Environments of Northeast U.S. Severe Thunderstorm Events from 1999 to 2009

2014 ◽  
Vol 29 (1) ◽  
pp. 3-22 ◽  
Author(s):  
Melissa M. Hurlbut ◽  
Ariel E. Cohen
Keyword(s):  
Large Scale ◽  
Weather Forecasting ◽  
Convective Available Potential Energy ◽  
Severe Weather ◽  
Severe Thunderstorms ◽  
Weather Events ◽  
Upper Level ◽  
Upper Level Jet ◽  
Lapse Rates ◽  
Jet Structure

Abstract An investigation of the environments and climatology of severe thunderstorms from 1999 through 2009 across the northeastern United States is presented. A total of 742 severe weather events producing over 12 000 reports were examined. Given the challenges that severe weather forecasting can present in the Northeast, this study is an effort to distinguish between the more prolific severe-weather-producing events and those that produce only isolated severe weather. The meteorological summer months (June–August) are found to coincide with the peak severe season. During this time, 850–500- and 700–500-hPa lapse rates, mixed layer convective inhibition (MLCIN), and downdraft convective available potential energy (DCAPE) are found to be statistically significant in discriminating events with a large number of reports from those producing fewer reports, based on observed soundings. Composite synoptic pattern analyses are also presented to spatially characterize the distribution of key meteorological variables associated with severe weather events of differing magnitudes. The presence of a midlevel trough and particular characteristics of its tilt, along with an accompanying zone of enhanced flow, are found in association with the higher-report severe weather events, along with cooler midlevel temperatures overlaying warmer low-level temperatures (i.e., contributing to the steeper lapse rates). During the meteorological fall and winter months (September–February), large-scale ascent is often bolstered by the presence of a coupled upper-level jet structure.

Multiscale aspects of the 26–27 April 2011 tornado outbreak. Part II: Environmental modifications and upscale feedbacks arising from latent processes

2021 ◽  
Author(s):  
Manda B. Chasteen ◽  
Steven E. Koch
Keyword(s):  
Large Scale ◽  
Vertical Wind Shear ◽  
Convective Systems ◽  
Upper Level ◽  
Large Scale Flow ◽  
Jet Streaks ◽  
Upper Level Jet ◽  
Jet Structure ◽  
Tornado Outbreaks ◽  
Jet Streak

AbstractOne of the most prolific tornado outbreaks ever documented occurred on 26–27 April 2011 and comprised three successive episodes of tornadic convection that culminated with the development of numerous long-track, violent tornadoes over the southeastern U.S. during the afternoon of 27 April. This notorious afternoon supercell outbreak was preceded by two quasi-linear convective systems (hereafter QLCS1 and QLCS2), the first of which was an anomalously severe nocturnal system that rapidly grew upscale during the previous evening. In this Part II, we use a series of RUC 1-h forecasts and output from convection-permitting WRF-ARW simulations configured both with and without latent heat release to investigate how environmental modifications and upscale feedbacks produced by the two QLCSs contributed to the evolution and exceptional severity of this multi-episode outbreak.QLCS1 was primarily responsible for amplifying the large-scale flow pattern, inducing two upper-level jet streaks, and promoting secondary surface cyclogenesis downstream from the primary baroclinic system. Upper-level divergence markedly increased after QLCS1 developed, which yielded strong isallobaric forcing that rapidly strengthened the low-level jet (LLJ) and vertical wind shear over the warm sector and contributed to the system’s upscale growth and notable severity. Moreover, QLCS2 modified the mesoscale environment prior to the supercell outbreak by promoting the downstream formation of a pronounced upper-level jet streak, altering the midlevel jet structure, and furthering the development of a highly ageostrophic LLJ over the Southeast. Collectively, the flow modifications produced by both QLCSs contributed to the notably favorable shear profiles present during the afternoon supercell outbreak.

scholarly journals A Total Lightning Trending Algorithm to Identify Severe Thunderstorms

2010 ◽  
Vol 27 (1) ◽  
pp. 3-22 ◽  
Author(s):  
Patrick N. Gatlin ◽  
Steven J. Goodman
Keyword(s):  
Severe Weather ◽  
Lightning Flash ◽  
Severe Thunderstorm ◽  
Critical Success ◽  
Severe Thunderstorms ◽  
Weather Events ◽  
Total Lightning ◽  
Jump Algorithm ◽  
Early Indication ◽  
Critical Success Index

Abstract An algorithm that provides an early indication of impending severe weather from observed trends in thunderstorm total lightning flash rates has been developed. The algorithm framework has been tested on 20 thunderstorms, including 1 nonsevere storm, which occurred over the course of six separate days during the spring months of 2002 and 2003. The identified surges in lightning rate (or jumps) are compared against 110 documented severe weather events produced by these thunderstorms as they moved across portions of northern Alabama and southern Tennessee. Lightning jumps precede 90% of these severe weather events, with as much as a 27-min advance notification of impending severe weather on the ground. However, 37% of lightning jumps are not followed by severe weather reports. Various configurations of the algorithm are tested, and the highest critical success index attained is 0.49. Results suggest that this lightning jump algorithm may be a useful operational diagnostic tool for severe thunderstorm potential.

scholarly journals An Initiation Process of Tropical Depression-type Disturbances under the Influence of Upper-level Troughs

2021 ◽  
Author(s):  
Yuya Hamaguchi ◽  
Yukari N. Takayabu
Keyword(s):  
Large Scale ◽  
Convective Available Potential Energy ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
Dimensional Structure ◽  
Convective Heating ◽  
Upper Troposphere ◽  
Tropical Depression ◽  
Upper Level ◽  
Extratropical Forcing

AbstractIn this study, the statistical relationship between tropical upper-tropospheric troughs (TUTTs) and the initiation of summertime tropical-depression type disturbances (TDDs) over the western and central North Pacific is investigated. By applying a spatiotemporal filter to the 34-year record of brightness temperature and using JRA-55 reanalysis products, TDD-event initiations are detected and classified as trough-related (TR) or non-trough-related (non-TR). The conventional understanding is that TDDs originate primarily in the lower-troposphere; our results refine this view by revealing that approximately 30% of TDDs in the 10°N-20°N latitude ranges are generated under the influence of TUTTs. Lead-lag composite analysis of both TR- and non-TR-TDDs clarifies that TR-TDDs occur under relatively dry and less convergent large-scale conditions in the lower-troposphere. This result suggests that TR-TDDs can form in a relatively unfavorable low-level environment. The three-dimensional structure of the wave activity flux reveals southward and downward propagation of wave energy in the upper troposphere that converges at the mid-troposphere around the region where TR-TDDs occur, suggesting the existence of extratropical forcing. Further, the role of dynamic forcing associated with the TUTT on the TR-TDD-initiation is analyzed using the quasi-geostrophic omega equation. The result reveals that moistening in the mid-to-upper troposphere takes place in association with the sustained dynamical ascent at the southeast side of the TUTT, which precedes the occurrence of deep convective heating. Along with a higher convective available potential energy due to the destabilizing effect of TUTTs, the moistening in the mid-to-upper troposphere also helps to prepare the environment favorable to TDDs initiation.

scholarly journals The Impact of the Storm Prediction Center's Convective Outlooks and Watches on Emergency Management Operational Planning

2021 ◽  
pp. 36-46
Author(s):  
Heather A. Cross ◽  
Dennis Cavanaugh ◽  
Christopher C. Buonanno ◽  
Amy Hyman
Keyword(s):  
Emergency Management ◽  
Severe Weather ◽  
Emergency Operations ◽  
Risk Levels ◽  
Severe Thunderstorms ◽  
Emergency Managers ◽  
Weather Events ◽  
Storm Prediction ◽  
Near Term ◽  
The Impact

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.

scholarly journals The Dynamic and Thermodynamic Structures Associated with a Series of Heavy Precipitation Events over China during January 2008

2010 ◽  
Vol 25 (4) ◽  
pp. 1124-1141 ◽  
Author(s):  
Xiaohui Shi ◽  
Xiangde Xu ◽  
Chungu Lu
Keyword(s):  
Large Scale ◽  
East Coast ◽  
Heavy Precipitation ◽  
Chinese History ◽  
Physical Processes ◽  
Ice Storms ◽  
Upper Level ◽  
Upper Level Jet ◽  
The Western Pacific ◽  
Precipitation Events

Abstract In the winter of 2008, China experienced once-in-50-yr (or once in 100 yr for some regions) snow and ice storms. These storms brought huge socio economical impacts upon the Chinese people and government. Although the storms had been predicted, their severity and persistence were largely underestimated. In this study, these cases were revisited and comprehensive analyses of the storms’ dynamic and thermodynamic structures were conducted. These snowstorms were also compared with U.S. east coast snowstorms. The results from this study will provide insights on how to improve forecasts for these kinds of snowstorms. The analyses demonstrated that the storms exhibited classic patterns of large-scale circulation common to these types of snowstorms. However, several physical processes were found to be unique and thought to have played crucial roles in intensifying and prolonging China’s great snowstorms of 2008. These include a subtropical high over the western Pacific, an upper-level jet stream, and temperature and moisture inversions. The combined effects of these dynamic and thermodynamic structures are responsible for the development of the storms into one of the most disastrous events in Chinese history.

scholarly journals Association of the Poleward Shift of East Asian Subtropical Upper-Level Jet with Frequent Tropical Cyclone Activities over the Western North Pacific in Summer

2017 ◽  
Vol 30 (14) ◽  
pp. 5597-5603 ◽  
Author(s):  
Xian Chen ◽  
Zhong Zhong ◽  
Wei Lu
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
East Asian ◽  
Teleconnection Pattern ◽  
Reanalysis Dataset ◽  
Poleward Shift ◽  
Upper Level ◽  
Upper Level Jet

The NCEP–NCAR reanalysis dataset and the tropical cyclone (TC) best-track dataset from the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center were employed in the present study to investigate the possible linkage of the meridional displacement of the East Asian subtropical upper-level jet (EASJ) with the TC activity over the western North Pacific (WNP). Results indicate that summertime frequent TC activities would create the poleward shift of the EASJ through a stimulated Pacific–Japan (PJ) teleconnection pattern as well as the changed large-scale meridional temperature gradient. On the contrary, in the inactive TC years, the EASJ is often located more southward than normal with an enhanced intensity. Therefore, TC activities over the WNP are closely related to the location and intensity of the EASJ in summer at the interannual time scale.

scholarly journals Potential Vorticity Diagnosis of the Severe Convective Regime. Part II: The Impact of Idealized PV Anomalies

2008 ◽  
Vol 136 (5) ◽  
pp. 1582-1592 ◽  
Author(s):  
John W. Nielsen-Gammon ◽  
David A. Gold
Keyword(s):  
Potential Vorticity ◽  
Severe Weather ◽  
Jet Stream ◽  
Balance Equations ◽  
Upper Level ◽  
Height Fields ◽  
Upper Level Jet ◽  
The Impact ◽  
Analysis Errors ◽  
Pv Gradient

Abstract Idealized numerical experiments are conducted to understand the effect of upper-tropospheric potential vorticity (PV) anomalies on an environment conducive to severe weather. Anomalies are specified as a single isolated vortex, a string of vortices analogous to a negatively tilted trough, and a pair of string vortices analogous to a position error in a negatively tilted trough. The anomalies are placed adjacent to the tropopause along a strong upper-level jet at a time just prior to a major tornado outbreak and inverted using the nonlinear balance equations. In addition to the expected destabilization beneath and adjacent to a cyclonic PV anomaly, the spatial pattern of the inverted balanced streamfunction and height fields is distorted by the presence of the horizontal PV gradient along the upper-tropospheric jet stream. Streamfunction anomalies are elongated in the cross-jet direction, while height and temperature anomalies are elongated in the along-jet direction. The amplitude of the inverted fields, as well as the changes in CAPE associated with the inverted temperature perturbations, are linearly proportional to the amplitudes of the PV anomalies themselves, and the responses to complex PV perturbation structures are approximated by the sum of the responses to individual simple PV anomalies. This is true for the range of PV amplitudes tested, which was designed to mimic typical 6-h forecast or analysis errors and produced changes in CAPE beneath the trough of well over 100 J kg−1. Impacts on inverted fields are largest when the PV anomaly is on the anticyclonic shear side of the jet, where background PV is small, compared with the cyclonic shear side of the jet, where background PV is large.

A Review of Planetary Boundary Layer Parameterization Schemes and Their Sensitivity in Simulating Southeastern U.S. Cold Season Severe Weather Environments

2015 ◽  
Vol 30 (3) ◽  
pp. 591-612 ◽  
Author(s):  
Ariel E. Cohen ◽  
Steven M. Cavallo ◽  
Michael C. Coniglio ◽  
Harold E. Brooks
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Turbulent Mixing ◽  
Convective Available Potential Energy ◽  
Lower Troposphere ◽  
Cold Season ◽  
Severe Weather ◽  
Parameterization Schemes ◽  
Lapse Rates ◽  
Local Schemes

Abstract The representation of turbulent mixing within the lower troposphere is needed to accurately portray the vertical thermodynamic and kinematic profiles of the atmosphere in mesoscale model forecasts. For mesoscale models, turbulence is mostly a subgrid-scale process, but its presence in the planetary boundary layer (PBL) can directly modulate a simulation’s depiction of mass fields relevant for forecast problems. The primary goal of this work is to review the various parameterization schemes that the Weather Research and Forecasting Model employs in its depiction of turbulent mixing (PBL schemes) in general, and is followed by an application to a severe weather environment. Each scheme represents mixing on a local and/or nonlocal basis. Local schemes only consider immediately adjacent vertical levels in the model, whereas nonlocal schemes can consider a deeper layer covering multiple levels in representing the effects of vertical mixing through the PBL. As an application, a pair of cold season severe weather events that occurred in the southeastern United States are examined. Such cases highlight the ambiguities of classically defined PBL schemes in a cold season severe weather environment, though characteristics of the PBL schemes are apparent in this case. Low-level lapse rates and storm-relative helicity are typically steeper and slightly smaller for nonlocal than local schemes, respectively. Nonlocal mixing is necessary to more accurately forecast the lower-tropospheric lapse rates within the warm sector of these events. While all schemes yield overestimations of mixed-layer convective available potential energy (MLCAPE), nonlocal schemes more strongly overestimate MLCAPE than do local schemes.

scholarly journals Model and Observational Analysis of the Northeast U.S. Regional Climate and Its Relationship to the PNA and NAO Patterns during Early Winter

2006 ◽  
Vol 134 (11) ◽  
pp. 3479-3505 ◽  
Author(s):  
M. Notaro ◽  
W-C. Wang ◽  
W. Gong
Keyword(s):  
New York ◽  
Great Lakes ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Early Winter ◽  
Upper Level ◽  
Upper Level Jet ◽  
The Impact ◽  
Nao Pattern

Abstract The relationship between the large-scale circulation and regional climate of the northeast United States is investigated for early winter using observational data and the State University of New York at Albany regional climate model. Simulated patterns of temperature, precipitation, and atmospheric circulation compare well with observations, despite a cold, dry bias. Ten December runs are analyzed to investigate the impact of the Pacific–North American (PNA) pattern on temperature, precipitation, clouds, and circulation features. During a positive PNA pattern, the simulated and observed eastern U.S. jet shifts to the southeast, coinciding with cold, dry conditions in the Northeast. This shift and intensification of the upper-level jet stream during a positive PNA pattern coincides with a greater frequency of cyclones and anticyclones along a distinct southwest–northeast track. Despite increased cyclone activity, total wintertime precipitation is below normal during a positive PNA pattern because of enhanced stability and subsidence over land, along with lower-atmospheric moisture content. Lower surface air temperatures during a positive PNA pattern result in enhanced simulated cloud cover over the Great Lakes and Atlantic Ocean due to increased thermal contrast and fluxes of sensible and latent heat, and a reduction in clouds over land. Interactions between the PNA and North Atlantic Oscillation (NAO) patterns impact the Northeast winter climate. Observed frontal passages through New York are most abundant during a negative PNA and positive NAO pattern, with a zonal upper-level jet positioned over New York. A positive PNA pattern is frequently characterized by an earlier observed Great Lakes ice season, while the greatest lake-effect snowfall occurs during a positive PNA and negative NAO pattern. The NAO pattern has the largest impact on northeast U.S. temperatures and the eastern U.S. upper-level jet during a positive PNA pattern.

Colorful Language: Investigating Public Interpretation of the Storm Prediction Center Convective Outlook

2021 ◽  
Author(s):  
Sean Ernst ◽  
Joe Ripberger ◽  
Makenzie J. Krocak ◽  
Hank Jenkins-Smith ◽  
Carol Silva
Keyword(s):  
Statistical Tests ◽  
Weather Forecast ◽  
Severe Weather ◽  
Logistic Regression Models ◽  
Public Interpretation ◽  
Severe Thunderstorms ◽  
Weather Events ◽  
The Us ◽  
Storm Prediction ◽  
Future Work

AbstractAlthough severe weather forecast products, such as the Storm Prediction Center (SPC) convective outlook, are much more accurate than climatology at day-to-week time scales, tornadoes and severe thunderstorms claim dozens of lives and cause billions of dollars in damage every year. While the accuracy of this outlook has been well documented, less work has been done to explore the comprehension of the product by non-expert users like the general public. This study seeks to fill this key knowledge gap by collecting data from a representative survey of U.S. adults in the lower 48 states about their use and interpretation of the SPC convective outlook. Participants in this study were asked to rank the words and colors used in the outlook from least to greatest risk, and their answers were compared through visualizations and statistical tests across multiple demographics. Results show that the US public ranks the outlook colors similarly to their ordering in the outlook but switch the positions of several of the outlook words as compared to the operational product. Logistic regression models also reveal that more numerate individuals more correctly rank the SPC outlook words and colors. These findings suggest that the words used in the convective outlook may confuse non-expert users, and that future work should continue to use input from public surveys to test potential improvements in the choice of outlook words. Using more easily understood words may help to increase the outlook’s decision support value and potentially reduce the harm caused by severe weather events.

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