Lake Erie Wind Analysis
Gay Games Sailing 2014
Published June 2014
Introduction
The 2014 Gay Games sailing competition begins Monday, August 11 on the nearshore waters of Lake Erie, just west of downtown Cleveland, Ohio. The regatta, hosted by Edgewater Yacht Club (EYC), is comprised of nine preliminary races scheduled through Wednesday August 13, with three final races on Thursday, August 14. Training for the event begins on Sunday August 10.
Lake Erie’s shallow waters and the race course’s location near the city can create unique sailing conditions. This article offers an overiew of the prevailing marine weather conditions in early August, as well as an examiniation of the potential influence of lake breezes on the race course.
Prevailing Weather Patterns
A review of wind observations from the National Data Buoy Center (NDBC) Station 45005, moored on the international border in Lake Erie’s western basin, shows the prevailing wind direction in August to be southwesterly (see wind rose, figure 1). The average wind speed at NDBC 45005 for the same period is approximately seven knots (see chart, figure 2), and July and August represent the lightest winds for the year. Consistent with the modest wind speeds, July and August also have the lowest annual wave heights, with a minimum average wave height of one-half foot (click here to review the graph).
While NDBC 45005 is an excellent resource, its location 35 nautical miles NW of EYC is well beyond the influence of lake breezes -- a very common near-shore marine weather pattern during early August.
Lake and Land Breezes
A typical August day across the lower Great Lakes is accompanied by a large dome of high barometric pressure parked over the region. Lake breezes are subtle circulations resulting from the temperature difference between the Lake's surface and the land along the shore. Since moderate to strong large-scale winds disrupt lake breezes, the weak pressure gradient associated with high pressure areas nurture the development of small-scale thermally-induced lake breezes along Lake Erie's southern shore.
The thermal properties of land and water are dramatically different. Land heats up quickly during a sunny summer day and cools off just as quickly as the sun sets. In contrast, the surface temperature of a large body of water such as Lake Erie changes very little over the course of a single day. When the synoptic wind is weak, heating of the land during the day promotes the development of a zone of low pressure along the shore. As shown on the schematic of a lake breeze (figure 3), the barometric pressure of the relatively cooler air over the water is higher, therefore a pressure gradient exists between the region of cooler air over the water and land near the shore. And since pressure gradient produces wind, a gentle breeze flows towards the land from the lake.
As the sun sets, the cycle reverses itself as the land quickly cools. This cooling along the shore promotes the development of a zone of relatively higher pressure (figure 4). The pressure gradient reverses itself as the zone of higher pressure is now over the shore and a region of lower pressure is above the warmer water. The land breeze, in the form of air flowing from the land towards the water, is created. Lake and land breezes can only form in situations when the overall synoptic pressure gradient is weak because strong winds disrupt the formation of the small zones of low and high pressure and the requisite pressure gradient.
The prevalence of lake breezes along the Lake Erie shore can be best understood by reviewing wind observations from an automated weather station on the lake front. The nearest NDBC station to Edgewater Yacht Club is CND01. Located on the shore of Lake Erie approximately five nautical miles northeast of EYC, CND01 is in a perfect location to study the wind patterns on the Gay Games race course. (Click here for a map showing the relative locations of EYC and CND01.)
Wind observations were collected from CND01 for the first half of August from 2009 through 2013. The data set was further restricted to the time period from 10:00 am to 7:00 pm to correspond to the time of the regatta and to accurately represent the characteristics of lake breezes on the racecourse. A data set similar to CDD01 was also created for NDBC 45005.
A review of the wind rose from NDBC CND01 (figure 5), shows the prevalence of the northerly winds associated with the lake breeze (click here for annotated version). In contrast, the wind rose for NDBC 45005 (figure 6) for the same time period shows the prevailing southwesterly wind direction. NDBC 45005 is simply too far from shore (approximately 25 miles) to be within the lake breeze circulation.
The most common direction associated with the lake breeze near Cleveland is northeasterly (nearly 13% of all observations), although the lake breeze near Cleveland is characterized by northwesterly through northeasterly winds. Based upon a review of the wind directions in the CND01 data set, a lake breeze forms on approximately 65% of the days in mid-August.
Due to its thermal origin, the speed associated with a lake breeze is typically modest. The chart in figure 7 shows the distribution of observed wind speeds (figure 7) shows the distribution of observed wind speeds from CND01. During the nine-hour period of this study, winds at CND01 were 10 knots or less approximately 65% of the time. Wind speeds of 15 knots or less were observed over 87% of the time. Lake breezes also tend to be stronger in the afternoon and early evening due to maximum daytime heating. Between 10 am and 1 pm in early August, the average wind speed at CND01 is 7.8 knots. Later in day, between 1 pm and 7 pm, the average increases to 9.1 knots -- approximately a 10% increase over the late morning average.
Although lake breeze wind speeds are relatively modest, they are preferable to the absence of wind typically associated with the prevailing area of high pressure. Very often in August, the lake breeze is the only breeze there is for sailing.
A Short Word On Waterspouts
August also marks the beginning of waterspout season on Lake Erie. Readers interested in understanding the conditions that contribute waterspout development are encouraged to read my analysis of waterspout that occurred during the 2012 Opti Championship (click here).
Marine Weather Forecasts
While a climatological analysis provides competitors with an awareness of the average conditions on Lake Erie during early August, it is weather -- not climatology -- that rules a regatta. For the latest marine weather forecasts and links to a wide range of marine forecasting resources, please visit the LakeErieWX Lake Erie Marine Weather Dashboard.