The State of the Atmosphere: Sunday, December 7, 2014

Between a lot of traveling on our end and a rather benign (to put it gently) weather pattern, it's been a quiet few weeks at Weather5280.com. It's now time to start looking at a potential pattern shift as we head into the latter half of December. There have been some great discussions as to if this pattern will ever break (we love hearing from you!), but we continue to think there is real reason to believe it will. This of course will take time -- perhaps more than the snow-lovers among us would like.

Good news/bad news
This week will feature more of what we’ve already seen to start the month of December. Temperatures are forecast to remain above average through at least Friday, with daytime highs in the 50s, and possibly 60s through the next five days. Great news if you’re enjoying this prolonged period of quiet, mild weather, bad news if you’re eager for snow.

There’s good agreement between ensembles through midweek, positive height anomalies (red) for the middle of the country and another east coast storm.

GFS/Canadian 500 heights Wed 12z | WeatherBell Analytics

Blip in the radar?
It’s after Friday that we really need to start watching things. An strong Pacific storm system will begin to move inland Thursday, then dig into the southwest by Friday as it pushes east. The question is-- will this system finally deliver snow to Denver?

At the moment it appears the answer is likely no, and, in the outside chance that we do see any, not much. That’s not to say some models aren’t trying. The operational GFS, for example, spent the last 48 hours producing big time snow for eastern Colorado before finally backing off with today’s 12z run. Model agreement just isn’t there, with many operational models wavering between a four corners low, a deep southern solution, and at times an even more open and north scenario. Latest operational runs are now diving the upper level low too far south, keeping much of the energy and moisture south and east of Colorado. What the GFS/EURO/Canadian ensembles do agree on is a large upper level low moving through somewhere between Wyoming and Texas, and we all know eventual track means everything. There will be a lot of back and forth over the coming days, and while this system does not look too promising at the moment, this may be our best chance at snow across eastern Colorado in several weeks.

Here’s a look at the 500 level for GFS early next Sunday. On the left is last night’s run; notice where the closed upper level low tracking along the New Mexico/Colorado border, while today’s run for the same time is dropping much further south into Texas. The northern track in this instance would be more favorable for snow across eastern Colorado, but this gives a good idea of the fluctuation we’ll continue to see between model runs. For what it’s worth, today’s EURO deterministic produced just 0.04” QPF (i.e., basically nothing) for Denver next weekend, but it’s ensembles were wetter at 0.3" precip at DIA.

WeatherBell Analytics

We’ll continue to watch this very closely and offer updates as needed. For now plan on another quiet week, but know we need to keep an eye on next weekend. If ensembles continue to take the bulk of the energy south Denver’s snow chances will be low next weekend, if we see the trend move further north, that could very well change.

Long range thoughts
Beyond next weekend there’s reason to believe our storm track remains relatively active, though somewhat unconvincingly at times. The GFS/EURO/Canadian ensembles all show the next disturbance moving through around the 20th of December.

We had been watching the MJO forecast for the last two week’s of December which for a time supported a significant flip in the pattern from the warm and dry we’ve been experiencing. The most recent runs look less impressive with this possible evolution, with it still forecast to move into phase 8 to end the month, but not nearly as strong. It is nice to see it forecast to move out of phase 5 and 6, however, as this is a warm setup for the CONUS for Nov-Jan.

So if the MJO is less of a factor through the end of the month, do we still think the pattern flips to cold? Maybe. Even if we don’t see much in the way of cold, there’s at least still the possibility for a more transient, unsettled pattern emerging. Ensemble long range forecasts continue to show our ridging pushing further north and west through the next 15 days, which would help open the door for more systems to make it inland through the period. While we’re not seeing any big cold shots (virtually anywhere), with each disturbance pushing across a southerly storm track there will be waves of anomalous cold, especially for the west, southern, and eastern United States. Both the AO and PNA are forecast to remain neutral or positive through the 15th of December, which are not particularly cold signals from the plains eastward.

This active storm track does not necessarily guarantee we see a snowy second half of December in Denver, or any snow for that matter, but odds will be better than what we’ve seen to start the month. If next weekend’s storm doesn’t pan out, I think we see at least one more shot before January, if not several.

Living and dying by each model run is a hard thing to do right now, especially if you’re eager for snow. As we move into the last 10 days of the month a few differences start appearing between the models. The Canadian and EURO have generally looked colder for the west, and the GFS colder in the east. Even as the pessimistic one in the group, I continue to think the latter part of December could have tricks up its sleeve.

In short, no clear-cut cold or snow showing up over the next few weeks, but there are signs there will be more potential than we’ve seen of late, especially across southern Colorado. Enjoy the warm week ahead, and we’ll continue to work on narrowing in on how this pattern may look beyond the 12th.

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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