Update-12/24/14>>>Extended Models Intimating Notable Pattern Change Christmas Week - HO HO HO?

12/24/14-Update 230p
Very little change from earlier thinking, any residual moisture behind this system will fall as rain and snow showers. Temperatures will be contrary to any snow accumulations except possibly in the Saginaw Valley where moisture will be last to leave and temperatures first to fall. Any light accumulations would be on grassy areas in that area and mainly an inch or less. Overnight lows will fall into the 30s to around 40 and hover in that range Christmas Day.

Latest Indications Point To a Wet Christmas Eve & Light Snow and Snow Showers For Christmas Day  

A reasonable pattern evolution of the Christmas week storm is unfolding for the Great Lakes and Southeast Lower Michigan. The storm development previously blogged below, remains intact while the Great Lakes tract depicted as one of the possibilities, the most likely winner. 

Jet structure and max winds depict a large negatively tilted trough developing over the region on the 23rd into the 24th, Christmas Eve. At the surface, a deep cyclone will develop along a slow moving - quasi stationary cold front extending from the Gulf States northward into Lower Michigan during the day on Christmas Eve. This deepening storm center will pull substantial moisture and moderate warmth northward into the Great Lakes and Southeast Lower Michigan in the form of rain on the 24th and then light snow and snow showers Christmas Day. With any luck, we'll see enough snow showers on Christmas for a "snow in the air" Christmas but I wouldn't count on an official "white Christmas" this year - at least as things look now. I wish I could be more hopeful for a white Christmas but possibly enough moisture will remain behind the system in the seasonably colder air to generate the inch needed /per GFS/, so will update as the time rolls on closer. Speaking of "White Christmas" look for my annual "Ghost of Christmases Past; The Whitest of Christmases and Other Christmases Past, shortly. 

Surface Maps Particulars

Note the European is faster and further north with the low over Lower Michigan by Christmas Eve 7AM, whereas the GFS brings the center into the region by Christmas Eve 7PM.

Then by Christmas morning on Thursday, the Euro has the center of the storm
well up into Canada where as the GFS holds more moisture and energy aloft along with the surface reflection over the Great Lakes and thus, a better chance for light snow and snowshowers.

Look for a further update early this week.
Merry Christmas & A Happy and Healthy New Year

12/15/14 - Initial Post

Meteorologists and Weather Enthusiasts have seen it before, too many times to count in extended model la la land, an overhaul or notable change of the prevailing pattern being suggested a week to 10 days out. This time, the pattern change is rather strongly intimated by the GFS and European model right around Christmas - or at least Christmas week /22nd-28th/. Each day something new and different pops up; a snowstorm for the East Coast, the Midwest or the Ohio Valley and Great Lakes followed by a sharp cold blast in its wake. The only thing for "certain" is that an overall Jet Stream pattern change will evolve sometime the latter part of December and that will likely create a mess for someone (more further below) around the holiday.

Autumn into Early Winter 

No one has to be told it's been a rather tranquil and boring beginning of the meteorological winter /Dec-Feb/ and this coming after a rip-snortin' unusually cold, blustery and busy November (which had its deep cold roots in place by Halloween time). Looking back, the pattern this fall into early winter was well projected by upper air and surface patterns of the past with similar hemispheric traits in the Autumn Outlook.

Fall is cited for its wild swings in temperatures and this fall certainly should be no different as impressive upper lows in Canada dive south and southeast into the U.S. The aggressiveness of this overall, now common-place pattern shows little change in the last year. Both upper air and analogues also do suggest typical to strong cold outbreaks along with some contrasting upper ridging to bring classic Indian Summer weather.

Oscillations of upper and related surface patterns with a preference toward troughing and cooler than normal weather should be balanced out somewhat, leaving us with an average or normal fall with notable sharply contrasting patterns. I look for temperatures to average around normal...or within two degrees of the normal. 

As it turned out; temperatures this past autumn did fall well within the projected spread of the selected analogues and Outlook across Southeast Lower Michigan averaging exactly a degree /-1.0/ below normal at 49.8 /norm 50.8/. September and October averaged near to slightly above normal where as our cold November, averaged well below normal.

This "now suitable, now brutal" kind of weather regime was projected to persist into the winter with strongly oscillating weather patterns resulting in cold, mild, stormy and tranquil kind of winter. I bring this all up because as you know; recently we've had a few weeks of the rather tranquil weather to start off December and the winter thus far - BUT there is a change afoot!


Back to the present and future...

Many meteorological indicators are pointing to a colder and stormy pattern with this change, certainly not uncommon and pretty much expected. It's the questions of where (and thus who), what and when that have to be answered.  The NAO and AO both are pointing to radical hemispheric change later in the month while the PNA remains weakly positive (or suggests troughing east of the Rockies). Both the NAO and especially AO are rather extreme with their collapse into negative territory (likelihood of colder weather). There still are variances in the overall decline from positive to negative and thus, problems in forecasting are strongly affected.




It is easy to see as both oscillations advanced into their positive phases beginning in December, the month became more tranquil and progressively milder over Southeast Lower Michigan, the Great Lakes and East. And generally, when there is a notable change like this projected there is a storm-a-brewin for someone and some part of the country. Here's some scenarios spit out by the GFS & European models for Christmas time.


Dec 15th 00z GFS, Snowstorm for the Eastern Lakes Christmas Eve 12/24>>>


This morning's, Dec 15th 12z GFS run (note the storm is again over the Eastern Lakes but it's now Friday morning 12/26)


The Dec 15th 12z Euro has a different view, she puts most of her eggs in a Northwestern Lakes Low Christmas Eve Day with a second forming just west of the Appalachians but as you can see (second map below), it undoubtedly makes headway toward the Northeast Coast just in time for Christmas



Of course, there is a lot of time between now and Christmas week and thus, numerous scenarios will be created in model la la land. In the meantime, it would be prudent to keep abreast of this change in the weather projections since it is definitely a heavily traveled time.


As the time gets closer I'll look at what's the most likely scenario - and where and when.


Merry Christmas & A Happy and Healthy New Year

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian

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