Western North America on the long term 2 Dec

Hey guys, this is the Snowy Hibbo for the first Northern Hemisphere long range outlook, the North American Snow outlook. For those who don’t know what I do, I look at the EC Monthly charts and the CFS charts, and explain the output. This year I am going to talk more about the climate drivers. Anyway let’s start….

19-21 Dec

It starts on EC Monthly, as a massive system that slams into California and the PNW, giving heavy snowfall on the late 19th and early 20th. But it weakens over the next day or so, bringing moderate snowfall to Utah and Idaho and surroundings. CFS shows a deep low coming over South BC and the PNW. It brings heavy snowfall on the 19th into the 20th, dissipating over the Inland PNW. The Bering Sea Rule(organic forecasting technique) shows potential for upper level troughing in California, the PNW and the US West Coast in general over the 20-22 December period.

22-24 Dec

It is a similar system to the previous, slams into the Sierra Nevada and PNW with heavy snowfall overnight 22/23 Dec on the EC Monthly. It then weakens over the Rocky states, bringing light-moderate snowfall. CFS shows a system during this period, with precipitation stretching from Northern BC to SoCal on the 22nd. It weakens over the Rockies by the 24th.

24-26 Dec

Heavy snowfall is brought by the NP jetstream to South BC and Washington as a Christmas present to those mountains. Early Boxing Day shows it contracting to light snowfall over the Inland PNW, according to the EC Monthly. CFS yet again shows another big low, blasting heavy snowfall to the Sierra Nevada and PNW over late 24th and 25th. It shows moderate snowfall across the Rockies and the Sierra Nevada over late Christmas Day and into Boxing Day. Over the 27th, the moderate snowfall moves to NM and AZ, before weakening later that day.

27-29 Dec

EC Monthly shows the jet slamming another system onto BC and the PNW early on the 27th, but it continues over the PNW and down to UT/CO, before fully weakening by the 29th. CFS shows the jet slamming into the PNW and NoCal late 27th and into the 28th, but it doesn’t get further inland than the Sierra Nevada and Cascade ranges.

28-30 Dec

EC Monthly shows yet another system, slamming into the South BC and PNW regions early 29th Dec with moderate snowfall, before weakening by the next day over the Inland PNW. CFS shows two weak small systems, bringing light-moderate snowfall for Southern BC/Washington and Tahoe on the 29th.

30 Dec-1 Jan

EC Monthly shows a wider system, stretching from BC to NoCal. This produces heavy snowfall for BC, PNW and Tahoe. It continues to the Rockies and gives the region a heavy dose of snowfall by New Years. CFS shows a slamming of the NP jet into South BC and the PNW over the 30th and 31st, producing moderate-heavy snowfall.

31 Dec-2 Jan

EC Monthly hints at another system hitting BC New Year’s Day, with exciting snowfall prospects. CFS also shows a system hitting BC on New Years Day, with potentially very heavy snowfall on the BC Coast.

Climate Drivers

The Arctic Oscillation is forecast to go negative on GEFS for the first half of December. This typically means a higher chance of ridging across the Western USA. CFS also shows a -AO outlook for the entire month of December, which may mean less snowfall for the West.

This chart mirrors CFS’s prog for high latitude blocking(-AO) until Mid January.

CFS also produces a chart for the PNA, which shows a +PNA for December. This correlates with ridging in the Western US.

However the PNA is expected by CFS to switch to a mostly -PNA pattern in January, which favours troughing in the West.

The last CFS chart I am going to review shows the Stratospheric Polar Vortex status.

GEFS(and EPS and most other models) forecast a weakening of zonal winds around the polar vortex, which creates a weakening of the vortex, which in turn creates a -AO. CFS shows a restrengthening of the zonal winds later in the month, which could make a better setup for the West. But it shows weakening of zonal winds beyond late December into the new year, which could induce another -AO setup.

The MJO is forecast by most major models to go under a Phase 4-5-6-7 regime, and possibly beyond that.

EC Monthly shows this perfectly. GEFS is going for a stronger MJO, compared to EC though. MJO Phase 4-5-6 plus about a week, gives good potential for an atmospheric river event for the US West Coast if the other factors align. MJO Phases 6-7 however are correlated with a Sudden Stratospheric Warmings, which create a -AO setup, meaning less snow for the West.

AAM is currently forecast to stay negative, which also correlates with a -AO. East Asian Mountain Torque is currently weak, creating a more negative AAM and also weakening the North Pacific Jetstream, which weakens precipitation for the US West Coast.

So the overall climate driver outlook is for a -AO setup, that creates a +PNA ridge across the Western US, and a trough over the East. Therefore more snow for the East, and less snow for the West. However early January does look somewhat better.

Thanks so much for reading. I hoped you enjoyed it….

Disclaimer: There is low skill asssociated with using long range model forecasts to find snow systems. All systems you see here will change, as the date gets closer and may not eventuate all together. I don’t give much accuracy to these forecasts, but you can give these a bit of your time and your dreams might come true 😉 I find the chase of these long range snow systems awesome, so come and join me! The climate driver forecasts tend to have a bit more skill than the model forecasts, but certainly don’t put all your money on them. However, climate drivers are an awesome tool to explain the weather around us.

Thanks again for reading this Western US long Range snow forecast, follow me on Twitter @longrangesnow and subscribe to my email list by clicking on the tab on the main header above

edit: image links fixed.

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