A field research campaign, the Hail Spatial and Temporal Observing Network Effort (HailSTONE), was designed to obtain physical high-resolution hail measurements at the ground associated with convective storms to help address several operational challenges that remain unsatisfied through public storm reports. Field phases occurred over a 5-yr period, yielding hail measurements from 73 severe thunderstorms [hail diameter ≥ 1.00 in. (2.54 cm)]. These data provide unprecedented insight into the hailfall character of each storm and afford a baseline to explore the representativeness of the climatological hail database and hail forecasts in NWS warning products. Based upon the full analysis of HailSTONE observations, hail sizes recorded in Storm Data as well as hail size forecasts in NWS warnings frequently underestimated the maximum diameter hailfall occurring at the surface. NWS hail forecasts were generally conservative in size and at least partially calibrated to incoming hail reports. Storm mode played a notable role in determining the potential range of maximum hail size during the life span of each storm. Supercells overwhelmingly produced the largest hail diameters, with smaller maximum hail sizes observed as convection became progressively less organized. Warning forecasters may employ a storm-mode hail size forecast philosophy, in conjunction with other radar-based hail detection techniques, to better anticipate and forecast hail sizes during convective warning episodes.
A database of upper-air soundings was collected for weak (EF0/EF1), significant (EF2/EF3), and violent (EF4/ EF5) tornadoes that occurred within 100 km and 6 h of the rawindsonde observation. After case filtering and quality control, a total of 50 proximity soundings for violent tornadoes and randomized samples of 100 proximity soundings for significant tornadoes and 102 for weak tornadoes were obtained. Key convective parameters were analyzed between the tornado datasets. Low-level instability parameters (0-3-km lapse rates and 0-3-km mixed-layer convective available potential energy) were noteworthy predictors of the highest tornado damage rating, whereas mixed-layer lifted condensation level, wind shear, and effective storm relative helicity displayed little predictive skill distinguishing significant and violent tornado environments. The ability of the significant tornado parameter (STP) to discriminate between significant and violent tornadoes also was analyzed. This analysis found that STP does statistically discriminate between violent and significant tornadoes, with mixedlayer convective available potential energy the best discriminator of its variables. Because of the skill in the lowlevel instability parameters, this study also offers a new violent tornado parameter that includes the low-level instability fields in order to better differentiate between significant and violent tornado environments. ABSTRACT (Manuscript
On 15 May 2013, 19 tornadoes occurred across north and central Texas, killing 6, injuring over 50, and causing more than $100 million in property damage. The majority of the impacts to life and property were the direct result of category-3 and category-4 enhanced Fujita scale (EF-3 and EF-4) tornadoes that affected the communities of Cleburne and Granbury, Texas. This study focuses on an examination of the north Texas integrated warning team (IWT) communications through a thorough analysis of interactions between IWT members during this event. Communications from all members of the IWT were collected and organized so that a quantitative analysis of the IWT communications network could be performed. The results of this analysis were used to identify strengths and weaknesses of current IWT communications to improve the consistency of hazardous weather messaging for future high-impact weather events. The results also show how effectively communicating within an IWT leads not only to more consistent messaging but also to broader dissemination of hazardous weather information to the public. The analysis techniques outlined in this study could serve as a model for comprehensive studies of IWTs across the country.
For many emergency managers (EMs) and National Weather Service (NWS) forecasters, Convective Outlooks issued by the Storm Prediction Center (SPC) influence the preparation for near-term severe weather events. However, research into how and when EMs utilize that information, and how it influences their emergency operations plan, is limited. Therefore, to better understand how SPC Convective Outlooks are used for severe weather planning, a survey was conducted of NWS core partners in the emergency management sector. The results show EMs prefer to wait until an Enhanced Risk for severe thunderstorms is issued to prepare for severe weather. In addition, the Day 2 Convective Outlook serves as the threshold for higher, value-based decision making. The survey was also used to analyze how the issuance of different risk levels in SPC Convective Outlooks impact emergency management preparedness compared to preparations conducted when a Convective Watch is issued.
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