An official website of the United States government
Potential factors affecting the inland penetration and orographic modulation of lake-effect precipitation east of Lake Ontario include the environmental (lake, land, and atmospheric) conditions, mode of the lake-effect system, and orographic processes associated with flow across the downstream Tug Hill Plateau (herein Tug Hill), Black River valley, and Adirondack Mountains (herein Adirondacks). In this study we use data from the KTYX WSR-88D, ERA5 reanalysis, New York State Mesonet, and Ontario Winter Lake-effect Systems (OWLeS) field campaign to examine how these factors influence lake-effect characteristics with emphasis on the region downstream of Tug Hill. During an eight-cool-season (16 November–15 April) study period (2012/13–2019/20), total radar-estimated precipitation during lake-effect periods increased gradually from Lake Ontario to upper Tug Hill and decreased abruptly where the Tug Hill escarpment drops into the Black River valley. The axis of maximum precipitation shifted poleward across the northern Black River valley and into the northwestern Adirondacks. In the western Adirondacks, the heaviest lake-effect snowfall periods featured strong, near-zonal boundary layer flow, a deep boundary layer, and a single precipitation band aligned along the long-lake axis. Airborne profiling radar observations collected during OWLeS IOP10 revealed precipitation enhancement over Tug Hill, spillover and shadowing in the Black River valley where a resonant lee wave was present, and precipitation invigoration over the western Adirondacks. These results illustrate the orographic modulation of inland-penetrating lake-effect systems downstream of Lake Ontario and the factors favoring heavy snowfall over the western Adirondacks.
more »
« less
Intrastorm Variability of the Inland and Orographic Enhancement of a Sea-Effect Snowstorm in the Hokuriku Region of Japan
Abstract A prolonged period of winter monsoonal flow brought heavy sea-effect snowfall to the Hokuriku region along the west coast of the Japanese island of Honshu from 2 to 7 February 2010. Snowfall in some locations exceeded 140 cm, but the distribution within the event was highly variable. We examine the factors contributing to these variations using data from a Japan Meteorological Agency (JMA) C-band surveillance radar, JMA soundings, surface precipitation observations, and a Weather Research and Forecasting (WRF) Model simulation. There were three distinct periods during the event. Period 1 featured relatively weak flow with precipitation confined mainly to the coast and lowlands. Precipitation maxima were located where the flow ascended: 1) over terrain-blocked air, 2) at the foot of a high flow-normal barrier, or 3) relatively unimpeded over the lower mountain ranges. Flow strengthened during period 2, yielding stronger vertical velocities over the terrain with precipitation maxima shifting inland and to higher elevation. The flow strengthened further in period 3, with the precipitation maxima shifting higher in elevation and into the lee, with almost no precipitation falling in the lowlands. Thus, greater inland penetration and enhancement of precipitation occurred as the flow speed increased, but additional factors such as the subcloud sublimation of hydrometeors and the convective instability also contribute to differences between periods 2 and 3. These results illustrate the importance of incident flow strength in modulating the distribution and enhancement of snowfall in global lake- and sea-effect regions.
more »
« less
- Award ID(s):
- 1635654
- PAR ID:
- 10196271
- Date Published:
- Journal Name:
- Monthly Weather Review
- Volume:
- 148
- Issue:
- 6
- ISSN:
- 0027-0644
- Page Range / eLocation ID:
- 2527 to 2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Abstract Over mountainous terrain, windward enhancement of stratiform precipitation results from a combination of warm-rain and ice-phase processes. In this study, ice-phase precipitation processes are investigated within frontal systems during the Olympic Mountains Experiment (OLYMPEX). An enhanced layer of radar reflectivity (Z H ) above the melting level bright band (i.e., a secondary Z H maximum) is observed over both the windward slopes of the Olympic Mountains and the upstream ocean, with a higher frequency of occurrence and higher Z H values over the windward slopes indicating an orographic enhancement of ice-phase precipitation processes. Aircraft-based in situ observations are evaluated for the 01-02 and 03 December 2015 orographically-enhanced precipitation events. Above the secondary Z H maximum, the hydrometeors are primarily horizontally oriented dendritic and branched crystals. Within the secondary Z H maximum, there are high concentrations of large (> ~2 mm diameter) dendrites, plates, and aggregates thereof, with a significant degree of riming. In both events, aggregation and riming appear to be enhanced within a turbulent layer near sheared flow at the top of a low-level jet impinging on the terrain and forced to rise above the melting level. Based on windward ground sites at low-, mid-, and high-elevations, secondary Z H maxima periods during all of OLYMPEX are associated with increased rain rates and larger mass-weighted mean drop diameters compared to periods without a secondary Z H maximum. This result suggests that precipitation originating from secondary Z H maxima layers may contribute to enhanced windward precipitation accumulations through the formation of large, dense particles that accelerate fallout.more » « less
-
Landfalling lake- and sea-effect (hereafter lake-effect) systems often interact with orography, altering the distribution and intensity of precipitation, which frequently falls as snow. In this study, we examine the influence of orography on two modes of lake-effect systems: long-lake-axis-parallel (LLAP) bands and broad-coverage, open-cell convection. Specifically, we generate idealized large-eddy simulations of a LLAP band produced by an oval lake and broad-coverage, open-cell convection produced by an open lake (i.e., without flanking shorelines) with a downstream coastal plain, 500-m peak, and 2000-m ridge. Without terrain, the LLAP band intersects a coastal baroclinic zone over which ascent and hydrometeor mass growth are maximized, with transport and fallout producing an inland precipitation maximum. The 500-m peak does not significantly alter this structure, but slightly enhances precipitation due to orographic ascent, increased hydrometeor mass growth, and reduced subcloud sublimation. In contrast, a 2000-m ridge disrupts the band by blocking the continental flow that flanks the coastlines. This, combined with differential surface heating between the lake and land, leads to low-level flow reversal, shifting the coastal baroclinic zone and precipitation maximum offshore. In contrast, the flow moves over the terrain in open lake, open-cell simulations. Over the 500-m peak, this yields an increase in the frequency of weaker (<1 m s−1) updrafts and weak precipitation enhancement, although stronger updrafts decline. Over the 2000-m ridge, however, buoyancy and convective vigor increase dramatically, contributing to an eightfold increase in precipitation. Overall, these results highlight differences in the influence of orography on two common lake-effect modes.more » « less
-
Abstract The pathways air travels from the Pacific Ocean to the Intermountain West of the United States are important for understanding how air characteristics change and how this translates to the amount and distribution of snowfall. Recent studies have identified the most common moisture pathways in the Intermountain West, especially for heavy precipitation events. However, the role of moisture pathways on snowfall amount and distribution in specific regions remains unclear. Here, we investigate 24 precipitation events in the Payette Mountains of Idaho during January–March 2017 to understand how local atmospheric conditions are tied to three moisture pathways and how it impacts snowfall amount and distribution. During one pathway, southwesterly, moist, tropical air is directed into the Central Valley of California where the air is blocked by the Sierra Nevada, redirected northward and over lower terrain north of Lake Tahoe into the Snake River Plain of Idaho. Other pathways consist of unblocked flows that approach the coast of California from the southwest and then override the northern Sierra Nevada and southern Cascades, and zonal flows approaching the coast of Oregon overriding the Oregon Cascades. Air masses in the Payette Mountains of Idaho associated with Sierra-blocked flow were observed to be warmer, moister, and windier compared to the other moisture pathways. During Sierra-blocked flow, higher snowfall rates, in terms of mean reflectivity, were observed more uniformly distributed throughout the region compared to the other flows, which observed lower snowfall rates that were predominantly collocated with areas of higher terrain. Of the total estimated snowfall captured in this study, 67% was observed during Sierra-blocked flow.more » « less
-
Lyell, Victoria (Ed.)There are contrasting models for the role of coastal trading ports in the Maya economy throughout prehistory, but particularly in the Terminal Classic (A.D. 800-1000). Hammond (1972) presented a model of obsidian trade from the Maya highlands to the lowlands, in which El Chayal source obsidian was transported via inland routes, whereas Ixtepeque obsidian was traded along the Caribbean coast and then inland via rivers to the southern Maya lowland cities. Healy et al. (1984) and McKillop et al. (1988) suggested that obsidian from both sources was transported along the Caribbean coast but that El Chayal was the dominant source used in the Classic period and Ixtepeque during the Terminal and Postclassic periods. Hammond (1976) suggested that offshore trading ports were used as transshipment stations between maritime and riverine routes. This model was adopted by various researchers (Andrews et al. 1989; Cobos 2023; Guderjan and Garber 1995; Graham and Pendergast 1989; McKillop 2004, 2005a). Cobos (2023) asserts that after the abandonment of inland cities in the southern Maya lowlands at the end of the Classic period, the northern Yucatecan city of Chichen Itza developed a redistributive economy based on tribute and controlled trading ports around the Yucatan peninsula of Mexico and Belize. In the Classic period, the island trading port of Wild Cane Cay was integrated into a regional network of trade between the coast and inland communities. The inland trade was anchored by the dietary need for salt, produced on the coast but absent inland where this basic dietary necessity was in demand. The pattern of coastal-inland trade was replicated along the Caribbean coast of Belize and the Yucatan. Abandonment of inland settlements at the end of the Classic period did not end coastal settlement. Evidence presented in this paper illustrates that Wild Cane Cay was as an independent trading port integrated into a regional marketplace economy and not a node on a redistribution/tribute route controlled by Chichen Itza.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1175/MWR-D-19-0390.1
