September 5 update:
Into the month of September now, and the urge to ski powder grows stronger with each passing day. Been taking a long look at the charts over the past couple days hoping to see anything that would suggest a good winter. Mother nature is still playing her cards close to her chest and isn’t showing anything too extraordinary. Arctic is really starting to cool down which is a sure sign that winter is on it’s way. High temps in Northern AK are barely breaking freezing. Sounds nice after the hot summer we’ve been having. August was again above normal temperature-wise and below normal precipitation-wise pretty much everywhere across Utah except for portions of southern Utah that had a couple weeks of flash flooding.
CFSv2 long range model has been backing off slightly on the El Niño-like conditions for this year. Forecasted sea surface anomalies also showing a slightly weaker El Niño. We have been seeing ENSO neutral conditions for the past few months and I expect that to continue for one more month before the weak El Nino kicks in during the month of October and last through at least the first part of the winter. A weaker El Niño is not necessarily a bad thing for us in Northern Utah as the moisture, while not as abundant, will not be forced as far south as it would be in a strong El Nino.
Historical records show that the last time we were in this situation, a moderate La Niña season preceding a weak-to-moderate El Niño, was heading into the 2006-07 season. As many of you may remember, that was not the best year we’ve ever seen, with Alta failing to break 400″ annual snowfall. Does history repeat itself? That has yet to be seen. There are other factors, like the AO, PNA, and MJO, just to name a few that can play a huge role in continental weather patterns. Still have no reason to change our current winter forecast of 105% of normal for the Wasatch south of I-80 and near normal precip for the Wasatch range north of the I-80. From now on, we will update when warranted as we are now in the season when the Pacific can start revving the engine and cool Pacific storms are possible.
My friends, it is now August, the month in which most long-range forecasters will tell you they start to get a grip on what the upcoming winter might look like. Up until now, most winter forecasting is just guesswork based on historical trends. And unless there is a really strong ENSO cycle occurring, it is usually very difficult to predict the winter prior to August. For that matter, it’s still very difficult to say with confidence what we’ll see during the winter all the way up until October or November. But at least WSF is bold enough to make a few educated guesses at this point. So here we go . . .
Our friends over in the NOAA’s Climate Prediction Center released their monthly ENSO update today. What they’ve been telling us for the past couple months was that there was a chance for El Niño to develop this winter based on SST’s (Sea surface temperatures) in the Pacific and a few models hinting at El Niño development. July’s discussion essentially gave us a 50% chance for a weak to moderate El Niño to develop. This month, more models have come into consensus with this idea and they’ve upped the chance of El Niño to “likely”. If El Niño were to develop, we’d see it occurring gradually over the next two months. At this point, it does not look to be a strong El Niño winter.
Before we go into specifics about winter, let’s look at the next couple months. Remember, the Wasatch has seen snow at the beginning of September before, so we are closer to ski season than it may seem based on the 103-degree high temp observed at the SLC airport yesterday. Long-range models have suggested that the desert Southwest will continue to see strong monsoonal moisture pushing north well into the month of September. This moisture will likely periodically make it far enough north to give the Wasatch and adjacent valleys diurnal convective activity, aka afternoon thunderstorms. This is the 3-month outlook for the U.S. from the CPC:
As you can see, areas to our south shaded in green are likely to see above average precipitation through mid-October. So don’t be surprised to see a continuation of flash flooding in the canyons of Southern Utah and Arizona when and where thunderstorms pop up.
As we head toward winter, we see the overall pattern in the Northern Hemisphere become more winter-like. Arctic air is already starting to pool up near the North Pole, which is normal, and it is only a matter of time before that starts leaking south into North America. El Niño, as we’ve mentioned in the past, generally favors wetter-than-average weather for the southern part of the Western United States, and dryer-than-normal conditions for the Pacific Northwest. The Wasatch, with our mid-latitude location, usually has a fairly average winter during El Niño, as with La Niña years. Looking at historical data, WSF believes that when there is a particularly strong ENSO event (El Niño or La Niña), we can see snowier-than-normal seasons. Examples: 1982-83 was a strong El Niño years and good snow year for us. 2010-11 was a fairly strong La Niña and as many of us know, a great snow year. However, weak instances of El Niño and La Niña are much less likely to be good snow years. In fact, they can be pretty poor. This last winter was a weak La Niña that didn’t turn out so solid for us.
This season, with a weak to moderate El Niño becoming increasingly likely, I see us having a fairly normal year. That is to say, at this time, I don’t see any other factors that could really push us way above or below normal. As we get closer to winter, there will be other meteorological factors that can influence our climate, but at this time, we are still too far out to factor those in. The CFSv2 model shows the influence of El Niño in this graphic (below) which depicts the Precipitation anomalies for North America during the upcoming months of Jan-Feb-Mar 2013, or the heart of winter:
As you can see, the farther south you are along the west coast, the more likely you are to see above-average precipitation. This extends inland into Arizona but not so much into the Great Basin east of the Sierra Nevada. The Wasatch is in the neutral white coloring, indicating equal chances of above or below average precip. It is because of this that I feel our winter is going to be near normal. The only thing that pushes me to predict more than normal is a combination of the law of averages and historical evidence. I feel like since we had such a bad snow year last winter, we are due for at least a bit more than average this winter–not very scientific but I can hope, right? Also, when I look at winters in the past that follow weak La Niñas, I see a slight trend of above average snow years. Not much, but a bit. This being said, now WSF is going to post our first preliminary forecast for us for the winter of 2012-2013 for the Wasatch. We expect 105% of normal snowfall south of I-80 with average (or 100% of normal) snow for areas north of I-80. This discrepancy accounts for the fact that El Niño favors areas that are farther south.
So there you have it… our first prediction. Of course we will fine tune this as we get closer and everything becomes significantly clearer, but it’s always fun to make a prediction this far out and see how it compares when all is said and done.
Hope stoke levels are high for this winter! It’ll be here before you know it!!