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Rainfall can be unfair and mother nature always has the final say.
Two rain-bearing systems have crossed NSW during the past week. The first was a band of rain and storms that swept across the state from west to east between Thursday and Saturday. A second bout of showers and thunderstorms occurred on Tuesday and Wednesday as an upper-level trough moved towards the Tasman Sea.
The cumulative effect of these two systems has helped many locations across NSW exceed their monthly average rainfall by Wednesday morning.
Unfortunately, this hasn’t been the case everywhere.
Some of the winners so far this month include areas in the Upper Western, Snowy Mountains and South Coast districts and smaller pockets of the North West and Central West Slopes and Plains.
Hay Airport recorded more than a month’s worth of rain during the 24 hours to 9am on Friday, when 42mm hit the gauge. Further north, West Wyalong has nearly doubled its May average, with 72mm so far this month. If Tamworth picks up another 4mm before next Wednesday, this will be their wettest May in 20 years.
By contrast, places that haven’t fared too well this month include Collarenebri (1mm), Dubbo (5mm) and Williamtown (11mm). Adding to their pain are significantly higher totals at nearby rain gauges. Rowena, less than 30km out of Collarenebri, has picked up more than 20mm this month.
So, why is there such a marked rainfall discrepancy across such small distances?
A number of factors determine when and where the heaviest rain will fall as a system moves across NSW. This includes the amount of moisture available in the air, the movement of air horizontally near the surface and vertically through the lower few kilometres of the atmosphere and topography. If these factors align favourably near your place you’re going to see rain, while neighbouring towns could miss out altogether.
The small-scale discrepancies of rainfall make it one of the most difficult weather phenomena to predict ahead of time.