mid-Atlantic.
This La Niña footprint is pretty intuitive. Given the northward shift of the storm track, relatively cold and wet conditions are favored over the northern Rockies and northern Plains, resulting in the enhancement of snowfall. Warmer and drier winters are more likely during La Niña over more southern states, and this is exactly where seasonal snowfall tends to be reduced (4). The more vigorous storm track and slight tilt toward colder temperatures over the northern tier of U.S. during La Niña modestly increases the chance of a relatively snowy winter.
Snow and Strength
We can break up the snow pattern further and look at the weakest and strongest La Niña events. Splitting La Niña events into strength reveals some interesting differences worth investigating further. In this preliminary analysis below, there is a suggestion that weaker events are snowier over the Northeast and northern and central Plains on average.
On the other hand, stronger La Niña events (see below) are snowier across the Northwest, northern Rockies, western Canada, and the Alaska panhandle. Also, there is a tendency toward below average snowfall over the mid-Atlantic, New England, and northern and central Plains, which is not seen during weak La Niña.
Overall, stronger La Niña events exert more influence on the winter climate pattern over western North America. Weaker events appear to be associated with more widespread above-average snow over the northern United States. Because a weak La Niña means that the forcing from the Pacific is weaker than normal, it may imply other mechanisms (e.g. Arctic Oscillation) may be at play and is worth further investigation.
The predictability of seasonal snowfall may be somewhat similar to precipitation in that one or two big events can dramatically affect the seasonal average. Thus, in general, the expected prediction skill is likely to be lower than for temperature. However, because temperature also plays an important role in snowfall, some predictability is likely nonetheless. And like for seasonal temperature and precipitation, knowing the state of ENSO is a pretty reasonable place to start.
Lead editor: Michelle L’Heureux
(1) This new dataset is documented in Kluver et al. (2016) “Creation and Validation of a Comprehensive 1° by 1° Daily Gridded North American Dataset for 1900-2009: Snowfall” in the Journal of Atmospheric and Oceanic Technology. The dataset for this analysis goes up to 2009, so we are going to look at winters from 1950-51 to 2008-09. Total cold season snowfall accumulation from October through April is used here.
(2) This is consistent with the temperature pattern: the storm track is enhanced where the temperature gradient is stronger than normal.
(3) Here we are using composite analysis to show snowfall. In this case we take just the La Niña years between 1950-51 and 2008-09 and compute the mean. For the strength composites, we divide the 18 La Niña winters between 1951-2009 into weak or strong cases. The median ONI valueused to split them is -0.95°C during December-February (DJF) average. We need to be cautious drawing too many conclusions based on the large reduction in our sample size. Composites also emphasize variance: regions with more year-to-year variability will have higher amplitude composite signals.
(4) The areas in the South that favor below-average snowfall during La Niña are most evident where the snowfall climatology is reasonably high. That is where the signal is most likely to come through the noise.