Lots more rain to come – flooding likely

Saturated ground, showers increasing, heavy falls likely - and a surface trough to further increase rain totals...lots of weather to talk about.

It’s raining already – and there is a lot more to come. The analysis chart from 11pm last night gives some hints as to why:

The light colours show a pool of cold air up high, with warm wet air moving into the coast down at the surface level. Warm air likes to rise – and it will continue to rise as long as it is warmer than the surrounding air. As it rises it cools down – and releases the moisture as rain. You can also see this coming together on the latest satellite image – the showers and storms focussed around the cold pool inland, and the showers moving onto the coast:

That cold pool is going to move slowly east over the coming days. That will further increase instability further across coastal areas, with a surface trough likely to develop close to the coast. You can see this happen on the forecast charts with the cold pool moving across and the dip in the isobars at the 72 hour mark:

With a simple onshore flow we know that we’ll see showers right along the coast…and that will be the case to kick off this event. The deepening surface trough along the coast will add some complications to the mix with a big increase in showers and storms just to the south of the trough, with much lighter falls to the north. Right now it looks like the heaviest falls will just be to our south, but the exact location is still up in the air….and even if the heaviest falls are to our south we’ll still see some BIG totals from the onshore flow before the trough develops. Here’s the latest 7 days totals from a range of models – and you can see the size of some of the falls predicted but also the differences in the forecast locations of the heaviest falls:

This means we know that big rains are coming – but that we need to keep an eye out and watch what is happening in real time to know who will see the heaviest falls. We should see a Flood Watch from the BoM coming out soon – I will edit this post to include once it is available.

EDIT: Flood Watch now out:


Initial Flood Watch for the Orara, Bellinger and Nambucca Rivers
Issued at 10:44 am EDT on Wednesday 17 March 2021

FLOODING POSSIBLE FOR THE ORARA, BELLINGER AND NAMBUCCA RIVERS

Rainfall is forecast along the New South Wales Coast from Thursday and will continue into the weekend. The rainfall has the potential to cause minor to moderate flooding along the the Orara, Bellinger and Nambucca Rivers. Flooding may develop from late Thursday into the weekend.

A coastal trough is expected to deepen near the northern New South Wales coast on Thursday morning and then gradually extend south on Friday generating unsettled weather and heavy rain. Heavy rainfall may develop from Thursday morning along the mid north coast. This may then spread south towards the Hunter, Sydney and Illawarra during Friday and Saturday.

Catchments likely to be affected by flooding are currently wet following rainfall earlier in the week.

The weather system is expected to cause flooding for the catchments listed from Thursday into the weekend as the weather system moves south. Flood Classes (minor, moderate, major) are only defined for catchments where the Bureau provides a flood warning service.

Catchments likely to be affected include:

Orara River minor to moderate flooding
Coffs Coast
Bellinger and Kalang Rivers minor flooding
Nambucca River minor to moderate flooding


The BoM have also issued a Severe Weather warning for our region with flash flooding possible:


Severe Weather Warning for Heavy Rainfall for Mid North Coast Forecast District.

Issued at 11:16 am Wednesday, 17 March 2021.

HEAVY RAIN DEVELOPING FOR THE MID NORTH COAST FROM THURSDAY MORNING

Weather Situation
A coastal trough is expected to deepen near the northern New South Wales coast on Thursday morning and then gradually extend south on Friday. HEAVY RAINFALL for the following areas:
Mid North Coast
HEAVY RAINFALL, possibly leading to FLASH FLOODING, may develop from Thursday morning across the Mid North Coast. Rainfall may ease a little on Thursday night, however, heavy rainfall may spread further south as the trough extends southwards on Friday. As catchments are relatively wet in the Mid North Coast, RIVERINE FLOODING is also possible. A Flood Watch has been issued.
Locations which may be affected include Coffs Harbour, Port Macquarie, Taree, Woolgoolga, Sawtell and Dorrigo.


These warnings will update over time – check the BoM warning page via the link below for the latest updates.

The takeout for us: showers increasing over the coming few days with heavy falls likely. A trough will likely develop along the coast late week / over the weekend. When it develops areas just to the south will likely see some very heavy falls, but conversely areas to the north will see a decrease in showers. It looks like the heaviest falls will be just to our south, but definitely one to keep an eye on very closely.

As we know our rivers are already up and the ground is saturated. Any further heavy rain will bring about some quick rises and this looks very likely over the coming days. It would be useful to have a well stocked larder if you live in an area that could be cut off.

Looking further ahead it’s still looking fairly wet – though likely not as wet as these coming days. I’ll post again tomorrow as we head into the event.

Live river heights are available here.
Live river cams available here.
Live weather information for Bellingen town is available here – however with the peak rainfall more likely on the hills it would also be worth keeping an eye on the BoM rainfall monitors across our region – and you can find them here.
Any warnings from the BoM can be found here.
Local SES warnings can be found here.

Thanks and credits: Snapfrozen | Kombu Wholefoods | BSCH | Tropical Tidbits | Meteologix

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