Widespread rain across NSW to reduce threat of bushfires leading up to Christmas
Widespread rain will spread through NSW over the next few days. (ABC News: Jack Ailwood)
The most widespread rain in three months will develop across New South Wales during the coming days, reducing the threat of bushfires in the lead-up to Christmas.
Modelling is predicting an average of 20 to 50 millimetres for the state's east, including across the major firegrounds from the Central West to the Hunter and Mid North Coast.
However, without follow-up rain during the coming weeks, a heightened fire threat could again return as peak summer temperatures arrive in January.
Loading...Dry spring primed NSW for major bushfires
Rainfall in many parts of NSW through October and November was in the lowest decile, meaning totals were in the range covering the lowest 10 per cent of years.
For example, the rain gauge at Crawford on the edge of the Bulahdelah fire has received just 42mm since late September, less than 20 per cent of the long-term average.
This severe rainfall deficit since an exceptionally wet winter in NSW is leading to a rapid decline in the hydrologic health of the state.
According to the NSW Department of Primary Industries and Regional Development, 51 per cent of the state is now officially in a drought category, up from 26 per cent in September.
And while drought is spreading, soil moisture, a critical component in the daily fire danger, is in rapid decline.
Data from the Bureau of Meteorology (BOM) shows during the first week of summer, the amount of water in the top 1 metre of NSW fell to a percentage rank of only around 15 per cent — an indication that moisture available for vegetation to protect itself from combustion is severely lacking.
When combined with bursts of hot, dry winds from the interior, this dry environment created the optimal conditions for last week's devastating bushfires.
Best falls since September
The best defence against bushfires is rain, since it adds moisture to both the soil and ground fuels like twigs and litter.
And thankfully, rain is ahead during the coming days as tropical moisture moves south and interacts with a series of troughs.
The event will kick off with a few thunderstorms on Wednesday afternoon in the state's north and east, and while brief heavy rain is possible under the more intense storms, falls on Wednesday will average only about 1 to 5mm.
Showers and thunderstorms will then become far more widespread on Thursday and Friday as twin waves of cold air aloft destabilises the atmosphere.
The heaviest falls during this peak 48-hour period should impact the northern inland and the central stretch of the coast, including Sydney and its surrounds.
The bulk of activity will then track offshore on Friday night. However, another lighter band of showers should follow over southern and central NSW on Saturday.
A solid soaking is ahead during the coming days with areas of more than 50mm possible in the east and north.
All up, this four-day spell of unsettled weather should bring an average of 20 to 40mm to most regions of NSW apart from the far north coast and far west — easily the most widespread rain in three months.
Some modelling even predicts pockets of 100mm in Sydney, the Illawarra, and possibly the northern ranges — about a month's worth of rain.
Unfortunately, the hit-and-miss nature of storms also means some areas could miss out and receive less than 10mm.
Welcome relief, but forecast uncertain
Another benefit of widespread rain, in addition to the immediate dampening of the fire threat, is a reduction in the number of pre-existing fires before the next day of extreme fire danger arrives.
And while this week's rain will not completely extinguish all fires, even blazes that continue smouldering will burn at a reduced and more controllable rate.
After this week’s rain, the BOM's modelling shows no clear sign of whether rain will be above or below average heading to the new year.
How long a dousing then lowers the risk depends on the weather conditions that follow, and modelling is hinting that relief may be limited as another spell of hot and dry weather arrives across south-east Australia next week.
Further ahead, fortnightly outlooks indicate mixed prospects through late December, meaning a close to even chance of above or below median rain.
Under the scenario without follow-up rain, the worst of the NSW fire season may still be ahead, while additional summer soakings will suppress the danger.
What is certain though, NSW will welcome a lowering of the general fire threat in the short-term, with the reassurance that a repeat of Black Summer is not heading our way for Christmas.