2015 déjà vu–does wettest April in 43 years portend May, June floods?

Weather Blog
El Nino globe_1556591151126.png.jpg

In a pattern eerily similar to spring 2015, a weak El Niño Ocean pattern is likely contributing to unusually heavy rainfall across Central Texas, including 7.28 inches of rain last month–the 9th wettest April on record in Austin since 1897, and the wettest since 1976.

The concern for potential flooding is growing as there is no sign of change in the current wet pattern, with some models indicating isolated totals in excess of five inches over the next 5-6 days.

With Lake Travis and Lake Buchanan now full, river flooding in the Colorado River basin could quickly create flooding on those lakes.

Tropical Pacific Sea Surface Temperature Animation

Pacific El Niño pattern is expected to persist through summer, possibly fall

Unusually warm water across the equatorial Pacific and a large patch of warmer-than-normal water west of Mexico’s Baha Peninsula are providing moisture and heat energy to the atmosphere, likely contributing in some measure to the frequent, anomalously heavy rainfall this spring. And, the Climate Prediction Center’s new 8-14 day outlooks indicate more rain than normal may continue into the middle of May.

Tropical Pacific Sea Surface Temperature Anomalies Animation

Large patch of warmer-than-normal water west of Mexico’s Baha region also contributing to wet pattern

Four storms in four weeks dropped 5-10 inches of rain across much of the KXAN viewing area in April, and the fifth storm in five weeks is bringing another round of potentially heavy rain this week.

This system will be followed by a series of disturbances originating in the Pacific that could bring week-long totals of 3-6 inches of rain or more to parts of Central Texas.

May and June run neck-and-neck as Austin’s wettest months of the year, with more than four inches of rain on average each month. The Climate Prediction Center’s new outlook for the entire month of May indicates May will be wetter-than-normal across most of Texas.

As long as the rainfall is evenly distributed throughout this period like it was in April, flooding problems should be minimal. However, as the ground gets wetter, it can hold less rain before it turns to runoff, thus smaller rain totals can produce flooding. 

Devastating flooding in May 2015 was also associated with a weak El Niño pattern. More than 17 inches of rain fell in Austin–an all-time May record. Several tornadoes and flooding marred Memorial Day weekend with numerous fatalities. 

Here are the entries from our First Warning Weather Diary from May 23-25, 2015:

May 23, 2015:

CATASTROPHIC FLOODING AND TORNADO TOUCHDOWNS BEGIN DEADLY AND DESTRUCTIVE MEMORIAL DAY WEEKEND. Back-to-back bowing line segments created the largest flood the Blanco River at Wimberley has ever seen, and triggered dozens of water rescues and hundreds of evacuees from San Marcos and Wimberley. Small tornado touched down in Dripping Springs with no injuries reported. From NWS: Historic flash and river flooding occurred on Saturday, May 23rd and into Sunday, May 24th across portions of South-Central Texas. The worst rivers impacted by far were the Blanco and San Marcos Rivers that ran through Wimberley and San Marcos, TX that resulted in severe impacts to life and property. Additional flash flooding occurred on Memorial Day, May 25th, affecting large areas of Williamson, Travis, Bastrop, and Caldwell counties. Click this link http://www.weather.gov/media/ewx/wxevents/ewx-20150524.pdf for an overview of the May 23-24 event from the weather set-up, the National Weather Service product and warning timeline, satellite and radar videos, river hydrographs, and pictures. Click here http://www.weather.gov/media/ewx/wxevents/ewx-20150525.pdf for more on the tornado outbreak.

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May 24, 2015:

HISTORIC FLOODING OF BLANCO RIVER WASHES HOMES/CABINS DOWNRIVER AT WIMBERLEY. A DOZEN KILLED ALONG THE BLANCO, TWO MORE DIED IN WILLIAMSON & TRAVIS, 14 TOTAL. Quiet after the storm. Extensive clean up began today following historic flood. Many people missing, In Hays Co. 321 homes destroyed, 322 suffer major damage, 376 minor damage. 2,100 homes wiped out or damaged in Hays Co. 12,000 trees destroyed between Blanco and San Marcos. $33 million damage. Partly to mainly cloudy skies with just a few isolated showers today. From NWS: Historic flash and river flooding occurred on Saturday, May 23rd and into Sunday, May 24th across portions of South-Central Texas. The worst rivers impacted by far were the Blanco and San Marcos Rivers that ran through Wimberley and San Marcos, TX that resulted in severe impacts to life and property. Additional flash flooding occurred on Memorial Day, May 25th, affecting large areas of Williamson, Travis, Bastrop, and Caldwell counties. Click this link http://www.weather.gov/media/ewx/wxevents/ewx-20150524.pdf for an overview of the May 23- 24 event from the weather set-up, the National Weather Service product and warning timeline, satellite and radar videos, river hydrographs, and pictures.

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May 25, 2015:

MEMORIAL DAY FLASH FLOODS AND TORNADO OUTBREAK. Record daily rainfall at Mabry and ABIA. New May record at Mabry with 16.72″, surpassing 14.90″ record from 1895. 3rd wettest month on record. Worst flood on Shoal Creek since 1981 damages Lamar businesses, destroys turf at House Park, where man is rescued by AFD. From NWS: Historic flash and river flooding occurred on Saturday, May 23rd and into Sunday, May 24th across portions of South-Central Texas. The worst rivers impacted by far were the Blanco and San Marcos Rivers that ran through Wimberley and San Marcos, TX that resulted in severe impacts to life and property. Additional flash flooding occurred on Memorial Day, May 25th, affecting large areas of Williamson, Travis, Bastrop, and Caldwell counties. Click this link http://www.weather.gov/media/ewx/wxevents/ewx-20150524.pdf for an overview of the May 23-24 event from the weather set-up, the National Weather Service product and warning timeline, satellite and radar videos, river hydrographs, and pictures. Click here http://www.weather.gov/media/ewx/wxevents/ewx-20150525.pdf for more on the tornado outbreak.

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