Joe’s Weather Blog: Another run of warmth is starting (TUE-12/7)

Weather Blog

KANSAS CITY, Mo. — If you didn’t read the Winter Forecast blog yesterday, you can check it out here.

The weather pattern is now gradually shifting back into a warmer regime that will continue (with a few brief interruptions) all the way into Christmas week. There are some signs that maybe during Christmas week a colder setup will materialize, and perhaps a more wintry setup as well in terms of risks of snow or “something,” but that is about two weeks away. Until then, there may be opportunities to challenge record highs, including one this week.

This blog will be getting into the weeds somewhat and speculates where things may go towards Christmas week based on various indices and looking into the tropical Pacific.

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Forecast:

Today: Clouds this morning with developing afternoon sunshine. Breezy and cool with highs in the 42-45° range but with the breeze going it will feel colder.

Tonight: Fair skies and seasonable with lows in the mid-20s.

Tomorrow: Nice overall with highs 50-55°.

Thursday: Warmer with highs back into the lower 60s.

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Discussion:

We sit and wait for our first accumulating snow. While that sounds “sexy,” really for Kansas City, it isn’t at this point of the month or season. We typically wait for our first “measurable” snow (1/10 inch or more) until Nov. 27. Then our first inch of snow on average is around Dec. 15, so this really isn’t that crazy.

Other cities though, different story. Denver… still waiting. Salt Lake City… still waiting. The setup though this week does favor some late-week snow for both cities so that may indeed change.

So far this month, even with yesterday’s chillier day, we’re running over 11° above average. This is the 11th warmest start to December, granted though small sample size.

We’ll wobble around a bit for the next few days but as we head towards next week, we’ll go up the list once again.

So we start this off with a look at the 8-14 day forecast. Remember these are probabilities: the darker the red colors, the higher probability of warmer-than-average temperatures.

This is pretty impressive. That swath of darkest red is pretty stunning for December.

So really what more is there to say. This would be for the middle and end of next week.

So you can see the trend is warm, and the first half of December will likely end up being in the top 10 of warmest starts to December in Kansas City weather history, perhaps even top five.

Let’s go farther down the road and take the ensemble gander at day 16. This would be for the 21st heading into Christmas week. The chart below shows the 5,000-foot temperature anomalies.

6PM December 21st

I’ve outlined the colder regime that is sitting up across southwestern Canada and into the western U.S.

As we head towards Christmas week, that air mass in western Canada will need to be watched. There are a couple of “teleconnections” that are starting to show signs that that cold air could be brought down into the U.S. in some form. The ones that I’m talking about are the Arctic Oscillation (AO) and the North America Oscillation (NAO). We’ve talked about these before. Let’s start with the AO, and in particular we’re looking at whether each index is either positive or negative and by how much.

When the AO is positive…the colder air typically stays bottled up in Canada
When the AO is negative…this colder air can be brought southwards into the US.

Take a look at the model forecasts for the AO values, both the EURO and the GFS.

Slide right for the EURO and left for the GFS

In particular, look towards the week of the 21st or so. See the reversal on the EURO? The GFS doesn’t do it. You can see the raging positive values connected to our warmth coming.

Another index that we look at is the NAO. When negative, higher risks of colder air. When positive, opposite.

Via CPC

Both indices are connected to pressure patterns in various parts of the northern hemisphere.

Here are the two models showing the trends:

EURO slide right…GFS slide left

Again, you can see the drop off the cliff on the EURO more so than the GFS. The GFS does go negative towards the last week or so on the chart, Christmas week.

When they work in unison, odds increase or decrease on the colder air.

There are certainly other tools in the toolbox including tropical forcing. Believe it or not, what happens in the tropical Pacific, from south of Hawaii all the way westwards to the eastern coast of Africa. It makes sense because the waters there are at their warmest and various areas will flare up with immense and large-scale thunderstorm areas that in turn influences the atmosphere through a variety of processes all the way through the northern hemisphere. We study these influences using the MJO or Madden Julian Oscillation.

Here is a FAQ from the CPC:

  1. What is the Madden-Julian Oscillation (MJO)?
    The Madden-Julian Oscillation (MJO) is a tropical disturbance that propagates eastward
    around the global tropics with a cycle on the order of 30-60 days. The MJO has wide
    ranging impacts on the patterns of tropical and extratropical precipitation, atmospheric
    circulation, and surface temperature around the global tropics and subtropics. There is
    evidence that the MJO influences the ENSO cycle. It does not cause El Niño or La Niña,
    but can contribute to the speed of development and intensity of El Niño and La Niña
    episodes.
  2. How does MJO activity vary over the course of the year?
    The MJO is often quite variable, with periods of moderate-to-strong activity followed by
    periods of little or no activity. Because MJO impacts are well known, especially in the
    global tropics, periods when the MJO is active offer opportunities for enhancing NWS
    climate prediction and decision assistance. Typically, the norther

Certain “phases” during the year favor certain weather regimes in the U.S. These have been studied previously and when rain anomalies are maximized in specific areas of the tropical Pacific, they are assigned a phase number (there are other things involved in this but this is the simplest way of looking at it). The phases go from 1-8.

We do know in studying these phases that there is higher correlation in the winter when the MJO goes into phases 7-8-1 that there is a higher likelihood of colder weather in parts of the U.S. Add in the favorable other indices that we look at and if things are working in concert, then a longer-range forecast can be more agreed upon.

These MJO cycles go from 30-60 days or so. This has been around for quite some time. Certain phases favor warmer weather. For the current phase, 6. Others as mentioned favor colder air.

Again, we’re in phase 6. Most models favor a phase 7 towards the third week of December. With the thoughts of the other indices that I referred too (AO/NAO) acting in concert, one can then forecast at least a colder outlook.

Here is a look at how the various phases influence the U.S. temperatures. This is a three-month composite for November through January.

See how phase 7-8-1 are the colder ones? The various pieces of data we have indicate a setup for at least phase 7, perhaps a progression into 8 as well for the end of the month and early January.

Now go back to this chart from earlier in the blog, the day 16 EURO look at the 5,000 temperature anomalies. See that cold air in western Canada on the 21st? Just sitting there.

That cold air should get tapped. Will there be snow cover in the northern U.S. at the same time or will the snow be melted away beforehand? That snow cover could help to sustain the colder air coming. Again, a lot of juggling happening here.

So in my opinion, a return to a colder regime is becoming more likely towards Christmas and into the New Year…

Will that be the time for snow? Well it depends. It very well could be. It just depends on the setups that present themselves. I have a hard time imagining that there won’t be some sort of significant storm towards Christmas week. If we’re going from so much warmth to a much colder regime, that has to bring a storm to the Plains. Where that storm goes though, and what that means for us (severe weather…snow?) won’t show up in the data for another 7-10 days or so. Again you can see how this can progress to a stormier regime in the Plains for Christmas week.

Remember there are strong correlations to not getting December snow and a corresponding lack of winter snow in Kansas City.

That is a lot of travel through the weeds. Hope it made somewhat sense to you…

The feature photo comes from Vicki Anderson Dolt.

Joe

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