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April 2016 North American storm complex

The large upper-level low and accompanying cold front draped across the Central United States on April 18
Type	Cold-core low Winter storm Blizzard Flood
Formed	April 15, 2016 (2016-04-15)
Dissipated	April 23, 2016 (2016-04-23)
Lowest pressure	1006 mb (29.71 inHg)
Maximum snowfall or ice accretion	Snow – 51.3 in (130 cm) near Pinecliffe, Colorado Rainfall – Near 20 in (51 cm) around the Houston, Texas areas
Fatalities	8 confirmed
Damage	$2.7 billion
Power outages	147,000
Areas affected	Texas (especially the city of Houston), Western United States (Rocky Mountains)
Part of the 2015–16 North American winter and United States floods of 2016

The April 2016 North American storm complex was a major storm system that resulted from an upper-level low in the United States stalling and producing record-breaking rain in and around Houston, Texas, resulting in severe flooding, as well as a major snowstorm in the Rocky Mountains. There were more than 17 inches of rain in one day in parts of the city, and up to 4 inches of rain per hour that morning at George Bush Intercontinental Airport. It is described as the wettest April in the city on record.

As the most widespread flood event there since Tropical Storm Allison in 2001, it caused a state of emergency to be declared in nine counties.

Meteorological history

In mid-April 2016, a large, slow-moving upper-level low emerged from the Four Corners region in Rocky Mountains over the Central United States. Simultaneously, a ridge became anchored over the Eastern United States with another low to the east, creating an omega block—a stagnant weather pattern. The low near the Rockies pulled large quantities of moisture north from the Gulf of Mexico, leading to both heavy snow in the mountains and widespread heavy rain to the plains. During the overnight hours of April 15–18, a nearly stationary mesoscale convective system developed over the Houston Metropolitan Area. Southeasterly flow from a low level jet fueled the system with ample moisture, leading to widespread rainfall rates of 2 in (51 mm) per hour. Rainfall intensified throughout the night into the morning of April 18 with rainfall rates reaching 4 in (100 mm) per hour, leading to a life-threatening situation. At 4:39 a.m. CDT, a flash flood emergency was declared for parts of Colorado, Waller, Grimes, Montgomery, Harris, and Austin counties, later expanding to Fort Bend.

Accumulations peaked at 17.6 in (450 mm) along Little Mound Creek at Mathis Road to the northwest of Houston. Other significant totals include 16.48 in (419 mm) along Cypress Creek at Sharp Road, 16.32 in (415 mm) along Langham Creek at Longenbaugh, and 16.22 in (412 mm) in Monaville. George Bush Intercontinental Airport saw 9.92 in (252 mm), bringing the monthly rainfall total to 11.38 in (289 mm). This marked the wettest April on record for Houston.

At the same time, the upper low produced a major snowstorm in the Rocky Mountains and High Plains from April 16–17. Due to the omega block, snowfall remained concentrated around the Denver metropolitan areas. Because of this, some snowfall totals ranged up to 3–4 feet (36–48 in) in some areas. This definitely led to areas coming close to breaking their top-snowiest days in April. A climate study analyzing the 2015 flood in Texas and Oklahoma has found an intensified El Niño effect on the climatologically wet season of spring, and the intensification has a trace of anthropogenic climate warming.

The upper low began to move eastward on April 19, as the omega block began to break down. It was expected to reach the East Coast by April 22, with much less rainfall totals as it began to accelerate.

Impact

Over 47,000 customers lost power in Colorado, and to the west of Denver, portions of Interstate 70 closed. In addition, portions of Interstate 80 closed in southeastern Wyoming. The torrential rains resulted in widespread, severe flooding across Houston and surrounding suburbs—the worst since Tropical Storm Allison in 2001. 5 people died in flood-related incidents. In Harris County alone, more than 1,800 high water rescues were conducted; 744 homes and 400 apartments were inundated with water. School districts across the county suspended activities for two days to three days. Immediately after the storm, property damage was estimated at $5 billion.

References

1. "WPC Surface Analysis Archive". Weather Prediction Center. Retrieved 2016-05-15.
2. ^ "Winter Storm Vexo, Major April Snowstorm, Pounds the Rockies, High Plains (RECAP)". The Weather Channel. April 17, 2016. Retrieved April 20, 2016.
3. "Dangerous Flood Threat Ongoing in Texas; Water Rescues Reported Near Houston (FORECAST)". The Weather Channel. April 17, 2016. Retrieved April 26, 2016.
4. "8 confirmed deaths after flooding across Houston area". click2houston. 21 April 2016. Retrieved 10 May 2022.
5. Michael Pearson and Melissa Gray (April 18, 2016). "Houston flooding: At least 5 dead - CNN.com". CNN. Retrieved April 19, 2016.
6. "Nearly 900 Rescued as Severe Flooding Strikes Houston". KTIC Radio. Archived from the original on April 19, 2016. Retrieved April 19, 2016.
7. ABC News (2016-04-19). "In Houston Nearly 900 Are Rescued as Severe Flooding Sweeps Through City". ABC News. Retrieved April 19, 2016.
8. ^ Allison Ann Santorelli (April 17, 2016). Storm Summary Number 01 for Central and Southern Plains Heavy Rainfall (Report). College Park, Maryland: Weather Prediction Center. Retrieved April 20, 2016.
9. ^ Angela Friz (April 14, 2016). "'Omega block' will create warmth and sun for some, feet of snow for others". The Washington Post. Retrieved April 20, 2016.
10. Gregory M. Gallina (April 17, 2016). Mesoscale Precipitation Discussion 0127 (Report). College Park, Maryland: Weather Prediction Center. Retrieved April 20, 2016.
11. Gregory M. Gallina (April 18, 2016). Mesoscale Precipitation Discussion 0128 (Report). College Park, Maryland: Weather Prediction Center. Retrieved April 20, 2016.
12. "Severe Weather Statement: Flash Flood Warning". National Weather Service in Houston/Galveston, Texas. National Oceanic and Atmospheric Administration. April 18, 2016. Retrieved April 20, 2016.
13. "Severe Weather Statement: Flash Flood Warning". National Weather Service in Houston/Galveston, Texas. National Oceanic and Atmospheric Administration. April 18, 2016. Retrieved April 20, 2016.
14. Jason A. Krekeler (April 20, 2016). Storm Summary Number 11 for Central and Southern Plains Heavy Rainfall (Report). College Park, Maryland: Weather Prediction Center. Archived from the original on May 3, 2016. Retrieved April 20, 2016.
15. "...Houston's April Top 10 List..." National Weather Service Office in Houston/Galveston, Texas. National Oceanic and Atmospheric Administration. April 20, 2016. Retrieved April 20, 2016.
16. Simon Wang, S.-Y.; Huang, W.-R.; Hsu, H.-H.; Gillies, R. R. (16 October 2015). "Role of the strengthened El Niño teleconnection in the May 2015 floods over the southern Great Plains". Geophysical Research Letters. 42 (19): 8140–8146. Bibcode:2015GeoRL..42.8140S. doi:10.1002/2015GL065211..
17. Winter Storm Vexo, Major April Snowstorm, Pounds the Rockies, High Plains (RECAP), The weather Channel, April 18, 2016
18. Mike Morris and Mihir Zaveri (April 20, 2016). "As rescues continue, officials eye recovery from flood". Houston Chronicle. Retrieved April 20, 2016.
19. "Houston: City underwater". The Week. 29 April 2016.

• 2016 floods in the United States
• 2016 in Texas
• Floods in Texas
• History of Houston
• 2016 meteorology
• April 2016 events in the United States
• Natural disasters in Colorado