Monday AM: All SE Texas Now Under Moderate Risk for Flash Flooding This Week

The National Weather Service has produced a 3-day excessive rainfall map that show all of SE Texas under a moderate risk for flash flooding this week. “Moderate” means we have a 20-50% chance of exceeding flash-flooding guidance. Flash flooding occurs when short-duration, high-intensity rains exceed the drainage capacity in areas.

Issued Monday at 3AM Houston time by the National Weather Service.

Jeff Lindner, Harris County’s meteorologist, sees heavy rainfall and flash flood threats increasing through the week. “A flash flood watch will likely be required for portions of the area later today,” he said.

Chance of Thunderstorms 70% and Increasing

The National Weather Service predicts a 70% chance of thunderstorms for the Lake Houston Area through Tuesday night. The chance increases to 80% for Wednesday and Thurday. The chances decrease to 70% for Friday, 60% for Saturday and 40% for Sunday.

It is difficult to predict exact amounts of rainfall for any specific location, such as Lake Houston, that far in advance. However, conditions are in place to produce heavy rainfall. The main threat for today is slow moving storms that could produce street flooding this afternoon. But chances increase tomorrow, Wednesday and Thursday.

“This pattern will support heavy rainfall and flash flooding especially during the mid-week period. But really every day this week has potential,” says Lindner.

Space City Weather likens the conditions in place to those that produced the May 2019 floods in Kingwood.

Rainfall Amounts

Since yesterday, there has been no change. Models suggest a fairly high limit on potential totals. “As seen yesterday, this air mass is capable of excessive short term rainfall amounts. Widespread amounts of 4-8 inches will be likely over much of the area over the next 5 days with isolated totals of 10-12 inches or more. Short duration rainfall rates of 2-4 inches per hour will be possible leading to rapid urban flash flooding,” says Lindner.

Grounds in the Houston area are already wet and water supply lakes near full capacity. As of this morning, the City has started lowering Lake Houston by one foot. The SJRA is not releasing water from Lake Conroe.

From as of Monday 5/17/21 at 9am.

Lindner says that rises on area watersheds are likely given the widespread nature of this event. “It is certainly possible some watersheds will experience flooding at some point this week. Which watersheds potentially get hit the hardest remains uncertain…but the risk for flooding will be increasing,” he says.

Posted by Bob Rehak on Monday morning at 9 am, 5/17/21 based on information by HCFCD, NWS, and Space City Weather

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