Snow for Denver This Weekend

Well, after waiting for new information on the storm system all week, I can officially say that the original model forecast of snow is looking correct. The snowfall amounts weren’t necessarily correct, but the precipitation type was nailed down pretty well by those early models. As each run has come out, temperatures have been dropped lower behind this storm system and they will, ultimately, lead to a fairly decent amount of snowfall. Currently, the amounts are still up for debate a bit, but Denver and the surrounding areas are currently looking quite a bit of snow and there might be up to three feet in the foothills and elevated terrain.

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

  1. National Weather Service Winter Storm Warning
  2. Storm Timing
  3. Current Information and Data (including preliminary snowfall accumulation predictions)
  4. What Information We’re Waiting On and How It Can Impact The Forecast
  5. Impacts on Travel
  6. Final Thoughts

National Weather Service Winter Storm Warning

THE NATIONAL WEATHER SERVICE IN DENVER HAS ISSUED A WINTER STORM
WARNING...WHICH WILL BE IN EFFECT FROM LATE FRIDAY NIGHT THROUGH
LATE SATURDAY NIGHT.

* SNOW ACCUMULATIONS...ACCUMULATIONS OF 8 TO 14 INCHES WILL BE
  POSSIBLE BY SUNDAY MORNING. THE HIGH DENSITY SNOW WILL TEND TO
  SETTLE AS IT ACCUMULATES...SO THAT SNOW DEPTHS COULD REMAIN LESS
  THAN 8 INCHES.

* WIND/VISIBILITY...NORTH TO NORTHEAST WINDS 15 TO 25
  MPH...ESPECIALLY EAST OF I-25.

* IMPACTS...SNOW-COVERED AND SNOW PACKED ROADS ARE
  EXPECTED...ESPECIALLY ON BRIDGES...OVERPASSES AND SECONDARY
  STREETS. THE SNOW WILL BE A WET AND HEAVY SNOW WITH HIGH LIQUID
  DENSITIES. ACCUMULATING SNOW ON TREE BRANCHES MAY CAUSE TREES TO
  BREAK. THE SNOW WILL ALSO BE HEAVY TO SHOVEL...AND RESIDENTS
  SHOULD BE CAUTIOUS TO AVOID OVER-EXERTION WHILE SHOVELLING.

Storm Timing

The first bits of moisture from this storm system are entering the western part of the state now as rain showers and thunderstorms that you can see in the image below on the Colorado/Utah border. That moisture will begin reaching Denver and the front range tomorrow afternoon when a surface low pressure sets up over the southeastern part of the state and begins developing upslope winds that will sling moisture into the mountains. The storm will intensify over night on Friday night and will continue through Sunday afternoon.

20160414_radar

Radar Reflectivity from Grand Junction, Colorado Showing Rain Showers in Green and Thunderstorms in Yellow and Orange/Red

Current Information and Data

One of the biggest questions about this storm system was “Will it be cold enough to snow?” and that question has been answered over the last few days by each consecutive run of the models. The temperatures have been continually dropped by the models and this will, indeed, be a snow storm. Now, we will probably start as rain tomorrow afternoon and will switch to snow some time over night, but for the remainder of the weekend, we should see primarily heavy and wet snow. The best part of this storm system is that, as many of you have heard me mention in the past, we finally have a blocking feature to keep the storm right on top of us and prevent it from heading east.

Accumulations for this storm depend on two factors, the actual temperature when the snow falls and the amount of moisture available. As a rule of thumb for these spring storms, we generally assume a 10:1 or 8:1 ratio for snow meaning that at colder temperatures we’ll see 10″ of snow for every 1″ of water or, at warmer temperatures, we’ll see 8″ of snow to every 1″ of water in the atmosphere. The models have been shifting a bit with total precipitable water, but we’ve been consistently between 2-3″ of water which would equate to between 16-24″ of snowfall for the warmer temperatures that we’re expecting. If we cool down further, we could be looking at 20-30″. Another complication on top of the already difficult to predict snow totals is trying to time when the rain will switch to snow. If it switches early, obviously accumulations will be higher, a later change to snow will result in less accumulation. Finally, the ground temperatures are extremely warm due to the nice weather we’ve had lately. This means that a lot of the snow that initially falls will most likely melt on the roadways and ground. So, realistically, we’re looking at around 8-16″ around Denver and the front range with much higher amounts to the south and west as we can see in the map below.

Screen Shot 2016-04-14 at 7.34.28 PM

Projected Snowfall Totals Through Sunday Night from the North American Model

What Information We’re Waiting On and How It Can Impact The Forecast

The next couple of model runs will give us our best chance at determining the best predictions for snowfall totals. They should give us a better idea of how much moisture we will have in the atmosphere, how cold our temperatures will be, and how long the system will hang out with us. Depending on how each of these parameters changes with the new runs, snow totals can be altered pretty dramatically. So, do not think that these snow totals are written in stone! They could go up, they could go down.

Impacts on Travel

Beginning on Friday night and continuing through the weekend, travel will be hazardous. Air travel delays and cancellations are a high possibility from Saturday morning through Sunday afternoon which means that checking with your airline before you leave the house is extremely important. 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

There is still plenty of time for the forecast to change and for snow accumulations to be altered. This will definitely be a pretty major spring storm, but its impacts are still not fully understood and probably won’t be until we start to experience them. The snow contained in this system will be wet and very heavy which means that you will need to clear it from trees that already have leaves or it will break and destroy branches. We’ll watch the latest runs and make updates as needed with one final forecast update early tomorrow afternoon before the storm hits.

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

 

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