Mississippi River Flooding 2019: Surpassing the Great Flood of 1927?
It’s no secret this year has been a wet one for much of the eastern half of the country. In fact, Mississippi alone has already surpassed the annual average rainfall and there is still 5 months left of 2019. Many of the communities settled along the river in the Mississippi Delta have been underwater since the record rainfall that occurred in early March and, unfortunately, they may not be returning home anytime soon after all the rain from Hurricane Barry. The Mississippi River has flooded before, during the Great Mississippi Flood in April 1927.
The Great Mississippi Flood of 1927 is still considered one of the worst natural disasters in the history of the United States. Heavy rainfalls were to blame, and levees all down the river had given way. Some places were submerged under 30 feet of water and it would be two months until the people of those communities would be allowed to go back. About 250 people died during this tragic event and even more went missing. The picture above is in Arkansas City, Arkansas.
This year can compare quite scarily to this event as the Mid-South faced nonstop heavy rainfall in March and April of this year, bringing the Mississippi to dangerous flood stages that hadn’t been reached in years. The highest crest during this event was near 40 ft, which would deem the river being at “Moderate Flood Stage”. While still under the momentous 49 ft crest during the flood, this is still significant as times have changed and population has grown substantially, and urbanization has increased. Thankfully, Barry did not drop as much rain as anticipated, with most areas only getting at most around four inches. What was forecasted for areas along the Mississippi would have surely brought the river back to record flood stages and leave the people whose communities are still underwater with no hope of getting home anytime soon. The river has not receded back to moderate levels and is expected to continuously decrease for the remainder of the 28-day forecast that the Lower Mississippi River Forecasting Center has put out. The picture below is a picture from Chickasaw County in Mississippi during the rainfall in March and many parts of the county underwater to this day.
For residents along the Mississippi River, this is good news as the river continues to decrease with size. Many forecasters in the National Weather Service in Memphis were quite concerned that the river could peak to stages close to that of 1927 as the rain was relentless this spring, but it stopped just in time to save what it could. Many farmers across the Mid-West and the Mid-South have lost most, if not all, their crops for the year. However, as floodwaters decrease, people will be able to move back to their communities and begin to rebuild and recover from the awful start to 2019.
Meteorologist Ashley Lennard
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8 Inch Hail Falling From the Sky? How Large Hail is Formed (Credit: NWS Aberdeen and NSSL)
On July 23, 2010, a hailstone that shattered records fell in Vivian, South Dakota. This hailstone weighed roughly 1.9375 lbs and was 8 inches in diameter. A typical hailstone is nowhere near this large, so how did a phenomena like this occur?
Barry: A Discussion of How a Weakening Tropical Storm Can Still Cause a Disaster
On July 13th, 2019, Tropical Storm Barry made landfall on the coast of Louisiana in the early afternoon hours. After briefly becoming a Category 1, Barry weakened as it approached the coast and proceeded to pose numerous risks to those in the southeastern portion of the United States. After landfall, Barry moved into the interior United States at a slow pace, which led to flooding threats into the states that were in its path. Barry’s impacts were felt as far away as Toronto, Ontario, Canada, when they reported seeing about 60 millimeters of rain on July 17th, when the remains of Barry were just to the south of the city.
This storm, at landfall, was a tropical storm and not powerful enough to be measured on the Saffir-Simpson Scale. However, Barry’s impacts were known before making landfall. For example, New Orleans, Louisiana received a total of 6-9 inches from this storm of the city to flood. This disrupted travel and caused some businesses to shut down. The flooding was magnified due to abnormally high water levels of the Mississippi River. New Orleans started to experience flooding a few days prior to landfall because of Barry’s asymmetrical shape.
Furthermore, Gulf Coast coastal cities experienced life-threatening storm surge due to the movement of water caused by Barry. For example, Biloxi, Mississippi had to deal with 2-4 feet of storm surge, which prompted the National Weather Service to issue a storm surge warning to anyone within their area of coverage. While 2-4 feet of storm surge may not seem like a whole lot, it was powerful enough to cause the sand on Biloxi’s beaches to wash across the road and shut down some of the roads near the coast.
Once Barry made landfall, the threats of flooding continued to move inland. The storm did not go back out to sea, but it dumped all of its energy out as rain inland. In Tennessee, the rainfall totals from the remains of Barry totaled around 2-8 inches, which prompted flash flood warnings throughout the state and only increased the damage from this year’s high counts of flooding.
Overall, it is estimated Barry caused between roughly 500-900 million dollars worth of damage Weaker storms like Barry can and will have life-long effects, even though they may not be as powerful as major hurricanes. The key thing to remember is that a tropical storm, no matter the strength, can have impacts that extend far beyond the coast where it made landfall.
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Sources: https://www.nhc.noaa.gov/archive/2019/BARRY.shtml?,https://upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Barry_2019_track.png/800px-Barry_2019_track.png, https://www.weather.gov/images/lix/5day_BarryRainfall_2019_07_16.png
©2019 Weather Forecaster Shannon Sullivan
Early Convection and Atmospheric Changes leading to decreased intensity of Evening Convection
Weather forecasts are important in dictating our plans for the day, week or even longer. We are reliant on forecasts and timing of potential storms to figure out when we should leave our homes. Simple tasks can turn troublesome such as grocery shopping, a commute to work or a day at the beach due to unexpected rain. Unfortunately, people are quick to criticize (often broadcast) meteorologists — whether storms are in the forecast for the evening but turned out to be a brief shower that cleared up quickly, or sunshine was forecasted but a stray storm passed by unexpectedly. The importance of monitoring forecasts throughout the day is critical for safety and preparation, but also to create a low-stress environment for your plans.
Photo: Thunderstorm structure with emphasis on warm air being the necessary fuel to form clouds and storms (Courtesy of Encyclopedia Britannica).
Convective storms are common types of thunderstorms we are used to that can be capable of producing damaging winds, large hail, or even a tornado. These storms, similarly to rain showers can occur at any time of the day and often dictate potential changes during the day. One of the main ingredients that is necessary for storms to form is heat, usually from the sun (solar heating) that warms the surface to generate the rising air necessary for storms to form. While there are more ingredients involved for storms, heat is the main driver in this situation.
Evening convection is the most common type of convection during summer months since it follows peak heating times (allowing for rising air to fuel storms). Forecasters and storm chasers alike look toward the evening hours to find supercells or lines of convective storms in their region during the early to late summer months. This is the most common type that we see, but that doesn’t mean it’s the only one.
Since evenings are seen as the most common time for storm generation, we may get into the routine of seeing rain in the forecast and expecting it in the evening. The timing of a storm and different atmospheric changes can inhibit the generation of evening storms.
Consider the situation of expecting storms at 5pm (1700) local time, but an earlier line of storms passed by around 2pm (1400) that resulted in significant cooling (due to rain cooled air). Because of the cooling that occurred after the first storm, the expected evening storms may not be nearly as severe, if they occur.
Consider another example: storms have been passing through the area in the early morning and cloud cover has lasted until noon, but storms are still in the forecast for the evening. The cooler air caused by an earlier rain mixed with the lack of solar heating could greatly impact a forecast for storms in the evening. This results in a lack of heat to fuel the storm and thus reduces the severity of the storm.
Multiple factors impact the chance of evening convection aside from lack of solar heating from cloud cover and earlier storms or rain. These are only a few instances where the heat necessary to fuel a storm is taken away. Atmospheric changes can play a factor in an adjusted forecast like a cold frontal passage or cool lake breezes. These factors can actually help a storm form or destroy it. A cold front can pass through a hot and humid air mass that will force the hot air upward and aid storm generation. Similarly, a lake breeze that creates a frontal boundary can meet a warm frontal boundary that helps creating a rising motion. Depending on the strength of these cooler boundaries, they can inhibit the formation of storms by cooling the air in a region where a storm is headed, thus causing the storm to continuously lose heat and energy it needs to strengthen or keep its current strength.
Incoming lines of storms seen on the radar for hours can easily lose energy when coming in contact with a cooler environment. A gust front or outflow boundary is often present with a larger line of storms and act as a cold front. In turn, the storm will move into a cooler environment and quickly lose energy. As you watch the storm move closer to your area and notice it lacks the same energy it had hours before, then there is some environmental factor playing a role.
Overall, forecasts are important during all parts of the day. Keeping a close eye on changes and understanding the multiple factors that go towards a forecast can help you understand why a call for severe weather may not happen as planned. These ideas hopefully expanded your understanding of the expectation of rain throughout a day and provided insight on some of the changes that can occur.
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@2019 Meteorologist Jason Maska