Thunderstorms were widespread over western and southern parts of WA on Wednesday, delivering more than the normal total monthly rainfall to some places. A broad low pressure trough fed by moist westerlies caused storms to develop over the region, with around 700 lightning strikes recorded within 200km of Wagin between 2 and 4pm. Katanning and Wagin in the Great Southern received 35mm, their heaviest rain since last summer. For Wagin this is almost three times their normal total rainfall during December. Parts of the South Coastal also received a soaking. Albany had 20mm to 9am on Thursday, their wettest December day in five years, while Ongerup hasn't had as much rain in almost a year, with 23mm. Merredin in the Central Wheatbelt has now had 160% of their normal December rainfall after 19mm fell in the gauge. In the Gascoyne Bulga Downs had their wettest day since March with 32mm. The trough will continue to track eastwards during Thursday and thunderstorms will redevelop and spread into South Australia. A Severe Thunderstorm Warning was issued for the Gascoyne, Goldfields and Southern Interior, noting the risk of flash flooding, large hail and damaging winds. This rain comes after what was a particularly wet November for these districts, with most places receiving well above average rainfall. The outlook this summer is for above average rain in western and southern parts of WA.