UPDATE: The Bureau of Meteorology has issued a severe storm warning for the Toowoomba region and surrounding areas.
The warning, which covers Toowoomba, Oakey, Crows Nest, Pittsworth and Caboolture, says flash flooding is a possibility.
"Severe thunderstorms are likely to produce heavy rainfall that may lead to flash flooding in the warning area over the next several hours," the alert said.
Residents are encouraged to stay away from flooded areas, keep inside and avoid using a landline telephone during the storm.
For emergency assistance, call the SES on 132 500.
EARLIER: Keep the umbrellas handy - Toowoomba looks set for a wet start to the working week.
The Bureau of Meteorology has predicted storms and showers to roll into the Toowoomba region this evening, with the potential for falls of up to 45mm.
Meteorologist Andrew Busalino said some parts of the eastern Darling Downs could also receive up to 100mm if they were under a heavy storm cloud.
"We're expecting showers and storms to develop this evening, with some heavy falls - for tomorrow, we've got 15-45mm (predicted)," he said.
"(We're) still expecting some storms tomorrow, but moving into rainy conditions.
"There is the potential for heavy falls, but they'll be quite isolated."
The cloud and rain will cause a drop in temperatures as well, with the predicted maximum of 23ºC about three degrees below the March average for Toowoomba.
Overnight rain has also caused isolated flooding that has shut certain roads, including the Leichhardt Highway between Moonie and Goondiwindi and Yumboora Rd in Dalby.
Rest of Sunday: Showers, chance of storm; 29ºC
Monday: Rain at times, possible storm; 21-24ºC
Tuesday: Showers; 19-22ºC
Wednesday: Possible shower; 18-22ºC
Thursday: Partly cloudy; 17-22ºC