NATIONAL WEATHER PICTURE - MORNING EDITION - THURSDAY 20TH MAY 2021.

Headlines


  • Cold and foggy through the east once again this morning.

  • Weak front pushing through southeast Australia.

  • Finally a pattern flip for the nation coming into the weekend and next week.

  • Showery weather developing for the west of WA and east of NSW.

It has was again been a cold and foggy start to the day over the east with high pressure dominating the synoptic scale. On the west side of the high, a warmer and drier airmass is in place leading to well above average temperatures for both day and nights. That pattern will continue until the weekend.


Isolated showers have developed near a cold front over the southeast of Australia this morning with only very light falls achieved. That weather moving on by the end of the day. No rainfall will move north of about Ballarat to Wallan to Marysville in Victoria.


As the high begins to reconsolidate over the east during Friday an easterly wind shift will occur over the NSW coast with showers developing in that airstream, but heavy falls are not expected. More nuisance, coastal showers are anticipated for the weekend, and some of this will extend inland a tad and into SE QLD.


The high will get a kick on to the east during the weekend as a cold front begins to move over southwest WA. That will see the pattern flip take full effect, with a warmer few days for eastern Australia with a northerly wind. In the west showery weather will increase with the front, with moderate to some heavy falls over the SWLD as the front peaks over the region. Much colder weather will develop for the region after a week or two of well above average temperatures.


That front will move into the east on Tuesday next week.


National Satellite Imagery - Valid Thursday May 20th 2021. Note the weak cold front south of Tasmania, and the remnant moisture field being shredded by the stable airmass over the central parts of the nation.

The modelling is largely unchanged for the period showing the front out of WA encountering that large high pressure system in the east, and being shunted to the southeast as it approaches over the weekend. That will mean the bulk of the rainfall will likely peak out west, with patchy rainfall coming into SA and then into VIC, TAS and NSW. So rainfall rates will be less but with the moisture content still there, extensive cloud and patchy rainfall will be likely falling.


After that, there is still a stronger signal for a zonal pattern to develop as the Southern Annular Mode turns negative, bringing the westerly wind belt further north and more frontal impacts to southern Australia. This will lift rainfall chances as we end the month and kick off June.


Precipitable Water and MSLP flow pattern for the coming 2 weeks - Valid May 20th 2021. Note the green shading becoming more wavy in association with frontal weather over southern Australia, that bringing bursts of rainfall later in the month and into June. Also note the moisture working it's way into the front early next week in the east.


So overall the next 10 days of rainfall is looking more favourable out west over WA but the numbers are coming up for southern parts of the nation later in the month in association with the climatic driver shift.


Rainfall for the next 2 weeks - Valid Thursday May 20th 2021. The rainfall signals are largely unchanged from the 00z run on Wednesday 19th of May 2021.


Rainfall for the next 10 days - Euro Ensemble - Valid Thursday May 20th 2021. This is the most accurate medium term model and the strength in rainfall signals over WA is improving and shifting further north and east, which may be encouraging signs for SA coming into June.

Showers will increase in the short term for eastern NSW and QLD, along the coast, thanks to the onshore flow developing around the high. Guidance has not shifted on this overnight, with the bulk of the rainfall developing from Friday through Monday with 20-30mm possible for some locations and isolated accumulated falls towards 50mm.


Rainfall for the next 7 days - Valid Thursday May 20th 2021.

Showers over WA will increase through Saturday with the approach of a strong cold front. This will bump the warmth and drier airmass that has been sitting over the region for the best part of the last 10 days.


Some of the showers will be heavy and turn to rain periods along the front as it passes through. Gusty thunderstorms will accompany the change on Saturday with that colder shift also likely to hit the region by Saturday afternoon.


Rainfall for the period Saturday to Monday could exceed 50mm in the SWLD with 20-40mm likely for Perth and 5-20mm for inland areas as the front decays and loses it's integrity moving inland.


Rainfall for the next 10 days - Valid Thursday May 20th 2021. Rainfall guidance for the west has largely remained unchanged overnight with westerly winds bringing more fronts later in the period as well.

The pattern flip will be felt nationally with the temperature shift, with the peak of the heat arriving in the east during Monday with a gusty northerly flow as the front approaches. This will be the first time the temperatures have been above average for around a fortnight over the east.


Temperature anomalies for Monday May 24th 2021.

So the pattern is becoming more concrete in its tracking and placement of high pressure and there will be better agreement now on how that front behaves as it tracks over southern Australia. Then by the weekend we should know more about how the end of the month and early June develops.


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