Introduction Wednesday, November 27, 2019 was a wild day on Lake Erie thanks to the passage of a deep low pressure system and its accompanying cold front. The surface forecasts issued by the Weather Prediction Center (WPC) suggested the powerful and fast-moving low and its cold front would reach Lake Erie’s western basin around sunrise on the 27th (Figure 1) and the eastern end of Lake Ontario by early evening (click here for forecast graphic). Continue reading →
Introduction Even when the atmosphere is supportive of thunderstorms, a source of lift is necessary to provide the upward motion required by a fledgling storm’s updraft. A reliable source of lift is often found near a cold, warm, or stationary front accompanying an approaching low pressure system (figure 1). Terrain or the leading edge of a downdraft from an existing thunderstorm (outflow boundary) can also provide a storm with this all-important ingredient. Continue reading →
Sailors have been watching clouds since the first boat was launched. As aficionados know, clouds come in an infinite variety of shapes and sizes. The overall shape of a cloud and the altitude where it forms help tell the story of current and short-term weather patterns.
By any measure, the 2017 Chicago Yacht Club Race to Mackinac was no picnic. The Race started on Saturday under very pleasant southwesterly breezes and the fleet made good progress toward Mackinac Island. However, as the fleet worked north, two weather features delivered a one-two punch that prompted nearly a third of the competitors to withdraw from the Race. (Click here for Matt Gallagher’s thorough analysis of the reasons competitors gave for retiring.)
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 →
In part one (click here), I introduced surface weather maps, meteorological time-keeping systems, the difference between Issued and Valid, and barometric pressure. In part two, we’ll look at the symbols and meteorological shorthand used on surface weather maps.
The solid black lines winding across the country on the forecast map valid at 00Z on Thursday, February 23, 2017 (figure 1) are isobars, which are contours of constant sea level barometric pressure measured in millibars (mb). Isobars are typically drawn at 4 mb intervals on NWS maps and are labeled somewhere along the contour. The 1012 mb isobar, for example, starts northeast of the Bahamas and crosses the US coast near the border of Georgia and South Carolina (click here for annotated image). After heading west for a bit, the 1012 mb isobar makes a right turn and heads northeast parallel to the Appalachian Mountains. At any point along this isobar, sea-level pressure is forecast to be 1012 mb. Isobars allow forecasters to understand the overall pressure pattern and quickly identify areas of low and high pressure, along with other surface features such as troughs and ridges. Continue reading →
Surface weather maps offer a wealth of information to the weather-savvy boater. However, the key to unlocking the vast treasure of information displayed on these maps is understanding the terminology and symbols used by forecasters to portray current and future weather patterns. In this first installment of a two-part series, I’ll introduce surface maps, some key terminology, meteorological time systems, and barometric pressure.
Types of Surface Maps
Surface weather maps come in two varieties — analyses and forecasts. These two types of maps are very similar in appearance but their purpose is quite different. Analyses show recent surface weather observations and features (Figure 1) and are published every three hours by NOAA’s Weather Prediction Center (WPC) (http://www.wpc.ncep.noaa.gov/). The observations used to prepare these analyses such as temperature, dew point, barometric pressure, and wind speed/direction, are collected by thousands of automated weather stations across the country. These stations, which comprise the Automated Surface Observing System (ASOS), are usually located at airports. 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 →