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#1432332 - 31/08/2017 19:33 Re-analysis of past 2 weeks forecasts
Kino Online   content
Weather Freak

Registered: 10/08/2017
Posts: 663
Loc: Wollongong, NSW, Aus
Hi all - thought I'd monitor forecasts issued for my local area over the past 2 weeks to see their accuracy. The forecasts were issued on the day before.

There is clearly a glaring problem here...consistent over-forecasting for both mins and max temps (up to 4c one day).


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#1432381 - 01/09/2017 10:58 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
Steve777 Offline
Weatherzone Addict

Registered: 20/10/2011
Posts: 3430
Loc: Artarmon (Sydney North Shore)
Your graphs do show a systematic undershooting of actual versus forecast for that two week period.

It could be a peculiarly of the site, with the forecast not taking account of local features.

I am most familiar with OH. At that site, there seems to be a tendency to overforecast maxima on fine days in Summer (underestimate strength of sea breeze at that site perhaps) but under-forecast for Winter, although in Winter it tends to be close for other Sydney sites. I don't have any data though, just a general feel.

Meanwhile, I recall another poster from Coffs Harbour last Winter talking about consistent significant over-forecasting of Winter minima, while in Summer, as I recall, Hunter Valley posters were complaining of significant under-forecasting maxima during heat waves.


Edited by Steve777 (01/09/2017 10:59)
Edit Reason: First para

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#1432382 - 01/09/2017 11:05 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
Wave Rider Offline
Meteorological Motor Mouth

Registered: 27/01/2014
Posts: 6181
Loc: Wollongong, NSW
I don't even look at forecast minimums for Albion Park, they are always wrong. And when they are right it's probably only a fluke anyway. They seem to assume it's a more coastal exposed site than it actually is.
_________________________
2016-17 season storm total for here= 15

Oct- 21st
Nov- 9th, 28th
Jan- 24th
Feb- 11th, 12th, 17th, 18th(2)
Mar- 13th, 16th, 22nd
Apr- 9th, 26th
May- 24th

The longer you wait for things, the more you appreciate them.

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#1432386 - 01/09/2017 11:35 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
Kino Online   content
Weather Freak

Registered: 10/08/2017
Posts: 663
Loc: Wollongong, NSW, Aus
The min's aren't as bad, though the error rate larger, the variability is quite pronounced (the line bounces around) whereas the max temps IMO are terrible - consistently forecast 2c above what is recorded. And this is only 24 hours before.

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#1432395 - 01/09/2017 12:22 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
Wave Rider Offline
Meteorological Motor Mouth

Registered: 27/01/2014
Posts: 6181
Loc: Wollongong, NSW
On your graph definitely the max forecasts are worse. Maximum temps should be easy to forecast.. Nights are harder but you can guess what it will be close to by looking at dew points early in the night and the humidity.
_________________________
2016-17 season storm total for here= 15

Oct- 21st
Nov- 9th, 28th
Jan- 24th
Feb- 11th, 12th, 17th, 18th(2)
Mar- 13th, 16th, 22nd
Apr- 9th, 26th
May- 24th

The longer you wait for things, the more you appreciate them.

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#1432397 - 01/09/2017 12:24 Re: Re-analysis of past 2 weeks forecasts [Re: Wave Rider]
Kino Online   content
Weather Freak

Registered: 10/08/2017
Posts: 663
Loc: Wollongong, NSW, Aus
Originally Posted By: Wave Rider
On your graph definitely the max forecasts are worse. Maximum temps should be easy to forecast.. Nights are harder but you can guess what it will be close to by looking at dew points early in the night and the humidity.


I'm going to do a maritime and land analysis this month and see how they go.

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#1432508 - 02/09/2017 14:24 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
Steve777 Offline
Weatherzone Addict

Registered: 20/10/2011
Posts: 3430
Loc: Artarmon (Sydney North Shore)
We've seen examples of overshooting and undershooting in September at OH, illustrating common situations for that site.

1st and 2nd: both underforecast by 1 degree, with OH one of the warmer sites in the Sydney area. Both days had Southerlies and a reasonable amount of sunshine.

3rd: an early Seabreeze will probably keep the max below 20, making OH one of Sydney's coolest sites today. Assuming a max of 20, that's an over-forecast of 2.

So +1+1-2 =0. So far this month, on average the BOM was right for maxima.

EDIT: and now the smoke's starting to arrive. The NE'er normally keeps it at bay, but not when the burning is near the coast.


Edited by Steve777 (02/09/2017 14:26)

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#1432510 - 02/09/2017 14:59 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
Wave Rider Offline
Meteorological Motor Mouth

Registered: 27/01/2014
Posts: 6181
Loc: Wollongong, NSW
Well the forecast here today was 22 degrees and it has only reached 19 so quite a decent margin off the forecast. And that comes off the back of this morning's fail too!!
_________________________
2016-17 season storm total for here= 15

Oct- 21st
Nov- 9th, 28th
Jan- 24th
Feb- 11th, 12th, 17th, 18th(2)
Mar- 13th, 16th, 22nd
Apr- 9th, 26th
May- 24th

The longer you wait for things, the more you appreciate them.

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#1432936 - 05/09/2017 20:35 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
Josh from SH Offline
Cloud Gazer

Registered: 23/08/2017
Posts: 3
BoM is never correct really, especially out here. They really need a weather station atleast at Oberon instead of using Mount Boyce.

It's like two seperate climates between Shooters Hill and Mount Boyce.

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#1432974 - 06/09/2017 09:06 Re: Re-analysis of past 2 weeks forecasts [Re: Kino]
DaveM Offline
Meteorological Motor Mouth

Registered: 21/05/2001
Posts: 9667
Loc: Bathurst NSW about 700 m asl
Agree 100% Josh.

Mt Boyce is at times handy but is definitely NOT reliable for Oberon due to the fact the majority of interesting weather for both locations comes from different directions.

How many times is one location clear whilst the other is clagged in.

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