THE WINDS OF CHANGE ARE RUSTLING...

Well, after another stellar day of December weather, the drumbeat is not as heavy going forward and that can only mean one thing, the winds of change are beginning to rustle. Before I get to that topic, I'll show some respect for Thursday's temperatures which at peak heating came in like this over the central U.S. Look at those mid 70s in Kansas and Missouri. That's wrong.

Here are the temperature departures. The entire Midwest was above average with much of the central Midwest a good 15-25 degrees above the norms.

That equated to the classic look of the MJO (Madden Julien Oscillation) in December.

Much more to come in this post below following this announcement.

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THE CHANGES BEGIN

Getting back to those winds of change, we won't feel their first impacts until Saturday. Friday promises to be well above normal again with highs cracking the 50s. A front actually does pass through during the day but the cold air lags behind and does not arrive until nightfall. For most it's going to be a dry frontal passage. The exception could be in the far north from Dubuque into NW Illinois where a few light showers could roam around very early in the day.

Saturday readings hold in the low 40s with weak ridging in place. Warm advection is well under way by Sunday morning as a healthy clipper rolls across Minnesota dragging a strong cold front into the region late in the afternoon. Stiff southerly winds should bring enough moisture for scattered showers and perhaps a stray thunderstorm? Instability is limited in the north by highs in the upper 40s. However, much warmer readings are expected in the south where mid to upper 50s are likely. That could produce just enough CAPE for those rogue thunderstorms. As far as rain goes, this system is another that is starved for moisture. The EURO has this for rain totals.

The GFS is in good agreement showing a moisture deprived system until it crosses the Mississippi.

One thing seems certain is the fact Monday is going to be a frisky day. Highs in the upper 20s are likely in the north while low to mid 30s prevail south of HWY 30.

Brisk NW winds will keep wind chills hovering in the upper teens and low 20s all day long. Keep the coat handy!

The next challenge on the table is snow chances next week. The first chance comes with a disturbance Tuesday. Models are still fidgeting around but in general are low on moisture and dynamics and turn this into a light over-running event. The EURO has been the most consistent the past couple of days and right now I like what it's showing for accumulations of 1 to perhaps 2 inches. We're still many days away on this so keep in mind the amounts are just model guidance and not an actual forecast. The numbers will change but hopefully the trends remain consistent.

The EURO

The Canadian GEM (it goes way to the south)

The GFS

Another system appears to be in the cards late next week (December 10th/11th). All models are picking up on the trend but there's a big spread in solutions. Some show snow, some rain, or a transition of one to the other. It's a hot mess. Phasing is going to be a big issue and at this distance I would put little faith in any guidance but just to show you what's on the alter, here's what's currently indicated for snow totals. As you will see there's no consistency.

The EURO

The GEM

The GFS

Something I am pleased to see is the long range EURO which now shows the MJO moving strongly into phase 7 around December 20th, and remaining there the rest of the month before entering phase 8. I'm hoping it's "lucky phase 7" for me as that correlates well with below normal readings. Phase 8 is even colder in January and that implies the potential for some "frigid air" if we can get there. There's also a stratwarm to consider which really enhances it.

I talk about the MJO on this site on a regular basis in winter as it's the best teleconnection available to see pattern changes. Many of you have inquired as to what the MJO actually is? NOAA states: "Unlike ENSO, which is stationary, the MJO is an eastward moving disturbance of clouds, rainfall, winds, and pressure that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days, on average. This atmospheric disturbance is distinct from ENSO phases (such as the La Nina were in this winter), as once they are established they are associated with persistent features that span several seasons or longer over the Pacific Ocean basin. There can be multiple MJO events within a season, and so the MJO is best described as intraseasonal tropical climate variability (i.e. varies on a week-to-week basis)." The 8 MJO phase regions are shown below.

Often convection along the Intertropical Convergence Zone tends to focus most on the Indian Ocean to central Pacific which is where the MJO is measured. That is because water is warmest there, climatologically speaking. The phase of the MJO is determined by the location of the existing convection. It's that basic convective energy that drives the downstream pattern across North America. The MJO can give us a heads up where our weather is trending well before models see it.

In La Nina's like we are experiencing this year, the eastward progress is slowed by the coldness of the water. That may be why the MJO is currently forecast to only ease its way through 7 towards 8 in the next 3 weeks. You can see the cold Pacific equatorial waters nicely in the above graphic in blue.

Another thing that excites me is the EPO (EASTERN PACIFIC OSCILLATION) going negative on the EURO Weeklies. Most of November it's been well into positive territory but around December 18th it starts trending negative and goes deep into the tank January 8th. The EPO is critical because it signifies ridging over western North America and that opens the door to cold throughout the heartland.

The 7 day temperature departure December 23rd-30th on the weeklies is getting chilly.

It's growing even colder January 10-17th. What I like about this set-up if it holds is that we are in the cold air but the reds to the southeast indicate ridging. That keeps my area just NW of the storm track, a good place to be for snowstorms.

Had enough yet? Okay, I'll stop it there. Have a happy Friday and roll weather...TS

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