Thomas is an avid weather enthusiast, landscaper and organic gardener. This blog is dedicated to Northeast and tropical weather forecasting. Enjoy!
By: sullivanweather , 11:09 PM GMT on October 03, 2009
Over the last several days global forecast models have been insisting on building an anomalously cold airmass over central Canada and dropping it into the eastern US next week following the passage of a significant storm system. Several model runs have shown 850mb temperatures dropping into the negative 10's Celsius along the US-Canadian border with -6°C air @850mb moving across the Great Lakes. An airmass this cold has shown in years past to produce early-season lake-effect snowfall. Other model runs have shown a more modified solution, with air still cold enough for wet snow to mix in with lake-effect rain, but nothing substantial in terms of accumulating snow. Models have centered on the 12-13th as the coldest days of the upcoming 'arctic' blast, which is a popular date for early-season snowfall, it seems.
Three years ago today numerical models were giving meteorologists fits. First to appear on the always questionable-in-the-long-term GFS model near the end of September was an anomalously deep and cold trough diving into central Canada and across the Great Lakes delivering a winter-like blast of arctic air capable of producing a lake effect snow event. Initially shrugged off as a couple of anomalous runs, support slowly gathered. Once within the forecast range of the operational Global GEM (Canadian) model and the operational ECMWF (European) model the same deep and cold trough was there, daring climatology. 850mb temps were progged to be nearly 5-sigma below normal as the core of this cold airmass descended into the US but would this actually happen?
As the event grew near and it became apparent that there would be an outbreak of arctic air new questions arose. It had just been the second warmest summer on record, nearly beating out the Dust Bowl year of 1936, and despite a cooler than average September across the Great Lakes region, water temperature anomalies in the Great Lakes ranged 5-8°F above normal, running at all-time highs for early October. Could such anomalously warm lake temperatures yield any lake effect snow or would they moderate the airmass enough to produce lake effect rain?
The front moved through the western lakes on the 11th with the lake effect beginning quickly in its wake. First, rain showers moved off Lake Superior but those slowly changed over to snow showers by the evening. As the night progressed snowfall picked up in intensity off Lake Superior as even colder air flowed over the lake in a lightly sheared surface-700mb environment with several communities in favored areas picking up 6-8 inches of snow by morning. However, lake-effect snow off Lake Superior, the coldest of the five Great Lakes, isn’t all too uncommon in mid-October. For the communities downwind of Lakes Michigan, Erie and Ontario, mid-October lake-effect snow isn’t just uncommon, it’s rare. And climatology was hard to overcome at first. Through the early morning of the 12th most of the lake-effect precipitation moving off Lake Michigan was in the form of rain, save a few localized areas in northern-lower Michigan. But the airmass had other plans. Temperatures aloft continued to cool and by mid-morning, the lake-effect rain had changed over to snow in most areas across the State of Michigan. Even communities close to the lake shore started to see a mixing of precipitation types which eventually changed over to snow.
So the airmass was, in fact, cold enough to deliver the goods in terms of snowfall. Not only was there snow falling but there was snow accumulating. Widespread accumulations of 2-4 inches across southern Michigan were common and in some localized areas, such as Cheboygan, Michigan, near the Straits of Mackinac, up to a foot of snow fell! But would this cold air have enough drive to complete its journey across the Great Lakes to deliver snow to the eastern Great Lakes region, where water temperatures were warmer still? The average temperature of Lake Erie on the morning of the 12th was 65°F, about 5 degrees above normal. And due to the position of the low to the northwest of Lake Erie, the wind flow would have to come down the entire length of the lake, allowing plenty of time for the air to moderate as opposed to the flow over Lake Michigan, which cut widthwise across the lake, leaving less time for a moderation of temperatures.
At first, it seemed the warmer waters of Lake Erie would win out. The front crossed the Niagara Frontier mid-morning of the 12th and several hours after its passage only lake-effect rain fell. But nature always has tricks up her sleeve. The airmass coming over Lake Erie was anomalously cold, but yet not yet cold enough to produce snowfall after moving down the length of warm Lake Erie through early afternoon. Models had projected 850mb temperatures to drop to a marginal -4 to -6°C and upon reaching those temperatures rain continued; some other factors were needed to conjure up a snowstorm. They would soon be realized.
Models are a great tool for guidance but they don’t hold a candle to real-world observation. 1800Z soundings from around the Great Lakes showed an underestimation of how truly cold this airmass was. 850mb temps were a couple degrees Celsius cooler than models had projected them to be. Soon, areas of western New York away from the lake began to mix with graupel and change over to all snow by 2pm. Buffalo airport began to change over to snow around 3pm and snow eventually started falling right to the shores of Lake Erie. A very odd confluence of events started taking shape.
Special upper air soundings from Buffalo showed a dramatically cooling 3,000-6,000’ layer indicating a dynamically cooling atmosphere typical of ‘top down’ snow events. Additionally, inversion heights were off the scale, over 20,000’ and nearly double all previous known events. By 3pm the National Lightning Detection Network (NLDN) noted several cloud to ground lightning strikes within the developing lake band, indicative of frozen precipitation. Due to the unidirectional surface-700mb wind flow, extreme lake-induced instability and incredible inversion heights, as the band developed and intensified the extreme upward vertical motion over the lake required an equally strong inflow of air in the low-levels of the atmosphere. This was the wild card. The air at low-levels was abnormally dry, which aided in evaporative cooling of the column and likely the final factor leading to a complete changeover to snow, despite a lake temperature more than 30°F above freezing!
The snowfall in western New York came in two stages. The first stage resulted in a very heavy wet snow that only accumulated 2-6” during the afternoon and early evening hours. In most locales this initial snowfall melted on contact with the warm ground early on, then later in the afternoon started to coat trees and elevated surfaces. It wasn’t until the sun set that the wet snow began to add up and due to its high moisture content, just two inches was enough to start tree damage. What would follow during the overnight hours was truly one of the more remarkable weather events the Buffalo-metro area would ever see.
As night fell and the atmosphere cooled further, the lake-effect band intensified. Snow rates picked up and snow:water ratios rose from 6:1 to 12:1. For about 12 hours the band remained stationary, producing heavy lake-effect thundersnow over the Buffalo-metro area and points towards the northeast extending to the southwest suburbs of Rochester. During the time 12-18 additional inches of snow fall, resulting in a crippling snowstorm. Most trees were still in full leaf and simply couldn’t handle the weight of 1-2 feet of snow. Tens of thousands of trees fell during this storm, knocking out power to over 400,000 residents. The tree damage was exacerbated by abnormally wet weather during the month of September, amounting to 6.95” at the Buffalo airport. Some locations remained without power for up to two weeks due to the widespread damage inflicted by the heavy wet snow. The Buffalo Airport reported a 24-hour snowfall total of 22.6”, which would end up being the city’s 6th largest 24-hour snowfall total, no matter what time of year.
This event will go down in the record books as the earliest lake-effect snowfall of such intensity on record. Looking back through history no other event on record produces as much snow as early as this event. There have been instances of snow falling earlier in the season but those events don’t compare in regard to the amount of snow that actually fell. There is one event where snowfall amounts were similar, but this occurred a week later in the year, on October 19-20th, 1930.
Other notable early-season lake-effect snow events are as follows:
September 29th, 1895 – An unusually strong low pressure moving from Montana to the Great Lakes region tapped into an unseasonably cold airmass over the Canadian Prairies. This cold air was then transported over the lakes resulting in an early season snowfall for much of the region. Buffalo saw up to 6” of snow with snow being reported as far south as Philadelphia! The arrival of this system was anticipated up to 24 hours in advance by telegraph from the Chicago Weather Bureau with a forecast for gales on the Great Lakes, which ended up being a fairly accurate forecast. What took folks by surprise was the snow that accompanied the high winds.
October 10th, 1906 – Once again, a very strong cold front connected to a gale center over Ontario swept over the Great Lakes and Northeast, delivering an unseasonably cold airmass on strong west winds. Snowfall from this storm piled up over a foot in the southern suburbs of Buffalo, causing similar damage to that of the October 12-13, 2006 event. However, the bulk of the snowfall remained south of the city, unlike the 2006 event where the entire metro area was pummeled. Snow was reported as far south as eastern Kentucky, resulting in the earliest snowfall on record for several weather bureaus located in the state. Additionally, killing frosts covered a wide area of the Ohio and Tennessee Valleys.
October 12-13th, 1909 – An early season snowstorm moved from the Northern Plains to the Upper Midwest, depositing 10-22 inches of heavy wet snow to the northwest of the low track across Minnesota, northern Wisconsin and Upper Michigan. As the low pressure pulled into Canada cold west to northwest winds behind the low pressure activated an early-season lake-effect snow event. Generally 2-4” of snow fell downwind of the lakes with several areas picking up as much as a foot of snow. Buffalo, NY recorded 6” of snow by the time it tapered off and killing frosts covered much of the Northeast in the days following.
October 18-19th, 1930 – Similar to the 1906 and 2006 events, one to two feet of snow fell on the Buffalo-metro area downing trees and power lines. Now in the age of the automobile and fast-paced commerce, the snowstorm had devastating effects on the local infrastructure and transport of goods. Many vehicles were stranded by the heavy wet snow, which made roads impassable.
References and further reading.
Bigelow, F.H., 1895: AREAS OF HIGH AND LOW PRESSURE. Mon. Wea. Rev., 23, 325–329. - http://docs.lib.noaa.gov/rescue/mwr/023/mwr-023-09-0325d.pdf
Hamilton, Robert S., Zaff, David and Niziol, Thomas, 2006: “A catastrophic lake-effect snowstorm over Buffalo, NY October 12-13, 2006” – http://ams.confex.com/ams/pdfpapers/124750.pdf
GARRIOTT, E.B., 1906: FORECASTS AND WARNINGS. Mon. Wea. Rev., 34, 478–481. - http://docs.lib.noaa.gov/rescue/mwr/034/mwr-034-10-0478.pdf
COX, H.J., 1909: DISTRICT No. 4, LAKE REGION. Mon. Wea. Rev., 37, 734–741. - http://docs.lib.noaa.gov/rescue/mwr/037/mwr-037-10-0734.pdf
BENNETT, M.C., 1930: THE WEATHER ELEMENTS. Mon. Wea. Rev., 58, 427–428. - http://docs.lib.noaa.gov/rescue/mwr/058/mwr-058-10-0427.pdf
Current watches, warnings and advisories.
Fig.1 - Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.
Radar: Northeast Region Loop
Fig.2 - Radar loop of the Northeast region. Courtesy of Weather Underground.
Fig.3 Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.
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