Winter '12 / '13 - The Change

A pattern change appears to be finally in the works as a stable...four wave flow regime with an anti-cyclone parked over the Pole sets up by D+10.

Initial state starts with the 'never-say die' blocking ridge over the Bering Sea and a deep trof in the Gulf of Alaska where SSTAs are below normal thanks to the PDO.

These two persistent teleconnection features have kept the PNA underwater for months...wasting the cold air potential of a negative AO and its sister index..the NAO.

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All that is forecast to change in 10 days as the Bering Sea HIGH becomes pinched off and shoved to a position directly over the Pole...where its circulation is re-enforced by the flow around four trofs at lower latitudes.

 The Gulf of Alaska LOW is replaced by the PNA ridge....achored by a cut-off LOW offshore of SOCAL.  The ridge delivers cold air and short-wave energy embedded in the Polar jet stream into the Lower 48 where it has opportunities to phase with short-wave energy ejecting from the cut-off LOW and moisture transport y the sub-tropical jet stream.

This scenario was more-or-less forecast by PSD's GFS '8-14 day' ensembles earlier in the month altho the model had the change in place about ten days too soon.

Even the GFS shows large chunks of arctic air reaching the Gulf of Mexico and Miller 'A' storms moving along the east coast.

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Images courtesy Plymouth State Wx

Winter '12 / '13 - Arctic Oscillation: Meteorological Winter - Day 15

Not sure what if anything it means but here's the state of the AO on Day 15 of meteorological winter during its 63 year period-of-record.

Blue line is the observed AO on 15-DEC.

Red line is a 9-point binomial filter.  The filter removes noise from the signal to highlight trends.

The 15-DEC-12 AO ranks 19th (25th percentile).

Same idea for AO/s sister...the North Atlantic Oscillation (NAO).

The 15-DEC-12 NAO ranks 36th (57th percentile).

Winter '12 / '13 - Mid-DEC Snow Scenes

Times Sq
13-DEC-33



NYC

13-DEC-60







Haverhill...MA
12/13-DEC-1890



Haverhill...MA

14-DEC-1890

 


Winter '12 / '13 - White Christmas

White Christmas in the US is defined as 1" on-the-ground on 25-DEC.  The criteria are different in other countries.

The probability of an event is determined by dividing the number of times something happened in the past by the number of times it could have happened.

If there was a white Christmas five times over 20 years...the probability is 25% in any given year.

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Folklore predictions...
- A green Christmas; a white Easter.

- If there's thunder during Christmas week...
The Winter will be anything but meek.

- The nearer the New Moon to Christmas Day...the harder the Winter.
[ed:  New moon 13-DEC-12]

- If Christmas day be bright and clear
There’ll be two winters in the year.

- Thunder in December presages fine weather.

- Like in December like all the year long.

Winter '12 / '13 - Go to Sleep and Dream of Snow

Repost from JAN-07...

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Snow
It won't be long before we'll all be there with snow
Snow
I want to wash my hands, my face and hair with snow

Snow
I long to clear a path and lift a spade of snow
Snow
Oh, to see a great big man entirely made of snow


Where it's snowing
All winter through
That's where I want to be
Snowball throwing
That's what I'll do
How I'm longing to ski
Through the snow-oh-oh-oh-oh



Those glist'ning houses that seem to be built of snow
Snow
Oh, to see a mountain covered with a quilt of snow

What is Christmas with no snow
No white Christmas with no snow
Snow

I'll soon be there with snow
I'll wash my hair with snow
And with a spade of snow
I'll build a man that's made of snow
I'd love to stay up with you but I recommend a little shuteye
Go to sleep
And dream
Of snow

Winter '12 / '13 - AER Goes All In for Eastern Cold

Based on Eurasian snow cover in October:  Ridge-W / Trof-E!

From OurAmazingPlanet...

...the model forecasts cold weather through February for the United States from the Rockies to the East Coast, Cohen said...last week at the annual meeting of the American Geophysical Union.

...cold-hardy Alaskans are complaining about the unusually bitter weather so far, counter to the model's prediction. An omega block, a center of atmospheric pressure sitting over the Bering Sea, is keeping the state at below-freezing temperatures. According to the National Weather Service, November 2012 was the sixth-coldest November for Fairbanks on record.

"When the Arctic Oscillation is negative, as it is now, Alaska is supposed to be warm, but it's not...  The North Pacific seems to be doing something separate from what would normally happen," said Cohen.

More...
Cohen/s AGU conference presentation abstract here.

Winter '12 / '13 - Siberian Express

The ECMWF has been advertising a significant cold intrusion into the lower 48 over the past few runs...along with a cross-polar shift of the polar vortex from Baffin Bay toward a position INVOF the south Kara Sea bordering northern Russia.

The yellow region on the map marks the location of 'warm' air at 100 mb.  This area is also where low heights in the troposphere are found.

This Siberian visitor should be enough to change the long wave flow regime just in time for the holidays.

Winter '12 / '13 - VCP 32: What's the Big Holdup?!

Winter '12 / '13 - Eurasia Snow Cover: November

Actual:  22,031,257 km²
Normal:  20,334,319 km²

Eurasia/s November snow cover was one standard deviation (dashed yellow line) and 8% above normal.  Second year in a row November was above normal.



Blue - observations
Red - 9-point binomial filter
Orange - median
Dash yellow - one standard deviation

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Eurasian snow cover and departure from its median year-to-date.
July/s snow cover was 84% below normal.



October/s charts here.
Raw data here.

Winter '12 / '13 - Stratospheric Sudden Warming: Watch #1

UPDATE2:  Earlier suggestions of a fizzled SSW event appears to have fizzled.  No long lasting effects are expected from this short-lived event; however...the PV did reverse course as forecast.

Warm colors shown on the stage-right image from the Japan Meteorological Agency (JMA) depict easterly wind flow.  East winds over the Pole means an anti-cyclone has replaced the normal cyclonic circulation associated with the PV.

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UPDATE:  Earlier suggestions of a SSW event appears to have fizzled.

Forecasts of a split PV @100 mb peaks during the next day or two followed by a return to a single vortex center and a return to deep-layer cyclonic flow over the Pole.

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The ECMWF continues to depict a sudden stratospheric warming event during late November into early December.

The polar vortex (PV) is forecast to begin splitting in two at 100 mb early next week with distinct centers of circulation over Victoria Island...CN and south-central Russia by 03-DEC.

The effects would be felt at the surface in about three weeks if this feature develops as forecast.

Deep layer easterlies are also progged over high latitudes by D+10 indicating the presence of an Arctic anticyclone.

The QBO is in the waning stage of its easterly cycle such that the PV is already in a 'weakened' state.  Major winter stratospheric warmings preferentially occur during the easterly phase of the QBO. Holton and Tan (1980)

The QBO determines the character of the early winter, leading to a colder and more stable polar vortex in December and January during the west phase of the QBO and a more disturbed and warmer Arctic during the east phase of the QBO.⁽¹⁾

From Thompson et. al...

Pronounced weakenings of the NH wintertime stratospheric polar vortex tend to be followed by episodes of anomalously low surface air temperatures and increased frequency of occurrence of extreme cold events throughout densely populated regions such as eastern North America, northern Europe, and eastern Asia that persist for ~2 months.⁽²⁾

The Arctic Oscillation (AO) is heading for a cliff.  The GFS forecast takes the AO on a deep dive where it remains negative through D+10.