Today is the busiest travel day of the year for the US on the eve of Thanksgiving. On the road today? Looks like a tricky drive if travelling west of the Mississippi but up and down the East Coast, your in luck.

Big snows are now affecting the mountains of the West from Sierra to the Colorado Rockies and eventually a heavy snow and ice event takes aim at the Texas and Oklahoma Panhandles of the latest cross country system pull arctic air ever further south.

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Models don’t appear to show the connection between northern and southern branch over the next 48 hours and therefore there doesn’t look to be a major Northeast trough as initially thought. Had there been that phasing or connection between the two branches and warm and cold energy coming together, one could have expected a major snow and cold event to open December.

The below ECMWF shows the arctic air diving south on the backside of the system but notice heights remain strong further east and therefore the system drops into Texas and then lifts NNE to the WEST of Chicago.

Looking out into December and there’s strong support leading to a mild if not warm December across much of the Lower 48.

Despite the cold, snowy West, the models are showing more and more a southern Canada positioned ridge which supports more of a zonal, Pacific flow through a large part of December. It’s looking the same for Europe and throughout the mid-latitudes of the hemisphere. A likely by product of this years strong/super El Nino.

The latest plunge of arctic air looks to be generally confined to the West and Plains and this will gradually decay in the coming days as Pacific air is set to flood the country west to east with a strengthening Pacific jet stream.

There’s clear evidence which suggests for the first time in 3 winters, the Aleutian low will be stronger while the Icelandic low while strong now, may weaker later in the winter.

The Canadian ridge spanning almost coast to coast along with the North Atlantic trough reflective the strong positive NAO/AO and essentially cuts off the arctic door to both the Lower 48 and Europe with a fast flowing, flat trans-hemispheric jet stream that’s flooding both continents with maritime air.

As for the polar vortex, it looks like to hold strong and largely fixed over the pole.

7 days from now.

10 day from now.

GFS ensemble 5-day mean 500mb height anomalies show a more southerly ridge position over south-central Canada and this certainly suggests a milder pattern for much of the Lower 48.

Note the strong Aleutian and Greenland troughs. These will hold the ridge over southern Canada.

Despite the warm outlook, snow cover across Eurasia and the northern hemisphere is very extensive and above normal for late November. This ‘above normal’ snow cover has been linked to a -AO winter but as Dr Judah Cohen states in a recent publication, a lot depends on how active the energy transfer is from troposphere to stratosphere in December. Not a strong enough transfer will mean there’s little disruption to the PV and therefore it stays strong.

I urge caution with the above! Remember what was said in both the Winter Forecast and December Outlook. December was likely to be relatively mild and uneventful. The ocean sea surface temperature profile is very different now compared to 1997. The North Atlantic is opposite.

2015

1997

Notice in the animation below how waters are expected to warm around Greenland and north of the UK into the heart of winter. This at least supports blocking highs.

Another positive factor for us winter lovers here is the models show a stronger Aleutian low/trough this season, something not seen during the past 2 winters and this could suggest a weaker Icelandic low/trough and therefore more positive in the place we want it… Greenland/Iceland…

The Met Office model shows just that for the December-February period.

See today’s video for the discussion.

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