Heavy Rainfall Potential Tonight, Through Weekend

UPDATED AS OF 10PM THURSDAY – Jeff Lindner, Harris County’s meteorologist, warns that heavy rainfall potential will spread across the region tonight through the weekend.

Rainfall accumulations expected by NWS in next 5 days. Updated at 5:51PM Houston time on 4/29/2021.

National Weather Service has issued a Flash Flood Watch for much of Southeast Texas tonight through Sunday morning. However, the risk is slight.

Most of the Houston region has a marginal or slight risk of flash flooding – less than 20%.

Lakes Houston, Conroe Being Lowered

Houston Public Works is currently lowering Lake Houston by 12 inches, from 42.5 feet to 41.5 feet in response to the newly updated forecast – 3 inches of rain in our watershed within 24 hours. Property owners along the lake should secure property along the shoreline. To monitor current water levels at Lake Houston, visit www.coastalwaterauthority.org.

The SJRA had stopped its seasonal release from Lake Conroe. Rains from last weekend pushed the lake back up past its normal full pool level of 201 feet. As of 7pm Thursday, the SJRA had not resumed releasing any water, but by 10pm it had.

Lake Conroe level as of 7pm on 4/29/2021
As of 10pm, SJRA had started releasing 530 cubic feet per second.

To monitor SJRA releases, see the dashboard on their home page.

Inflow from Gulf Will Collide With Stalled Front over SE TX

“A slow-moving, upper-level, low-pressure system over the southwest will combine with a surface front that will move into southeast Texas later today,” says Lindner. He expects the fronts to stall over our area. He says they will produce numerous rounds of showers and thunderstorms from late this afternoon into Sunday.

Onshore flow has increased moisture over the region with dewpoints running in the low to mid 70’s. The surface front extends from northeast Texas to near Laredo. It will move slowly into southeast Texas late this afternoon and then likely stall between downtown and the coast by Friday morning. Other disturbances, says Lindner, will ride along this frontal boundary toward the northeast helping to produce several rounds of showers and thunderstorms.

With the upper level winds becoming increasing parallel to the stalling surface front and moisture levels remaining high into the weekend, the threat for heavy rainfall will be increasing. Storm motions are expected to slow on Friday, but coverage remains scattered, so some areas could see some decent rainfall while other get little.

Threat Remains Through Sunday

Expect widespread storms to develop on Saturday morning as the threat for cell training increases.

The slow moving upper level low will then move directly across the area on Saturday night into Sunday with additional rounds of thunderstorms…some of these storms could be severe along with more heavy rainfall.

Widespread rainfall amounts of 1-3 inches will be possible with isolated totals of 4-5 inches. With all the moisture in place, high rainfall rates could cause street flooding.

Jeff Lindner, Harris County Meteorologist

Lindner warns potentially higher totals are possible given the overall slow moving nature of the weather pattern.

Increasing Runoff as Grounds Saturate, Marginal Risk of Flash Flooding

The dry ground conditions now in place means soil will absorb much of this rainfall. Regardless, Lindner predicts rises on area creeks and bayous. He says that grounds will begin to saturate over the weekend yielding greater run-off as the storm wears on.

The National Weather Service has all of southeast Texas in a marginal risk for flash flooding starting Friday and into Saturday.

Posted by Bob Rehak on 4/29/2021 based on information by Harris County Meteorologist Jeff Lindner and the National Weather Service

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