Theses List

A Multiscale Examination of Surface Flow Convergence in the Mohawk and Hudson Valleys

 Creators/Contributors

Mike Augustyniak, Lance F. Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Contents/Summary

Forecasters have surmised that the unique terrain found in eastern New York and western New England plays a pivotal role in modulating various weather phenomena in the region. Several studies have examined the interplay between low-level channeled airflow within the Mohawk and Hudson River valleys, the surrounding hilly terrain (i.e., the Adirondack, Catskill, Green, and Berkshire Mountains), and the overall effect on warm-season severe weather events. To date, however, the impact on cold-season weather events of low-level flow channeling in eastern New York and western New England has gone largely unmentioned in the peer-reviewed literature. The goal of this study is to examine, on the synoptic and mesoscale, the occurrence of a low-level convergence zone, which forms during the cold season from time to time, where the Mohawk and Hudson valleys intersect. Known to pose a challenge to local forecasters and referred to colloquially as the “Mohawk–Hudson convergence zone” (MHC), the development of the convergence zone generally does not lead to high-impact weather; however, convergence-related precipitation can wreak havoc if it occurs with little or no warning or at peak travel times. 

 

Cool-Season Regime Transition and its Impact on Precipitation in the Northeastern United States

 Creators/Contributors

Heather Archambault, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Richard Grumm
National Weather Service,
State College, PA

Contents/Summary

Past research has indicated that reconfigurations of the large-scale flow may alter regional weather patterns due to shifts in storm tracks and associated eddy transports of heat, momentum, and vorticity. Meteorological wisdom also suggests that high-impact weather events tend to occur during large-scale flow reconfigurations. Therefore, if this wisdom is valid, certain types of large-scale flow reconfigurations, or regime transitions, may be associated with an increased probability of a significant precipitation event impacting the northeastern United States (U.S.). Up until this point, no known study has explored relationships between regime transitions and Northeast precipitation. To address this need, this research seeks to identify relationships between phase transitions of weather regimes such as the North Atlantic Oscillation (NAO) and the Pacific/North American (PNA) pattern and cool-season precipitation in the Northeast. These relationships will be explored through the use of a statistical climatology and composite analyses of NAO and PNA phase transitions.

 

Cool-Season High Wind Events in the Northeast U.S.

 Creators/Contributors

Jonas V. Asuma, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

John S. Quinlan, Thomas A. Wasula, Hugh W. Johnson IV, Kevin S. Lipton
National Weather Service, Albany, NY

Contents/Summary

High winds, defined as gradient- or thunderstorm-driven winds greater than or equal to 25 m s−1 or damaging winds of any speed, can be challenging for National Weather Service (NWS) forecasters in the Northeast (NE). In the cool season, the NE experiences approximately 22 high-wind events per cool season, defined as October through April. The main goals of this thesis are to: 1) diagnose the climatological frequency of high winds in the NE and adjacent regions; 2) construct composite charts that represent the synoptic environments and mechanisms that lead to the production of high winds in the NE; 3) examine specific high-wind events that illustrate important atmospheric processes associated with the occurrence of high winds; and 4) increase situational awareness of the mechanisms that can lead to the production of severe high winds.

 

Synoptic And Mesoscale Aspects of Ice Storms in the Northeastern U.S.

 Creators/Contributors

Christopher Castellano
University at Albany, State University of New York, Albany, New York

Contents/Summary

Ice storms are among the most hazardous, disruptive, and costly meteorological phenomena in the northeastern United States. The accretion of freezing rain during ice storms endangers human safety, compromises public infrastructure, and causes economic losses on local and regional scales. Furthermore, ice storms present a major operational forecast challenge due to the combined influence of synoptic, mesoscale, and microphysical processes on precipitation type. In consideration of these socioeconomic impacts and forecast issues, we have identified three primary objectives for this thesis: 1) create long-term climatologies of freezing rain and ice storms in the northeastern U.S., 2) identify antecedent environments conducive to ice storms and dynamical mechanisms responsible for freezing rain, and 3) increase situational awareness of the synoptic and mesoscale processes that govern the evolution of ice storms.

 

Predecessor Rain Events in Advance of Tropical Cyclones

 Creators/Contributors

Matthew R. Cote, Lance F. Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Micheael L. Jurewicz, Sr.
National Weather Service,
Binghamton, NY

Contents/Summary

The purpose of this thesis is to document the spatial structure and temporal evolution of heavy rainstorms that sometimes develop well poleward of landfalling or near-coastal-tracking Atlantic basin tropical cyclones (TCs) (refer to the appendix for a list of acronyms used in this thesis). A statistical and composite climatology of these predecessor rain events (PREs) was established using a database of 47 cases occurring downstream of 21 TCs between 1998 and 2006. The PREs from three TCs—two from within the climatological period and one from before—were chosen for detailed synoptic-scale and mesoscale study based on their capacity to illustrate significant findings from the climatology as well as physical mechanisms crucial to their formation. A null case also was selected so the environment downstream of the TC could be contrasted with those cases that spawned PREs. The aim of this type of approach is to continue the mission of the warm-season project of the Collaborative Science, Technology, and Applied Research (CSTAR) program under which the research was conducted—namely, to improve the prediction of heavy precipitation events over the northeastern U.S. through integration of academic research into useful operational frameworks.

 

Distribution of Precipitation over the Northeast Accompanying Landfalling and Transitioning Tropical Cyclones

 Creators/Contributors

David DeLuca, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Contents/Summary

Landfalling and transitioning tropical cyclones pose a significant forecast challenge in predicting the distribution of heavy precipitation in the northeastern United States. The forecast challenge is heightened because the heavy rainfall distribution associated with these tropical cyclones can be modulated significantly when the poleward-moving storms interact with mobile midlatitude upper-level troughs and coastal fronts over regions of complex terrain. The purpose of this thesis is to document the large spatial and temporal variability of heavy precipitation that accompanies landfalling and transitioning tropical cyclones and to determine the physical basis for the observed rainfall distribution.

 

Evaluation of Lightning Jums as a predictor  of Severe Weather in the Northeastern US

 Creators/Contributors

Pamela Eck ,  Lance Bosart and Brian Tang
University at Albany, State University of New York, Albany, New York

Michael Evans, Joseph Villani and Thomas A. Wasula
National Weather Service,
Albany, NY

Matthew Kramar
National Weather Service,
Pittsburgh, PA

Contents/Summary

Severe weather events in the northeastern United States can be challenging to forecast, given how the evolution of deep convection can be influenced by complex terrain and the lack of quality observations in complex terrain. To supplement existing observations, this study explores using lightning to forecast severe convection in areas of complex terrain in the northeastern United States. A sudden increase in lightning flash rate by two standard deviations, also known as a lightning jump, may be indicative of a strengthening updraft and an increased probability of severe weather.  This study assesses the value of using lightning jumps to forecast severe weather during July 2015 in the northeastern United States. Total lightning data from the National Lightning Detection Network (NLDN) is used to calculate lightning jumps using a 2 lightning jump algorithm with a minimum threshold of 5 flashes min-1 . Lightning jumps are used to predict the occurrence of severe weather, as given by whether a Storm Prediction Center (SPC) severe weather report occurred 45 min after a lightning jump in the same cell. Results indicate a high probability of detection (POD; 85%) and a high false alarm rate (FAR; 89%), suggesting that lightning jumps occur in sub-severe storms

 

Large Scale Circulation Anomaly

 Creators/Contributors

David Groenert, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Richard Grumm
National Weather Service,
State College, PA

Contents/Summary

The purpose of this research project under the Collaborative Science, Technology, and Applied Research (CSTAR) program is to better understand the relationship between large-scale circulation anomalies such as the North Atlantic Oscillation (NAO) and the Pacific/North American (PNA) pattern with precipitation events over the northeastern US. The tendency for large-scale circulation anomaly phase changes to be associated with the significant precipitation events over the Northeast will be established through the correlation of daily large-scale circulation anomaly indices and specific precipitation events. The relationship between large-scale circulation anomalies and research results from other CSTAR projects regarding mesoscale substructure and 500 hPa cutoff lows will also be presented.

 

Case Studies of Cool Season 500 hPa Cutoff Cyclone Precipitation Distribution

 Creators/Contributors

Anthony R. Fracasso, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Michael S. Evans
National Weather Service,
Binghamton, NY

Contents/Summary

The generation, evolution, and prediction of upper-air cutoff cyclones (also referred to as closed lows) and their influence on sensible weather have been an ongoing challenge to forecasters. An integral component of this challenge is quantitative precipitation forecasting (QPF). Forecasting improvements on the overall synoptic scale (e.g., pressure fields) have improved greatly with the advent of regional models such as the Nested Grid Model (NGM) (e.g., Junker and Hoke 1990). However, skill in QPF has lagged behind since the scale of precipitation is quite variable and much smaller than the typical synoptic scale (e.g., Anthes 1983; Roebber and Bosart 1998). This lag in forecast skill is certainly true with regard to cutoff cyclones, which are associated with 30% of the annual precipitation in the northeast United States (US) (Atallah and Aiyyer 2002). With such a considerable fraction attributed to cutoffs, the need for improved forecasts of precipitation in association with these systems is clearly self-evident.

 

The Motion Of Mesoscale Snowbands In Northeast U.S. Winter Storms

 Creators/Contributors

Jaymes  S. Kenyon
University at Albany, State University of New York, Albany, New York

Contents/Summary
The distribution of snowfall accumulation attending winter storms is a product of both precipitation intensity and duration. Many heavy snowfall events are associated with distinct mesoscale snowbands that strongly modulate snowfall accumulation. Mesoscale snowbands are known to be favored within environments characterized by frontogenesis in the presence of weak moist symmetric or gravitational stabilities. Although the development of mesoscale snowbands often can be anticipated at 24−36-h ranges, anticipating band residence time at a fixed location remains a forecasting challenge. However, given that snowband residence time is related to characteristics of band motion, improved understanding of band motion presents an opportunity to improve snowfall accumulation forecasts. This study investigates environmental attributes associated with specific snowband motion characteristics. A classification scheme for snowband motion is developed, wherein bands are categorized into four modes: laterally translating, laterally quasi-stationary, pivoting, and hybrid. Laterally translating bands exhibit predominantly cross-axis motion, thereby favoring quasi-uniform snowfall accumulation along their paths. In contrast, laterally quasi-stationary bands are characterized by near-zero crossaxis motion, favoring heavy snowfall accumulation along a narrow corridor that may extend for several hundred kilometers. Pivoting bands exhibit pronounced rotation such that heavy snowfall accumulation is particularly favored near the center of rotation. Finally, hybrid bands are dominated by along-axis motion, but with a concurrent crossaxis component of motion.

 

Mesoscale Structure of Precipitation Regions in Northeast Winter Storms

 Creators/Contributors

Matthew D. Greenstein, Lance F. Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

David J. Nicosia
National Weather Service,
Binghamton, NY

Contents/Summary

While forecasters can predict likely areas of precipitation, problems remain in correctly anticipating mesoscale precipitation patterns within those areas. In northeastern United States snowstorms, precipitation takes on numerous patterns, or modes, in radar reflectivity imagery, e.g., relatively uniform, fractured, and banded. Better forecasts of these mesoscale characteristics would allow for enhanced prediction of snowfall amount and variability and for the differentiation between high-impact and low-impact snows. Twenty “heavy snow” events in the Northeast from the winters of 2002–03 through 2004–05 are selected for analysis using several criteria based on precipitation type, snowfall, time of year, and location. High-resolution WSI Corporation NOWrad composite reflectivity radar mosaics are used to identify five main precipitation modes, or mesoscale patterns, among the cases. The NCEP North American Regional Reanalysis is used to create plan-view maps and cross sections in order to ascertain which aspects of the ingredients—lift, instability, moisture, and microphysics—can assist in distinguishing the observed precipitation modes.

 

Mesoscale Precipitation Structures Accompanying Landfalling and Transitioning Tropical Cyclones in the Northeast United States

 Creators/Contributors

Jared Klein, Lance F. Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

David Vallee
National Weather Service,
Taunton, MA

Contents/Summary

The purpose of this thesis is to demonstrate how the observed mesoscale distribution of heavy rainfall in landfalling and transitioning tropical cyclones (TCs) is modulated by interactions between synoptic and mesoscale features in the presence of the complex physiography of the northeast U.S. This research focuses on understanding the key surface and tropospheric dynamics that routinely accompany these TCs. A dataset containing 52 landfalling and transitioning TCs producing greater than 100 mm (~4 in.) of rainfall over the northeast U.S. for 1950–2006 was used to generate a climatology of these TCs. Three representative cases were selected for further study in order to document and illustrate how the dynamical forcing controls the observed mesoscale distribution of heavy precipitation and to provide operational forecasters information that can be utilized for predicting landfalling and transitioning TCs. The remainder of this chapter will review the previous research related to landfalling and transitioning TCs, such as extratropical transition (ET), jet dynamics, frontogenesis (including coastal frontogenesis), orographic precipitation enhancement, and precipitation distribution.

 

Dynamical and thermodynamic processes contributing to thundersnow events over the northeast U.S.

 Creators/Contributors

Kyle Meier
University at Albany, State University of New York, Albany, New York

Contents/Summay

Thundersnow often occurs in conjunction with mesoscale snowbands and may be associated with regions of locally heavy snowfall (15–30 cm) and intense snowfall rates (5–10 cm h−1 ). The availability of the National Lightning Detection Network (NLDN) system and operational Doppler weather radars during the past 20 years has allowed meteorologists to produce comprehensive national lightning maps and to identify localized areas of enhanced snowfall associated with thundersnow. The purpose of this thesis is to take advantage of the NLDN data and other contemporary observing systems in order to construct climatological, composite, and case study analyses of the atmospheric environment during thundersnow occurrence. Emphasis was placed on determining the dynamical and thermodynamic processes that contribute to thundersnow events over the northeast U.S.

 

Cool-Season Cyclones Associated with Significant Upper- Level Easterly Wind Anomalies

 Creators/Contributors

Adrian Mitchell
University at Albany, State University of New York, Albany, New York

Contents/Summary

A subset of Northeast U.S. cool-season cyclones is associated with upper-level easterly flow and, occasionally, well-defined easterly jet streaks. These events occur approximately once per year and may be associated with retrograding surface cyclones and precipitation caused by northerly warm-air advection, leading to forecast challenges. The deepest extratropical cyclone that affected the Northeast U.S. during the 2009–2010 cool-season was associated with an upper-level easterly jet streak, and produced a record snowfall total of 85 cm in Burlington, Vermont. Orographic precipitation enhancement in this case resulted from an interaction of the low-level flow with the complex topography of northern Vermont. This thesis explores the multi-scale aspects of similar anomalous cyclone events (ACEs) in the Northeast U.S. through climatological, composite and case study analyses.

 

Synoptic-Scale Environments and Dynamical Mechanisms Associated with Predecessor Rain Events Ahead of Tropical Cyclones

 Creators/Contributors

Benjamin J. Moore, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Michael L. Jurewicz, Sr.
National Weather Service, Binghamton
, NY

Contents/Summary

Predecessor rain events (PREs) are distinct mesoscale regions of heavy rainfall that develop ahead of landfalling tropical cyclones (TCs) as a continuous polewardmoving stream of deep tropical moisture emanating from the TC encounters a region of ascent to produce heavy, prolonged rainfall. PREs present a forecast challenge because they have the potential to cause significant inland flooding, given that they are typically characterized by large rainfall totals (>100 mm in 24 h). An increased risk of flooding is posed if the TC rain shield subsequently passes over the region affected by the PRE. The primary objectives of this thesis are to: 1) document the distinct synoptic-scale configurations favorable for the development of PREs, and 2) examine the dynamical mechanisms associated with PREs. Accomplishing these objectives will ultimately lead to the development of a set of operational forecasting tools and techniques not only to diagnose the potential for PRE development but also to predict how a PRE may evolve in time and space.

 

Forecasting heavy precipitation associated with warm-season cutoff cyclones

 Creators/Contributors

Jessica Najuch, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Kenneth D. Lapenta, Thomas A. Wasula
National Weather Service,
Albany, NY

Contents/Summary

Forecasting heavy precipitation associated with warm-season cutoff cyclones presents a particularly challenging forecast problem in the northeastern US. This challenge arises in part from physiographic features that modulate the distribution of precipitation and severe weather, and the rapid changes in the character of precipitation due to the evolution and motion of the cutoff cyclones. As part of the Collaborative Science, Technology, and Applied Research (CSTAR) program, this project contributes to an improved understanding of the distribution of heavy precipitation associated with cutoff cyclones as well as the reasons for precipitation enhancement. The results of a 51- year (1948–1998) northeastern US climatology of precipitation associated with cutoff cyclones are presented based on the National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC) Unified Precipitation Dataset (UPD). Other portions of the climatology including preferred warm season monthly cutoff cyclone tracks, are derived using four-times daily (0000, 0600, 1200 and 1800 UTC) 500 hPa gridded geopotential height analyses from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset. In this thesis, cutoff cyclones are identified objectively and are defined as a geopotential height minimum surrounded by at least one closed 30 m interval contour.

 

Mesoscale band formation in extratropical cyclones

 Creators/Contributors

David Novak, Lance F. Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Contents/Summary

Accurate Quantitative Precipitation Forecasting (QPF) has been a long-standing goal of the operational forecasting community. However, this goal has proved elusive since mesoscale precipitation features largely affect precipitation accumulation. Mesoscale band formation in extratropical cyclones has been a popular focus for study in improving QPF, since these features can dramatically affect the basic intensity, timing, and subsequent accumulation of precipitation. The effects of mesoscale bands are especially evident during the cold season, when snowfall associated with the bands can produce “white out” conditions and significant snowfall accumulations. Despite these dramatic effects, the mesoscale nature of precipitation bands has made their diagnosis and prediction challenging.

 

Climatology of Warm Season 500 hPa Cutoff Cyclones and Two Case Studies

 Creators/Contributors

Matthew J. Novak, Lance F. Bosart, and Daniel Keyser, Anantha Aiyyer
University at
Albany, State University of New York, Albany, New York

Kenneth D. Lapenta, Thomas A. Wasula
National Weather Service,
Albany, NY

Contents/Summary

Accurate Quantitative Precipitation Forecasting (QPF) has been a long-standing goal of the operational forecasting community. However, this goal has proved elusive since mesoscale precipitation features largely affect precipitation accumulation. Mesoscale band formation in extratropical cyclones has been a popular focus for study in improving QPF, since these features can dramatically affect the basic intensity, timing, and subsequent accumulation of precipitation. The effects of mesoscale bands are especially evident during the cold season, when snowfall associated with the bands can produce “white out” conditions and significant snowfall accumulations. Despite these dramatic effects, the mesoscale nature of precipitation bands has made their diagnosis and prediction challenging.

 

Forecasting Precipitation Distributions Associated with Cool-Season 500-hPa Cutoff Cyclones in the Northeastern United States

 Creators/Contributors

Melissa Payer, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Neil A. Stuart, Thomas A. Wasula
National Weather Service,
Albany, NY

Contents/Summary

Forecasting precipitation distributions associated with 500-hPa cool-season cutoff cyclones can be a challenge in the Northeast U.S. (NE).   Forecast uncertainties often arise due to variation in cutoff cyclone speed/location and interaction with the complex topography in the NE Identifying signatures differentiating between precipitation distributions would help forecasters.  This research creates composites of cutoff cyclones categorized by tilt, structure, and precipitation amount.  It also performs case studies of difficult-to-forecast cutoff cyclones as well as cutoff cyclones associated with varying precipitation distributions.  Finally it identifies signatures differentiating between various precipitation distributions

 

Multiscale Analyses of Inland Tropical Cyclone-MidLatitude Jet Interactions: Camille(1969) and Danny(1997)

 Creators/Contributors

Matthew S. Potter, Lance F. Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Contents/Summary

TC Camille (1969) and TC Danny (1997) both interacted with the equatorward entrance region of an upper-tropospheric jet as they traversed the Appalachian Mountains; however, their societal impacts differed. During the 12-h period starting 0000 UTC 20 August 1969, 690 mm of rain fell over Massies Mill, Virginia, as TC Camille traversed the central Appalachian Mountains. On 24 July 1997, TC Danny underwent inland reintensification while moving across the Carolinas. TC Danny’s minimum central mean sea level pressure decreased from 1012 hPa to 1000 hPa and its maximum sustained wind speed increased from 20 kt to 40 kt during the 18-h period starting 0000 UTC 24 July. The main objectives of this thesis are to document the synoptic-scale environments and underlying mesoscale processes responsible for each TC–jet interaction, and to document important mechanisms and processes that lead to inland flooding associated with TC–jet interactions and inland reintensifying TCs that interact with midlatitude jets.

 

Forecasting Distributions of Warm-Season Precipitation Associated with
500-hPa Cutoff Cyclones

 Creators/Contributors

Matthew A. Scalora, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Neil A. Stuart, Thomas A. Wasula
National Weather Service,
Albany, NY

Contents/Summary

The forecasting of heavy precipitation and severe weather associated with warmseason 500-hPa cutoff cyclones is a challenge over the northeastern United States (U.S.). Numerical weather prediction models have difficulty predicting aspects of the evolution of cutoff cyclones, such as their deepening or filling rates and tracks. In particular, forecasting the distribution of precipitation in cutoff cyclones can be challenging. The purpose of this research is to increase the understanding of the structure and evolution of cutoff cyclones from which improvements in the skill of forecasting cutoff cyclones can follow. This research was conducted under the National Weather Service Collaborative Science, Technology, and Applied Research (CSTAR) program. The results of this research are intended to provide forecast methodologies and contribute to increased situational awareness concerning cutoff cyclones over the northeastern U.S. during the warm season.

 

Cutoff Cyclones: A Global and Regional Climatology and Two Case Studies

 Creators/Contributors

Brandon A. Smith , Lance Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Dan St. Jean
National Weather Service
Gray, ME

Contents/Summary

Cutoff cyclones are associated with many significant forecasting problems in the northeastern United States. Given the complex terrain in the Northeast, the precipitation distribution associated with slow-moving cutoff cyclones is often challenging to predict. An understanding of the behavior of cutoff cyclones in the Northeast is a first step to improving the precipitation forecasts associated with them. To gain a perspective of northeast US cutoff cyclones, an understanding of the global distribution of cutoff cyclone activity must be developed. As an initial step toward addressing this challenge and as part of the Collaborative Science and Technology Applied Research (CSTAR) program, the results of a 54-year (1948–2001) global and regional climatology of 500 hPa cutoff cyclones is presented in order to map the spatial and temporal distributions of these features. This task is accomplished by using four-times daily (0000, 0600, 1200 and 1800 UTC) 500 hPa gridded geopotential height analyses from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset.

 

Ensemble Variability In Rainfall Forecasts of Hurricane Irene

 Creators/Contributors

Molly Smith, Kristen Corbosiero and Ryan Torn
University at Albany, State University of New York, Albany, New York

Stephen DiRienzo
National Weather Service, Albany, NY

Mike Jurewicz
National Weather Service, Binghamton, NY

Contents/Summary

As tropical cyclones (TCs) move into the midlatitudes, they are often associated with extensive heavy precipitation. This precipitation can lead to widespread flooding events, such as occurred with Hurricane Irene (2011) over the northeastern United States. Despite the highimpact nature of these events, there are relatively few studies that explore the sensitivity of precipitation forecasts to model initial conditions, instead focusing on the variability in TC track. The goal of this work is to understand what modulates precipitation forecasts over the northeastern United States during Hurricane Irene. This is investigated using the Global Forecasting System (GFS) ensemble prediction system, initialized at 0000 UTC 27 August 2011. The ensemble members that forecast the largest precipitation totals (i.e., wet members) over the Catskill Mountains of New York (where over 15” of rain were observed) are then compared to the members that predicted the least precipitation (i.e., dry members), to diagnose the processes that lead to the rainfall differences. Results indicate that the amount of rainfall is tied to storm track, with wetter members clustered on the western side of the track envelope, and drier members on the east. Variability in storm track is associated with variability in each member’s potential vorticity field at model initialization.

 

A Multiscale Analysis of Major Transition Season Northeast Snowstorms

 Creators/Contributors

Rebecca Steeves, Andrea Lopez Lang, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Neil A. Stuart, Thomas A. Wasula
National Weather Service,
Albany, NY

Contents/Summary

Motivated by the opportunity to improve scientific understanding and forecaster situational awareness of major transition season Northeast snowstorms, this study examined this class of snowstorms by means of a multiscale analysis. The multiscale analysis included both a climatology and composite analysis and emphasized ARs and lower-tropospheric cold air. Major transition season Northeast snowstorms used in the climatology and composite analysis were identified from NCEI’s monthly Storm Data publication during 1983–2013.

 

Appalachian Lee Troughs And Their Association with Severe Weather Events

 Creators/Contributors

Daniel B. Thompson, Lance Bosart, and Daniel Keyser

University at Albany, State University of New York, Albany, New York

Thomas A. Wasula
National Weather Service, Albany, NY

Contents/Summary

Forecasting convective storms in the mid-Atlantic region of the U.S. (hereafter mid-Atlantic) is important because of the proximity of the convective initiation region to major East Coast cities. These forecasts can be challenging because of the weak synoptic-scale forcing for ascent and abundant convective instability typical of the midAtlantic warm season (May–September). As a result, mesoscale boundaries such as the Appalachian lee trough (ALT) play an important role in initiating convective storms.  This thesis examines the association between ALTs and warm-season severe convective storms in the mid-Atlantic in order to understand how ALTs modulate the frequency and distribution of severe convective storms and to provide enhanced situational awareness for forecasters.

 

An Analysis Of High Impact Low Predictive Skill Severe Weather

 Creators/Contributors

Matthew Vaughan
University at Albany, State University of New York, Albany, New York

Contents/Summary

An objective evaluation of Storm Prediction Center slight risk convective outlooks, as well as a method to identify high-impact severe weather events with poor-predictive skill are presented in this study. The objectives are to assess severe weather forecast skill over the northeast U.S. relative to the continental U.S., build a climatology of high-impact, low-predictive skill events between 1980–2013, and investigate the dynamic and thermodynamic differences between severe weather events with low-predictive skill and high-predictive skill over the northeast U.S. Severe storm reports of hail, wind, and tornadoes are used to calculate skill scores including probability of detection (POD), false alarm ratio (FAR) and threat scores (TS) for each convective outlook

 

Cool-Season Moderate Precipitation Events in the Northeastern United States

 Creators/Contributors

Keith Wagner, Lance Bosart, and Daniel Keyser
University at Albany, State University of New York,
Albany, New York

Michael S. Evans
National Weather Service,
Binghamton, NY

Contents/Summary
Moderate precipitation events, defined as event total liquid precipitation amounts of 0.6–1.3 cm or snowfall accumulations of 6.4–19 cm, contribute a significant percentage of all cool-season precipitation events in the northeast United States. While most of the public, and many forecasters, tend to focus on heavy cool-season precipitation events, the lesser events may have a greater long-term impact. Moderate events during the cool season help build up the water table and reservoirs, thus providing crucial water supplies during dry summers. Conversely, frequently occurring moderate events can cause problems for humans and wildlife. Areas that experience consistent moderate snowfalls will build up the snowpack, thus increasing the likelihood for flooding from snowmelt. Frequent moderate rain events can also lead to flooding, especially when followed by a heavy rain event. Such situations can lead to property damage or even loss of life.
 

Warm Season Lake Sea Breeze Severe Weather in the Northeast

 Creators/Contributors

Patrick Wilson, Lance F. Bosart, and Daniel Keyser
University at Albany, State University of New York, Albany, New York

Thomas A. Wasula
National Weather Service,
Albany, NY

Contents/Summary

Thunderstorms that form along lake-/sea-breeze convergence zones over the northeastern U.S. sometimes are observed to become severe when they migrate from their source regions. These thunderstorms can be challenging to forecast because they can form in the absence of clearly defined synoptic-scale or mesoscale precursor disturbances. The dynamical and thermodynamical processes, modulated by physiographic effects, that are responsible for creating severe weather from lake-/sea-breeze convergence zones are discussed through selected case studies. Eleven cases were selected for analysis in the northeastern U.S. between 2000 and 2006 where lake-/sea-breeze circulations helped to initiate or suppress convection. The National Centers for Environmental Prediction–North American Regional Reanalysis gridded dataset, the Rapid Update Cycle gridded dataset, radar data, soundings, and surface observations were used to construct the analyses. These 11 cases were divided into two categories: pure cases, where lake-/sea-breeze convergence zones were primarily responsible for initiating severe weather in the apparent absence of synoptic-scale forcing, and mixed cases, where synoptic-scale forcing acted in conjunction with mesoscale forcing from the lake and sea breezes to generate severe weather. The 11-case sample includes one null event where the arrival of marine air from a sea breeze suppressed convection.