Understanding Heavy Lake-Effect Snowfall: The Vertical Structure of Radar Reflectivity in a Deep Snowband over and downwind of Lake Ontario

Abstract The distribution of radar-estimated precipitation from lake-effect snowbands over and downwind of Lake Ontario shows more snowfall in downwind areas than over the lake itself. Here, two nonexclusive processes contributing to this are examined: the collapse of convection that lofts hydrometeors over the lake and allows them to settle downwind; and stratiform ascent over land, due to the development of a stable boundary layer, frictional convergence, and terrain, leading to widespread precipitation there. The main data sources for this study are vertical profiles of radar reflectivity and hydrometeor vertical velocity in a well-defined, deep long-lake-axis-parallel band, observed on 11 December 2013 during the Ontario Winter Lake-effect Systems (OWLeS) project. The profiles are derived from an airborne W-band Doppler radar, as well as an array of four K-band radars, an X-band profiling radar, a scanning X-band radar, and a scanning S-band radar. The presence of convection offshore is evident from deep, strong (up to 10 m s−1) updrafts producing bounded weak-echo regions and locally heavily rimed snow particles. The decrease of the standard deviation, skewness, and peak values of Doppler vertical velocity during the downwind shore crossing is consistent with the convection collapse hypothesis. Consistent with the stratiform ascent hypothesis are (i) an increase in mean vertical velocity over land; and (ii) an increasing abundance of large snowflakes at low levels and over land, due to depositional growth and aggregation, evident from flight-level and surface particle size distribution data, and from differences in reflectivity values from S-, X-, K-, and W-band radars at nearly the same time and location.

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The OWLeS IOP2b Lake-Effect Snowstorm: Dynamics of the Secondary Circulation

Monthly Weather Review ◽

10.1175/mwr-d-16-0462.1 ◽

2017 ◽

Vol 145 (7) ◽

pp. 2437-2459 ◽

Cited By ~ 10

Author(s):

Philip T. Bergmaier ◽

Bart Geerts ◽

Leah S. Campbell ◽

W. James Steenburgh

Keyword(s):

Doppler Radar ◽

Vertical Plane ◽

Wrf Model ◽

Lake Ontario ◽

Radar Data ◽

Secondary Circulation ◽

Land Breeze ◽

Lake Effect ◽

Axis Parallel ◽

Convergence Zones

Intense lake-effect snowfall results from a long-lake-axis-parallel (LLAP) precipitation band that often forms when the flow is parallel to the long axis of an elongated body of water, such as Lake Ontario. The intensity and persistence of the localized precipitation along the downwind shore and farther inland suggests the presence of a secondary circulation that helps organize such a band, and maintain it for some time as the circulation is advected inland. Unique airborne vertical-plane dual-Doppler radar data are used here to document this secondary circulation in a deep, well-organized LLAP band observed during intensive observing period (IOP) 2b of the Ontario Winter Lake-effect Systems (OWLeS) field campaign. The circulation, centered on a convective updraft, intensified toward the downwind shore and only gradually weakened inland. The question arises as to what sustains such a circulation in the vertical plane across the LLAP band. WRF Model simulations indicate that the primary LLAP band and other convergence zones observed over Lake Ontario during this IOP were initiated by relatively shallow airmass boundaries, resulting from a thermal contrast (i.e., land-breeze front) and differential surface roughness across the southern shoreline. Airborne radar data near the downwind shore of the lake indicate that the secondary circulation was much deeper than these shallow boundaries and was sustained primarily by rather symmetric solenoidal forcing, enhanced by latent heat release within the updraft region.

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LLAP Band Structure and Intense Lake-Effect Snowfall Downwind of Lake Ontario: Insights from the OWLeS 7–9 January 2014 Event

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-19-0288.1 ◽

2020 ◽

Vol 59 (10) ◽

pp. 1691-1715

Author(s):

Philip T. Bergmaier ◽

Bart Geerts

Keyword(s):

Doppler Radar ◽

Model Simulation ◽

Lake Ontario ◽

Radar Data ◽

Heat Fluxes ◽

Secondary Circulation ◽

Land Breeze ◽

Surface Heat Fluxes ◽

Lake Effect ◽

Axis Parallel

AbstractModeling and observational studies stemming from the 2013–14 Ontario Winter Lake-Effect Systems (OWLeS) field campaign have yielded much insight into the structure and development of long-lake-axis-parallel (LLAP) lake-effect systems over Lake Ontario. This study uses airborne single- and dual-Doppler radar data obtained during two University of Wyoming King Air flights, as well as a high-resolution numerical model simulation, to examine and contrast two distinctly different LLAP band structures observed within a highly persistent lake-effect system on 7–9 January 2014. On 7 January, a very cold air mass accompanied by strong westerly winds and weak capping aloft resulted in a deep, intense LLAP band that produced heavy snowfall well inland. In contrast, weaker winds, weaker surface heat fluxes, and stronger capping aloft resulted in a weaker LLAP band on 9 January. This band was blocked along the downwind shore and produced only light snowfall closer to the shoreline. Although the two structures examined here represent opposite ends of a spectrum of LLAP bands, both cases reveal a well-organized mesoscale secondary circulation composed of two counterrotating horizontal vortices positioned on either side of a narrow updraft within the band. In both cases, this circulation traces back to a shallow, baroclinic land-breeze front originating along a bulge in the lake’s southern shoreline. As the band extends downstream and the low-level baroclinity weakens, buoyancy increases within the band—driven in part by cloud latent heating—leading to band intensification and a deeper, stronger, and more symmetric secondary circulation over the lake.

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The Evolution of Lake-Effect Convection during Landfall and Orographic Uplift as Observed by Profiling Radars

Monthly Weather Review ◽

10.1175/mwr-d-15-0117.1 ◽

2015 ◽

Vol 143 (11) ◽

pp. 4422-4442 ◽

Cited By ~ 28

Author(s):

Justin R. Minder ◽

Theodore W. Letcher ◽

Leah S. Campbell ◽

Peter G. Veals ◽

W. James Steenburgh

Keyword(s):

Vertical Structure ◽

Lake Ontario ◽

Radar Data ◽

Horizontal Distance ◽

Field Campaign ◽

Lake Effect ◽

X Band ◽

Liquid Precipitation ◽

K Band

Abstract A pronounced snowfall maximum occurs about 30 km downwind of Lake Ontario over the 600-m-high Tug Hill Plateau (hereafter Tug Hill), a region where lake-effect convection is affected by mesoscale forcing associated with landfall and orographic uplift. Profiling radar data from the Ontario Winter Lake-effect Systems field campaign are used to characterize the inland evolution of lake-effect convection that produces the Tug Hill snowfall maximum. Four K-band profiling Micro Rain Radars (MRRs) were aligned in a transect from the Ontario coast onto Tug Hill. Additional observations were provided by an X-band profiling radar (XPR). Analysis is presented of a major lake-effect storm that produced 6.4-cm liquid precipitation equivalent (LPE) snowfall over Tug Hill. This event exhibited strong inland enhancement, with LPE increasing by a factor of 1.9 over 15-km horizontal distance. MRR profiles reveal that this enhancement was not due to increases in the depth or intensity of lake-effect convection. With increasing inland distance, echoes transitioned from a convective toward a stratiform morphology, becoming less intense, more uniform, more frequent, and less turbulent. An inland increase in echo frequency (possibly orographically forced) contributes somewhat to snowfall enhancement. The XPR observations reproduce the basic vertical structure seen by the MRRs while also revealing a suppression of snowfall below 600 m AGL upwind of Tug Hill, possibly associated with subcloud sublimation or hydrometeor advection. Statistics from 29 events demonstrate that the above-described inland evolution of convection is common for lake-effect storms east of Lake Ontario.

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Radar and ground-level measurements of precipitation collected by EPFL during the ICE-POP 2018 campaign in South-Korea

10.5194/essd-2020-134 ◽

2020 ◽

Author(s):

Josué Gehring ◽

Alfonso Ferrone ◽

Anne-Claire Billault–Roux ◽

Nikola Besic ◽

Kwang Deuk Ahn ◽

...

Keyword(s):

Doppler Radar ◽

Ground Level ◽

Two Dimensional ◽

W Band ◽

X Band ◽

Precipitation Type ◽

École Polytechnique ◽

Liquid Precipitation ◽

Polarisation Measurements ◽

Precipitation Events

Abstract. This article describes a four-month dataset of precipitation and cloud measurements collected during the International Collaborative Experiments for PyeongChang 2018 Olympic and Paralympic winter games (ICE-POP 2018). This paper aims to describe the data collected by the Environmental Remote Sensing Laboratory of the École Polytechnique Fédérale de Lausanne. The dataset includes observations from an X-band dual-polarisation Doppler radar, a W-band Doppler cloud profiler, a multi-angle snowflake camera and a two-dimensional video disdrometer (https://doi.pangaea.de/10.1594/PANGAEA.918315, Gehring et al. (2020a)) . Classifications of hydrometeor types derived from dual-polarisation measurements and snowflake photographs are presented. The dataset covers the period from 15 November 2017 to 18 March 2018 and features nine precipitation events with a total accumulation of 195 mm of equivalent liquid precipitation. This represents 85 % of the climatological accumulation over this period. To illustrate the available data, measurements corresponding to the four precipitation events with the largest accumulation are presented. The synoptic situations of these events were contrasted and influenced the precipitation type and accumulation. The hydrometeor classifications reveal that aggregate snowflakes were dominant and that some events featured significant riming. The combination of dual-polarisation variables and high-resolution Doppler spectra with ground-level snowflake images makes this dataset particularly suited to study snowfall microphysics in a region where such measurements were not available before.

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Thunderstorm Characteristics during the Ontario Winter Lake-Effect Systems Project

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-17-0188.1 ◽

2018 ◽

Vol 57 (4) ◽

pp. 853-874 ◽

Cited By ~ 4

Author(s):

Scott M. Steiger ◽

Tyler Kranz ◽

Theodore W. Letcher

Keyword(s):

Boundary Layer ◽

Wind Turbines ◽

Winter Season ◽

Primary Source ◽

Lake Ontario ◽

Field Campaign ◽

Lake Effect ◽

Lightning Detection ◽

Axis Parallel ◽

And Behavior

AbstractThe Ontario Winter Lake-Effect Systems (OWLeS) field campaign during the winter season of 2013/14 provided unprecedented data with regard to the structure and behavior of long-lake-axis-parallel (LLAP) lake-effect storms. One of the interesting characteristics of LLAP storm bands is their ability to initiate lightning. The OWLeS datasets provide an opportunity to examine more thoroughly the kinematics and microphysics of lake-effect thunder-snowstorms than ever before. The OWLeS facilities and field personnel observed six lake-effect thunderstorms during December–January 2013/14. Most of them produced very little lightning (fewer than six cloud-to-ground strokes or intracloud pulses recorded by the National Lightning Detection Network). The 7 January 2014 storm had over 50 strokes and pulses, however, which resulted in 20 flashes over a 6-h period (0630–1230 UTC), making it the most electrically active storm during the field campaign. Relative to the 18 December 2013 storm, which only had three flashes, the 7 January 2014 case had a deeper boundary layer and greater instability. Also, 45% of the lightning during the 7 January storm was likely due to flashes initiated by wind turbines or other man-made antennas, along with all of the lightning observed during 18 December. No lightning was documented over Lake Ontario, the primary source of instability for these storms.

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Lake-Effect Mode and Precipitation Enhancement over the Tug Hill Plateau during OWLeS IOP2b

Monthly Weather Review ◽

10.1175/mwr-d-15-0412.1 ◽

2016 ◽

Vol 144 (5) ◽

pp. 1729-1748 ◽

Cited By ~ 25

Author(s):

Leah S. Campbell ◽

W. James Steenburgh ◽

Peter G. Veals ◽

Theodore W. Letcher ◽

Justin R. Minder

Keyword(s):

New York ◽

Weather Forecasting ◽

Lake Ontario ◽

Short Wave ◽

Operational Forecasts ◽

Radar Echoes ◽

Lake Effect ◽

Axis Parallel ◽

Upper Level ◽

Precipitation Enhancement

Improved understanding of the influence of orography on lake-effect storms is crucial for weather forecasting in many lake-effect regions. The Tug Hill Plateau of northern New York (hereafter Tug Hill), rising 500 m above eastern Lake Ontario, experiences some of the most intense snowstorms in the world. Herein the authors investigate the enhancement of lake-effect snowfall over Tug Hill during IOP2b of the Ontario Winter Lake-effect Systems (OWLeS) field campaign. During the 24-h study period, total liquid precipitation equivalent along the axis of maximum precipitation increased from 33.5 mm at a lowland (145 m MSL) site to 62.5 mm at an upland (385 m MSL) site, the latter yielding 101.5 cm of snow. However, the ratio of upland to lowland precipitation, or orographic ratio, varied with the mode of lake-effect precipitation. Strongly organized long-lake-axis parallel bands, some of which formed in association with the approach or passage of upper-level short-wave troughs, produced the highest precipitation rates but the smallest orographic ratios. Within these bands, radar echoes were deepest and strongest over Lake Ontario and the coastal lowlands and decreased in depth and median intensity over Tug Hill. In contrast, nonbanded broad-coverage periods exhibited the smallest precipitation rates and the largest orographic ratios, the latter reflecting an increase in the coverage and frequency of radar echoes over Tug Hill. These findings should aid operational forecasts and, given the predominance of broad-coverage lake-effect periods during the cool season, help explain the climatological snowfall maximum found over the Tug Hill Plateau.

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Climatological Characteristics and Orographic Enhancement of Lake-Effect Precipitation East of Lake Ontario and over the Tug Hill Plateau

Monthly Weather Review ◽

10.1175/mwr-d-15-0009.1 ◽

2015 ◽

Vol 143 (9) ◽

pp. 3591-3609 ◽

Cited By ~ 32

Author(s):

Peter G. Veals ◽

W. James Steenburgh

Keyword(s):

New York ◽

Lake Ontario ◽

Cool Season ◽

Lake Effect ◽

Fort Drum ◽

Axis Parallel ◽

Radar Imagery ◽

Orographic Enhancement ◽

The Mean ◽

Liquid Precipitation

Abstract Lake-effect snowstorms east of Lake Ontario are frequently intense and contribute to substantial seasonal accumulations, especially over the Tug Hill Plateau (hereafter Tug Hill), which rises at a gentle 1.25% slope to ~500 m above lake level. Using a variety of datasets including radar imagery from the KTYX (Fort Drum, New York) WSR-88D, this paper examines the characteristics of lake-effect precipitation east of Lake Ontario over 13 cool seasons (16 September 2001–15 May 2014). During this period, days with at least 2 h of lake effect account for 61%–76% of the mean cool-season snowfall and 24%–37% of the mean cool-season liquid precipitation. Mean monthly lake-effect frequency and snowfall peak in December and January. The highest lake-effect frequency and snowfall occur over the western and upper Tug Hill, with an arm of relatively high lake-effect frequency and snowfall extending to the southeast shore of Lake Ontario. To the east (lee), lake-effect frequency and snowfall decrease abruptly over the Black River valley, although relatively high frequency and snowfall extend downstream into the western Adirondack Mountains. Broad coverage and long-lake-axis-parallel (LLAP) bands dominate the lake-effect morphology throughout the region. There is no diurnal modulation of lake-effect frequency during winter, but weak modulation in fall and spring, especially of LLAP bands. Collectively, these results quantify the role that lake effect plays in the cool-season hydroclimate east of Lake Ontario. The increase in lake-effect frequency and snowfall over Tug Hill suggest an inland/orographic intensification of many lake-effect systems, with evidence for shadowing in the lee.

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Circulations, Bounded Weak Echo Regions, and Horizontal Vortices Observed within Long-Lake-Axis-Parallel–Lake-Effect Storms by the Doppler on Wheels*

Monthly Weather Review ◽

10.1175/mwr-d-12-00226.1 ◽

2013 ◽

Vol 141 (8) ◽

pp. 2821-2840 ◽

Cited By ~ 27

Author(s):

Scott M. Steiger ◽

Robert Schrom ◽

Alfred Stamm ◽

Daniel Ruth ◽

Keith Jaszka ◽

...

Keyword(s):

Great Lakes ◽

Velocity Structure ◽

Lake Ontario ◽

Shear Instability ◽

Doppler Velocity ◽

Horizontal Shear ◽

Structure And Dynamics ◽

Lake Effect ◽

Axis Parallel ◽

Western Great Lakes

Abstract The eastern Great Lakes (Erie and Ontario) are often affected by intense lake-effect snowfalls. Lake-effect storms that form parallel to the major axes of these lakes can strongly impact communities by depositing more than 100 cm of snowfall in less than 24 h. Long-lake-axis-parallel (LLAP) storms are significantly different in structure and dynamics compared to the much more studied wind-parallel roll storms that typically form over the western Great Lakes. A Doppler on Wheels (DOW) mobile radar sampled several of these storms at fine spatial and temporal resolutions (and close to the surface) during the winter of 2010–11 over and downwind of Lake Ontario to document and improve understanding of how these storms develop. Over 1100 observations of vortices were catalogued within the 16 December 2010 and 4–5 January 2011 events. The majority of these vortices were less than 1 km in diameter with a statistical modal difference in Doppler velocity (delta-V) value across the vortex of 11 m s−1. Vortices developed along boundaries, which formed within the bands, suggesting horizontal shear instability was the main cause. Other features noted in the DOW observations included bounded weak echo regions, anvils, and horizontal vortices, typically on the south side of west–east-oriented LLAP bands. The reflectivity and velocity structure of LLAP bands were found to be much more complex than previously thought, which may impact localized precipitation amounts and errors in forecast location/intensity.

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Measurements and Simulations of Nadir-Viewing Radar Returns from the Melting Layer at X and W Bands

Journal of Applied Meteorology and Climatology ◽

10.1175/2009jamc2033.1 ◽

2009 ◽

Vol 48 (11) ◽

pp. 2215-2226 ◽

Cited By ~ 9

Author(s):

Liang Liao ◽

Robert Meneghini ◽

Lin Tian ◽

Gerald M. Heymsfield

Keyword(s):

Water Content ◽

Doppler Radar ◽

Tropical Rainfall Measuring Mission ◽

Dielectric Constants ◽

Doppler Velocity ◽

Regional Study ◽

Melting Layer ◽

Bright Band ◽

W Band ◽

X Band

Abstract Simulated radar signatures within the melting layer in stratiform rain—namely, the radar bright band—are checked by means of comparisons with simultaneous measurements of the bright band made by the ER-2 Doppler radar (EDOP; X band) and Cloud Radar System (CRS; W band) airborne Doppler radars during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida-Area Cirrus Experiment (CRYSTAL-FACE) campaign in 2002. A stratified-sphere model, allowing the fractional water content to vary along the radius of the particle, is used to compute the scattering properties of individual melting snowflakes. Using the effective dielectric constants computed by the conjugate gradient–fast Fourier transform numerical method for X and W bands and expressing the fractional water content of a melting particle as an exponential function in particle radius, it is found that at X band the simulated radar brightband profiles are in an excellent agreement with the measured profiles. It is also found that the simulated W-band profiles usually resemble the shapes of the measured brightband profiles even though persistent offsets between them are present. These offsets, however, can be explained by the attenuation caused by cloud water and water vapor at W band. This is confirmed by comparisons of the radar profiles made in the rain regions where the unattenuated W-band reflectivity profiles can be estimated through the X- and W-band Doppler velocity measurements. The brightband model described in this paper has the potential to be used effectively for both radar and radiometer algorithms relevant to the satellite-based Tropical Rainfall Measuring Mission and Global Precipitation Measuring Mission.

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Perbandingan Karakteristik Distribusi Butiran Hujan yang Berasal dari Awan Laut dan Awan Darat di Kototabang

Jurnal Fisika Unand ◽

10.25077/jfu.5.3.273-282.2016 ◽

2016 ◽

Vol 5 (3) ◽

pp. 273-282

Author(s):

Nur Fadillah ◽

Marzuki Marzuki ◽

Wendi Harjupa ◽

Toyoshi Shimomai ◽

Hiroyuki Hashiguchi

Keyword(s):

Size Distribution ◽

Doppler Radar ◽

Radar Reflectivity ◽

Two Dimensional ◽

Raindrop Size Distribution ◽

X Band ◽

Raindrop Size ◽

Coupling Processes

Karakteristik distribusi ukuran butiran hujan atau raindrop size distribution (RDSD) dari hujan yang berasal dari awan laut dan awan darat di Kototabang, Sumatera Barat, telah dibandingkan. Asal hujan diamati menggunakan X-band Doppler radar (XDR) selama proyek Coupling Processes in the Equatorial Atmosphere (CPEA)-I (10 April 2004 - 9 Mei 2004). Data RDSD berasal dari pengamatan two-dimensional video disdrometer (2DVD). RDSD dimodelkan dengan distribusi gamma dan parameternya didapatkan menggunakan metode momen. Dari penelitian ini terlihat bahwa intensitas curah hujan yang tinggi lebih banyak pada hujan dari awan darat dibandingkan dengan yang dari awan laut. Selain itu, butiran hujan yang berukuran besar pada awan darat lebih banyak daripada awan laut. Banyaknya butiran hujan dengan ukuran yang besar ini berdampak kepada nilai radar reflectivity (Z) pada awan darat yang lebih besar dibandingkan dengan awan laut untuk intensitas curah hujan yang sama. Hal ini mengakibatkan persamaan Z-R antara awan darat dan awan laut berbeda dimana nilai koefisien A dari persamaan Z-R untuk awan darat lebih besar daripada awan laut. Dengan demikian, perbedaan karaktersitik RDSD antara awan darat dan laut sebaiknya dipertimbangkan dalam pengembangan radar meteorologi di kawasan tropis. Penggunaan Z-R tunggal (Z = 200R1,6) untuk mengkoversi data radar cuaca di Sumatera terutama Sumatera Barat tidak akan akurat terutama untuk hujan dari awan laut.Kata kunci: distribusi butiran hujan (RDSD), awan darat, awan laut, Kototabang

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