 The largeupper-level low and accompanyingcold front draped across theCentral United States on April 18 | |
| Type | Cold-core low Winter storm Blizzard Flood |
|---|---|
| Formed | April 15, 2016 (2016-04-15)[2] |
| Dissipated | April 23, 2016 (2016-04-23)[1] |
| Lowest pressure | 1006 mb (29.71 inHg) |
| Maximum snowfall or ice accretion | Snow – 51.3 in (130 cm) nearPinecliffe,Colorado[2] Rainfall – Near 20 in (51 cm) around theHouston, Texas areas[3] |
| Fatalities | 8 confirmed[4] |
| Damage | $2.7 billion |
| Power outages | 147,000[2] |
| Areas affected | Texas (especially the city ofHouston),Western United States (Rocky Mountains) |
Part of the2015–16 North American winter andUnited States floods of 2016 | |
TheApril 2016 North American storm complex was a major storm system that resulted from anupper-level low in the United States stalling and producing record-breaking rain in and aroundHouston, Texas, resulting in severeflooding, as well as a major snowstorm in theRocky Mountains.[5] There were more than 17 inches of rain in one day in parts of the city, and up to 4 inches ofrain per hour that morning atGeorge Bush Intercontinental Airport. It is described as the wettest April in the city on record.[6]
As the most widespread flood event there sinceTropical Storm Allison in 2001, it caused astate of emergency to be declared in ninecounties.[7]
In mid-April 2016, a large, slow-movingupper-level low emerged from theFour Corners region inRocky Mountains over theCentral United States.[8][9] Simultaneously, aridge became anchored over theEastern United States with another low to the east, creating anomega block—a stagnant weather pattern.[9] The low near the Rockies pulled large quantities of moisture north from theGulf of Mexico, leading to both heavy snow in the mountains and widespread heavy rain to the plains.[8] During the overnight hours of April 15–18, a nearly stationarymesoscale convective system developed over theHouston Metropolitan Area. Southeasterly flow from alow level jet fueled the system with ample moisture, leading to widespread rainfall rates of 2 in (51 mm) per hour.[10] 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.[11] At 4:39 a.m.CDT, aflash flood emergency was declared for parts ofColorado,Waller,Grimes,Montgomery,Harris, andAustin counties,[12] later expanding toFort Bend.[13]
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) inMonaville.George Bush Intercontinental Airport saw 9.92 in (252 mm),[14] bringing the monthly rainfall total to 11.38 in (289 mm). This marked the wettest April on record for Houston.[15]
At the same time, the upper low produced a majorsnowstorm in theRocky Mountains andHigh Plains from April 16–17.[2] Due to the omega block, snowfall remained concentrated around theDenver 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[16] has found an intensified El Niño effect on the climatologically wet season of spring, and theintensification 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 theEast Coast by April 22, with much less rainfall totals as it began to accelerate.
Over 47,000 customers lost power inColorado, and to the west ofDenver, portions ofInterstate 70 closed. In addition, portions ofInterstate 80 closed in southeasternWyoming.[17] The torrential rains resulted in widespread, severe flooding across Houston and surrounding suburbs—the worst sinceTropical 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.[18] Immediately after the storm, property damage was estimated at $5 billion.[19]