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Monday, December 19, 2016

A little snow late this week and details regarding our post-Christmas thaw

We took a couple of gut punches Sunday and we should prepare ourselves for 1-2 more before 2016 comes to a conclusion. The blocking at high latitudes is diminishing and some key teleconnection indices are turning and will continue to turn toward numbers supporting some late month adversity. We've talked about it a few times but the region of the planet that will key some of these changes occurs between 110 west longitude and the International Date Line (180). Across western North America it will be the dropping PNA index which will show up as a very definable and persistent west coast jet stream trough. Farther west over the Pacific Ocean, it will be a tightening jet stream which will promote a retreating polar jet.

We do have some snow to talk about this week fortunately. It comes from an Alberta Clipper type system which we hoped would get an infusion of moisture and energy from the Atlantic Ocean. It doesn't appear that any such infusion will happen in a material way but the limited available moisture will result in some snowfall beginning early on Thursday and continuing as some snow showers Thursday night. It looks like a 2-4 inch event right now but this could change as the final track of this storm is fine tuned over the next day or two.

Temperatures are generally going to stay below the freezing mark through Christmas Eve and that's about the time when the trouble could start. The European model and some of its ensemble members showed us a glimmer of hope over the weekend. They showed us a "way out" or at least a "way through" this potential late month mess by showing arctic air, which will remain close by in Canada, reestablishing itself over New England even as much of the rest of the eastern United States stays relatively mild. This however was not the weather picture that was painted both Monday morning and afternoon. All three major ensembles key in on some of these important teleconnection indices discussed above and are showing two surges of mild air next week. One which will probably last about a day and could feature some rainfall around December 26th or 27th. After a brief chill down, another surge of mild air and potentially another rain event could hit around the time of December 30th. Given that all this is still a week or more out, one has to respect both the colder and the milder weather pictures. I think some of what the Euro suggested over the weekend could be incorporated into next weeks weather forecast ultimately, but I also think it will be very difficult to find a way through to 2017 without a major outbreak of mild weather,  which will include a day of 50-degree temperatures more significant rain and some substantial damage to our base.

Beyond the time of  New Years Day there are no glaring indications of a return toward a colder pattern. The best piece of information out there is probably the MJO and EPO forecasts which are two indices that are correlated. The MJO or the Madden-Julian Oscillation described convective cycles in the lower latitudes of the Pacific but the various phases of the MJO can correspond to the tightening and loosening of the jet in the Pacific. We are expected to return toward a phase in the MJO which supports a loosening of the jet stream in the Pacific by around the New Year. Thus the EPO or the Eastern Pacific Oscillation is expected to go from positive to neutral after about two weeks time. Aside from these items there isn't much else. High latitude blocking is expected to be glaringly absent late this month and there are no indications it will return, even around New Years Day.

1 comment:

2 Castlerock said...

Naughty. No gifts for you.