Tag Archive for: excessive rainfall

Powerful Thanksgiving Storms Could Bring Flooding

Rainfall predictions associated with approaching Thanksgiving storms keep increasing. Jeff Lindner, Harris County’s meteorologist now says approaching storms will bring widespread impacts from Thursday through Saturday. He also warns that heavy rainfall may lead to street flooding and rises on area creeks/bayous. Models now show a band of 5-7 inches of rain in places.

Thursday

Lindner says a surface warm front will approach the upper TX coast early Thursday and move inland. He expects showers to increase in coverage and intensity near the front, which may approach the US 59 corridor by midday before slowing and potentially stalling Thursday afternoon.

Along and south of the warm front be prepared for isolated severe storms and excessive rainfall with inflow off the Gulf. All the elements are in place for flash flooding “and warm fronts are notorious in these sort of setups for producing excessive rainfall,” says Lindner.

The best case for inland areas is that the warm front is held closer to the coast.

Friday – Saturday

Models have now slowed down the movement of an upper level low to our west. Lindner now predicts a break in the rainfall Friday morning, before another round of widespread, heavy rains move back into the area Friday afternoon and evening.

Expect grounds to become increasingly saturated and runoff to increase. Showers may linger into midday Saturday, before this system finally exits to the east.

Rainfall Amounts

Predicted rainfall associated with the Thanksgiving storms has increased compared to earlier forecasts. That’s because of the potential for slow moving and training thunderstorms Thursday afternoon and the longer duration of rainfall now expected into Friday and Saturday.

Widespread amounts of 1-3 inches can be expected on Thursday afternoon with isolated totals upwards of 5-6 inches.

Some models show a band of 5-7 inches near the warm front Thursday afternoon and this is concerning.

Hourly rainfall rates of 2-3 inches may be possible Thursday afternoon and this will lead to rapid street flooding and significant rises on creeks and bayous.

Jeff Lindner, Harris County Meteorologist

Additional rainfall amounts of 1-3 inches can be expected Friday/Saturday on top of what falls on Thursday and this will only worsen ongoing run-off from the Thursday rainfall.

Runoff 

Soils are primed for run-off with recent wetting rainfall over the region. Our main concern is street flooding, but Lindner cautions us about the potential for significant rises on area watersheds, especially if the higher totals are realized in portions of Harris County.

His greatest concern is for the southern and southeastern portions of Harris County where soils are the wettest and potential rainfall the highest. But he still isn’t confident enough to pinpoint the exact locations of the highest rainfall.

He says most watersheds can handle 3-4 inches. But if we start to exceed 5 inches, the concern for flooding from the bayous and creeks listed below will increase.

IF 5-7 inches, streams most in danger of flooding will be:

  • Clear Creek and its tributaries
  • Armand Bayou
  • Hunting Bayou
  • Halls Bayou (upper around I-45)
  • Little Cypress Creek
  • Willow Creek
  • South Mayde Creek (lower near Greenhouse)
  • Keegans Bayou (lower near Beltway 8/US 59/Wilcrest area)
  • Willow Waterhole
  • Brickhouse Gully
  • Spring Branch Creeks (Spring Branch, Buttermilk, Briar Branch)

Thursday’s Excessive Rainfall Potential

From National Weather Service

If you’re out and about over the holidays, remember. Be wary of underpasses and bridges. If you can’t see the roadway, you don’t know how deep the water is. Turn around and don’t drown.

Also remember. Seven inches was the amount of rain Woodridge Village received on May 7, 2019. Woodridge now has much more stormwater detention capacity. But there are plenty of other clearcut areas around the area that don’t have much if any yet.


Friday’s Excessive Rainfall Potential

From National Weather Service

Keep your eye on the sky if you head out the door this holiday. Don’t let the Thanksgiving storms ruin your holidays.

Posted by Bob Rehak on 11/23/22 based on a forecast by HCFCD

1912 Days since Hurricane Harvey

Severe Weather Threat Increasing for Tomorrow, Up to 7″ Now Possible

Severe Weather, Flash Flood Likelihood Increasing for Monday Afternoon into Early Tuesday

Updated at 7:30 PM:

According to Jeff Lindner, Harris County Meteorologist, a powerful storm will move into Texas over the next 24 hours bringing multiple hazards to the area. The chances of severe weather and heavy rainfall by Monday afternoon and evening continue to increase. They are also expanding over a wider area. Since the original post, Harris County’s Meteorologist, Jeff Lindner has raised concerns about rises on the San Jacinto River West and East Forks to flood stage over the next few days. Rises on other creeks and bayous in Harris County also look likely, especially where we experience cell training and higher rainfall totals. Lindner advises to monitor weather closely on Monday and Monday night.

Outlook tomorrow for severe weather from the NWS Storm Prediction Center.

Higher Likelihood of Severe Weather Including Tornados Starting Monday Afternoon

There were some doubts yesterday about the likelihood for supercells to develop. But as we get closer to the storm’s arrival and certainty increases, supercell formation looks increasingly likely. “All severe modes will be in play including tornadoes, large hail, and damaging winds,” says Lindner. “There could be a few strong tornadoes, especially for locations north of I-10.” Yesterday, the main likelihood was north of SH105.

The National Weather Service Storm Prediction Center has expanded the enhanced risk (3 out of 5) outline to include more of Southeast Texas. The severe threat will begin in the mid-afternoon hours on Monday and continue into the late evening hours.

6-7 Inches, Flash Flooding Possible 

While the heaviest rainfall will likely occur over North Texas, the potential for high-precipitation supercells to develop and train across Southeast Texas is increasing for Monday afternoon and evening. As the front slows over Southeast Texas Monday night, Lindner expects the severe threat to gradually shift toward heavy rainfall and possible flash flooding throughout the night.

The greatest threat will generally be along and north of I-10. A slow-moving line of supercells will raise the flash-flood threat. If you get caught under one that’s training across your area as we saw back in January, be prepared.

Lindner has virtually doubled his rainfall predictions since yesterday. Instead of widespread 0.5-2 inches across the area, he now sees widespread 3-4 inches. And whereas yesterday he saw isolated rainfall totals up to 4 inches, today he estimates up to 6-7 inches.

Hourly rainfall rates of 2-3 inches will be possible leading to rapid onset flash flooding over urban areas. Street flooding will be the primary threat, but under corridors of excessive rainfall, significant rises on creeks and bayous will be possible.

Jeff Lindner, Harris County Meteorologist

In an update at 7:30 PM Sunday night, Lindner specifically mentioned the possibility of the East and West Forks of the San Jacinto rising to flood stage if we receive the higher rainfall totals in the forecast.

The NWS Weather Prediction Center has upgraded the area north of the I-10 corridor to a moderate risk for flash flooding.

National Weather Service outlook tomorrow for excessive rainfall.

Monday afternoon and evening will be active over the area. So have multiple ways to receive warnings. Make sure you have fresh batteries in your weather radio and flashlights; it could be a long night.

Putting Forecast in Perspective

To put this in perspective:

  • The supercells that spawned tornadoes over Kingwood in January dumped approximately 5 inches of rain. I talked with a lady on Facebook this morning whose home was destroyed by a tornado in that storm. She said she received warnings seconds before the tornado struck. She barely had enough time to get to an interior hallway before her home started crumbling around her.
  • The May 7th, 2019, storm that flooded more than 200 homes in Elm Grove dumped 7 inches of rain. But less than 20% of the floodwater detention capacity on Woodridge Village had been built at that point.
  • The City announced at 5:15 this afternoon that it will lower Lake Houston by 1 foot starting tonight. A forecast greater than 3 inches triggers the Lake Houston lowering protocol.

How To Get Warnings

NOAA broadcasts warnings on weather radio in a continuous loop during emergencies.

The National Weather Service lets you sign up for watches and warnings for your address.

Harris County’s Flood Warning System also lets you sign up to receive rainfall or flooding alerts for your location. The site also contains maps that show real-time rainfall, and river-channel monitoring and forecasting at gages throughout the region.

USGS has a web app called Water On the Go that shows water elevations at flood gages wherever you go in Texas.

Harris County Flood Control District’s Storm Center can connect you to a wide variety of preparedness articles and ways to summon help in an emergency.

A number of companies offer good apps for cell phones that offer warnings. I especially like one called Dark Skies that bills itself as “hyper-local” weather. It frequently tells me to the minute when a storm will arrive at my exact location…wherever I am.

You can also find links to dozens of other weather related apps and sites on my Links Page. Check them out before the storm arrives. You never know when a storm will knock out a web site, a cell tower, or power. So be prepared with multiple backups.

Posted by Bob Rehak on 3/20/2022 based on input from the NWS, HCFCD and City of Houston

1664 Days since Hurricane Harvey

Excessive Rainfall Threat from Beta Spreads Inland

As of mid-day Sunday, all of East Texas now faces some level of excessive rainfall and flash flood risk from Tropical Storm Beta.

The projected path of the storm has shifted inland, so rainfall will reach father north. The latest track now takes the storm on a path right up US59 from Sugar Land to Humble and Kingwood. However, Beta likely be a tropical depression by the time it reaches the north side.

Kingwood is the blue dot next to Spring.

Six to 15 Inches of Rain Now Predicted

According to the local National Weather Service office and the National Hurricane Center, most of the Houston region can expect 6 to 15 inches with the highest totals closer to the coast.

Harris, Montgomery and Liberty Counties (and the whole Houston region) face a high to moderate threat of flooding rains. The first rainbands from Beta have already started to move onshore today, but the heaviest rain will not occur until Monday into Tuesday.

North Houston Under Moderate Flooding Rain Threat

Flash Flood Watch in Effect

The entire region is under a flash flood watch. Coastal areas also face storm surge and tropical storm warnings.

Slow Moving Storm Will Produce Prolonged Rains

Beta is meandering slowly at about 3 mph northwest toward the coastline west of Houston and will then curl back over Houston. It should move inland sometime Monday or Monday night and turn from a storm into a depression by the time it reaches Houston.

However, Beta could dump rain on us from later today all the way through Wednesday.

40-50% Chance of Tropical Storm Force Winds Reaching North Houston

The North Houston Area has a 40-50% chance of seeing tropical storm force winds from Beta.

If the high winds reach this far inland, they would likely arrive Monday evening. Winds extend outward from the center for 195 miles as of Sunday morning.

Feeder Bands Extend Outward 190 Miles

In fact, at 11 a.m. Sunday morning, the first feeder band was approaching the eastern side of Houston, as you can see in the radar image below.

This image shows how the wind and rain from Beta could remain with us for days as the storm’s center wanders around the Gulf.

These feeder bands reach out 190 miles. That is roughly the distance from Houston to San Antonio. So Beta will produce long-duration rainfall from the middle Texas coast to southern Louisiana. 

Flash, Urban, and River Flooding Likely 

The National Weather Service warns that coastal flooding will remain a threat through midweek with the worst of the storm surge anticipated on Monday and Tuesday. 

Elsewhere impacts from the excessive rain include:

  • Rainfall flooding may prompt evacuations and rescues.
  • Rivers and tributaries may rapidly overflow their banks.
  • Small streams, creeks, canals, and ditches may become dangerous rivers.
  • Flood control systems and barriers may become stressed. 
  • Flood waters may cover escape routes. 
  • Streets and parking lots may become rivers of moving water with underpasses submerged.
  • Driving conditions may become dangerous. 
  • Many roads and bridges may close with some weakened or washed out.

Lake-Level Situation

According to the SJRA, Beta has the potential to dump up to 8 inches of rain in Montgomery County. 

SJRA is operating under standard protocols for a severe weather event and will be onsite at Lake Conroe throughout the duration of Tropical Storm Beta.  

Lake Conroe remains 18 inches low, and based on the current forecast, no reservoir releases are expected. 

SJRA

Real-time information on lake level can be found on the SJRA homepage at the “Lake Operations and Rainfall Dashboard” link.

At of this writing, Lake Houston is down a foot compared to its normal pool level (41.38 vs 42.4). You can monitor Lake Houston levels via the Coastal Water Authority website.

Monitor Downstream River Levels

You can monitor stream and river levels in near-real time at Harris County Flood Warning System. Make sure you check out the inundation mapping feature.

Posted by Bob Rehak on 9/20/2020 based on information from the National Weather Service and National Hurricane Center

1118 Days after Hurricane Harvey