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A Climatology of Freezing Rain in the Great Lakes Region of North America

TitleA Climatology of Freezing Rain in the Great Lakes Region of North America
Publication TypeManual Entry
Year of Publication2000
AuthorsCortinas, John
Monthly Weather ReviewMonthly Weather Review
Pagination3574 - 3588
Date Published2000
PublisherAmerican Meteorological Society
Short TitleMon. Wea. Rev.
Citation Key1062
Community Notes

Freezing Rain Mechanisms in the Great Lakes:

"Case studies of Great Lakes events show that freezing rain can occur with extratropical cyclones that move across the Great Lakes soon after a polar air mass has established itself across the region. As these cyclones move east or northeast across or south of the Great Lakes, warm and moist air between 850 and 700 hPa is advected northward over the cold subfreezing surface air. The upward vertical motion associated with this warm advection pattern produces precipitation that freezes upon contact with subfreezing objects on the ground (Stewart and King 1987, 1990; Martner et al. 1993). Other notable observations during Great Lakes events include strong vertical shear near the bottom of the warm layer, precipitation organized in linear bands, and the occurrence of other types of precipitation with freezing rain (e.g., rain, snow, and ice pellets). Aside from these case studies, the author is unaware of any studies that have analyzed the distribution of many freezing rain events and summarized the synoptic-scale processes associated with them in the Great Lakes region."

"An examination of the synoptic-scale conditions associated with events in each region shows that most events are associated with synoptic-scale upward motion associated with strong low- and midlevel warm advection and increasing positive vorticity advection with height. These conditions occur as a result of a shortwave trough moving eastward across the Great Lakes region."

"Besides the general increase of freezing rain from west to east across the Great Lakes, the areas immediately to the west of Lake Huron, Lake Erie, Lake Michigan, and southwest of Lake Ontario experience a lower frequency of freezing rain than areas farther inland. This climatological distribution suggests that the Great Lakes may play a role in regulating the production of freezing rain. One may speculate that this distribution is the result of fall and spring events during which subfreezing air moves across an unfrozen lake and warms to a temperature equal to or greater than 0°C because of sensible heat flux from the lake surface. During these conditions, the predominant type of precipitation along the coast would be rain; although, freezing rain may occur briefly if the temperature of exposed objects is equal to or less than 0°C from a prior period of subfreezing temperatures."

When the lake waters are open (above freezing) there is a tendency for decreased freezing rain near the lake shores but the frequency of freezing rain during times when the lake is frozen over is similar for lake side and in-land locations.

Data Set Description:

Hourly surface observations from the National Climatic Data Center (NCDC) from 1976-90.  Some data quality measures were taken including only incorporating locations that had at least 80% of the present weather reports for 10 of the 15 years were used.  "The thermodynamic structure of freezing rain events was examined using rawinsonde data from the NOAA Radiosonde Data of North America CD-ROM."  Only a few select locations in Michigan and Wisconsin were studied in the radiosonde data.

Article's Climatology of Freezing-Rain:

"an infrequent mesoscale event"

"Freezing rain is reported most often between the months of December and March"

"The predominant intensity of freezing rain is light, reported for 98% of all freezing-rain observations"

"reezing rain often does not occur concurrently with other types of precipitation at a particular location"

"the event duration usually defines the severity"