scholarly journals Multidecadal Changes in the Frequency and Ambient Conditions of Warm Season Convective Storms over the Northeastern United States

2014 ◽  
Vol 27 (19) ◽  
pp. 7285-7300 ◽  
Author(s):  
Harrison Li ◽  
Brian A. Colle
Keyword(s):  
United States ◽  
General Pattern ◽  
Warm Season ◽  
Convective Precipitation ◽  
Ambient Conditions ◽  
Northeastern United States ◽  
Convective Storm ◽  
Linear Discriminant ◽  
Low Level ◽  
Storm Frequency

Abstract Long-term changes in warm season (April–September) convective storm frequency over the northeastern United States (NEUS) and the environmental conditions favoring such storms are explored from 1979 to 2010. Linear discriminant analysis (LDA) was used to create thresholds for predicting annual warm season convective storm frequency over various small regions of the NEUS by relating the convective precipitation fields from the North American Regional Reanalysis (NARR) and the Climate Forecast System Reanalysis (CFSR) along with reflectivity data from the National Operational Weather Radar (NOWrad) archive at 2-km grid spacing from 1996 to 2006 to convective parameters in the reanalyses. On average, convective frequency is greatest across inland areas of the NEUS, particularly southern Pennsylvania, with a sharp decrease along the immediate coast. Across western Pennsylvania convective storm frequency has significantly (p < 0.01) decreased from 1979 to 2010, while closer to the coast convective frequency has increased slightly. There has also been a corresponding trend in warm season convective precipitation amounts, with decreasing amounts over inland Pennsylvania and increasing amounts near the coast. This general pattern of inland decreases and coastal increases is largely related to trends in low-level instability, which are attributable mainly to changes in low-level moisture. Analyzing convective parameters over small regions is an important consideration for future climate studies of convection, since using a single LDA threshold over a region encompassing a large portion of the NEUS failed to capture significant spatial differences in convective frequency and was substantially less accurate than using separate thresholds for smaller regions of the NEUS.

scholarly journals Future Changes in Convective Storm Days over the Northeastern United States Using Linear Discriminant Analysis Applied to CMIP5 Predictions

2016 ◽  
Vol 29 (12) ◽  
pp. 4327-4345 ◽  
Author(s):  
Harrison Li ◽  
Brian A. Colle
Keyword(s):  
United States ◽  
Discriminant Analysis ◽  
Linear Discriminant Analysis ◽  
Warm Season ◽  
First Century ◽  
Historical Period ◽  
Northeastern United States ◽  
Convective Storm ◽  
Linear Discriminant ◽  
Twenty First Century

Abstract Future changes in the frequency of environmental conditions conducive for convective storm days (“CE days”) are determined for the northeastern United States (NEUS) during the warm seasons (April–September) of the twenty-first century. Statistical relationships between historical runs of seven models in phase 5 of the Coupled Model Intercomparison Project (CMIP5) and radar-classified convective storm days are developed using linear discriminant analysis (LDA), and these relationships are then applied to analyze changes in the convective environment under the high-emissions representative concentration pathway 8.5 (RCP8.5) scenario over the period 2006–99. The 1996–2007 warm seasons are used to train the LDA thresholds using convective precipitation from two reanalysis datasets and radar data, and the 1979–95 and 2008–10 warm seasons are used to verify these thresholds. For the CMIP5 historical period (1979–2005), the frequency of warm season CE days averaged across the CMIP5 models is slightly greater than that derived using reanalysis data, although both methods indicate a slight increasing trend through the historical period. Between 2006 and 2099, warm season CE day frequency is predicted to increase substantially at an average rate of 4–5 days decade−1 (50%–80% increase over the entire period). These changes are mostly attributed to a predicted 30%–40% increase in midlevel precipitable water between the historical period and the last few decades of the twenty-first century. Consistent with previous studies, there is decreasing deep-layer vertical wind shear as a result of a weakening horizontal temperature gradient, but this is outweighed by increases in instability led by the moisture increases.

Convective Storm Structures and Ambient Conditions Associated with Severe Weather over the Northeast United States

2011 ◽  
Vol 26 (6) ◽  
pp. 940-956 ◽  
Author(s):  
Kelly A. Lombardo ◽  
Brian A. Colle
Keyword(s):  
United States ◽  
Rhode Island ◽  
Coastal Zone ◽  
Severe Weather ◽  
Ambient Conditions ◽  
Northeastern United States ◽  
Convective Storm ◽  
Convective Structures ◽  
Cellular Events ◽  
Linear And Nonlinear

Abstract This study documents the convective storm structures and ambient conditions associated with severe storms (wind, hail, and tornado) over the northeastern United States for two warm seasons (May–August), including 2007 and a warm season comprising randomly selected days from 2002 to 2006. The storms were classified into three main convective organizational structures (cellular, linear, and nonlinear) as well as several subcategories. The same procedure was applied to the highly populated coastal zone of the northeastern United States, including New Jersey, Connecticut, Rhode Island, and New York. The coastal analysis included six warm seasons from 2002 to 2007. Over the Northeast, severe wind events are evenly distributed among the cellular, linear, and nonlinear structures. Cellular structures are the primary hail producers, while tornadoes develop mainly from cellular and linear structures. Over the coastal zone, primarily cellular and linear systems produce severe wind and hail, while tornadoes are equally likely from all three convective structures. Composites were generated for severe weather days over the coastal region for the three main convective structures. On average, severe cellular events develop during moderate instability [most unstable CAPE (MUCAPE) ~1200 J kg−1], with low-level warm-air advection and frontogenesis at the leading edge of a thermal ridge collocated with an Appalachian lee trough. Severe linear events develop in a similar mean environment as the cellular events, except that most linear events occur with a surface trough upstream over the Ohio River valley and half of the linear events develop just ahead of progressive midlevel troughs. Nonlinear severe events develop with relatively weak mean convective instability (MUCAPE ~460 J kg−1), but they are supported by midlevel quasigeostrophic (QG) forcing for ascent.

scholarly journals Are biogenic emissions a significant source of summertime atmospheric toluene in rural Northeastern United States?

2008 ◽  
Vol 8 (3) ◽  
pp. 12283-12311 ◽  
Author(s):  
M. L. White ◽  
R. S. Russo ◽  
Y. Zhou ◽  
J. L. Ambrose ◽  
K. Haase ◽  
...  
Keyword(s):  
United States ◽  
Loblolly Pine ◽  
Seasonal Pattern ◽  
Warm Season ◽  
Growing Season ◽  
Emission Rates ◽  
Industrial Emissions ◽  
Northeastern United States ◽  
Mixing Ratios ◽  
Fuel Evaporation

Abstract. Summertime atmospheric toluene enhancements at Thompson Farm in the rural northeastern United States were unexpected and resulted in a toluene/benzene seasonal pattern that was distinctly different from that of other anthropogenic volatile organic compounds. Consequentially, three hydrocarbon sources were investigated for potential contributions to the enhancements during 2004–2006. These included: 1) increased warm season fuel evaporation coupled with changes in reformulated gasoline (RFG) content to meet U.S. EPA summertime volatility standards, 2) local industrial emissions and 3) local vegetative emissions. The contribution of fuel evaporation emission to summer toluene mixing ratios was estimated to range from 16 to 30 pptv d−1, and did not fully account for the observed enhancements (20–50 pptv) in 2004–2006. Static chamber measurements of alfalfa, a crop at Thompson Farm, and dynamic branch enclosure measurements of loblolly pine trees in North Carolina suggested vegetative emissions of 5 and 12 pptv d−1 for crops and coniferous trees, respectively. Toluene emission rates from alfalfa are potentially much larger as these plants were only sampled at the end of the growing season. Measured biogenic fluxes were on the same order of magnitude as the influence from gasoline evaporation and industrial sources (regional industrial emissions estimated at 7 pptv d−1) and indicated that local vegetative emissions make a significant contribution to summertime toluene enhancements. Additional studies are needed to characterize the variability and factors controlling toluene emissions from alfalfa and other vegetation types throughout the growing season.

scholarly journals The Association of the Elevated Mixed Layer with Significant Severe Weather Events in the Northeastern United States*

2010 ◽  
Vol 25 (4) ◽  
pp. 1082-1102 ◽  
Author(s):  
Peter C. Banacos ◽  
Michael L. Ekster
Keyword(s):  
United States ◽  
Mixed Layer ◽  
Trajectory Analysis ◽  
Source Region ◽  
Warm Season ◽  
The United States ◽  
Severe Weather ◽  
Lapse Rate ◽  
Northeastern United States ◽  
Weather Events

Abstract The occurrence of rare but significant severe weather events associated with elevated mixed-layer (EML) air in the northeastern United States is investigated herein. A total of 447 convective event days with one or more significant severe weather report [where significant is defined as hail 2 in. (5.1 cm) in diameter or greater, a convective gust of 65 kt (33 m s−1) or greater, and/or a tornado of F2 or greater intensity] were identified from 1970 through 2006 during the warm season (1 May–30 September). Of these, 34 event days (7.6%) were associated with identifiable EML air in regional rawinsondes preceding the event. Taken with two other noteworthy events in 1953 and 1969, a total of 36 significant severe weather events associated with EML air were studied via composite and trajectory analysis. Though a small percentage of the total, these 36 events compose a noteworthy list of historically significant derechos and tornadic events to affect the northeastern United States. It is demonstrated that plumes of EML air emanating from the Intermountain West in subsiding, anticyclonically curved flows can reinforce the capping inversion and maintain the integrity of the EML across the central United States over a few days. The EML plume can ultimately become entrained into a moderately fast westerly to northwesterly midtropospheric flow allowing for the plume’s advection into the northeastern United States. Resultant thermodynamic conditions in the convective storm environment are similar to those more typically observed closer to the EML source region in the Great Plains of the United States. In addition to composite and trajectory analysis, two case studies are employed to demonstrate salient and evolutionary aspects of the EML in such events. A lapse rate tendency equation is explored to put EML advection in context with other processes affecting lapse rate.

The effects of aerosols on intense convective precipitation in the northeastern United States

2009 ◽  
Vol 135 (643) ◽  
pp. 1367-1391 ◽  
Author(s):  
Alexandros A. Ntelekos ◽  
James A. Smith ◽  
Leo Donner ◽  
Jerome D. Fast ◽  
William I. Gustafson ◽  
...  
Keyword(s):  
United States ◽  
Convective Precipitation ◽  
Northeastern United States

scholarly journals Structure and Evolution of Precipitation along a Cold Front in the Northeastern United States

2009 ◽  
Vol 10 (5) ◽  
pp. 1243-1256 ◽  
Author(s):  
Yan Zhang ◽  
James A. Smith ◽  
Alexandros A. Ntelekos ◽  
Mary Lynn Baeck ◽  
Witold F. Krajewski ◽  
...  
Keyword(s):  
United States ◽  
New York ◽  
New Jersey ◽  
Heavy Rainfall ◽  
Frontal Zone ◽  
Extreme Rainfall ◽  
Convective Precipitation ◽  
Northeastern United States ◽  
Flash Flooding ◽  
Urban Corridor

Abstract Heavy precipitation in the northeastern United States is examined through observational and numerical modeling analyses for a weather system that produced extreme rainfall rates and urban flash flooding over the New York–New Jersey region on 4–5 October 2006. Hydrometeorological analyses combine observations from Weather Surveillance Radar-1988 Doppler (WSR-88D) weather radars, the National Lightning Detection Network, surface observing stations in the northeastern United States, a vertically pointing lidar system, and a Joss–Waldvogel disdrometer with simulations from the Weather Research and Forecasting Model (WRF). Rainfall analyses from the Hydro-Next Generation Weather Radar (NEXRAD) system, based on observations from WSR-88D radars in State College, Pennsylvania, and Fort Dix, New Jersey, and WRF model simulations show that heavy rainfall was organized into long-lived lines of convective precipitation, with associated regions of stratiform precipitation, that develop along a frontal zone. Structure and evolution of convective storm elements that produced extreme rainfall rates over the New York–New Jersey urban corridor were influenced by the complex terrain of the central Appalachians, the diurnal cycle of convection, and the history of convective evolution in the frontal zone. Extreme rainfall rates and flash flooding were produced by a “leading line–trailing stratiform” system that was rapidly dissipating as it passed over the New York–New Jersey region. Radar, disdrometer, and lidar observations are used in combination with model analyses to examine the dynamical and cloud microphysical processes that control the spatial and temporal structure of heavy rainfall. The study illustrates key elements of the spatial and temporal distribution of rainfall that can be used to characterize flash flood hazards in the urban corridor of the northeastern United States.

scholarly journals The Seasonal Nature of Extreme Hydrological Events in the Northeastern United States

2015 ◽  
Vol 16 (5) ◽  
pp. 2065-2085 ◽  
Author(s):  
Allan Frei ◽  
Kenneth E. Kunkel ◽  
Adao Matonse
Keyword(s):  
United States ◽  
Extreme Precipitation ◽  
Extreme Event ◽  
Warm Season ◽  
The United States ◽  
Cold Season ◽  
Northeastern United States ◽  
Extreme Precipitation Events ◽  
Extreme Hydrological Events ◽  
Precipitation Events

Abstract Recent analyses of extreme hydrological events across the United States, including those summarized in the recent U.S. Third National Climate Assessment (May 2014), show that extremely large (extreme) precipitation and streamflow events are increasing over much of the country, with particularly steep trends over the northeastern United States. The authors demonstrate that the increase in extreme hydrological events over the northeastern United States is primarily a warm season phenomenon and is caused more by an increase in frequency than magnitude. The frequency of extreme warm season events peaked during the 2000s; a secondary peak occurred during the 1970s; and the calmest decade was the 1960s. Cold season trends during the last 30–50 yr are weaker. Since extreme precipitation events in this region tend to be larger during the warm season than during the cold season, trend analyses based on annual precipitation values are influenced more by warm season than by cold season trends. In contrast, the magnitude of extreme streamflow events at stations used for climatological analyses tends to be larger during the cold season: therefore, extreme event analyses based on annual streamflow values are overwhelmingly influenced by cold season, and therefore weaker, trends. These results help to explain an apparent discrepancy in the literature, whereby increasing trends in extreme precipitation events appear to be significant and ubiquitous across the region, while trends in streamflow appear less dramatic and less spatially coherent.

scholarly journals Are biogenic emissions a significant source of summertime atmospheric toluene in the rural Northeastern United States?

2009 ◽  
Vol 9 (1) ◽  
pp. 81-92 ◽  
Author(s):  
M. L. White ◽  
R. S. Russo ◽  
Y. Zhou ◽  
J. L. Ambrose ◽  
K. Haase ◽  
...  
Keyword(s):  
United States ◽  
Loblolly Pine ◽  
Seasonal Pattern ◽  
Warm Season ◽  
Growing Season ◽  
Emission Rates ◽  
Industrial Emissions ◽  
Northeastern United States ◽  
Mixing Ratios ◽  
Fuel Evaporation

Abstract. Summertime atmospheric toluene enhancements at Thompson Farm in the rural northeastern United States were unexpected and resulted in a toluene/benzene seasonal pattern that was distinctly different from that of other anthropogenic volatile organic compounds. Consequently, three hydrocarbon sources were investigated for potential contributions to the enhancements during 2004–2006. These included: (1) increased warm season fuel evaporation coupled with changes in reformulated gasoline (RFG) content to meet US EPA summertime volatility standards, (2) local industrial emissions and (3) local vegetative emissions. The contribution of fuel evaporation emission to summer toluene mixing ratios was estimated to range from 16 to 30 pptv d−1, and did not fully account for the observed enhancements (20–50 pptv) in 2004–2006. Static chamber measurements of alfalfa, a crop at Thompson Farm, and dynamic branch enclosure measurements of loblolly pine trees in North Carolina suggested vegetative emissions of 5 and 12 pptv d−1 for crops and coniferous trees, respectively. Toluene emission rates from alfalfa are potentially much larger as these plants were only sampled at the end of the growing season. Measured biogenic fluxes were on the same order of magnitude as the influence from gasoline evaporation and industrial sources (regional industrial emissions estimated at 7 pptv d−1 and indicated that local vegetative emissions make a significant contribution to summertime toluene enhancements. Additional studies are needed to characterize the variability and factors controlling toluene emissions from alfalfa and other vegetation types throughout the growing season.

scholarly journals Areal Probability of Precipitation in Moist Tropical Air Masses for the United States

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 255
Author(s):  
Cade Reesman ◽  
Paul Miller ◽  
Rebecca D’Antonio ◽  
Kevin Gilmore ◽  
Ben Schott ◽  
...  
Keyword(s):  
United States ◽  
General Public ◽  
Warm Season ◽  
Stage Iv ◽  
The United States ◽  
Convective Precipitation ◽  
Air Masses ◽  
Precipitation Estimates ◽  
Probability Of Precipitation ◽  
Erratic Behavior

Moist tropical (MT) air masses routinely host convective precipitation, including weakly forced thunderstorms (WFTs). These short-lived, isolated events present recurring forecasting challenges due to their spatially small footprints and seemingly erratic behavior in quiescent warm-season environments worldwide. In particular, their activity is difficult to accurately characterize via probability of precipitation (POP), a common forecast product for the general public. This study builds an empirical climatological POP distribution for MT days over the continental United States using Stage IV precipitation estimates. Stage IV estimates within MT air masses between May–September (i.e., the boreal warm season) 2002–2019 are masked into precipitation (≥0.25 mm) and nonprecipitation (<0.25 mm) areas and standardized by the number of MT days. POPs are higher when MT air masses are present. For the Southeast U.S., POP generally increases ~15% compared to the overall warm-season value. At 1800 UTC (1–2 PM LT) daily, POPs are confined to coastal areas and east-facing ridges, and advance inland by 2100 UTC (4–5 PM LT). Climatologically, ~50% of the warm-season precipitation in the Southern U.S. occurred in MT environments. This study emphasizes the need for better forecasting tools and climatological analyses of weakly forced environments.

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