Deep low pressure brings thunderstorms and strong winds

By Peter Nelson on January 23, 2017
  • Deep low pressure brings thunderstorms and strong winds

    A deep low pressure brought variable thunderstorm rainfalls and strong winds.

Another deep low pressure passed through our regions last Friday 20th January bringing variable thunderstorm rainfalls and strong winds. 

The low pressure complex developed over inland SA and deepened rapidly as it crossed Victoria. 

The central pressure in Melbourne fell to 992 mbs and this was the lowest barometer reading for January since 1994 and the sixth lowest for January since 1861. 

It was also the lowest reading for the second half of January in Melbourne for 118 years. 

Since last May there has been more than 10 times when deep low pressures below 996 mbs have passed over Melbourne. 

There were similar occurrances in the last 155 years from May to January only on six occasions in the same year and these happened in 1962, 1955, 1946, 1923 and 1874. 

It is interesting to note that the following year after these cases were not dry years over most of the Nation. 

Much property damage was done in SA around Adelaide where 21 mms rain fell. 

On top of 86 mms in December it is already the wettest December to January in Adelaide since 1962-62 and the third wettest since 1936-37 when a record 148 mm fell during December and January. 

Other wet December-January periods in Adelaide were in 1891-92, 1920-21, 1951-52, 1973-74, 1992-93 and 1993-94. 

Only the last case, 1994 was a dry year. 

The deep low brought the heaviest daily rainfall for January on record at Leigh Creek in the fat north of SA. 

Heavy rain also occurred as far north as Tennant Creek which is having it's wettest December to January since 1889. 

The monthly rainfall at Tennant Creek has exceeded the average every single month since last May and this has never happened before in 145 years of records. 

One of the heaviest rainfalls associated with this deep low was 83 mms at Mt. Hotham which is having it's wettest summer for 83 years. 

Another low pressure system is approaching from South Australia but is unlikely to deepen like last week's episode and thus less rain. 

Sea surface temperatures around the Nation are very interesting. 

Positive anomalies exist off the East Coast whilst negative anomalies have developed over the Indian Ocean. 

A very warm pocket is located east of Gabo Island which has been there since mid December. 

The negative anomalies in the Indian Ocean will no doubt reduce the likelyhood of tropical cyclones striking the WA coast.

By Peter Nelson on January 23, 2017

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