Unsettled weather next week: How do we know anything this far out?

Apprehension when it comes to long range forecasting is palpable amongst those that are trying to interpret it, and those that are trying to write it - what can we possibly know more than 3 days out?

In the wake of some impressive long range signatures of unsettled weather next week in the Black Hills, it’s a perfect time to ask some questions

  • “How do we know what we know this far out”
  • “What do we NOT know, and why don’t we know it?”
  • “What helpful information can we discern from these forecasts”

There are volumes that can fill libraries on the subject, but in the interest of a quick overview and not putting the reader to sleep lets break down some of the basic concepts of next week, as a prime example.

Jet Stream

The Jet Stream: An atmospheric superhighway of fast moving air high in the atmosphere. It controls the traffic of cold air, warm air, moisture, storm systems, seasons, you name it. If you want to learn more about jet streams, you can check out this article on the jet stream by Joey Kragness.

The jet stream is a massive, global network that circumnavigates that globe – It’s large, lumbering size makes it easier to forecast than smaller, mesoscale (small scale) features in weather such as thunderstorms or snow accumulations. Removing small scale factors and isolating large scale features like the jet stream helps computer models put out a more efficient product, farther out in time.

So for instance, next week the jet stream shows us three things for Wednesday through Saturday –

  1. The jet stream is dipping into the west coast, allowing cold air to spill into the intermountain west.
  2. The rising motion of the jet stream (south to north) indicates unsettled weather. The leading edge of a rising jet stream encourages counter-clockwise spin in the atmosphere… rising motion.
  3. The location of this “rising motion” is likely to descend off the rocky mountains into the front range, deepening into a potential storm system. If there is moisture present…. you have an even stronger storm system.

Regardless of location this has the markings of a powerful trough, many would consider this enough evidence to ring the alarm bells of an approaching storm system, but there are a few factors to consider.

  1. Although the broad nature of the jet stream does give us a “ballpark” location of this potential storm system – This could be as broad as New Mexico to North Dakota.
  2. The speed and angle of the approaching trough can shift a storm timeline by 48-72 hours.
  3. If the trough doesn’t line up correctly, it could starve the storm system of moisture, or not provide enough cold air to render snow even possible.

With these thoughts in mind, it is left to the meteorologist to recognize patterns, flaws, climatology, kinetics, bias and many other factors that can influence forecasts into giving you false information.

Picture 1

Models don’t talk to each other very well – so it’s up to meteorologists to piece together different pictures and to draw our own. Take for example this 6-10 day temperature map… It shows high confidence in colder air in the west and warmer air in the east. This has historically preceded large scale events along the front range… notice the slim gray area carving up the front range. This is a CLASSIC setup for many storm systems we have seen in the past. Think of two boxers, red and blue fighting it out, with the punches landing in the gray area… easy to see why there is heavy speculation of possible storms. The evidence is stacking up.

Picture 2

It can also be beneficial to add obvious maps such as long-range forecasted precipitation. It shows a mess of unsettled weather across the great plains and intermountain west… this map is not very confident in the location of any potential heavy precipitation, so its spread out across a large area.

So what’s the conclusion?

There is high confidence that a powerful trough will cross the front range of the United States sometime between Wednesday and Saturday of next week. This will likely produce a storm system, dragging cold air from the Northwest and warm, moist air from the southeast in a massive counter-clockwise spin. this storm system will follow the jet stream like a train on train tracks. Right now those train tracks are laid right across the front range and the Black Hills Region next week.

This will likely mean a cold front sometime between Wednesday and Friday, increased winds before and after the frontal passage and a likely strong storm system passing through or close-by the Black hills. It is unclear whether this storm system will have access to ample moisture.

The uncertainty lies in a couple things:

  • How fast does the jet stream push east… will the storm move east of us and leave us on the colder, drier side of things?
  • Will the trough be as strong as forecasted? If not, then a strong storm system will not be given the amplified energy to rapidly deepen and strengthen.

One ace in the sleeve we have left are trends.

  • Yesterday’s models had a weaker, faster jet stream. Today has a stronger, slower jet stream. We are trending stronger

Trends are a powerful force in forecasting and meteorology, allowing to see which elements are weak and undecided, and which ones are consistent or gaining strength. With each passing day, there is growing clarity as more factors become consistent, weaken or strengthen… allowing meteorologists to communicate potential impacts with more confidence.

Waiting on this clarity is frustrating, and tests the patience of both readers and authors of forecasts. Sometimes, trends and models have no consistency or clarity whatsoever only a few hours before the start of a storm… and that’s when meteorologists have to make some tough calls. Thankfully, we still have plenty of time – and this is one of the few cases where a strong argument can be made for early predictions into next week… given consistent signatures from upper level patterns and climatological factors such as past storms.

So… in short? Let’s stay tuned and watch the forecast evolve together, and continue to have open ended conversations.

Thank you for trusting us with your forecasts.. both large and small.

Brant

 

 

Categories: Local News, Weather Daily