A weather event shapes up

 On April one a post on the Mallacoota Community News Facebook Group (MCN) linked to a BoM Flood Warning page under the heading "Here we go again".  That seems to be a very fair call.  At 0730 on 2 April the Warning included 

"Minor to moderate flooding likely across parts of West and East Gippsland from overnight Saturday into Sunday with major flooding possible in the Cann and Genoa catchments during Sunday."

At home I recorded 5 mm of rain on 1 April and as at 0730 have 17.2mm since midnight (those data will not count towards the 2 April total due to the 0900 switchover 😠😠.  The current Bairnsdale 256km radar image suggests that we are in for a bath.

Cutting to the chase, we got an Olympic Pool rather than a bath.  On 2 April I recorded 144.2 mm (2nd highest recorded at Mallacoota out of ~17,000 observations) and on 3 April I had 120.6 mm (7th highest).  The 2 day total (264.8 mm) is ~30mm more than any other consecutive 2 days since records began. The BoM total for Mallacoota Airport was 213 mm (itself the third highest 2 day fall) and recordings there were generally lower than mine but a comment on Facebook by a resident, close to our house, indicated her readings were close to mine. 

Total rainfall since midnight, as at 1400hrs on 2 April was 83.2 mm at home according to my WS.  My Nylex had 81mm which is close enough to the same!

I went to Bastion Point to check out the state of the ocean: as shown here, a trifle lumpy.  I swung by the wharf to check the level in the Inlet.  It was at 0.56m, an increase of 0.08m since I was here at 1100 hrs: I'm not sure to what extent that is due to rain coming down into Bottom Lake; tidal variation; or the wind and swell driving the ocean inland.

By 1424 the radar was suggesting that the worst of the rain was occurring to our West and Mallacoota only had light, if any, rain.

Looking out the window, with the Narrows barely visible through the rain, suggests that is far from accurate.

The rain, together with a SE gale blowing water in through the mouth led to the Inlet being quite high for our morning walk on 2 April.

The official gauge at the Main Wharf was registering about 1.1m ( I couldn't get close enough to read accurately).

By midnight on 2 April my WS had recorded 144.4 mm of rain.  That is the second highest in the records for Mallacoota (the highest being 192.4 mm on 20 May 1978).  

• The BoM site at the airfield recorded 113.2 mm  (which would be the 9th highest reading in my data set) over the calendar day, while BoM at Gabo Island recorded 72.4 mm.  
• A wunderground station in the town centre has recorded 111 mm for calendar 2/4/2022.  
• At one point in the morning of 3 April a friend reported - somewhere on Facebook but I can't relocate it - that she had recorded 177mm at home on Intervale Drive.
• My Nylex, positioned about 5m from the WS)  continues to give readings very close to those of my WS.  

Obviously there are cells small embedded in the continual flow which greatly boost very localised falls.

The following charts show the hourly fall and rate across the day.

The rain has not gone far inland with Bombala AWS - near the head of the Genoa River only recording 5.2 mm since 0900 0n 2 April.

As Excel will not create column charts with two vertical axes I have used a line chart instead to show the falls on 3 April at my WS.

The Flood Warning early on the 2nd said 

"The Genoa River at The Gorge is currently at 1.25 metres and rising. The Genoa River at The Gorge is expected to exceed the minor flood level (2.20 m) overnight Saturday into Sunday. The river level is likely to reach the moderate flood level (2.90 m) Sunday morning."

In fact it got to minor flood level and has since receded.

Looking at a pressure map on the BoM site the event certainly appears to meet the criteria for an East Coast Low.  It also appears to be moving closer to the coast through at least the morning of Sunday 3 April.  That being said the latest radar images show no rain the area with the only registration being a band of squalls about Cooma!  

Obviously the last paragraph was a case of speaking too soon!  Shortly after composing it we went for our morning walk and it started raining again.  That is reflected in the hourly chart above.

I also downloaded the Meteye 3-hourly rainfall forecast totals for the next two days and will compare that with actual.  We are currently at the 25% probability level for the period starting at 0500.  By 1400 my WS had recorded falls greater than those forecast with 10% probability by BoM while the BoM site had recorded falls greater than those with 25% probability (but slightly below the 10% level).    This image shows a comparison across most of the 2-3 April period.

In summary for 7 of the 15 periods both my WS and Bom recorded falls > the Meteye 25% probability forecast and for the evening of 3 April both my WS and BoM recorded > the 10 % probability fall.  My WS also exceeded the 10% probability on 3 periods on the 2nd.  Allowing for some site-effect being evident with my WS the Meteye forecasts are I think pretty  good: we should have beaten the 25% level on 4 occasions and did so on 7: we should have beaten 10% on ~2 occasions and did so once.

A final note is to look at what has developed with my pro-rata estimates of the annual total for 2022.  In the past I have ignored the very high estimates generated by falls in the first week of January.  This year they have looked like the shape of things to come so I have left them in!