The State of the Atmosphere: Sunday, November 23, 2014

We’re heading into the final full week of November and Thanksgiving, 2014. As we discussed in our previous post, the weather pattern for eastern Colorado has been overwhelmingly ‘normal’ since early in the week, with ongoing mountain snows.

Snowfall across central and western Colorado will continue through Tuesday, with winter weather advisories and winter storm warnings up across the board. Snowfall totals will range from 10 to 20”+ through Monday evening. There will be a chance for a few snow showers across lower elevations through Tuesday as well, but we’re not expecting much impact from these showers. The latest hi-res NAM has a dusting of snow for Denver over this period, with a spotty inch or two across the Palmer Divide. Mean SREF plumes produce a ½” of snow at DIA, but likely most folks will see less or none. Greatest snow shower activity will likely be south and southeast of Denver Sunday. Temperatures will also be cooler over the next several days, with daytime highs near 40.

Here’s a look at the WPC’s snowfall probability map for 8” or more of snow through Wednesday -- probabilities of 80% for the north central mountains.

WPC 3 Day Snowfall Probabilities Colorado

Thanksgiving Week
The forecast for Thanksgiving across eastern Colorado has gone from what looked “interesting” regarding snow, to likely nothing. Late last week the EURO was indeed showing a pretty hefty cold front and chance for snow by Thursday for Denver, even then its own ensembles were a bit more finicky. Also, the Canadian (which had a few snowy runs) backed off quickly, and well, the GFS never really showed anything. Chalk one up for the GFS in the win column? Maybe.

It seems to me that we were way too far out for anyone to be getting too excited about anything in the first place. And the ECM tends to have a western bias at times with its troughing -- while the GFS can have an eastern bias as we saw much of early fall. It was worth watching if only because our preferred medium range model was showing snow -- but why anyone feels the need to share 10 day snowfall maps in any serious setting, is beyond me. Fact is, this time of year some model at any given run almost always shows a snowstorm 10 days out. Always look to see what the ensembles are trying to do, any if two of three models have no snow, maybe consider there’s something there. Get ready for a long winter of long-range maybe snows…

Most models and their ensembles now generally agree on ridging taking hold by midweek, which will lead to a more mild, dry Thanksgiving day. What we’ll likely need to watch Thursday is for a backdoor cold front that could make its way far enough west to knock temperatures down even for the Denver area, and maybe quite a bit across the eastern Plains of Colorado. Interestingly, it seems like a lot of the same folks calling for a Turkey-snow are now calling for warm, when we really need to watch the potential for cooler temps closely. The chance for snow in Denver, at this time, looks pretty low.

The GEM’s 5 day temperature anomaly from Nov 25 through Nov 30 actually looks pretty good to me. The coldest anomalies will be east of Colorado, but eastern Colorado will range from near normal to several degrees below normal through the period.

WeatherBell Analytics

Beyond Thanksgiving things become a bit more murky. Last week the ECM and Canadian models both showed a very active pattern through the first week of December, but latest runs are less convincing. Plenty of time to see how things will shake out here…

In short -- cooler temperatures Sunday and Monday with a few snow showers drifting off the mountains across the Denver area. Greatest chance for any accumulation east of the mountains will likely be along the Palmer Ridge, and even then any accumulation will be very light. Still a few questions especially with regard to temperatures for Thanksgiving day, but snow chances generally look low for the I-25 urban corridor on Turkey Day. We’ll keep a close eye on things and offer updates as needed.

All for now!

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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