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Cheech
18-07-2008, 09:38 AM
There seems to be a bit of discussion lately about Seabreeze being unreliable. I also noticed in another thread that others may be interested in understanding synoptic charts.

Now I am a long way from an expert, but I thought I would share my very laymans understanding of what I see when looking at the charts, and hopefully others that know more will add in their comments. This should help explain how they come up with the predictions, and why sometimes the predictions dramatically change.

Recently I have started to compare Seabreeze with BOM 4 day charts to try to understand how Seabreeze get their predictions from. Did you know that BOM is one of the places Seabreeze get their information for their model?

I printed these from BOM and Seabreeze yesterday. The first 2 days of charts from BOM show a big high right over Brisbane. As there is no change in barometric pressure, there is very little wind. You will see that there is a cold front heading our way. It is over Adelaide at the moment. This is indicated by the thick line with triangles on it. The other thing to note with the cold front is that the thin lines with the numbers on them (1012, 1016, 1020 etc) that state the barometric pressure are really close together. The closer together they are the faster the air is going to travel from one pressure area to the next. This means windy.

Then going into Friday, it is a similar story with the edge of the high still over Brisbane. You will see that the cold front that was over South Australia has now moved to the east coast, but has slipped by under Brisbane. Will mean that it is windy today on the NSW coast, but Qld will still have light winds.

http://i344.photobucket.com/albums/p351/craiggrendon/thursdayfridayforecast.jpg

Now if we look at Saturday and Sunday, Saturday is still looking good due to the high (and very wide gaps between the barometric lines). You will see that there is a second cold front moving through South Australia again, so will be windy there on Saturday.

Moving into Sunday, you see that the cold front that was over SA has now moved to the NSW coast. Thoug different to the earlier front on Friday, this time the front is coming through a bit higher. The outer edge of the close together pressure lines will go over Brisbane on Sunday morning. That means we will have a sharp increase in wind strength Sunday.

As BOM has only 4 days of chart predictions, if you have a look at what is coming our way, you will see that there is a real lot of wind on Sunday near teh WA/SA border, and that the tight lines extend up pretty high towards teh Northern Territory. As all the weather moves from left to right, you can expect this wind is going to eventually get to the east coast. If it was lower, it could slip below QLD, but because it is sitting high, the indication is that it will probably go through southern QLD and be windy for a few days into next week.


http://i344.photobucket.com/albums/p351/craiggrendon/saturdaysundayforecast.jpg


Now compare this with Seabreeze. Pretty close really.

http://i344.photobucket.com/albums/p351/craiggrendon/seabreezeforecast.jpg

You can also work out the expected wind direction because the highs rotate anti clockwise.

If others can add or correct any of the above, please do. As I said, I only have a basic understanding of it all, but I thought this would help some people in making there own decisions about the forecast rather than only working off one site.

I think we need to cut sites like Seabreeze a bit of slack, because (as an example) all it could take in the above projections is a weakening of the cold front, and the windy weather that is expected on Monday, Tuesday could easily slip below the Qld border, and be better than projected.

There is probably a lot that can be explained about wind directions and the impact of the highs across teh top of Australia. Hopefully someone can comment on that.

Cheech

Noelm
18-07-2008, 09:45 AM
you are right, I have said this many, many times, have a look at the charts, see what happens in your area with certain conditions, after a while you will get quite good at it, and will easily be able to spot possible "bad stuff" as it approaches, remember, the forecasters do just that, they can be wrong, but it does follow patterns season after season, very few really bad dangerous Weather conditions just "pop up" unanounced, it will appear on charts well before it gets to you.

sandbankmagnet
18-07-2008, 10:14 AM
one thing is that those charts don't show upper level troughs which can bring lots of rain. the charts are taken at sea level.

slyman
18-07-2008, 12:10 PM
Sea surface level charts dont show the upper atmoshere so they cant be relied upon completely, another thing with the National charts is the scale they show, they dont show a good level of detail for regional areas.

One thing I like to use from the BOM site is this link:

http://www.bom.gov.au/marine/index.shtml

You can click on the forecast wind map of OZ and zoom into a level that shows maroochydore to the border, and you can step through a sequence of forecast wind strengths and directions for a few days.

This is only a recent addition to the site, but I've found it pretty reliable so far.

If you want to find it from the BOM home page then click on MARINE SERVICES in the left hand menu.

Chong
18-07-2008, 03:35 PM
so are you going fishing on Sat??? :) :)

Cammy
18-07-2008, 04:08 PM
I just have a look in the backyard at the trees, if there not moving its fishing time!!:)

Cam

Cheech
18-07-2008, 05:34 PM
Sandbank and Simon,

Thanks for your comments. My intention was not to provide a full in depth forecast. I am not that knowledgeable in this area. It is really meant to assist those that look at forecasts such as seabreeze and do not know how or why they come up with the predictions, or why they can change. Or would like to start to understand the BOM charts to increase there boating safety. "Basic Forecasts 101", not "Advanced Forecasting 107".

I know what I have put together is very basic, but at least it is a start, and hopefully will be useful to some of the members.

But as an expansion to my post that just looks at the wind, it would be great if you can do a similar post and explain the troughs and upper atmosphere readings. Consider your lesson to be "Intermediate Forecasting 102" :)


Cheech

tigermullet
18-07-2008, 06:26 PM
You should be an instructor Cheech.

Met was always my worst subject even though I was very interested in it.

Big problem with the instructor - he put everybody to sleep. After snoring through dozens of lectures it's a wonder I passed.

SgBFish
18-07-2008, 08:26 PM
Cheech
Thanks for the info. The winter lows that can rapidly develop because of cold upper air could be another topic. These can cause very dramatic changes.
What your amalysis proves beyond any shadow of a doubt is that based on this weekends weather SE QLD is God’s country.

Scott

sandbankmagnet
18-07-2008, 09:48 PM
Sorry Cheech, I didn't mean to rain on your parade (so to speak). It's a good start for a lot of people in weather reading. I just wanted to point out that charts don't show everything. They do show general wind forecasts though.

I remember one of the members about 12 - 18 months ago starting a weather lesson series. He knew his stuff too.

I grew up on a farm and know a trick or two about the weather. There's plenty of them that I don't know though. A lot of maritime people know different ones. Maybe that can be Weather 103 - weather signs that we all see and how to read them.

Outsider1
18-07-2008, 09:53 PM
For SE Qld I love to see those high pressure systems across the middle of the continent. Usually means generally settled weather and some good solid windows of really good weather.

Of course there are other factors and the closeness of the isobars is important but if you get those highs then chances are you will get some good fishing and boating weather coming up.

Cheers

Dave

maztez
20-07-2008, 08:33 AM
This is why AUSFISH is such a great site .There are so many knowlegable members more than willing to share their expertise with other members such as me .Thanks guys its very much appreciated .
cheers Terry

aus2045
20-07-2008, 11:46 AM
Here are a few handy links that I like to look at before planning a trip.

ECMWF. This is a handy and rather accurate model out to about 5 days. It covers Mean sea level pressure, wind speed at 850 hPa and geopotential 500 hPa. http://www.ecmwf.int/products/forecasts/d/charts/medium/deterministic/msl_uv850_z500!Wind%20850%20and%20mslp!72!Australi a!pop!od!oper!public_plots!2007121112!!/ animate by clicking the play button next to Step (->valid time)

The following map displays the ocean surface winds at a 10m height from today's satellite passes as processed by NOAA/NESDIS, from near real-time data collected by NASA/JPL's SeaWinds Scatterometer aboard the QuikSCAT Satelite. Scroll down and click the area you want to see. You get wind spead and direction. It's more ocean related, but handy for those into wide trips http://manati.orbit.nesdis.noaa.gov/hires/

MTSat Loop, shows the progress of approaching troughs and fronts. http://www.goes.noaa.gov/sohemi/sohemiloops/shirgmscol.html

And if camping this gives Accumulated Precipitation Forecast for up to seven days.
http://forecasts.bsch.au.com/apf.html?region=aus&days=7.5

Bom Forecast wind spead and direction forecast.
http://www.bom.gov.au/jsp/watl/wind/index.jsp

pueter66
20-07-2008, 01:23 PM
Hi, I personaly look at the synoptic chart first then the local marine weather forecast. Then I look out the window at the water and presto its always 15 to 20 knots here in capricornia