When will flooding rain start in San Antonio? Here’s a timeline.

Hurricane Polo made landfall across the northern Mexican state of Sonora on Tuesday afternoon. After dissipating, some of the storm’s remnant moisture then traveled into parts of New Mexico and West Texas, bringing heavy rainfall to the region. Now, as an incoming cold front interacts with the leftover Pacific moisture, flooding rain is likely to expand across a large part of Texas.

According to the National Weather Service, between 2 and 4 inches of rain are expected across much of South-Central Texas through Saturday, but isolated rainfall amounts could reach 8 inches in a few spots.

“Much of this is going to be beneficial rainfall across most areas of South-Central Texas,” the weather service said in a web briefing on Tuesday, “but where the highest pockets of rainfall set up will be the risk area for flash flooding.”

In San Antonio, a flood watch will go into effect at 7 p.m. Wednesday. However, the greatest risk of flooding is not expected until Thursday, when the front moves closer to the Interstate 35 corridor. Here’s an updated timeline on when to expect the highest chance of rain.

Wednesday: For the most part, dry weather is expected in San Antonio on Wednesday, but the air will be very humid. Morning temperatures will sit in the mid- to upper 70s, rising into the upper 80s by noon. A brief morning shower is possible, with rain chances expected to be near 30%.

By Wednesday afternoon, temperatures are expected to reach 93 to 95 degrees under partly cloudy skies, but heat index values could peak as high as 104 degrees. An isolated storm will remain possible, but with just a 20% chance of rain in San Antonio.

Overnight, thunderstorms are expected to start moving through the Edwards Plateau and Hill Country, bringing the region’s initial threat of flooding.

Thursday morning: Storm chances are expected to rise significantly during this time, as a potential line of thunderstorms moves from the Hill Country eastward toward the Interstate-35 corridor. The San Antonio metro area will see about a 50% chance of rain between 4 a.m. and 8 a.m., but chances will rise to around 80% after 8 a.m. Scattered heavy downpours are possible.

Midday Thursday: Scattered off-and-on thunderstorms are expected to continue during this time with about an 70% chance of rain across the metro area between 11 a.m. and 4 p.m. Some storms could produce intense rainfall rates of more than 2 to 3 inches per hour, resulting in flash flooding.

A few isolated storms may also be strong, capable of producing small hail and damaging winds of up to 60 mph. An isolated tornado is also possible, although the overall threat is very low.

Thursday evening/night: The cold front is expected to move slightly south and east of San Antonio. Scattered thunderstorms will remain possible during this time, but chances will depend on the placement of the front. If it moves too far away, rain chances would decrease significantly. If the front stays closer, rain will continue.

“Thursday night through Friday will be the hardest part of the forecast given the uncertainty in the timing and placement of the cold front.” The national Weather Service said.

Friday morning/afternoon:  Rainfall is likely to redevelop along the stalled cold front, bringing more off-and-on showers and thunderstorms through the morning hours. San Antonio will have about a 70% chance of rain between 4 a.m. and 9 a.m, Friday, and heavy downpours could cause flooding across city streets and highways across San Antonio. Rain chances will fall to 50% during the afternoon and evening.

Chances for scattered showers will continue into the weekend, with about a 40% chance of rain Saturday, followed by a 20% chance on Sunday. The flood threat, though, will decrease significantly, as most rainfall will be light.

The cold front will also bring cooler air into the region, allowing temperatures to cool to slightly below-average levels for early October. Temperatures are likely to reach the mid- to upper 80s on Thursday before falling further into the lower 80s by Friday, Saturday and Sunday.

Meanwhile, morning temperatures are likely to hover near 70 degrees over the weekend before finally falling into the upper 60s by the start of next week. By the middle of next week, afternoons will likely warm slightly back into the mid-80s, while mornings stay in the upper 60s.