The Importance of Research Field Campaigns in Understanding Sub-Daily Forecasting (Credit: NOAA National Severe Storms Laboratory)
DISCUSSION: Field campaigns in the atmospheric sciences play a vital role in allowing forecasters and researchers to obtain further knowledge on the evolution of the state of the atmosphere. This is especially true in situations where high impact weather is expected to occur over densely populated areas. This year, The National Severe Storms Laboratory launched the Targeted Observations by Radars and Unmanned aerial surveillance of Supercells (TORUS) experiment designed to investigate the dynamics of ongoing severe thunderstorms and how their evolution may lead to the potential formation of tornadoes. The focus of the TORUS experiment is within the planetary boundary layer – the lowest layer in the atmosphere influenced by the frictional force of the wind, and how its constant changes could impact nowcasting and forecasting of ongoing severe weather threats. Much like the Mesoscale Convective Experiment (2013) and Plains Elevated Convection At Night (2015) experiment, an overarching goal of TORUS was to advance the current knowledgebase of supercells and how changes in their intensity as a function of the surrounding environment can help enhance or degrade a public forecast while also serving as extra information to ingest into weather models for enhanced predictability at relatively short time scales. The combination of ground-based equipment and techniques along with the use of NOAA’s Lockheed P-3 Orion “Hurricane Hunter” should return plenty of information.
Normally, the National Weather Service Weather Forecast Offices (NWS WFOs) launch radiosondes at 1200 and 0000 UTC (e.g., 8 AM/8 PM EDT) to sample the overall atmospheric profile and obtain valuable information for the prediction of severe storms. One particular case in where forecasters benefitted from the additional data supplied by TORUS was with the most recent high risk severe weather day on 20 May. The mobile soundings provide extra atmospheric data at unconventional times in the day that are the stepping stone to potential modifications for a forecast. For instance, a TORUS sounding taken near Vinson, OK at around 1930 UTC (2:30 PM CDT) showed a highly unstable environment and highly favorable for the development of significant supercells that could have led to long-track, violent tornadoes. Compared to a more traditional 1200 UTC sounding, that meant that over seven hours had elapsed which is ample timing for the environment to change considerably. Ultimately, this was not the case across much of central and southern Oklahoma on 20 May for which the reasoning is still up for much debate to this date, but it is information like these soundings that give forecasters a leg up on making the necessary quick decisions with a rapidly changing environment.
Even with the ability to interrogate the atmosphere with mobile soundings, it also elucidates more questions and unknowns for researchers to grasp onto moving forward. For example, why did the 20 May severe weather outbreak not materialize as expected despite environmental parameters suggesting an outbreak akin to the 27 April 2011 tornado outbreak over the Deep South states of Mississippi and Alabama? Or, how is it that “lower” severe weather risks issued by the Storm Prediction Center lead to more active days? These are good questions to ponder about and while mobile soundings may not provide the entire story to the eventual growth and while the world of research to operations (commonly known as R2O) has much to learn about sub-daily (and even sub-hourly) forecasts, field campaigns like TORUS provide the necessary benefits for forecasters and researchers alike to gain a richer understanding of quickly evolving atmospheric conditions.
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Sounding credit: Manda Chasteen
© 2019 Meteorologist Brian Matilla
DISCUSSION: In looking back to August 2017 and the Atlantic hurricane season, there is no debate that one of the events which stood out among the rest quite a bit was Hurricane Harvey. Hurricane Harvey is arguably most remembered for its impacts with respect to the major flooding the storm delivered in and around the city of Houston, Texas. However, the other major aspect of Hurricane Harvey which made headlines for quite a while was how the storm rapidly intensified from a Category 3 to a Category 4 just before making landfall in southeast Texas. There continued to be substantial interest in this topic which inspired and ultimately led to more comprehensive research on the issue from both academic institutions as well as various weather and climate research agencies. The main conundrum is the fact that as hurricanes approach shallower coastal waters and continue to induce substantial oceanic mixing, this brings up much cooler water which often helps to weaken the storm or stabilize any further intensification. However, this is not what transpired with Hurricane Harvey and hence, the reason for why much further research was needed. One such example of this research came from a research group over at Texas A&M University.
In this research, “They found the Bight was warm all the way to the seabed before Harvey arrived. Strong hurricane winds mix the ocean waters below the storm, so if there is any cold water below the warm water at the surface, the storm's growth will slow. But there wasn't any cold water for Harvey to churn up as it neared the coast, so the storm continued to strengthen right before it made landfall, according to the study's authors.
"When you have hurricanes that come ashore at the right time of year, when the temperature is particularly warm and the ocean is particularly well-mixed, they can absolutely continue to intensify over the shallow water," said Henry Potter, an oceanographer at Texas A&M and lead author of the new study in the American Geophysical Union's Journal of Geophysical Research: Oceans.
The researchers don't yet have enough temperature data to say if the Texas Bight was unusually warm in 2017. But the findings suggest hurricane forecasters may need to adjust the criteria they use to predict storm intensity, according to Potter. Forecasters typically use satellite measurements and historical data to make intensity predictions, but Harvey's case shows they need data collected from the ocean itself to know exactly how much heat is there, where that heat is located in the water column and if it's easily accessible to the storm, Potter said.”
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© 2019 Meteorologist Jordan Rabinowitz