A Hydrometeorological Assessment of the Historic 2019 Flood of Nebraska, Iowa, and South Dakota

During early 2019, a series of events set the stage for devastating floods in eastern Nebraska, western Iowa, and southeastern South Dakota. When the floodwaters hit, dams and levees failed, cutting off towns, while destroying roads, bridges, and rail lines, further exacerbating the crisis. Lives were lost and thousands of cattle were stranded. Estimates indicate that the cost of the flooding has topped $3 billion as of August 2019, with this number expected to rise. After a warm and wet start to winter, eastern Nebraska, western Iowa, and southeastern South Dakota endured anomalously low temperatures and record-breaking snowfall. By March 2019, rivers were frozen, frost depths were 60-90 cm, and the water equivalent of the snowpack was 30-100 mm. With these conditions in place, a record breaking surface cyclone rapidly developed in Colorado and propagated eastward, producing heavy rain towards the east and blizzard conditions toward the west. In areas of eastern Nebraska, western Iowa, and southeastern South Dakota, rapid melting of the snowpack due to this rain-on-snow event quickly led to excessive runoff that overwhelmed rivers and streams. These conditions brought the region to a standstill. In this paper, we will provide an analysis of the antecedent conditions in eastern Nebraska, western Iowa and southeastern South Dakota, the development of the surface cyclone that triggered the historic flooding, along with a look into the forecast and communication of flood impacts prior to the flood. The study used multiple datasets, including in-situ observations and reanalysis data. Understanding the events that led to the flooding could aid in future forecasting efforts

Improved Verification and Analysis of National Weather Service Point Forecast Matrices

Verification is the process of determining the quality of forecast information. Office and personal forecast verifications are significantly lacking throughout the National Weather Service for many reasons. The primary reasons are that verification is time consuming, tedious, and monotonous. This research attempted to ease that process by creating new computer procedures to automate the verification process. The new procedures were tested using two years of forecasting data from November 2007 to November 2009 from the Omaha/Valley Weather Forecasting Office to serve as a framework for future verifications. Point Forecast Matrices (PFM) produced by the National Weather Service twice daily and the GFS (Global Forecasting System) served as the forecasting data for this research. The analysis of the forecast data can provide valuable feedback to the Omaha/Valley Weather Forecasting Office. The GFS was very competitive against the PFM in terms of accuracy, but the PFM were an improvement for most forecasting situations. More difficult forecasting situations, such as snow cover and temperatures near climatic temperature records, received additional scrutiny. Snow cover forecasts were divided into non-freezing and freezing day forecasts. The division revealed the PFM to be more accurate for freezing days and the GFS to be more accurate for non-freezing days. Analysis of near climatic temperature records showed that the GFS handled warmer than normal temperatures well and the PFM were better at handling cooler than normal temperatures. In addition to analyzing accuracy, forecast consistency was also studied. The Forecast Convergence Score, a statistic which measures how often and how much a forecast changes from forecast to forecast, was used to measure forecast consistency. PFM Forecast Convergence Scores are a vast improvement over GFS Forecast Convergence Scores for all forecasting situations. When consistency is combined with accuracy, the use of PFM proves to be the most trusted forecasting system over the entire forecasting database. Adviser: Merlin Lawso

A Hydrometeorological Assessment of the Historic 2019 Flood of Nebraska, Iowa, and South Dakota

During early 2019, a series of events set the stage for devastating floods in eastern Nebraska, western Iowa, and southeastern South Dakota. When the floodwaters hit, dams and levees failed, cutting off towns, while destroying roads, bridges, and rail lines, further exacerbating the crisis. Lives were lost and thousands of cattle were stranded. Estimates indicate that the cost of the flooding has topped $3 billion as of August 2019, with this number expected to rise. After a warm and wet start to winter, eastern Nebraska, western Iowa, and southeastern South Dakota endured anomalously low temperatures and record-breaking snowfall. By March 2019, rivers were frozen, frost depths were 60-90 cm, and the water equivalent of the snowpack was 30-100 mm. With these conditions in place, a record breaking surface cyclone rapidly developed in Colorado and propagated eastward, producing heavy rain towards the east and blizzard conditions toward the west. In areas of eastern Nebraska, western Iowa, and southeastern South Dakota, rapid melting of the snowpack due to this rain-on-snow event quickly led to excessive runoff that overwhelmed rivers and streams. These conditions brought the region to a standstill. In this paper, we will provide an analysis of the antecedent conditions in eastern Nebraska, western Iowa and southeastern South Dakota, the development of the surface cyclone that triggered the historic flooding, along with a look into the forecast and communication of flood impacts prior to the flood. The study used multiple datasets, including in-situ observations and reanalysis data. Understanding the events that led to the flooding could aid in future forecasting efforts

A Hydrometeorological Assessment of the Historic 2019 Flood of Nebraska and Iowa

During early 2019, a series of events set the stage for devastating floods in eastern Nebraska and western Iowa. When the floodwaters hit, dams and levees failed, leaving towns cut off, while destroying roads, bridges, and rail lines, further exacerbating the humanitarian crisis. Lives were lost and cattle were stranded. Preliminary estimates indicate that the cost of the flooding has topped $3 billion, with this number expected to rise. After a warm and wet start to the winter, eastern Nebraska and western Iowa endured an extended pattern characterized by extremely low temperatures and record-breaking snowfall. By early March, rivers were frozen, frost depths were 60-90 cm deep, and the snow water equivalent of the snowpack was 30 to 100 mm. With these conditions in place, a significant surface cyclone rapidly developed in eastern Colorado and propagated eastward producing significant precipitation across Nebraska and severe weather across portions of the central and eastern United States. Rapid melting of the snowpack due to this rain-on-snow event quickly led to excessive runoff that overwhelmed local rivers and streams. With a blizzard in the west and flooding in the east, including the eventual downriver flooding across eastern Nebraska and western Iowa, the region was brought to a standstill. In this paper, we will provide an analysis of the antecedent conditions in eastern Nebraska and western Iowa, along with the development of the strong surface cyclone that ultimately triggered the historic flooding. Multiple datasets are utilized, including both in-situ observations and reanalysis data. Understanding the events that led to the flooding could aid in future forecasting efforts