Season 2014 snow depth prediction #5

One of a series; also see editions: #1, #2, #3, #4

It’s June, so the parameter estimates have firmed; time to update. Last time the prediction was 170 ± 45 cm.  The prediction formula is:

Spencers Creek peak depth (cm) = 1248 – 0.49 x year – 19.3 x AAO + 1.63 x SOI – 11.9 x IOD – 9.06 x PDO – 130.9 x SST

 

The parameters¹:

Antarctic Oscillation (AAO)

As foreshadowed, AAO has turned slightly positive. I’m sticking with what we had — a “3-month running mean” to the end of August of +0.5.

 

Southern Oscillation Index (SOI)

So far the SOI has stayed stubbornly positive, despite grave predictions of a strong El Niño:

 

And the Australian Bureau of Meteorology’s (BOM’s) POAMA model has now given up on El Niño altogether:

 

But international models are not so sanguine (BOM plots — will update, click for link):

Even if POAMA is wrong, it doesn’t look like El Niño can happen quickly enough (if it does at all) to be anywhere near as bad for our 2014 snow season as my earlier parameter pick implied. I’m shifting my winter average SOI forecast from -10 to -5 (remember a negative SOI correlates with a positive Nino 3.4 SST anomaly).

 

Indian Ocean Dipole (IOD)

BOM’s model now has this:

That is still essentially neutral, but slightly better for our snow season.  I’m dropping my June, July and August average IOD pick from +0.2 to 0.0.

 

Pacific Decadal Oscillation (PDO)

Little has changed here of course.  It was March that was +0.97 (last time I said February).  April was +1.13.  With two big months in a row, it’s just possible that this thing might be about to flip (but really far too early to say).  I’ll stick with -0.3 for the two year average to the end of August.

 

Sea Surface Temperature (SST)

Sea surface temperatures in our area of interest jumped calamitously in April (the latest Hadley Centre data):

 

That big April rise appears consistent with our very warm May across eastern Australia (PDF link). Here again is BOM’s SST anomaly plot for the last available week (will update; values vs the 1961-1990 average — add 0.13°C to get the 1951-1980 reference interval we use):

Things are still very warm in the north-west Tasman Sea, and fairly warm in the Great Australian Bight too. I’m lifting my winter average southern SST estimate from +0.5 to +0.6°C, which is pretty much right on trend.

 

Outcome

There are compensating changes there, but the net effect is slightly negative. My 2014 peak depth prediction falls from 170 cm to 168 cm, both ± 45 cm as before. That looks like this:

Interestingly, the revised parameter picks see the new prediction formula and the old prediction formula (without SST) give nearly the same answer for 2014.²

 

Notes:

1. For parameter descriptions see the notes to my earlier post.

2. Because the SST pick is near trend and the formula uses SSTs detrended about 2014.