RAINFALL TO BUILD OVER THE SOUTHWEST OF WA THIS WEEKEND.

After a dry few days with cold nights and sunny weather, a colder start for Saturday will give way to a milder afternoon with northerly winds developing. But the weather is set to turn on Sunday with the approach of a cold front with gusty showers and storms. Colder weather will return with a wintry chill to persist into next week.


Rainfall for the coming 10 days - Valid Friday 25th of June 2021.

I have reduced the rainfall amounts for inland areas as it looks like frontal weather will be out of phase and a fraction too far south to tap into the moisture plumes sitting over the Indian Ocean this time around. That means widespread rainfall for inland areas looks unlikely over the coming 7 days at this stage. Showers may be heavy at times over the southwest of the state with local hail and thunderstorms about.

Two fronts are expected to impact the southwest of the nation at this stage. That first front I mentioned earlier, is likely to spread a band of rain and thunderstorms through the southwest with moderate falls. Heavy falls are possible about the southwest capes and inland to about Bridgetown, exposed to the westerly wind regime.


Rainfall totals will rapidly taper off the further inland you go with the front weakening, in line with the system encountering a strong upper high over the east.


A second front is expected to ride up from the southwest and move over the SWLD during Monday night or Tuesday with another round of strong gusty winds and widespread showers. This frontal passage is the coldest of the two moving through, with local hail and thunderstorms for the coast, mainly impacting Albany around to Bunbury. The heavier rainfall will also be linked to these areas. Overall modest rainfall for the inland and along the south coast, tending moderate to heavy in the wet spots south of Perth.


Upper flow pattern for the coming 2 weeks, showing the strength of the first two fronts over the SWLD and the third front now expected to peak further east, and allowing a high to clear conditions in the back stages of next week.


GFS 18z run - 500mb/18000ft flow pattern - Valid Friday 25th of June 2021.

Moisture is not as deep with either systems moving through this week, but the showers will be locally heavy just with the instability moving through. Rainfall totals in response to a shallow moisture level will be lighter inland as a response and not extend as far north and east as what we saw in the previous event, which carried tropical moisture from Indonesia through the outback and along the west coast before moving eastwards.


GFS 18z run - Precipitable Water Values - Valid Friday 25th of June 2021.

For those over the pastoral districts and the farming zones, there will be a chance of more frost behind the fronts early next week, some severe. Then a drier phase developing for the second half of next week.


More rainfall is likely to return as you can see from the precipitable water values and surface pressure pattern to kick off July.


I have also added an update to the July Outlook for Rainfall and Temperatures as of today in the climate folder.


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