Major Pattern Changes On The Way

8-16 day temperature anomalies from the GFS are showing the very cold air across alaska, B.C, yukon and northern prairies moving southeastwards. This air mass is probable underdone for the east considering hudson bay is already beginning to freeze over so above normal departures are very unlikely which present big implications on the model which is not picking up on this. 

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Snow Cover:

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Watch the warmth fade away on the GEFS:

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Long range 500mb height anomalies depict a strong trough in the east:

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The deep snowpack in the NW at hour 192 argues for an air mass that is continuing to get colder and when it is triggered to come eastwards will be very cold.

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Indicies support this change with a tank in the ao and nao:

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PNA still negative so expect cold centered in the east but trough nationwide with widespread cold across southern canada and an active storm track. An alaskan ridge will pump and hold allowing this frigid air mass to move eastwards. The pattern change is coming and in a big way without any stratospheric support. As stratosphere continues to warm through december a sudden warming event may occur(favoured in an east QBO year) which would lock in a cold january.

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Southern Ontario First Significant Snowfall

The GTA and the golden horseshoe will experience its first significant snowfall of the season tomorrow. Light flurries will begin tonight with light bands of snow moving through the area after the midnight hour. As the night wears on, the snow will begin to pick up in intensity around 9 AM with more consistent bands of snow around the west end of lake ontario in particular which could pick up some precipitation enhancement from the lake. By 11 am the heaviest bands of precipitation will move through SW ontario first with a light burst of snow/freezing rain and sleet before moving northwards and effecting the GTA around noon. This band of snow will slowly move eastwards allowing for light snow to fall from orangeville, through the GTA, niagara, hamilton and the NW shores of lake erie between 10am and the late evening hours. This band of snow will be nothing special for southern ontario but it will promote an ENE to ESE wind off of lake ontario which may work to enhance snow totals. This has been advertised on the RAP, NMM and ARW high resolution models showing enhanced precipitation from hamilton to oakville and even the GTA to a lesser extent. Right now it is hard to tell if and where these bands will set up but my hunch tells me based on wind shear values, light easterly winds and a small temperature inversion that snow will stay light under this system causing 2-5cm amounts across the golden horseshoe. This will be enough snow to coat many cooler surfaces but will not present major problems for road travel. If under the event that lake enhancement does take place these amount can easily double with some areas picking up 5-10+cm of snow. I remember waking up one morning in january of 2011 with a surprise 15-25cm of snow due to lake effect bands off of lake ontario which can pack a quick punch if the correct setup presents itself including heavy snow rates.

NMM Similated Radar:

850mb Temperatures are supportive of snow:

Sounding for mid day friday:

2 Major Storms On The Table For The East

GFS precipitable water at hour 150 shows a system bombing out as it tracks west of japan. This track telleconnects to an apps runner storm track or an GLC track 6-10 days later which lines up with another potential storm between the 10th and 12th of december.

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The EPO is forecast to move towards neutral in that time period which coupled with a -ao and -nao may translate to a sizeable storm. The GFS has really been showing this over the last 8 runs.

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18z GFS:

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Another storm may come into play before hand which will be between the 7th and 9th which has support from the euro but not much on the GFS. A current east asian storm supports this as well. This storm is probably further east and weaker then the first one.

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Precipitable Water:

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Tropical Storm Bopha Recurving

Tropical Storm Bopha is forecast to weaken as it recurves to the east of Japan which will promote a trough in eastern north america in a week to ten days from now.

Forecast Track:

This favours a trough in the east between the 6th and 10th of december which will begin to trigger the pattern change I have been posting about lately. More cold air will begin to usher southwards into the prairies and northern plains before moving eastwards by mid december. Expect the models to trend stronger with this feature as we get closer to the event and warm members turn cooler effecting the mean.
12z GEFS shows the trough:

Even stronger and more frequent trough's will follow suit allowing the pattern change to take place with more western ridging as well as a west based -NAO pattern:

CFSv2 Frigid Long Range, White Christmas For Many

CFSv2 sends the cold charging southwards and is really highlighting the pattern change many have been posting about.
Forecast for the next ten days, ridge is in control but will move out

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Day twenty to twenty-five getting cold:

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Days twenty to twenty five frigid:

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Cold hangs on into January with ridging in the west:

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Predicted snow cover for christmas time will make many people happy:

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For those of us doubting winter, you may end up happy that the cold held off so far because if this turns out correct expect relentless cold for weeks on end and very exciting winter weather. This is still very far out but it is encouraging to see signs of a pattern change from the long range models.

Tropical Forcing Backs Mid December Pattern Change

 The stratosphere has began to warm gradually and will continue to do so over the next few weeks. This is being caused by numerous tropical influences. A major player, the -QBO phase means that warm air from the equator is being transported to the north pole. This means that we are in a pattern that should naturally want to warm the stratosphere, especially as we head into NDJ. In november the stratosphere as a whole has experienced record cold because of above normal solar activity which cools the stratosphere. The sun is quieting down now which will allow the stratosphere to begin warming. 2) Mountain torque values are on the rise in both east asia and north america which act as a trigger for a stratospheric warming event. Above normal torque found near 30N means that we can expect to see the stratosphere begin to warm significantly around the 10th of december. The extent of the warming is still unknown but in east QBO years this is common, usually occurring suddenly.

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Stratospheric temperature change is evident in the 240 hour forecast from the ecmwf:

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This would favour ridging across greenland, a trough over the bering sea, ridge in western canada and trough over the east.

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Remember the fact that modelling is beginning to pick up on this does not necessarily mean that this will occur. It is the observations that i want to look at in order to gain better support for a forecast. Now all of this tropical forcing supports a pattern change to colder weather over central and eastern canada. Now lets see what other indicators we can find too support this. Well we can see the trough recurving east of japan in this time period and AAM beginning to move below normal which supports changes in the pacific, particularly a shift to a -epo and possibly PNA. We need the persistent bering sea ridge to break down in order to bring the cold into the east.

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