2016 North American spring

The 2016 North American spring refers to spring in North America as it occurred across the North American continent in mid-2016. While there is no well-agreed-upon date used to indicate the start of spring in the Northern Hemisphere, there are two definitions of spring which may be used. Based on the astronomical definition, spring begins at the March equinox, which occurred on March 20, and ends at the summer solstice, which occurred on June 20. Based on the meteorological definition, the first day of spring is March 1 and the last day May 31. Both definitions involve a period of approximately three months, with some variability.
Seasonal forecasts
On March 15, 2016, the National Oceanic and Atmospheric Administration's Climate Prediction Center issued its U.S. Spring Outlook. In the precipitation outlook, dry conditions were expected to develop in the Upper Midwest, while the majority of the southern parts of the United States were expected to remain wet - likely denting or reducing drought conditions in the Southwestern U.S. Areas in the middle favored an equal-chance of both conditions. The temperature outlook predicted most of the nation receiving above average temperatures through April to June, with the expectation of the southwestern parts of Texas, which favored below average temperatures. The flood risk proposed moderate flooding in parts of the Southeast and Mississippi Valley, with other areas further out having minor or no flooding.
Events
Mid-April floods
In the early morning hours of April 18, deadly flooding took place in the southern parts near Houston, Texas, where as much as of rain fell, triggering deadly flooding. Multiple water rescue calls had to be made as well. The floods were part of a much larger storm complex that was producing all sorts of weather. Due to an omega block, the system stalled over the Rockies and High Plains, upping the potential precipitation accumulation total. 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 17-18, 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 per hour. Rainfall intensified throughout the night into the morning of April 18 with rainfall rates reaching 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 along Little Mound Creek at Mathis to the northwest of Houston. Other significant totals include along Cypress Creek at Sharp Road, along Langham Creek at Longenbaugh, and in Monaville. George Bush Intercontinental Airport saw , bringing the monthly rainfall total to . This marked the wettest April on record for Houston.
Late April severe weather outbreak
On the afternoon of April 26, the Storm Prediction Center issued a PDS tornado watch for most of the state of Oklahoma as well as portions of central Texas. A 10% hatched risk area for tornadoes extended from Nebraska to Texas, and multiple intense (EF2+) and long-tracked tornadoes were expected. However, the wind profile that evening did not support sustained supercell thunderstorms. As a result, only scattered weak tornadoes occurred, though EF1 tornadoes caused minor to moderate damage in parts of Oklahoma City and Tulsa. Weak tornado activity continued the following day in Nebraska, Iowa, Illinois, Missouri, and Kentucky, including an EF0 and an EF1 that caused minor damage in the western part of Omaha. An early morning EF0 blew a large tree over onto a mobile home near Tomball, Texas, killing an elderly woman inside. Overall, the outbreak produced at least 48 tornadoes and one death.
Early May nor'easter
On April 30, an extratropical cyclone formed while producing severe weather in the Plains. Slowly, over a period of roughly 3-5 days, it began to track to the east. This was due in part to an Omega block developing over the United States. As it did so, it rapidly began to fall apart. When it reached the East Coast by May 3 as a weak system, it moved offshore and transitioned into a stationary front. At the same time, another area of low pressure began moving in from the northwest near the United States-Canada border in association with a southwards dip in the jet stream due to the omega block. Quickly moving to the southeast during the course of May 4, the storm eventually stalled just inland over the Carolinas late on May 5, as it began to interact with the stationary front just to the east. Overnight, this merging of systems, along with the southwards dip of the jet stream, eventually resulted in a new area of low pressure forming just offshore the coast very early on May 6. The storm quickly transitioned into a nor'easter by 7:00am EDT the same day. Pulling moisture from the Atlantic Ocean, rainbands began to circulate around the central area of low pressure, affecting areas like Philadelphia, New York City, and Washington D.C as the center of the nor'easter began to move onshore southeast of the nation's capitol around 10am EDT. Heavy rainfall was reported at times as it moved ashore, at the same time, it began to weaken as it started to become disassociated with the remains of the stationary front. It eventually stalled near the Pennsylvania border late on May 6. It continued to weaken before dissipating early on May 7, as the omega block began to break down, finally putting an end to a near-week long period of wet weather for the Northeast.
Post-Mother's Day tornado outbreak
A violent and significant tornado outbreak occurred starting on May 7, in areas stretching from the West to the Ohio Valley. It started with a large EF2 tornado near Wray, Colorado on May 7. Over the next couple days, tornadoes formed across Nebraska, Illinois, Iowa, Oklahoma, Texas, Kansas, and Arkansas, with scattered activity on May 8 (Mother's Day), and the main activity through May 9-10. Tornadoes in southern Oklahoma on the afternoon of May 9 resulted in one fatality each in Garvin and Johnston counties. A large and violent tornado, rated an EF4, the first of 2016, ripped through the areas near Katie, Oklahoma, where one of the fatalities was reported. Another large tornado was confirmed near Sulphur, Oklahoma, and was given a EF3 rating.
Late May tornado outbreak sequence
During the evening of May 21, a supercell produced multiple tornadoes in west Kansas, near the city of Leoti. In the early afternoon of May 22, an Enhanced risk was issued by the Storm Prediction Center for extreme southwestern Kansas, the Oklahoma Panhandle, and northern Texas. A total of 40 tornadoes were reported, mainly in Texas but also in Kansas and South Dakota. Tornado activity continued into May 23, with several tornadoes touching down across the central and southern Plains. That night, a large and extremely dangerous tornado was reported near Turkey, Texas.
Tornadoes continued to occur into the evening hours of May 24 and eventually May 25 and 26, as several tornadoes began popping up near the state of Kansas, including a large and damaging tornado affecting areas west of Ness City, as well as an EF4 wedge tornado, about half a mile wide, tearing through areas near Chapman, KS on May 25.
Tropical Storm Bonnie
On May 24, the National Hurricane Center noted the possibility of an area of low pressure developing into a subtropical or tropical cyclone north of the Bahamas. Organization slowly improved over the coming days, resulting in the classification of Tropical Depression Two on May 27 at 21:00 UTC. The formation of Two was the Atlantic's first occasion of two pre-season tropical cyclones since Alberto and Beryl in 2012. The depression strengthened into Tropical Storm Bonnie later on May 28. Bonnie later made landfall at 8:30am EDT on May 29 in South Carolina a few miles east of Charleston as a weakened tropical depression, before degenerating into a remnant low on May 30. However, a combination of reorganization of thunderstorms, warm sea waters and lesser wind shear was able to prompt Bonnie to be re-analyzed as a tropical depression early on June 2. It strengthened into a tropical storm again and attained a new peak intensity by mid-day on June 3, however worsening conditions caused it to rapidly weaken and Bonnie was declared post-tropical for a second time late on June 4, as convection had nearly diminished entirely, and the low level center being nothing but a swirl of clouds.
Late May - early June floods
At the end of May, a deluge of heavy rainfall set precipitation records in Texas and Oklahoma. States of emergencies had to be declared, most commonly for the worst-hit areas.
Tropical Storm Colin
Just as Bonnie dissipated on June 5, another tropical depression developed to the east of the Yucatan Peninsula by mid-day. The depression strengthened into Tropical Storm Colin late on June 5, and dropped heavy rainfall over Florida. When it did, it became the earliest "C" named Atlantic tropical storm in recorded history, predating Chris from 2012 by nearly 2 weeks. Colin then began to accelerate to the northeast, and made landfall near the Big Bend area in Florida late on June 6 with sustained winds of . Later the next day, it transitioned into a post-tropical cyclone while situated off the Carolina coast, as the centre has become detached from the main convection, alias strengthening to .
Mid-June heat wave
Tropical Storm Danielle
On June 14, the National Hurricane Center began monitoring a tropical wave located in the western Caribbean Sea. While moving in a northwestward direction the disturbance slowly reached the Yucatán Peninsula, which hindered any development due to interaction with land. However, on June 18, the disturbance moved over the warm waters of the Bay of Campeche and spawned a low pressure area. During the next day, the NHC upgraded the disturbance to Tropical Depression Four. On June 20, conditions in the area became more favorable for strengthening, and the depression acquired better organization when convection increased around the center, prompting the NHC to upgrade it to Tropical Storm Danielle. The formation into a tropical storm marked the earliest formation on record of the fourth named storm within the Atlantic basin, beating the record of Tropical Storm Debby in 2012 by three days. At 03:00 UTC on June 21, just after landfall, Danielle weakened to a tropical depression. Danielle dissipated at 09:00 UTC on June 21, while located inland over Mexico.
Across all of Veracruz, officials suspended school activities and the Port of Veracruz was temporarily closed. Flooding in the Pueblo Viejo Municipality affected 1,200 families and prompted activation of public shelters.

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