The Australian Weather Forum

Hi MESO.
If l remember correctly ken said stormcast was based on GFS. I remember seeing a post recently on a forum where GFS was showing a low over VIC at that time.
However ACCCESS wasn't etc.
That would be why the nice storm intensity forecast by GFS/stormcast, l presume.. However the bad news is the wind forecast map is only showing a trough with a small low intrusion from the westerly belt over Vic, just like yesterday ( Sundays pattern) which might tone things down a little.It is also showing the change arriving late Friday night 10pm in the west VIC atm.
8 day rain forecast from BOM looks quite weak.( l suspect that is taken from ACCESS) However if models not lining up? then you never know.

crikey » Mon Nov 14, 2011 10:02 pm wrote:

crikey wrote: If l remember correctly ken said stormcast was based on GFS.

That's correct.

However the bad news is the wind forecast map is only showing a trough with a small low intrusion from the westerly belt over Vic, just like yesterday ( Sundays pattern) which might tone things down a little.

Storms also depend on what the mid/upper atmosphere's doing e.g. mid/upper troughs, midlevel cold air, jetstreams, etc.

8 day rain forecast from BOM looks quite weak.( l suspect that is taken from ACCESS) However if models not lining up? then you never know.

If you're referring to the WATL rainfall maps, that's based on a combination of leading models. But if you're referring to the one on weatherzone, that's ACCESS.

KEN
Re: storm variables.Yeah.. I am aware of what you suggested but have had difficulty finding the appropriate prognosis charts and find l have only lower level variables to observe.
Do you have links to
-upper atmosphere trough information ( 7 day prognosis)
-upper cold air charts ( 7 day prognosis)
-7 day jetstream prognosis

I have certainly seen the effects of jetstream pattern but would like to find a jetstream forecast .
I have asked around but no success.

What does WATL stand for? THe link l use is
http://www.bom.gov.au/jsp/watl/rainfall/pme.jsp" onclick="window.open(this.href);return false;
How often does this rainfall forecast update. Noticed it has changes a little since last night. ?

crikey, You can view temps through the different levels on bsch. Not sure what you'd look at to decipher if there is any upper level trough in the region though? Jet stream is just the 300mb shear I think.

Got a question for Ken...with the new storm potential and supercell charts...what do they take into account when being produced? I'm not asking for a full algorithm either, just a quick run down to satisfy my curiosity.

crikey » Tue Nov 15, 2011 4:11 pm wrote:

crikey wrote:Do you have links to
-upper atmosphere trough information ( 7 day prognosis)
-upper cold air charts ( 7 day prognosis)
-7 day jetstream prognosis

There's many out there but a couple include the Stormcast maps on the BSCH site (http://forecasts.bsch.au.com/stormcast.html) - mid/upper troughs typically show up on the upper wind charts (the "Shear" charts between around 700 and 300hpa... although they're actually only show the winds at those heights rather than true shear within a layer of atmosphere) like they do on surface wind charts.
Another one is the map viewer based on the ACCESS model at:
http://www.bom.gov.au/australia/charts/ ... u&model=CG - again, the same principle as above applies. Mid level cold air shows up on the 700 and 500hpa temperature charts on both sites while jetstreams can be identified on the 300hpa wind charts as ribbons and streaks of strong winds. Severe thunderstorms often occur under the left entrance and right exit regions of jet streaks provided there's also enough moisture and instability.

What does WATL stand for? THe link l use is http://www.bom.gov.au/jsp/watl/rainfall/pme.jsp" onclick="window.open(this.href);return false;
How often does this rainfall forecast update. Noticed it has changes a little since last night. ?

WATL stands for Water And The Land. It's the name for the section of the BoM website that has the rainfall, frost and wind forecast maps, etc on it. The 4 and 8 day total rainfall forecast maps update once a day while the daily rainfall maps are updated twice a day (in the early morning and early evening). Just remember that the forecast rainfall for an individual day is valid from 10pm AEST on the previous night til 10pm AEST on that day (due to model forecast time steps).

Meso: the storm potential maps are based on the SWEAT Index which uses the temperature, dew points, wind direction and speeds at 850 and 500hpa to work out the combination of instability and shear. The supercell charts use shear in the 0-6km layer and CAPE.

As for SE Oz rainfall, the WATL maps show a pretty impressive band of rain streaming down from the NW to the SE of the continent over the next several days... the North American Ensemble Forecast system is still painting moderate probabilities of >25mm rainfall for the more northern parts of SE Oz (eastern NSW and possibly into SE QLD) continuing into Week 2. This looks like it's part of the wet signal that POAMA 2 is suggesting for eastern/southern NSW (among other areas) over the next few months.

Absolutely fabulous. Thanks Ken and Meso. What a plethora of info'.
Click streamlines'' and just looks like a wind map and l can read those ok. Just have to learn how to find the troughs. I know a trough generally exists between 2 highs and l can see them on the upper wind diagrams.
Also found the upper air Relative -Humidity charts. Can you determine condensation level ( cloud formation 100% RH ) or rainfall from RH upper air charts or is soundings the only way?
I have heaps of questions but really need to sink this in first. Regards and thanks. I felt like father Xmas had been. Ho Ho Ho
Look forward to exploring these 'weather tools' in the future.. Thanks again

OMG Crikey, you're so darn cute getting excited about your early Christmas presents And now I'm having a fun time imagining Ken in a Santa Suit

There's a fantastic article on the BoM website about La Nina, IOD, SST's and all that jazz that can give us an idea of what to expect rain wise over summer. Breaks everything down nicely in a way that's easy to understand. It's about 3 weeks old, but I only just came across it.

This year we have a neutral Pacific Ocean (granted on the 'La Niña' side of things and a La Niña remains possible), a positive Indian Ocean Dipole and average to slightly cool temperatures off our northern coasts. For rainfall that's a two-thirds tick, a cross and bit of a dashed line.

http://www.bom.gov.au/social/2011/09/ch ... -and-dogs/" onclick="window.open(this.href);return false;

Yeah meso. Thanks for that link. It really was a great article. Emailed them to say so. Very balanced l thought. Here is an article on the news the other day re the la Nina
THE UN weather agency says that La Nina, a phenomenon linked to flooding and drought, has re-emerged in the tropical Pacific since August but its impact is expected to be weaker this time.

"This La Nina is expected to persist through the end of this year and into early 2012, possibly strengthening to moderate intensity," said the World Meteorological Organisation in a statement today.

"However, it is likely to be considerably weaker than the recent episode that was linked to flooding and drought in different parts of the world."

La Nina is characterised by unusually cool ocean surface temperatures in the central and eastern tropical Pacific.

It is the opposite of El Nino, which is marked by unusually warm ocean surface temperatures.

Both factor in the fluctuations of the world's climate.

In late 2008 La Nina was blamed for icy conditions that claimed dozens of lives across Europe.

The weather phenomenon can also bring about strong rainfall in Indonesia, Malaysia and Australia, as well as drought in South America.

The current La Nina follows closely behind the moderate to strong one that started in September 2010 and ended with neutral conditions established in May this year, the WMO said.

"Historical precedents and the latest outputs from forecast models suggest that peak intensity of this La Nina will be reached in late 2011 or early 2012, and that it is very unlikely to reach conditions as strong as those of the 2010-11 La Nina event," the statement said.

Read more: http://www.news.com.au/breaking-news/la ... z1LqlSLqNw" onclick="window.open(this.href);return false;

3 models have a low forming in NSW on Thursday and Friday before drifting into Northern Vic and then moving down into eastern Vic and out to sea. GFS on weatherzone doesn't have the low at all, but it as though it will form. So up 10mm up here maybe and more on the NE ranges. Some more model updates and it will become more clearer.

Edit: Latest EC has 22.2mm for here over friday and Sat.

Just got excited SSImpact when l checked out the wind forecast map. It is indicting a well formed low right over Victoria from Sat 4.00am and all through the day.
and as you say forming in the N/west first and then across vic to the s/east. Yeah !! rain. Shame it doesn't stay long..
May l say the southern hemisphere sat pic looks interesting tonight with some quite large cold pools of atmosphere behind whiter than usual cloud fronts.
Good tropical infeed into the mid-latitudes.. I can smell the damp earth and rain as l am typing.LOL Some cool snaps coming maybe and some rain and some warmth.to boot ?
Jane bunn and Livinia were definitely hinting rain for the weekend. She said maybe snow on Alps in the week, although she said that would happen today and it hasn't so even trained meteoroligists get it wrong sometimes.. R U going to write up a thread , its not too early only 4 days away...

I'm want to make sure that this low will impact Vic before making a thread, so tommorrow I might after a check of the models, atm it's looking ok but could change. Snow down to 1600m after the front goes through tommorrow night on the alps.

crikey » Wed Nov 16, 2011 6:12 pm wrote:

crikey wrote:Just have to learn how to find the troughs. I know a trough generally exists between 2 highs and l can see them on the upper wind diagrams. Also found the upper air Relative -Humidity charts. Can you determine condensation level ( cloud formation 100% RH ) or rainfall from RH upper air charts or is soundings the only way?

Sorry, I was going to add to my previous post that mid/upper troughs can be identified by elongated bands of cyclonic (clockwise) curvature to the wind streamlines. In the midlatitudes, they're evident by "bulges" in the general westerly airstream which protrude northwards.

As for forecast condensation levels, they're not readily available from most websites. You have to either get them directly from model data via meteorological software programs (which will then allow you to display them on maps, etc) or forecast soundings. Models also forecast the heights of cloud bases and tops. Rainfall is best estimated directly from the precipitation forecasts from models together with other relevant things like soundings, precipitable water amounts, synoptics, etc.

Back to SE Australian rainfall, still looking on track for widespread mod/heavy falls across much of northern, inland and eastern Australia (where possible local flooding) over the next several days.

Models are gradually developing this cut off low Thursday/Friday in an Easterly trough and pulling it more South right into Victoria with each run with an upper low attached to it over SE SA this morning, looks like EC, GFS and UKMET are onboard.

EDIT: Just saw CMC and it looks great. NOGAPS, JMA and ACCESS are all onboard too only difference is they keep the low bit further North and East than EC, UKMET, GFS & CMC.

If a thread hasn't been started perhaps it should.. Watch the forecasts change in the coming days for later in the week and weekend.

UKMET (2nd best model in my own opinon) throws up some cold air from the South on the weekend interacting with an Easterly trough over Vic and SE Oz on Sunday that sure throw up some instabilty (rain or showers).. EC and GFS are not interested at the moment but I did notice EC had this scenario 3-4 days ago

Here is UKMET for Saturday... http://www.weatheronline.co.nz/cgi-bin/ ... O=&PERIOD=" onclick="window.open(this.href);return false;

Sunday... http://www.weatheronline.co.nz/cgi-bin/ ... O=&PERIOD=" onclick="window.open(this.href);return false;

Like I said GFS and EC are not onboard at the moment but the fact UK is keeps me half interested

This is on the Age website, wasn't sure where to post it...

Australia could see the first severe tropical storms of the summer cyclone season hit the country in early December, the weather bureau warned today, pointing to computer modelling of sea temperatures and weather in the Indian Ocean.
"During the past week, the Madden-Julian Oscillation (MJO) has gained strength over the Indian Ocean as it progresses eastwards towards Australia. It is likely that this MJO event will spawn the first tropical cyclone for the Australian cyclone season," the bureau said in a climate alert.

Read more: http://www.theage.com.au/business/marke ... z1f4CTlJz4" onclick="window.open(this.href);return false;

You can also find the Bureau's weekly rundown of the effects from the MJO, ENSO, etc on the tropics over the next few weeks here:
http://reg.bom.gov.au/climate/tropnote/tropnote.shtml
To quote: "An active MJO event in the Australian region during December brings an increased probability of tropical cyclone formation, and development of the monsoon trough over northern waters. Rainfall across northern Australia is expected to be above average during this period. It is likely that this MJO event will spawn the first tropical cyclone for the Australian cyclone season, and the Bureau of Meteorology will be monitoring the situation very closely."

And here's some TC probability forecast maps for our region for the next few weeks from Meteo France, based on the statistical correlation between the current phase of the MJO, ENSO cycle, etc:
http://www.meteo.nc/espro/previcycl/cyclA.php#1

Extended GFS has been hinting at something late next week and into the wknd for the last few runs. Fingers crossed for a weekend summer storm outbreak! Still a while out tho, so I'll try to keep a lid on it.

The latest 10 day model outlooks interest me as they are showing an extended period of easterly flow around a large slow moving high which begins as soon as the high to our west moves over us early next week. From what I understand, summer easterly patterns extending to the SE corner of the continent are a lot more common and pronounced during La Nina years, whereas in other years, and particularly El Nino, we see a lot more of a westerly pattern continuing through summer. What this usually means is some very hot and dry air masses prevailing over SE AUS, however in a La Nina year with a lot of easterlies we get a heap of moisture pumped in which not only keeps the hottest days at a low mark but also increases the chance of prolonged periods of afternoon storms and upper level systems producing large rain events. When we get a substantial front coming through with a southerly change it is already running into high accumulated moisture and we usually see much higher rainfall than in an average summer. Many times in summer these fronts/troughs are mostly dry ones.

I would say in a neutral year we would see a general westerly pattern but regularly broken up by periods of easterlies which temporarily increase moisture and cause storm outbreaks and eventually a thundery change with rain once a substantial front comes through, and also the odd ex-tropical system wafting down, but then we return to dry westerlies and extreme heat becomes a risk as we progress through summer. This year, much like last year, I can see a lot more rain days and rain events than in a normal summer and a lower number of extreme heat days, although I'll probably be wrong. I don't think we will see anywhere near the rainfall we did last year but somewhat of an increase looks reasonably likely.

The big one is coming...the MJO is arriving and its strong, strong enough for the BOM to issue a statement about the possibility of the seasons first cyclone. That is all we lack from the killer blow, tropical moisture similar to last year. Next week is the set up, the week after could be the one.

Access is over doing the DPs, as if reaches 26 through the interior for 3 days as suggested we will all be dead. However with 18s a more realistic figure, especially feeding from the NT, and as Andrew said a NE flow also pumping moisture in from the NE, its just a matter of when. Could yet again be a big December. Stay tuned, next few days crucial to the set up, if Sunday turns out to be a not much affair, will change the ball game again.