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

Abstract

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.

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

“…The IOP2b event was one of the more intense, deep, and long-lived LLAP events encountered in OWLeS (Minder et al 2015;Frame et al 2015;Campbell et al 2016). A precipitation maximum [27 mm of snow water equivalent (SWE) in 12 h] occurred on the Tug, about 40 km downwind of the shore of Lake Ontario on 11 December 2013, according to National Centers for Environmental Prediction (NCEP) stage-IV data (Fig.…”

Forecasting the Inland Extent of Lake Effect Snow Bands Downwind of Lake Ontario

“…Niziol (1987) described how the synoptic environment-with regards to the existence of cyclonic vorticity advection at 850, 700, and 500 hPa-contributes to ascent aiding in LES band formation. Campbell et al (2016) detailed how the greatest snowfall rates were produced by LES bands that were accompanied by the passage or approach of upper-level short-wave troughs. Hjelmfelt (1990) found that forced orographic ascent enhances LES intensity.…”

Hotplate precipitation gauge calibrations and field measurements

“…NCAR operated a NOAH-II at GLE and BTL during 2012, and coauthors (Campbell and Steenburgh) operated a NOAH-II at OWL (December 2013 to January 2014; Campbell et al, 2016). The three NOAH-II gauges were outfitted with Alter shields (Goodison et al, 1998;hereafter G98).…”

“…4.7.1). Wind speeds used in that calculation are from the hotplate (at GLE and BTL) or from an anemometer (at OWL) (Campbell et al, 2016). Of course, we are assuming that the function from G98 mimics undercatch by our 12 inch (0.30 m; diameter) Alter-shielded NOAH-II gauge.…”

“…This adjustment corresponds to the lowest installation of the hotplate at OWL and decreases to 2.0 for measurements made after 17 December 201 2 . In our calculation of the R11 catch efficiency functions, the snow depth for the interval of interest (11 December 2013 to 29 January 2014) was set equal to the average (0.7 m) derived using an ultrasonic snow depth instrument operated at OWL (Campbell et al, 2016). This average and the AGL altitudes of the hotplate installation (Table 2) were used to derive the two wind-speed adjustment factors (2.9 and 2.0).…”