General March Weather

[TonyT]

s_wpac_cdas1_anom-1.pngNo need to wonder too much about why March was so warm.

Thanks Tony, I guess we can say goodbye to any sea level snow events in Canterbury this year, those SST's aren't shifting anytime soon, I can't think of any major reason winter this year will be any different to the warm winter last year?

You would have to suspect some similarities to last year, yes. I wouldn't rule out warm advection snow events as those warmer waters will fuel rapid low pressure developments if the broader synoptic patterns are right. But they would probably be isolated one-offs in a generally warmer winter. However, I am picking increased cloudiness as one of the key trends this winter, which would imply colder than normal day time temperatures and milder nights (fewer frosts).

[Bradley]

Thanks Tony, I guess we can say goodbye to any sea level snow events in Canterbury this year, those SST's aren't shifting anytime soon, I can't think of any major reason winter this year will be any different to the warm winter last year?

You would have to suspect some similarities to last year, yes. I wouldn't rule out warm advection snow events as those warmer waters will fuel rapid low pressure developments if the broader synoptic patterns are right. But they would probably be isolated one-offs in a generally warmer winter. However, I am picking increased cloudiness as one of the key trends this winter, which would imply colder than normal day time temperatures and milder nights (fewer frosts).

Yes if those warm advection events occur then areas above say 300m could do very well this winter though it will have to be one hell of a cold blast with those warm SST's in mind, event colder then in a normal year for it to snow down to sea-level

[RWood]

Looking at all 360 months' anomalies in the period 1981-2010, 101 were +0.50 or more above the average (28%), 161 (45%) were between +0.50 and -0.50 from average, and 98 (27%) were 0.50 or more below average.

[TonyT]

Looking at all 360 months' anomalies in the period 1981-2010, 101 were +0.50 or more above the average (28%), 161 (45%) were between +0.50 and -0.50 from average, and 98 (27%) were 0.50 or more below average.

That tells us that in March (for example, as its the only month we currently have the breakdown for), using the +/- 0.5deg criteria for assessing how "normal" the month is, fewer Marchs will be called normal than the long term average across all months. Or put another way, March is more likely to either be above normal or below normal than most other months.

[tich]

Yes if those warm advection events occur then areas above say 300m could do very well this winter though it will have to be one hell of a cold blast with those warm SST's in mind, event colder then in a normal year for it to snow down to sea-level

I recall 3 cold outbreaks last year which could've dumped snow down to sea-level in Canterbury - if they had occurred in winter. Instead they were in April and November. (twice)

[RWood]

Looking at all 360 months' anomalies in the period 1981-2010, 101 were +0.50 or more above the average (28%), 161 (45%) were between +0.50 and -0.50 from average, and 98 (27%) were 0.50 or more below average.

That tells us that in March (for example, as its the only month we currently have the breakdown for), using the +/- 0.5deg criteria for assessing how "normal" the month is, fewer Marchs will be called normal than the long term average across all months. Or put another way, March is more likely to either be above normal or below normal than most other months.

Got around to counting the "normal" months for each month of the year in 1981-2010:

Jan 13 Feb 14 Mar 11 Apr 13 May 12 Jun 14 Jul 12 Aug 17 Sep 12 Oct 16 Nov 15 Dec 12 (average 13.4)

[TonyT]

Interesting. So there is a 37% chance that a March will be "normal" but a 53% chance that an October will be.

[jamie]

Interesting. So there is a 37% chance that a March will be "normal" but a 53% chance that an October will be.

Now there’s some stats for you long range forecasters


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[RWood]

Interesting. So there is a 37% chance that a March will be "normal" but a 53% chance that an October will be.

I also looked at the month ==> next month transitions in 1981-2010 (plus Jan 2011 as a successor month). Calling the categories Low, Avg and High for brevity, the counts were:


Low-Low 40 [27]
Low-Avg 40 [44]
Low-High 18 [27]

Avg-Low 45 [44]
Avg-Avg 69 [72]
Avg-High 47 [45]

High-Low 13 [28]
High-Avg 53 [45]
High-High 35 [28]


The numbers in brackets are the expectation if the events were independent (which they aren't of course). As expected the non-average months show some persistence, though the average months look more neutral.