Chicago Wind Roses
Chicago area winds in June are constantly teetering on the edge of a number of potent forces. Wind prediction is often a tricky art in this area because winds can vary quite drastically over a fairly small area. Not only are lake breezes an important factor but the region resides in the early summer battlezone between cool dry Canadian air and hot humid Gulf air. Quite often the weather is dictated by where the frontal boundaries set up. Enclosed are 2 very different Wind Roses for the month of June in 2004. Data is courtesy of Great Lakes Environmental Resources Lab (GLERL) and the National Data Buoy Center (NDBC). GLERL sensor is located just offshore of the Chicago City while the NDBC site is towards the middle of the lake. The difference in wind characteristics for these 2 sites for the same time period couldn’t be greater and well illustrates the very localized nature of Chicago winds. June is a transitional month as it typically starts with very turbulent weather due to the many cold fronts, warm fronts, and occluded fronts pounding the area. Thunderstorms are quite common as are rapid temperature changes that can be as much as 30 degrees simply depending on if the winds are off the water. Cold fronts can offer some frustrations to tacticians as Lake Michigan water temperatures take a long time to rise yet the air masses preceding a cold front can be very hot. Thus West and SW winds that howl in the city can be all but missing along the water front until the cold air inversion breaks down. Warm fronts and stalled occluded fronts offer their own complications as cold and showery ESE to NE flow can stay in place for several days until these slow systems can clear the region. As the month of June progresses we see the frequency of synoptic events (frontal passages) reduce and occasionally we begin to see High pressure taking hold. The longest days of the year are during this time and often one can see temperatures in the city rising to the 90s while at the same time the waters of Lake Michigan remain in the mid 60s. This tremendous temperature difference can generate some healthy inshore winds with a strong lake breeze engine in place. The urban heat island of Chicago is a good magnet for these winds and thus typical lake breezes begin from the NE and veer to the ENE as they gain in strength. With the heat island we tend to see the lake breezes holding well into evening with just a gradual let down in flow. The “windy city” can and often does live up to it’s name. Knowing what forces are driving these winds is of great importance to gaining the edge on your competition. Sailflow.com provides real-time sensors as well as forecast products complimentary through the race period at www.sailflow.com/chicago. In cooperation with North Sails, Sailing Weather Service is offering free precision race forecasts for this event. Sign up at http://na.northsails.com/ew/ew_main.taf
