10-12 July

Outcome: A nice fall, finally

Outcome:

A nice combination of falls, if somewhat wetter in parts than would have been preferred — like Friday, as predicted in several updates, and Sunday night, as foreshadowed (but downplayed) in update 6. NSW resorts claimed 45-50 cm aggregate snowfall (which looks about right); the main Victorian resorts a bit less. We’ll have to wait to see if this coming week’s light falls bring the overall gain up to my “dump” threshold, which is 50 cm week-on-week gain.

Here are the charts for Sunday morning:

JMA precipitation inferred from satellite imagery

BOM surface chart archive

(Mr Cowan’s charts below are direct image links, and will progressively disappear as his monthly refresh cycle comes around.)

Update #6 (9 July):

My apologies for the endless updating, but the weather this year is as badly behaved as I can remember. Don’t worry, this one is still solid. I’m just moving the dates (again*) to include Sunday, which should see some further nice falls as the low moves into the Tasman and deepens. Temperatures may become marginal for snow as the tropical feed wraps the developing low, but I’m not too worried. The timing is good (early Monday morning, the coldest part of the day), and the thing will probably move off quickly enough to avoid damage:

GFS for Sunday night, 12 July (Levi Cowan)

ECMWF for Sunday night, 12 July

But the follow-up next week is now less secure (in the other post):

* It’s not at all unusual for modelled systems to drift later as reality approaches; it’s one of the most persistent deficiencies of the current crop of weather models (they advance southern systems too rapidly). I allow a bit for that in making timing calls, but 4 day’s shift over 2½ weeks is ridiculous. (A fair bit was due to my stupidly early call on this one, but what do you do with nothing on the ground at the end of June…)

Update #5 (8 July):

OK, this is pretty secure now; the models agree. The first snow is showing Friday the 10th, from a rather wet little trough. The temperatures will be marginal — snow level perhaps 1600 m. The precipitation looks heavy, but the heaviest area will probably miss the alps to the north. Perhaps 10-15cm; less in Victoria:

GFS for Friday morning, 10 July (Levi Cowan)

BOM’s ACCESS-R model for Friday morning, 10 July

Then the first phase of the main event arrives Saturday with a very cold south-westerly (though not as stupidly cold as at the last update!). There’ll be snow to low levels, perhaps 20+ cm:

GFS for Saturday night, 11 July (Levi Cowan)

BOM’s ACCESS-G model for Saturday night, 11 July

Then there’s more action coming in the second phase. (The separation between the two is less distinct now, but there is divergence in the models after Sunday, so I’ll stick with two separate posts.)

Update #4 (6 July):

For clarity, there now appear to be two sizeable snow systems approaching, associated with the passage of a strong polar node (see the spaghetti plot) and a very strong pulse of western Pacific Madden-Julian activity. This post covers the first system, with the dates moved forwards another day to 9-11 July. The second system, targeting 13-15 July, will be in a separate post.

The first system still has the initial upper atmosphere-related northerly feed I wrote about yesterday, due on Friday. That is followed by an extremely cold south-westerly on Saturday. Aggregate snowfall could easily exceed 20 cm. Saturday evening looks like this on the models; note the thicknesses*:

GFS for Saturday afternoon, 11 July (Levi Cowan)

ECMWF for Saturday night, 11 July (Levi Cowan)

* The 500 – 1000 hPa atmospheric thickness is an approximate measure of average lower troposphere temperature, via the universal gas equation (PV=nRT; thickness is just volume, V, which is proportional to absolute temperature, T). A thickness of 5400 m (the blue “540” line on the plot) is usually cold enough for snow in our alps.

Update #3 (5 July):

While others focus on the possible big follow-up system (13-15th July; post coming), this one is still alive and may yet surprise. On the American GFS model, the initial feed is wet and northerly, but the temperatures are just about cold enough to snow. The Australian Bureau of Meteorology’s ACCESS-G model has a similar pattern, also nearly cold enough.

Of the little pre-events, the first (2-3 July) is already in, with 8 cm claimed at Perisher Valley. The second on 6-7 July has weakened a bit, but should still see some snow.

GFS for Friday 10 July (Levi Cowan)

ACCESS-G for Friday, 10 July (BOM)

Update #2 (30 June):

It looks like we may see a series of weak fronts over the first week of July, starting with up to 10 cm from one on 2-3 July. The main event is now showing about 2 days later than I had it, so I’ve shifted the dates to 8-10 July. The top models now agree on it, but they also did at this stage for the last system…

GFS for Thursday night, 9 July (Levi Cowan)

ECMWF for Thursday night, 9 July (Levi Cowan)

Update #1 (26 June):

This has firmed nicely on the tail end of the European model (ECMWF); not so much on the US one (GFS — still there; just arriving later). Still a long, long way out; things could change:

GFS (Levi Cowan)

ECMWF (Levi Cowan)

Original post (23 June):

It’s a long way out, but at this stage I’m ready to clutch for any straw in a westerly breeze. The famous spaghetti plot is back up after a long server outage, and suggesting some possible action for 6-8 July:

That would coincide with the tropical Madden-Julian oscillation being strongly in phase 6, which is usually positive for Australian snowfalls: