April 2025 Weather Report

 This is starting off as a quick draft, with preparation commencing before the end of the month, focusing on a few core variables (although I have bolted down a few data-burrows in the rainfall area).  The key comments are that by the end of the period it had became a very wet and very warm month overall. Some key numbers are here.

Rainfall

For the 4th month in a row rainfall was well over the median value.  The outcome was the water level in the Inlet rising sufficiently to close Lakeside Drive.  While this is the first time I can recall that happening with the mouth open, a long-term resident has advised that "Lakeside Drive has always flooded in my memory. Closed or open to ocean Lake or not!".

The length of the period of over-median rainfall "felt" longer than usual.  On checking my long time series (including data from the BoM Airport site from May 1984 to March 2019) this seemed to be confirmed, but I am having difficulty in presenting this in a clear and rigorous manner. (The longest run is 10 months of below median falls from April 2019 until January 2020: no wonder the fire went so quickly!) 

The total fall for the month at Angophora Drive is 179.8mm (237% of median April fall at this site). I found the recorded numbers to agree well with the collection in my Nylex plastic gauge. The comparison with records from the BoM Stations at the Airport (154.6mm) and Gabo Island (146.6mm) are interesting in a number of ways.

• It is unusual for both sites to be lower than my WS.  As well as the check offered by my Nylex, other observers' records from Karbeethong and Mirrabooka correlate well with mine.
• It is difficult to compare the BoM daily falls (based on a historically based 0900hrs reset)  with my records based on a midnight reset.  However I have achieved that with some effort.

The unusual period is 22-23 April.  During that time the radar image tended to show a line of small cells heading directly up the Genoa valley between the Airport and Gabo Island.  It seemed as though the hills of the Drummer area and Howe Range were shepherding the weather.

For the year to date I have recorded 475mm (179% of the median fall to end April).  Using the records for the year to date to compile a chart of the development of my prorata estimate of the annual fall shows the continual rain in the area.  This contrasts with the rest of Victoria where anecdotes report significant dry weather, as shown in this BoM map (thanks Rob Clay for drawing it to my attention).

I suspect that the average used here is the mean rainfall rather than the median.  The mean is biased upwards by occasional months with very heavy falls in a small number of years.

The mean rainfall to the end of April is 303 mm compared with a median for the period of 265 mm.  It should also be noted that the BoM data will probably not have registered the heavy local falls described above.  Most importantly the map shows a 12 month average including several months in 2024 with very low rainfall in Mallacoota.

Temperatures

The value for the temperature anomaly in April was +1.47C.  The early part of the month was cool but after 7 April one of - or frequently both - maximum and minimum were above the average value for the date.

This continues recent experience resulting in the 12 month moving average plot of anomaly values turning upwards.  

The chart of daily extremes shows that the key contributor to the strongly positive anomaly is the high minimum temperatures.  Particularly at the end of the month maxima were close to or below the longer term average (as expected given the blanket of cloud).

There were only 2, widely separated, days on which both minimum and maximum were significantly above the average, although 12 days had both values above average (expected value 8). 

Minimum temperatures

The average minimum for the month was 13.50C, just below the highest for the District, at the BoM site at the Airport (13.54C in 2002).  It is clearly the warmest recorded at my WS.

The minimum was above average on 22 days, and significantly above average on 9 days.

Maximum temperatures

The average maximum for April was 22.6 C, well above the average for my WS since 2019.  It is below the maximum at the Airport, adjusted to be comparable with my WS which is estimated as 23.8C in 2016 and 2018.

The maximum was above average on 18 days and significantly above on 8 days.

Humidity

The average humidity at 0900 hrs (86.1%) was the equal highest recorded for an April at my WS.  For the afternoon (1500 hrs) the reading (70.9%) was above average, but below 2 of the 6 earlier years.  The daily values were not remarkable.  

Wind

The average wind run at 66.6 km was well below average.  This possibly reflects the wind coming from Southerly directions (14 of 30 readings at 0900 hrs by the Airport site came between SSW and SE) from which my WS is sheltered.