The forecasts are relatively on track this morning from yesterday. Model agreement that a powerful storm system will move into the Rocky Mountain region is still quite good. There is still quite a bit of disagreement between models as to whether snow or rain falls, temperatures and even the position of where the storm sets up. In Colorado, these are all critical to determining what type of storm we get or even if we get a storm at all.

It' Still Too Early To Tell

You hear me say this a lot but this far out from a storm, you have to take every model run with a grain of salt. This storm system is over the ocean and hasn't even really formed yet. This causes two issues for modeling:

  • We don't have good weather stations to give us data, so models are really shooting in the dark at this point in time. Without adequate data coming in from observers and station, models really are just giving us a best guess.
  • The storm system itself has not even really organized too much. Without seeing how the trough (low pressure) system forms and begins to move, we again don't have enough data to make good guesses.
Satellite view of the Pacific. Still waiting for storm initiation

Satellite view of the Pacific. Still waiting for storm initiation

Don't get me wrong, the accuracy of weather modeling has improved tremendously over the past few years. These programs are great at predicting patterns from even 1-2 weeks out, but the finer details are not usually spotted until much closer to the time the storm arrives.

Generally these models get more accurate within the 3-5 day time frame and are best withing 3 days of the storm arriving. We also see a huge jump in accuracy when the storm finally makes it onto land where we can get constant data from weather stations.

NWS post about uncertainty in forecasting

NWS post about uncertainty in forecasting this storm

This Storm Has a Lot of Water

This fact has not changed with any of the longer term models. Across the board, all models predict a strong storm with lots of moisture to work with. The GFS shows a ton of moisture accumulating along the front range of Colorado:

GFS quantitative precipitation forecast by 6AM Monday

GFS quantitative precipitation forecast by 6AM Monday

This model however, shows much warmer temperatures and has a large majority of it falling as rain. When you look at the total accumulated snowfall you see not much on the ground:

GFS predicted snowfall accumulation through Monday

GFS predicted snowfall accumulation through Monday

The Euro however, shows nearly all of this moisture falling as snow.

What Happens If Today's Forecast Verified

I'll play devils advocate again, what does this storm look like if the models are predicting exactly what will happen? This is tricky because of the two longer range models don't agree on rain vs. snow for the storm. So we take an average between the two. Take all of these predictions with a grain of salt though, these are just based on what models show at this time and is in no way meant to be final forecast!

  • Timing
    • There is agreement that the biggest impact looks to be on Sunday from this storm, but the effects will be felt on Saturday and probably Monday as well.
  • Snowfall
    • GFS calls for about 2 inches of snow in the Castle Rock area while the Euro calls for about 20, so we can take an average of that: 11 inches roughly. If you take all the models together and pick a range, we are looking at anywhere between 0-30 inches of snow...
  • Blizzard Conditions?
    • From the data I am seeing so far, this storm does not look as windy as the last one that brought big snow and big drifting. This still has plenty of time to change but not looking like blizzard wind conditions at this time.

Summary

At this point in time, with the storm still several days away from arriving and not even on the coast of the U.S. yet you will probably hear everything from 3 feet of snow to no snow at all from the media and other weather forecasters. One way or another, neither of those predictions are right or wrong. Meteorologists all look at the same data but have different interpretations and instincts. I don't steal other's forecasts I make my own; often times I'm right but sometimes I'm wrong. That is the nature of being a meteorologist!

The best advice I can give at this time is stay tuned. I don't expect the forecast to change a whole lot on Tuesday or Wednesday because the storm will still be off shore. We should begin to see model agreement by Thursday which could mean major shifts in the forecast.

Stay with us and we will update as new data comes in and we will also have updates should any major changes to the forecast look likely.

On another note: thank you to everyone who has followed me that last few days. I've enjoyed reading and replying to all your comments and enjoy discussing our awesome Colorado weather with you all!

~John