The coming Japanese season 2013-2014 weather

Sandy

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Stratus said:
How long until the regular winter pattern typically sets in?

There is a quantum change in the weather, usually sometime around the week of 15th - 22nd December. This is usually when the regular winter pattern sets in, and the big dumps start.
There may or may not be some good snowfalls earlier, but even then, these are usually slow base builders, rather than the start of the big dumping season.
 
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Donza

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I usually keep an eye on central Siberia (dominant ridge of High pressure)...rather than japan for the commencement of winter.
 

Donza

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Also look look at the migration of the subtropical ridge...
sandy posted re this a few years back
 
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Sandy

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Still looking good for a cold outbreak 11-13 November IMO. I reckon it should start turning up on the JMA site as little snow icons for Hokkaido.
 

ojisan

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Sandy said:
Still looking good for a cold outbreak 11-13 November IMO. I reckon it should start turning up on the JMA site as little snow icons for Hokkaido.

Just checked JMA, and you were right.. snowman icons have appeared for Sunday/ Monday
 
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Avon_Barksdale

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I found this summary of JMA's 3 month (Nov-Jan) outlook:

http://ds.data.jma.go.jp/tcc/tcc/products/japan/outlooks/latest.pdf

Interesting passages:
・ SSTs are predicted to be higher than normal in the western tropical Pacific and near normal in the tropical
Indian Ocean and eastern equatorial Pacific. In association with the SST anomalies, atmospheric
convection is predicted to be more active than normal in the western tropical Pacific.
・ As a result, the subtropical jet stream is predicted to meander northward around southern China and
southward around Japan in December and January.
・ In this association, the influence of cold air on Japan will be larger than normal in December and January.

And based on this the probabilities:

・ Three-month total precipitation is expected to be near or above normal, both with a 40% probability, on
the Sea of Japan side of northern and eastern Japan, and to be near or below normal, both with a 40%
probability, on the Pacific side of eastern and western Japan.
・ Three-month total amount of snowfall is expected to be near or above normal, both with a 40%
probability, on the Sea of Japan side of northern Japan.

I've looked at these long range forecasts over the last few years and wondered how or why they had come up with the percentage chances. Does anyone know if these predictions have been reliable in the past?
 

Sandy

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Avon_Barksdale said:
I found this summary of JMA's 3 month (Nov-Jan) outlook:

http://ds.data.jma.go.jp/tcc/tcc/products/japan/outlooks/latest.pdf

Interesting passages:
・ SSTs are predicted to be higher than normal in the western tropical Pacific and near normal in the tropical
Indian Ocean and eastern equatorial Pacific. In association with the SST anomalies, atmospheric
convection is predicted to be more active than normal in the western tropical Pacific.
・ As a result, the subtropical jet stream is predicted to meander northward around southern China and
southward around Japan in December and January.
・ In this association, the influence of cold air on Japan will be larger than normal in December and January.

And based on this the probabilities:

・ Three-month total precipitation is expected to be near or above normal, both with a 40% probability, on
the Sea of Japan side of northern and eastern Japan, and to be near or below normal, both with a 40%
probability, on the Pacific side of eastern and western Japan.
・ Three-month total amount of snowfall is expected to be near or above normal, both with a 40%
probability, on the Sea of Japan side of northern Japan.

I've looked at these long range forecasts over the last few years and wondered how or why they had come up with the percentage chances. Does anyone know if these predictions have been reliable in the past?

Generally, I don't find these to be reliable. Firstly, I don't quite like the terminology.
e.g.
"snowfall is expected to be near or above normal, both with a 40% probability, on the Sea of Japan side of northern Japan." So this says that there is a 40% chance it will be normal., 40% chance of above normal, 20% of below normal".
But using this terminology it's also saying "there is an 80% probability to be near or above normal", which sounds good, but that also means "there is an 60% probability to be near or below normal"
doh.gif


Anyway, terminology aside, these forecasts change quite a lot as winter approaches.

The biggest plus in that forecast IMO, is:
" SSTs are predicted to be higher than normal in the western tropical Pacific and near normal in the tropical
Indian Ocean and eastern equatorial Pacific. In association with the SST anomalies, atmospheric
convection is predicted to be more active than normal in the western tropical Pacific.
As a result, the subtropical jet stream is predicted to meander northward around southern China and
southward around Japan in December and January.
In this association, the influence of cold air on Japan will be larger than normal in December and January. "

Cold air is the single most important factor in the Japanese snow season. Remember, all Japan needs is a steady northerly wind, and it WILL snow!!! A winter could go by without a single storm system (i.e. Low pressure trough & cold front) and it would be a very good snow season!!
 
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Sandy

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ojisan said:
Sandy said:
Still looking good for a cold outbreak 11-13 November IMO. I reckon it should start turning up on the JMA site as little snow icons for Hokkaido.

Just checked JMA, and you were right.. snowman icons have appeared for Sunday/ Monday

Still looking good for the 11th-12th IMO. The 17-19th looks more like a big low pressure trough, with not so much cold air, and warm air sucked in from the south, with rain IMO.... but it's early for that predicted date ATM.
 
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Sandy

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So the first quantum step for autumn looks like coming in on Mon/Tue 11th/12th November.

For Hokkaido & northern Honshu, it means some snow.

For central Japan, where the nights have been dropping to 13-14 degrees and days up to 18-20 degrees, it looks like it will shift to lows of 7-10 degrees, and highs of 13-17.

I saw Mt Fuji this morning, and it now has snow on it!!! It's the first time I've seen any snow on it this autumn.

20131108_0743_Web.jpg
 
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