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Discussion in 'Alpine & Snow' started by thepass, Jul 12, 2006.
Whats this 'rain' you speak of? Its only 'showers and drizzle' in Winter!
More than we get in Sydney blue_neon. Normally when the fronts come through we get a few fluffy clouds zooming across a brilliant blue sky.
OK, then how about we work constructively to either prove or disprove these ideas Bogong? I have no idea where to get upper-level live temp readings for the areas the system is crossing over right now. I imagine these would be available from aviation sources, but would not have a clue where to begin looking. If this low is truly weird enough to produce really cold conditions on the ground and yet be relatively warm at 1500m then I concur that the rain damage will be significant - buts lets see the data (live, not models) first.
there is alot of mixed opinions... this should turn out to be very interesting. depending on who is right there could be alot of ego's hurt here... lol! I just HOPE it dumps!
Zyke - you should use Soundings to get ideas of Upper Level temperatures.
Although they are only located in major cities / areas in Australia, you should just choose the location closest to the area you are looking at (whether that be Alps or where the low is moving through now.)
Bogong... Good info but could you clarify something ?
Is there a "height" definition attached to "upper atmosphere"...??... & what sort of temperatures are we talking about at those levels?
As in rain i ment "Heavy falls"... i swear i see 'red' patches on the radar around Sydney! (maybe not recently though , but Melbuorne recorded only 16mm for the monthly June total!)
Melbourne *may* total more but mostly from small showers or drizzle in Winter! Certainly no 'rain'...well not yet!
Its been said many times this year but its worth repeating. Head to the link below and wait for soundings to update for a particular area. Follow the red line on the right to heights of 850hPa, then 700hPa then 500hPa. IMO, passable temps for a decent cold system are -1C at 850, -8C at 700 and -26C at 500. -2C and colder is better for 850, -10C is better for 700 and -28C or better is preferred for 500. Cut and paste this info to notepade for future reference. For aggressive cold air convection and not just wet snow, you need cold uppers.
Enter "bomw0007" for user id and "aviation" for
ED: Bogong might have more ideas on what he likes for upper air and mid level temps as well for the ski fields area.
Live upper air data is a bit hard to come by (other than the Alps themselves). The best that is easily available are the 10.00am soundings.
Below is the data from Woomera this morning from the University of Wyoming .
The data presentation is a bit crappy (can anyone help?) but the first column is the pressure level, the 2nd column is the height of that pressure level, the 3rd column is the temperature at that height, 4th column is dew point and 5th column is relative humidity.
As you can see the temp is a cold (for them) 8.8C at the surface. As you rise through the atmosphere the temp increases to + 9.2C at 861meters and is still +3.6C at 2244m and + 1.6C at 2,507m. So freezing level is around 2,700m despite it being less than 9C at the surface.
In this case the surface temps are not a good guide to the temps higher up. I will do this tomorrow after the morning soundings come in.
PRES HGHT TEMP DWPT RELH
hPa m C C %
1004.0 167 8.8 -2.2 46
1000.0 201 8.4 -1.6 49
958.0 554 6.0 -1.0 61
925.0 843 9.0 0.0 53
923.0 861 9.2 0.2 53
850.0 1541 6.4 -1.6 57
830.0 1736 5.4 -0.6 65
809.0 1946 6.2 -2.8 53
780.0 2244 3.6 -4.4 56
755.0 2507 1.6 -8.4 47
700.0 3112 -3.1 -5.7 82
500.0 5720 -17.1 -18.9 86
400.0 7350 -28.7 -31.9 74
300.0 9350 -44.3 -48.6 62
250.0 10540 -53.3 -59.3 48
248.0 10592 -53.5 -59.5 48
208.0 11735 -51.0 -75.8 4
200.0 11990 -50.5 -79.5 2
150.0 13840 -57.7 -85.7 2
Hmmmmm..... Bogong could be right. Woomera is closest to the centre of the action and the upper-level temps are not encouraging. However the Low does not seems to have crossd over there yet as the temp in Woomera has been around 13c all arvo with no rain yet. Pity there are no soundings above Ernabella or Ceduna. Might be wise to keep an eye on the Woomera readings tonight - if the ground temp drops and the rain starts, but the soundings still show the inversion then the Ski fields are in trouble.
I hope not!
OK totally confussed now. I looked at the ones for Woomera, Adelaide and Melbourne - Follow the red line on the right - correct? Well in all places at 500hpa (which I 'guess is something like 5000m) the temp is still not negative - If thats what I'm reading then these figues are crap - No way could an elevation, in winter, equiv in hieght to Mont Blanc have temps in the positive. What am I doing wrong?
Are you sure it's not the red line on the 'left'? That makes more sense for Woomera (about 0c at 850hpa) - but still crazy for Adelaide which has a 850hpa reading of -20c
Zyka - Your reading it wrong.
Take a look at the RED line on the RIGHT of the Melbourne sounding...now find the 500hPa surface on the left column, then scroll your eyes right to the red line (so you have lined it up).
Its about -21C...i think you may not be reading the temperature correctly, the temperature goes 'diagonally' down...not straight down .
Thanks Blue-neon I got it now - let me go look at the figs with fresh eyes now
OK I got it now - but it still looks strange to me. Please explain Adelaide & Melbourne to me 0c at 900hps (1000m) and back up to +5c at 850hpa - Can that be right?
The only reason why Woomera's upper temps aren't looking encouraging is because the low is to far north, as it moves south cold air will start to wrap around it and be pushed further north. EC is looking somewhat encouraging, by holding its strength in the uppper temps (thickness).
P.S Yes Zyka, its called an atmospheric inversion. Generally, a departure from the usual increase or decrease in an atmospheric property with altitude. Often find them on a stable day.
Yep - you got it. Its the temperature inversion caused by descending air ahead of the high that is rapidly moving across SE Aust ahead of the low.
It is a good example of why temps at the surface aren't always a good guide as to what they will be at the level of the snow fields (ie 850-800hpa).
bogong - Can the 850hPa surface be related to elevations of around 1500 - 1800m?
Its normally around the 1400-1500m mark in SE Aust. But it can be around 1300 or up to 1600m depending on passing pressure systems.
Ie if the pressure at the surface is say 1030 hpa, then you would have to go up to around 300m to get to a pressure of 1000hpa.
But if the next day surface pressure is around 1000hpa because a low is nearby, then obviously the 1000hpa level is at the surface (and is 300m lower than the previous day). Same for the 850hpa levels.
The 850hpa level will also be affected by temperatures. Cold air is denser than warm air. So if the pressure at the surface is 1000hpa, then the 850hpa level on a hot day will be higher than on a cold day - say 50-100m higher just due to temperature alone. So there is a bit of complexity here. That is why you need to look at both 850hpa temps and heights to work out what the temp will be at a particular elevation.
The models and soundings give you these.
But if you are lazy or haven't much time then if you work on 1450m over SE Aust in winter, that is a good rough guide.
Thanks for that info
OMG! this looks shocking for the VIC resorts.
Here's a rough guide i've setup for soundings - far from complete but its something.
All this talk of colder surface temps then at altitude makes me question one aspect of this theory.
What happens to the cold air that is currently at sea level when it hits the mountain ranges. Surely it just follows the ground level and assends to the top of the mountain range therefore bringing colder conditions to the mountains.
My thinking is 10deg and rain in Adelaide =SNOW. Always has always will. That is the general direction from where our weather comes from. Sure we may get a bit of pre frontal rain. That cold air that is currently moving across SA isnt just going to get warm all of a sudden. It still has a southerly feed.
Its currently -2.2c at the top of the V8 Perisher and -9.6 at the bottom of the freelander quad right now- So much for no more subzeros till sunday
Depends how cold the air is at is ascends. The air cools at a different rate as its forced over the ranges, depending on if its saturated or not. You also have to take into consideration air mixing with this air being lifted from levels that are higher up. Its too simplistic to use a 10 degree Adelaide = snow approach, IMO. You are also presuming the air mass will be indentical over the ski fields as it is over Adelaide and air masses are not like that, they change, sometimes a lot.
hhmmm hate to say it BH but not sure there is anyway for us of getting around the fact that soon that low will set up near us and start bringing in an active north easterly airstream from the tropics with much warmer temps.
You can see on this chart the low pressure cell pulling in winds from way up over northern Australia into the south east on Saturday morning.
However once that low moves east of us we will see that colder southerly fetch you were talking about and we'll be in business
IMO Bogong Flyer is on the money and rain is mostly what we will see until Sunday morning. I guess for us skiers the key is for the low to move through a bit faster than expected so less rain and get the colder snowy weather to us sooner. Farmers might not like that though!
Here's hoping, I'm getting desperate cause I am heading to Hotham for the first time in a week and a bit
It has been a very busy discussion in here!
GFS seems to have relatively stabilised on this, and it Looks like it will be very wet through into Sunday, turning cooler in the afternoon in NSW, and later that night in Vic. ECMWF and GASP seem to back it up too
NSW & Vic BoM think there will be snow on the peaks (> 1800m) though which I can't see with freeze levels looking to be around 2200m and higher based on GFS.
Weatherzone also are still going for a big dump on Saturday too (10-20cm) with a snow level of 1700m. Is that really a freeze level, or does actually imply a freeze level is around 1900m? The later is more believable.
Even if the freeze level was a little lower the upper air seems just too warm. Whether or not the ski fields do well out of this, there should be a lot of very happy farmers in Vic & NSW that are currently in desperate need of some r*in...
Djon: Nice to see your comments here. I couldn't be bothered reading through it all but u have summed it up
Ernabella S.A - 120kmh winds & 100+mm rain
I see rain but i dont see 120kmh winds? I also see the maximum was 51.2C at 8.30pm and its now -1.5C....hmm does this lower the credibility of the amount of rain shown?
I think you will find thats an error Zyka
It could have been that wet & windy... But that AWS certainly has problems with at least it's temperature sensor :
Makes you not want to trust the other numbers too much...
Just been updated too. Now up to 158.4mm with 120km/h wind gusts.
Latest static satellite image with radar overlay below (will update). Have a look at the <a href='http://www.theweatherchaser.com/weather/observations/radar/Animation_AusSat'>24hr animated version</a>. That's a lot of wet! Would be nice if there was more radar coverage inland for this sort of (albeit less common) event.
Originally posted by Zyka:
Houston, I think we,ve found it.
The AWS probably having a little trouble with more water than a system designed for a desert can cope with.
And the sad thing is, just to the east of Aus there is that lovely cold pool that is cold enough to bring a nice fall to the aussie ski fields and even the Blue Mountains.
OK, here's something else to throw into the mix....
Here's the satelite picture. I've drawn where the spinning of the low is CURRENTLY centred (red circle), giving the location of the centre of low pressure.
From earlier today, and the current position, I've drawn a red arrow, indicating the direction that the low is travelling for the moment. The blue line indicates the PROJECTED direction the low is EXPECTED to travel based on the BOM 10am 14th July forecast chart.
The town of Ernabella is located around the top right of the red circle, and has received 57mm of rain in just over half an hour(up to 9:06pm), and 156mm of rain in the last 12 hours.
Question for discussion: If the low follows the red arrow rather than the blue arrow, what consequences will it have?
mon morning, all day tues & wed morning off
Yeah but its not going to follow the red arrow. Great hypothetical but the reality is that come Sunday we will have sore heads from this most peculiar front.
I think we will see more rain on Sunday than most are expecting. The freeze levels are way to high to be any benefit to Vic and marginal to NSW.
hopefully better consequences??? with a link up to the front to the sw we all wish!!
I dont get it!!!! ARe we going to get SNOW or Rain???
lots of rain with some snow after
Can anyone explain why the NSW BOM might be calling for snow above 1800 on Saturday?
I dont see why the low would go in the way you are predicting it to end up Sandy?
Um i think they just explained it for you...