Introduction Lake Michigan sailors have had a challenging summer. In mid-July, competitors in the Chicago-Mac were treated to a rare type of downburst known as heat burst (or dry downburst) near Milwaukee late on Saturday night (click here for the summary). Three weeks later, sailors at the T-10 North American Championship near Chicago had an encounter with a different kind of downburst, one that blasted the fleet with hurricane-force winds. These downbursts, while similar in some ways, are very different in others. The downburst at the T-10 Nationals offers an opportunity to introduce a pair of relatively unknown Doppler weather radar products – storm heights (echo tops) and vertically integrated liquid (VIL) – that can help shed light on the evolution of an approaching thunderstorm.
Introduction After a challenging 2016 Chicago Mac (click here for a summary), this year’s competitors were likely hoping for an easier trip to the island. But as is often the case, Mother Nature wasn’t inclined to cooperate. Although the race started in pleasant sailing conditions, a rare weather phenomenon known as a heat burst, or dry microburst, caused two separate and frightening incidents late on Saturday night. The one-two punch of Saturday’s heat burst, combined with brisk northerly winds following the passage of a cold front on Sunday, caused nearly 30% of the fleet to retire from the race. Continue reading →
Introduction Weather-savvy mariners know the best resource for monitoring the location, size, intensity, and movement of thunderstorms is Doppler Weather Radar from the National Weather Service (NWS). In the first of a two-part series, I’ll explain the basics of radar and introduce the most common types of imagery. Continue reading →
Whether it’s a beer can race or a top tier regatta, weather often adds a bit of excitement to sailboat racing. This was particularly true for Windsor Yacht Club’s Wednesday night race on Lake St. Clair, held on August 24, 2016 (click here for a map). Not long after the 7:00 pm start, an unwarned cluster of thunderstorms rolled over the course, quickly producing 30 knot winds and torrential rain. Continue reading →
Competing in the Chicago-Mac is never easy – after all, it is at least 333 statute miles to Mackinac Island. And by all accounts, the 108th running of Mac was unusually challenging. Light easterly winds on Saturday afternoon made progress toward the Island difficult for the racing fleet. The most significant challenge, however, appeared on Saturday evening, delivered by prolonged periods of thunderstorm activity. The storms repeatedly battered the fleet, hampering progress and prompting the withdrawal of several competitors due to minor crew injuries and equipment issues.
Light Winds Hinder Progress
By early Saturday afternoon, Lake Michigan was under the influence of a large area of high pressure centered just north of Lake Superior. This high was bisected by a stationary front originating from an area of low pressure near North Dakota and extending east across southern Lake Michigan (click here for surface analysis). This pattern resulted in light easterly winds across the southern half of Lake Michigan, impeding the progress of the racing and cruising fleets. Continue reading →
Doppler Weather Radar is your best defense against a hair-raising and wind-blown encounter with thunderstorms. The 155 stations in the National Weather Service’s (NWS) network provide overlapping, ground-based coverage of the nation’s inland and coastal boating areas. With an effective range of approximately 120 nautical miles, data from the NWS radar network is not accessible if you are well offshore. (Regardless of how you obtain your radar imagery, you are viewing NWS data as theirs is the only national radar network.)
Scanning The Atmosphere
Strong thunderstorms may be several miles high, and so the radar station must collect data from the Earth’s surface up into the upper reaches of the atmosphere in order to completely analyze the storm. Stations use a variety of scanning strategies, called Volume Coverage Patterns (VCP) to accomplish this goal. The antenna makes an initial, or base, scan by making one complete revolution at an elevation of 0.5° above the Earth’s surface, alternating between emitting and collecting backscattered energy pulses. When this base scan is complete, the antenna completes additional scans, repeatedly increasing the elevation by about one degree, until the highest elevation of the VCP is reached. The highest elevation scanned by NWS radar is 19.5°. Continue reading →