Winter Outlook 2014-2015, Part 2: Forecast Models

In Part 1 of our winter outlook, we laid out the different analogs and surmised, in general, where we are likely heading for winter and spring. The tough part about using just analogs in this forecast is that there is no perfect analog for what is about to happen. Some are pretty close, but within those particular analogs something always comes up that makes it less than perfect. So, if we can use analogs to get an idea about the forecast, we should then supplement those analogs with computer model information to increase potential accuracy.

Many of you are thinking that this winter and spring may be similar to what has happened during October -- i.e., very warm and dry. I am going to show you why I haven’t jumped on that wagon, and why I think being patient with this forecast is what it is all about. One model has been consistent with its forecast. It likely has the best handle on what’s going on with the sea surface temperatures in the oceans, and that is as important as anything. It is the JAMSTEC Model…

JAMSTEC Model Sea Surface Temperature Anomaly Forecast (Red = Above Normal Blue = Below Normal)

December - February

Japan Agency for Marine-Earth Science and Technology

Notice the warmer than normal water across most of the Pacific Ocean. Two areas of interest are near the west coast of North America, and along the ENSO region off the west coast of South America. While water temperatures in the Gulf of Alaska and off the west coast of the US have been cooling, the model still forecasts SST anomalies to be above normal in this area. However, this warm pocket is much cooler and a lot less broad than what has been observed during the past year. Warmer than normal water is also observed in the ENSO region off the west coast of South America. While we are technically not meeting El Niño conditions right now, the JAMSTEC says we will likely move into El Niño territory during the early part of the winter. The interesting thing about the JAMSTEC is that it keeps the warmest water in the central part of the ENSO region. This would still be classified as a traditional El Niño, though not for long if the warm anomaly continues to move westward. Let’s take a look…

March - May

JAMSTEC SST MAM 2015

Warmest water in the ENSO region continues to favor the central region, but is expanding to the western region. This would suggest that any El Niño that develops would develop in a traditional manner, then shift to what we’ve discussed in the past...Modoki El Niño.

June - August

JAMSTEC SST JJA 2015

By summertime, the warmest water still resides in the central and western ENSO regions. The warm anomaly has cooled somewhat since the spring, and this is typical. Since the PDO shifted to its cool phase, we have not had an El Niño maintain its strength or strengthen during the summer. I see no reason to suggest that the summer of 2015 will be any different. Bottom line, I think we are still looking at a weak El Niño event that starts out traditional and evolves into Modoki. The map below shows the difference between the two:

El Niño and El Niño Modoki EOF Maps from JAMSTEC

A weak El Niño doesn’t have the same classic signals that a moderate or stronger El Niño portrays. Plus, this El Niño will likely end as a Modoki and that makes the forecast signal different too. I think you will see that in the JAMSTEC temperature and precipitation forecast.

JAMSTEC Model Temperature Forecast (Red = Above Normal Blue = Below Normal)

December - February

JAMSTEC Temp2 DJF

*March - May *

June - August

According to the model forecast, Colorado would experience colder than normal temperatures for the winter and spring. The pattern that would put this in motion is a ridge (not as strong as last year) in the Gulf of Alaska, and a weak, but stronger than usual, subtropical jet stream riding along the southern tier of the country. We would have a steady supply of colder than normal air from our north, combining with decent moisture just to our south. That is a recipe for more frequent moisture producing storms...storms that could potentially be good snow-producers and keep the ground and surrounding air temperatures cold.

JAMSTEC Model Precipitation Forecast (Green = Above Normal Brown = Below Normal)

December - February

JAMSTEC Precip DJF 2014-15

March - May

June - August

The JAMSTEC keeps Colorado in above normal moisture for the winter and keeps most of Colorado wet for the spring. This is especially true for the southern part of the state. The model then starts to dry us out a bit for the summer and actually has a negative moisture anomaly from southwest Colorado southward during monsoon season. If this were to pan out, most of Colorado would do very well in the snow department this winter and spring. Given the likely setup, it is feasible.

I should have included these in Part 1, but here are the analog year snow totals for both Denver and Colorado Springs.

Denver
Denver snowfall for analog years

Colorado Springs
Colorado Springs snowfall for analog years

The analogs generally give Denver “normal” snowfall while they give Colorado Springs above normal snowfall. Some nice snow totals for both cities during those analog years are seen, but also a dud or two...which many of you are worried about. ‘76-77 and ‘02-03 were both downers for snow lovers. Why do I say this about ‘02-03, despite 62” of snow for Denver? Because most of that winter was free of snow, until the monster mid March blizzard. So, don’t think for a minute that I am ignoring those two down years among our analogs...they bug me everytime I look at the numbers.

Here’s the bottom-line: this is a tough forecast and one that requires some patience. There are many conflicting signals, we’ve had a very warm and dry October, no analog matches our current conditions terribly well, and it is a long range forecast. However, I do feel good about Denver and the northern Front Range seeing AT LEAST NORMAL SNOWFALL. There is a decent chance it could be above normal, too, though with Colorado Springs and the southern Front Range more likely to see above normal snowfall for the winter. This is also true for the southern mountains and the Southeast Plains.

Over the coming week’s we’ll continue to hone in on which analogs appear to best fit the pattern going forward and weight accordingly as we head into the winter months. We’ll also be taking a look at what impact the biggest sunspot in over two decades may have on our winter forecast, and long-ranging forecasting all together.

Despite a warm fall so far, I also feel we will get pretty cold. This is especially true for the late winter and spring. With an active storm track, I believe we will struggle to warm up during the spring. So, if you thought winter was going to be a no show this year, think again. As I said at the Weather5280 Meetup, it is likely going to be a late show and possibly a good one.

Brian Bledsoe

Brian Bledsoe is Weather5280’s climate and long-range forecast specialist. Brian is chief meteorologist at KKTV in Colorado Springs. Follow him on Twitter @BrianBledsoe

Colorado Springs, CO
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