Wet Week for the South Island

[tgsnoopy]

Local radio is broadcasting this to start at mid day today.

A bit premature and hopefully won't lead to people thinking it's a non event and then getting into bother later.

The models sure do look ugly for here.

[CHCH Weather Chaser]

Last nights models went up from 54 mm to 77mm. This mornings model run for GFS shows 72.3mm. So staying in the 70's now!

[Janos]

Last nights models went up from 54 mm to 77mm. This mornings model run for GFS shows 72.3mm. So staying in the 70's now!

You will truthfully find the right answer eventually after the event has happened.

[carrot]

MS mt hutt forecast went from 80cm last night to 101cm today. Not that it means much for the plains.

[CHCH Weather Chaser]

WOW, the sun has been out for quite a time today after the morning drizzle cleared! Latest GFS model at 11am was still showing in the 70's.(79.1mm) Thats 3 runs in a row now so we are looking at something like that!!! The 7 day forecast rain outlook shows the rain intensity as being much greater . Blue skies has a watch for 50-100mm for Canterbury. Metservice has warnings out for CHCH amd Canterbury Area.

[trickytiger]

I just got told that on the rock they were saying 60-100mm of rain for Canterbury and telling people in Canterbury to stock up on things.

Maybe the heard that for another place and thought they said canterbury, I see the gfs is only showing 78.9mm, so I don't think much of that forecast up to 100mm

[melja]

Not much between 78.9mm and 100mm so i would say that accurate.

[trickytiger]

didn't think of that, so will be close to accurate maybe in chch close to the foothills and parts of inland canterbury? and maybe no more than 20-30mm in my area.

the 20-30mm guess i've made by looking at rain fall predictions near my area, then i took a little of those forecasted rainfalls.

[tich]

Looks like heaviest falls will be in the Central and North Canterbury foothills, but if it's expected to fall as snow above about 500m, wouldn't that reduce the amount of flooding from rivers coming from the area?

[trickytiger]

I wouldn't expect any rivers to flood in canterbury because of the snow above 500m, i'd just say a lot of surface flooding around, some small streams may flood though

[melja]

The ashley river has its catchment in the coastal foothills and it drains from a large flat valley that may not get the snow.

[trickytiger]

ok, I wasn't aware of the ashley river, but I know there is also a lot of rain forecast for the foothills (maybe the lower part) as well as the snow at 500m and above, so maybe it has a chance of flooding depending on where the catchment is and exactly where the snow falls?

[Storm Struck]

Now that we are close enough it is fair to say that there should be substantial rainfall totals in the next few days.
I am going for 100-130mm about the North Canterbury foothills and 70-90mm elsewhere eastwards north of Timaru.
A good point there with the snow at 500m, but the main problem could be the fact that paddocks already have surface water on them so there is going to be alot of run off storm water into creeks and rivers instead of soaking in.
Why has MS forecast severe gale easterly winds for Westland when the mountain ranges will actually help to shelter Westland from the flow.
Drizzle is beginning outside now, although not part of this system yet.
Cheers
Jason.

[gopolks]

TVNZhave just said 40-60 mm for canterbury,

[Gary McConnochie]

Jason, I think you will find it will be a bit like what we get in a North westerly but in reverse. Someone else might be able to give a better answer.

Gary

[jamie]

Yea Jason look at Te Aroha, it is right at the base of the mountain range and they got hammered by the winds from the bomb low. I cant remember what the name of the effect is but yes mountain ranges do sometimes enhance wind speed.

[melja]

Yes i remember taking the camper down that part of the coast in a weather system just like this and we had to stop driving as the wind came down those long valleys like a bloody hurricane.

[Michael]

Yea Jason look at Te Aroha, it is right at the base of the mountain range and they got hammered by the winds from the bomb low. I cant remember what the name of the effect is but yes mountain ranges do sometimes enhance wind speed.

Katabatic wind?

[trickytiger]

katabatic wind definition: "A katabatic wind, from the Greek word katabatikos meaning "going downhill", is a wind that blows down a topographic incline such as a hill, mountain, or glacier. Such winds, particularly when they occur over a wide area, are sometimes called fall winds."

Source: http://www.answers.com/topic/katabatic

Looks like that is the correct term for downhill wind.

[Willoughby]

It's not a Katabatic... Katabatic winds are like the opposite of sea breezes.. Gisborne gets them nicely from the NW on cool nights to equalise temperatures.

So in Westland's case it's more of a foehn downward wind than a Katabatic.

[gopolks]

Are they expecting any flooding in canterbury?

[NZ Thunderstorm Soc]

Maybe , there could be a reversal of the "NW Arch" over Westport. A "SE Arch" maybe???

JohnGaul
NZTS

[Ryan Thomas]

I thought they get warm temperatures out of SE's, isn't that how they get their warm temperature records? If so why only 15?

[NZ Thunderstorm Soc]

I wouldn't expect any rivers to flood in canterbury because of the snow above 500m, i'd just say a lot of surface flooding around, some small streams may flood though

There could be dry creeks like Coopers Creek, north of Orari, and the Selwyn River, near state Highway One, which could have some water in them?
I'd watch the Blue Slip, north of Kaikoura.

JohnGaul
NZTS

[melja]

Just talking to my father (works for ECAN) and he is getting sent to the eyre river( runs from oxford foot hills to the waimak) with a dozer to keep the river away from the bridge embankments as they think they may get damaged.