About a month ago I talked a lot about the course we are likely on as we head into fall. I addressed the potential for an El Niño and what type, and reiterated that our top analog for the next several months is late 2009 and early 2010. What happened in late 2009 and 2010? See for yourself…
The above map shows the temperature anomalies (or departures from normal) from September 2009 through March 2010. All of that blue and purple represent colder than normal temperatures. Conversely, all of the yellow, orange, and red represent warmer than normal temperatures. Basically, the southeastern two-thirds of the country was quite cold during that time, with Colorado being on the northwest fringe of the coldest air. What about precipitation?
The map above shows the precipitation anomaly for the same period. Blue represents wetter than normal conditions, while yellow, orange, red represent drier than normal conditions. During the winter of 2009-10, Denver received 60.6” of snow (~105% of normal). Half of that came in October (17.2 inches) and March (12.8 inches).
Given the pattern that we are in and how things played out in late 2009, my gut says that we will hit fall pretty early with the potential for some very active weather in October. Now, we base our forecasts more than just on gut feelings, so let’s see what one of our better computer models thinks of this theory.
The JAMSTEC Model is based out of Japan and seems to have the overall pattern nailed, ocean temperatures included, which is a major key to this puzzle.
JAMSTEC Temperature Forecast:
September - November:
The blue shading represents cooler than normal temperatures and the red shading represents warmer than normal temperatures. If you look at Colorado, you see that the state is shaded in light blue. This means the model is calling for cooler than normal conditions for the September through November period.
December - February:
Get a load of all that blue across most of the United States! The model is going crazy with colder than normal weather, especially for the central and southern part of the country. This includes Colorado, which is shaded in more than just light blue. The darker the blue, the colder the forecast. This would suggest a higher than normal probability of below normal temperatures during the heart of the winter months for Colorado.
March - May:
The spring of 2015 is also showing up as being colder than normal for the same locations that the model believes will have just endured a very cold December through February. To me this suggests three things: 1) a steady tap of cold air from Canada, 2) an active storm track bringing several rounds of snow, and 3) the snowpack on the ground being VERY reluctant to melt. All three of those things in combination make a perfect recipe for a colder than normal winter. Speaking of snowfall, lets look at that (by way of precipitation anomalies) a bit more closely.
JAMSTEC Precipitation Forecast:
September - November:
On this map, the green represents wetter than normal conditions, and the brown represents drier than normal conditions. As you can see, the model has a lot of the United States wetter than normal for the fall. This includes Colorado. Plus, do you notice the slightly darker shade of green from just off the coast of Mexico into Arizona and Colorado? That enhancement means that those locations will likely be even wetter than the surrounding areas. I have been saying for a while now that the active Eastern Pacific hurricane season MAY supply us with a tropical connection of moisture that may meet up with a storm coming in from the west or northwest. That “phasing” -- in effect, when two jet streams link up -- has the potential to produce a major late summer flooding event or an early fall big snow event...or both. The pattern suggests that it is possible, and certainly something to watch.
December - February:
The heart of the winter shows up with generally normal moisture for Colorado, with a slightly wetter than normal signal for far Southern Colorado. I think most of us would take a winter with normal snowfall, as they have been hard to come by of late. Either the mountains get hammered and the lower elevations don’t, or vice versa. Those winters when both the plains and mountains see good snowfall have been rare to say the least. However, the signal the model is set on is dry from central California into the Pacific Northwest (bad) and wet from Eastern New Mexico into the Mid-Atlantic. Look familiar? Pretty identical to the second map I showed you in this post.
March - May:
The spring looks very similar to what the model is forecasting for the fall. It shows Colorado as being pretty wet, along with all of the Western High Plains. Getting good and consistent spring moisture has also been a rarity for Eastern Colorado lately. However, we had excellent spring moisture in 2010, and Denver even measured 1.3 inches of snow in May. Not unheard of, but is a testament to how long the cooler than normal weather hung around that year.
I always try to give a confidence reading with the forecast, and I must say that my confidence in this forecast is higher than normal. I’ve been talking about it for months, I haven’t seen any of the major drivers change much, and something else...can you feel a difference in the weather already? The nights are getting more crisp, some of the Aspen trees are already starting to show color, and we will see additional cold fronts move through during the next 10 days. Fall is coming, and it is likely coming early…