Many areas in the southwest of WA over 200mm for the month and more rainfall is on the way during Monday with a significant cloud band and strong cold front, driving a band of heavy rain and strong winds to the region.
Satellite Imagery - 12pm WST - Sunday 11th of July 2021.
Again the science of the negative IOD before our eyes with another cold front tapping into moisture over the tropical basin and dragging south via the northwest winds in the upper atmosphere. Widespread rainfall developing along the front with a few thunderstorms as well. Colder weather to follow with another burst of showers hail and thunder for the west coast with that cold pool rotating near the low pressure centre.
18z GFS Rainfall for the coming 10 days - Valid Sunday 11th of July 2021.
Widespread rainfall developing Monday and persisting about coastal areas during Tuesday. Some of the falls may exceed 50mm once again over the SWLD. Up to 20mm through inland areas of the SWLD. The rain marching east mid week. Another set of fronts keeps the showers going mid to late week with a colder shift. So again an alert to farmers and graziers for cold and windy wet conditions later this week. Then another major rainfall event develops next week and that is off the back of temperatures well above average! So a spring preview perhaps for the west!
18z GFS Precipitable Water Values for the coming 16 days - Valid Sunday 11th of July 2021.
Extensive moisture coming out of the Indian Ocean in the second week of the outlook is something that needs to be watched as it could produce more heavy rainfall for very soggy parts of the southwest of WA which is nearing the monthly averages after this week. This is the wettest time of the year for the west coast.
18z GFS Surface Pressure Pattern for the coming 16 days - Valid Sunday 11th of July 2021.
Widespread cloud and rain early in the period with the major front and then we focus on shortwave fronts this week until another strong cold front arrives during Thursday sending a cold and unstable southwest burst through the region. We dry out during the weekend but a lot of moisture may return through the west and southwest of the nation during next week with a major cloud band coming in from the northwest.
Rainfall for the next 10 days
Widespread rainfall early Monday through Tuesday may bring 20-50mm to many areas of the SWLD. Showery periods bringing daily falls of 5-15mm Wednesday and Thursday before another 10-30mm arrives from later Thursday into Friday. A dry weekend then it is possible another 20-50mm of rainfall develops next week with yet another low and cold front connected to moisture from the Indian Ocean. That will be something that will watched this week and updates on that will appear separate to state based posts.
Thunderstorms are also a chance during Monday with the chance of flash flooding, damaging winds and small hail to follow the rain tomorrow night.
Thunderstorm Forecast Monday - Valid Sunday 11th of July 2021.
Squally rain developing with a strong cold front with embedded thunderstorms likely to feature ahead, with and following a front. The front will carry the highest chance of thunderstorm activity on Monday. Heavy rainfall may lead to flash flooding and damaging wind gusts are also a high chance.
There is a 90% chance of thunderstorms within 25km of a given point within the pink zones
Damaging Winds Risk Monday - Valid Sunday 11th of July 2021.
Squally showers with damaging wind gusts of up to 100km/h are possible during Monday, ahead, with and following a cold front. The most active damaging wind gusts will be found along the cold front. The risk then diminishes for inland areas following the front and the risk lowers to moderate following the front over coastal areas.
Low - 5-20%, Moderate - 21-40%, High - 41-60% chance of damaging winds observed within 25km of a given point.
Flash flooding risk Monday - Valid Sunday 11th of July 2021.
Heavy rainfall especially along a cold front passing through the region tomorrow, has the moderate to high potential to produce heavy showers and thunderstorms leading to intense rainfall rates and flash flooding. Given the ground is saturated after extensive rainfall, it will not take long for ponding to occur and flash flooding to take off so be weather aware during Monday.
Low - 5-20%, Moderate - 21-40%, High - 41-60% chance of flash flooding observed within 25km of a given point.
Hail risk forecast Monday - Valid Sunday 11th of July 2021.
Lower risk of widespread small hail as per previous fronts with the air a fraction warmer. But the cold pool rolling over the region overnight into Tuesday may bring a better chance of hail to the coastal areas.
Low - 5-20%, Moderate - 21-40%, High - 41-60% chance of small hail observed within 25km of a given point.
More details to come in the evening weather updates after 5pm.