Weather without the hype: Wednesday’s weekend storm update

Weather

Compared to 24 hours ago, there is actually greater disagreement about the path of the storm over the weekend between computer simulations of the atmosphere.

We continue to have a noticeable degree of uncertainty that remains in the forecast as a result. Investigate for yourself with this slider comparison.

Use the slider to look at the difference on Sunday morning between the American and European forecast models. There is greater disagreement on the track early Wednesday compared to the last few days.

The farther south the track of the circulation is, the greater the impacts will be over southern Colorado. A more south track brings more areas over the plains accumulating snow. You can use another slider comparison to see the difference.

Use the slider to compare the different forecast snow amounts and pattern between the American and European forecast models.

The amount of snow a particular area receives through the storm is important this weekend. The farther south the storm, the more areas will see hazardous travel as the wind increases Saturday night into Sunday.

So how will these questions get answered? We expect a unifying consensus over the next several days as we get more information about the storm.

This will come because of a couple reasons. The eastern edges of the storm get over land which allows us to observe and measure the storm’s impacts at the ground. We also launch more and more weather balloons into the storm around breakfast and dinner. These balloons carry a suite of weather instruments, called a radiosonde, that measures temperatures, moisture, air pressure, wind speed and direction as the balloon ascends vertically into the atmosphere – helping us get a better three-dimensional understanding of the storm.

The U.S. National Weather Service and other meteorological organizations across the world launch weather balloons at two agreed upon times each day to measure the atmosphere in 3D. This information is helpful in producing accurate forecasts. The balloons expand as they ascend and air pressure drops. The balloons usually burst after two hours and can travel more than 100,00 ft. vertically and more than 180 miles from the launch site.
The blue dots indicate sites over the western United States that launch National Weather Service weather balloons two times each day.

It does appear this morning that the storm will “get going” a little bit slower on Friday, with rain and snow confined to the mountains and areas very near them through the day on Friday. The storm will be in the southwest part of Colorado by Saturday morning and most areas should begin the weekend with rain or snow.

That is likely to change during the day on Saturday. We’ll still be ahead of the storm circulation and one of the things we need to figure out for Saturday is a dry punch of air coming up from the desert southwest. Where does this dry slot end up and how significant is it? This will be a big player in where the rain/snow line is too. We don’t have the answer to this yet – so stay tuned!

Southwest flow over the plains on Saturday afternoon is likely to bring dry air overhead.

As the storm circulation moves from the mountains onto the plains early Sunday a couple of important things will happen. The rain/snow line will drop in elevation and the wind will rapidly increase out of the north on the west side of the storm circulation. For areas that are seeing snow and have snow on the ground travel conditions will become very hazardous prior to daybreak.

By Sunday morning the storm circulation should be over the eastern plains and wind will be increasing very quickly on the backside of the storm.

The wind will get stronger after sunrise on Sunday and some areas will see wind gusts between 40 and 65 mph. Over the Palmer Divide this air is squeezed into a smaller space as it goes up and over the hill separating the South Platte River valley in the northeast quadrant of the state from the Arkansas River Valley in southern Colorado. This often leads to increase in wind speeds from Monument to Limon and from Colorado Springs eastward into Lincoln County. It’s highly likely that a Blizzard Watch or Warning will be issued by the National Weather Service for the Saturday night and Sunday timeframe for areas that get snow.

Given the information that we have this morning, historical records of storms, my 20 years of forecasting expeience in southern Colorado, and the conceptual model of the atmosphere I have in my head, this is a reasonable expectation of what may happen regarding snow amounts this weekend. It is purposefully broad right now as there are still more things to figure out! Notice how I keep saying that? Check back with us over the next few days.

My greatest confidence lies in a couple things:

  • The heaviest snow in Colorado should be from the northern Pikes Peak region to the Wyoming border.
  • The mountains will get heavy snow.
  • The Pikes Peak region (northern slopes of Pikes Peak, Rampart Range and northern half of El Paso County) will have the heaviest snow and greatest impacts.
  • This is likely to include blizzard conditions developing Saturday night and lasting through Sunday.

My greatest uncertainties are:

  • Where is the rain/snow line on Saturday.
  • How significant is the dry air punch into southeast Colorado.
  • Is the storm track far enough south to bring areas over the plains southeast of Colorado Springs snow and whiteout conditions on Sunday.

Here’s a simple graphic to try and help give you a sense of timing about how travel conditions are likely to deteriorate through the weekend.

It’s possible we are still dealing with some ground blizzard conditions over the Palmer Divide early Monday morning. Drifts may be significant in these areas. Stay tuned!

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