UPDATE: The southern and eastern parts of the metro area have seen significant accumulations with at least one report of 12+ inches in far southeast Centennial. The road and surface temperatures seem to have kept most of the snow from accumulating by melting it once it hits the ground. Based off of radar precipitation accumulations, most areas have already seen between 4-8″ of snow although most of it has melted.

Over the last week we’ve discussed every aspect of this storm in painstaking detail and

now we get to experience the truly fun part! We get to experience the storm and see whether all of our models, measurements, and analysis was correct or if mother nature will throw us a curve ball. Of course, we always want our forecast to be right. We like to think that we actually understand the atmosphere well enough to make broad predictions that can be used to aid in keeping people safe or, at the very least, making their lives more convenient by giving them the tools to make informed decisions about how they want to address the weather in their daily lives. Nothing feels better than nailing a forecast regardless of whether it’s a snow storm, thunderstorm, or even storm chasing and catching a tornado.

The atmosphere by definition is a chaotic system which means that the smallest force right now can dramatically affect tomorrow or next week’s weather. I’m sure that we all remember the scene from Jurassic Park when Ian Malcolm describes chaos to Dr. Ellie Sattler with the following analogy-

“It simply deals with unpredictability in complex systems. The shorthand is the Butterfly Effect. A butterfly can flap its wings in Peking and in Central Park you get rain instead of sunshine.”

While that’s an extreme example, the atmosphere is a chaotic system and what may have started as wind from a thunderstorm today, could wind up being a major storm system next week. The unpredictability of it is what makes it so fun. I know plenty of people (most of whom are weather geeks like myself, I must admit) who have been caught in an unexpected rain storm and had it turn into one of their favorite memories.

So, we want our forecast to verify and for our snowfall accumulation predictions to be true, a busted forecast is never a desired outcome, but it’s just another chance to learn about how you can improve in future forecasts. Ultimately, that’s why these storms are so fun! We never truly know what’s going to happen! We will analyze every model run, stare at surface measurements, and launch weather balloons to tell us about the upper atmosphere, but at the end of the day, it’s still just an educated guess and mother nature does not care about the forecast. This is why I tend to go into a frenzy and get (I’ll admit) a bit overly hyped with these big systems! Adventure! The Unknown! Man Vs. Nature! It’s so incredibly fun.

Anyway, enough of the philosophical stuff, ON TO THE FORECAST!

I’m going to break down this forecast into four different sections this time:

National Weather Service Winter Storm Warning Current Information an Storm Timing (including final snowfall accumulation predictions) Impacts on Travel Final Thoughts

National Weather Service Winter Storm Warning

...WINTER STORM WARNING REMAINS IN EFFECT UNTIL 6 AM MDT SUNDAY... * TIMING...MODERATE TO HEAVY SNOW WILL CONTINUE THROUGH SATURDAY AND THEN DECREASE SATURDAY NIGHT. * SNOW ACCUMULATIONS...8 TO 16 INCHES. * WIND/VISIBILITY...NORTHEAST WINDS 15 TO 30 MPH. VISIBILITY WILL FALL TO A QUARTER MILE OR LESS IN HEAVY SNOW AND BLOWING SNOW. * IMPACTS...ROADS WILL BECOME SLUSHY AND SNOW COVERED... ESPECIALLY ON BRIDGES...OVERPASSES AND SECONDARY STREETS. HEAVY SNOW ON TREE BRANCHES AND POWER LINES MAY CAUSE THEM TO BREAK...POSSIBLY CAUSING POWER OUTAGES. THE SNOW WILL ALSO BE HEAVY TO SHOVEL...AND RESIDENTS SHOULD BE CAUTIOUS TO AVOID OVER-EXERTION WHILE SHOVELING. PRECAUTIONARY/PREPAREDNESS ACTIONS... A WINTER STORM WARNING FOR HEAVY SNOW MEANS SEVERE WINTER WEATHER CONDITIONS ARE EXPECTED OR OCCURRING. SIGNIFICANT AMOUNTS OF SNOW ARE FORECAST THAT WILL MAKE TRAVEL DANGEROUS. ONLY TRAVEL IN AN EMERGENCY. IF YOU MUST TRAVEL...KEEP AN EXTRA FLASHLIGHT... FOOD...AND WATER IN YOUR VEHICLE IN CASE OF AN EMERGENCY.

Current Information and Storm Timing

Depending on your location around the metro area, you may have already experienced the first bit of this storm. Some light rain had developed on the west side of I-25 this afternoon around 5pm and has slowly tapered to what can be seen in the radar image below. You can see some light rain/snow west of I-25 and the heavier rainfall out east following the severe weather (including tornadoes!) that occurred earlier today.

As we progress tonight, rain/snow showers will increase in coverage between 10-11pm. Thanks to some cloud cover today, we did stay on the cooler side of temperatures and I think that we’ll actually see a switch over to snow a bit earlier than expected. Depending on where you live, you’ll most likely see a full switch over to snow between 10pm and 2am. The snow will increase in intensity over night due to the deepening low that is currently developing over southern Colorado that you can see in the image below. This low, which has counter-clockwise winds, will grab moisture from the Gulf of Mexico and push it up the slope (yes, that’s where the term comes from) of the Rocky Mountains causing the moisture to condense and give us heavy wet snow that will last through Saturday night.

While we do have a blocking pattern in place for this storm system, it will be moving out a bit faster than originally expected. Snow will taper off Sunday morning and while some light snow is expected all day, the heavier precipitation will move out to the eastern plains. This is going to decrease our snow totals slightly, but not much. Currently, the Denver metro area is looking at 7-14″ of heavy and wet snow with higher amounts of 9-18″ along the Palmer Divide to the south and the foothills to the west. A lot of this snow will melt when it first starts to fall and it will be so heavy that it will compress under its own weight once it’s on the ground. This means that while 7-14″ of snow may fall, it will probably look like less snow than that.

As I mentioned before, the heavy snow will finish over night on Saturday night which means that these are essentially one day accumulations.

Impacts on Travel

Airlines such as United have already started to cancel flights in anticipation of the storm and many airlines are offering vouchers as rewards for changing your flights in advance. One thing is certain, make sure that you check with your airline before leaving for the airport!

Initial road conditions will most likely be wet due to how warm the temperatures have been, but as heavy snow falls, wet and nasty slush will build up on the roadways eventually. The amount of slush or snow on the roadways obviously depends on how much snow we get and the temperatures which means that I’m not 100% sure just what road conditions will be, but they will most likely deteriorate during Saturday. Travel in the foothills will be nearly impossible as their surface temperatures are colder and they are expected to get much more snow than Denver.

Final Thoughts

While the storm is looking like it will be ~12 hours shorter than expected, we should still see plenty of snow and potentially hazardous conditions. Make sure that you knock off your trees if you get the chance as this will probably be a big branch-breaking storm! I will update on here, Reddit, and Facebook as conditons change and forecasts are tweaked.

If you want more frequent updates and/or daily forecasts from me, you can download the “My Weather Concierge” app and subscribe to the Denver forecast.

Thank you for reading!

-Andrew