THE FIGHT IS ON...
Last week I made a post entitled "Loaded for Bear". The emphasis was on a pattern that was energetic, full of potential for stormy weather, but challenging to forecast due to high latitude blocking. What's blocking? Feast your eyes on this 500mb jet stream configuration off the EURO for the evening of December 15th. All the red across Canada is high pressure, ridging in almost a horseshoe like configuration across northern Canada.
All that high pressure acts as a block forcing energy and storms underneath it in the Continental U.S. The high pressure by mid-week is also beginning to assert itself by displacing cold air relative to average and transporting it into the center of the nation as well. The EURO is all in on this idea as you can see in it's temperature departures around December 22nd. Readings from Montana and Wyoming into the central Plains are shown 40 to 55 degrees below normal! You can see in the lower right hand corner of the graphic someplace (most likely western Montana), is pegged to be 58.7 degrees below the norm. However, well into Canada, especially NW of Hudson Bay temperatures are as much as 25 degrees above the averages. The flip flop is the displacement of cold air that I'm talking about.
If the EURO has the correct idea, this could be one cold Christmas. Today's run shows lows in my area 15-20 degrees below zero in my area Christmas morning. That's a good 10-12 days away so the details and intensity of the cold remain unknown.
What's extremely interesting is the EURO MJO, (Madden Julien Oscillation) is moving out of phase 3 into 4, and 5 December 18th through Christmas.
Those are essentially blow torch phases with each one signaling well above normal temperatures.
However, we see the EURO ensemble depicting bitter cold. What is up?
The only thing that makes sense is that the AO (Arctic Oscillation), the EPO (eastern Pacific Oscillation), The NAO (north American Oscillation), PNA (Pacific North America Oscillation), and WPO (western Pacific Oscillation) are all in cold phases. The strength of those 5 teleconnections in tandem seems to be overpowering the MJO. Either that or the EURO is going to bust badly toward warmer temperatures. I see now that the GFS is also moving towards the bitter cold solution and that is a big card to play.
As badly as models have been performing in the long range, I'm not sure whether to bite the carrot just yet. I have mentioned an Arctic intrusion around this time several times so I feel the potential is very much there but my confidence is currently low to moderate on such an outcome until I see at least a couple more days where this trend is represented. Stay tuned.
Short term a big old upper air low is going to close off and spin northward until if runs into the blocking. Once that happens, it takes an eastward jog (the path of least resistance). Over the next 6 days you can watch the evolution of the 500mb energy as it does what I explained.
Overall there is now good confidence in this scenario. What that means is Tuesday SE winds and moisture will be in the increase. However, the mild air is only slowly entering the system so another chilly day is expected with mid 30s north to low 40s south expected. Later in the morning rain develops in the south and spreads NE into the rest of my area by evening. Aside from rain, wind will be an issue into Tuesday night with the potential for gusts to exceed 40 mph out of the SE. Tuesday is not going to be a pleasant day.
Late Tuesday night an in-wrapping dry slot spreads in from the W/SW cutting off moisture and the mechanism to drive precipitation other than some drizzle by morning. Steady or rising temperatures are expected.
By this time another nice precipitation event will have unfolded with many spots picking up 1/2 to as much as an inch of rain with standard deviations of 3 to 4. The EURO shows this for rain through early Wednesday.
The GFS indicates this for the same period.
Wednesday under the influence of the dry slot there could be a few breaks in the clouds, especially in the south. Precipitation looks minimal unless its some spotty showers or drizzle, mainly in the far northeast. Temperatures will be warmer ranging from the 40s north to perhaps the low 50s south. Winds will be lighter, especially in the afternoon as the stacked system gets closer. Early Wednesday night some fog is a distinct possibility until the occluded front passes through late in the night.
Thursday through Friday night the upper air low dumbbells' into Wisconsin allowing the system to go cold core which allows colder air to sweep in on the backside. Light snow or snow showers are expected to develop. The intensity and coverage will be dictated by the precise track of the center. The north closer to the core will have the best chances for enough wrap-around to get some light snow accumulations. The EURO suggests an inch or two is possible, especially near and north of I-80 with lighter amounts around 1/2 inch in the far south.
The GFS with a bit more northerly track keeps amounts in the north to about an inch with only trace amounts in the far south pointing to the importance of the precise path.
Once this is out of our hair, things turn cold and relatively quiet over the weekend and into Monday of next week. However, energy is already pouring into the pattern and there is a chance of more snow the 19th and evidence of another potential storm that could impact the Midwest around December 22 or 23rd. Indications are this could be a a decent snow producer. The track will be critical to amounts and it's far too early to get into that.
That's if for the here and now. Roll weather...TS