Coffs Harbour picks up the heaviest March rainfall since 1974. Heavy and persistent rainfall over the Mid North Coast of New South Wales was seemingly relentless yesterday as cool air in the mid-levels of the atmosphere exacerbated the effects of a weak coastal trough. The first of the thundery showers set in over the Coffs Harbour region at about 10:30 am yesterday and hardly eased up until about 9pm that evening. In the 12 hour period from 10:30am, Coffs Harbour managed to collect 182.6mm in the bucket, with a further few drops pushing to 9am total up to 183.4mm by 9am today. This monumental downpour makes it the most significant March rainfall since 1973. Irrespective of the month, Coffs hasn't seen rain this heavy since January 2013 when the remnants of Tropical Cyclone Oswald drenched much of the east coast of Australia. In fact, during the period that Ex-TC Oswald passed overhead, Coffs Harbour saw a 72 hour total of 423.1mm to 9am 29th of January, 229% of the January average in three days. One of the more interesting aspects of the event last night is the concentration of heavy rainfall. Within the vicinity there were comparable totals such as 152mm at Gundagai Street, 144mm at Bombaree Res and 138mm at Macauley Res. However, just inland Bellingen only received 46mm. Similarly, up and down the highway Woolgoolga and Nambucca Heads only picked up 29mm and 25mm respectively. The reason for this concentration of heavy rain is that the moisture laden surface winds were prevailing from the southeast. A topographic ridge line running in a southwest to northeasterly orientation through the Bombaree State Forest and Orara East State Forest (and surrounds) forced this moist air to rise, condense and therefore fall as rain. This phenomenon is also known as orographic lifting. Surround areas such as Woolgoolga and Nambucca Heads lack such a topographic feature. As midnight came and went, the showers managed to remain just offshore, giving the residents of the Mid North Coast a bit of relief. The odd light and isolated shower should hang around this morning, soon easing into the afternoon and evening.