Posts Tagged ‘weather’

PostHeaderIcon Stable

as it relates to an air mass, describes air that is colder than the surrounding air and that descends from higher altitudes, or that stays in place if already near the land’s or water’s surface. See also: high-pressure system. Compare to: unstable.

PostHeaderIcon Storm Trysail

a small, strongly built sail used in place of a mainsail during storm conditions. Often made from orange-colored material or with orange highlights. The sail is either rigged to the boom and mainsheet, or is free flown. With either setup, the head is hoisted on the mail halyard, and the trysail’s tack is attached to the tack ring at the gooseneck (or, if it has a long tack pennant, to a point at the mast base). If the trysail is rigged to the boom, the mainsail is removed from the boom and stored below. Both the outhaul and a reef line are connected to the clew, along with a Velcro clew safety strap, and the mainsheet is used to position the trysail. If the trysail is free flown, the boom’s aft end is lowered to the deck and secured, and sheets are run from each quarter to the trysail’s clew, often through the spinnaker sheet turning blocks.

PostHeaderIcon Insulating Layer

a middle clothing layer designed to keep heat in and cold out by creating a still or dead air layer between the fibers. Usually put on over a wicking or base layer. Two popular insulating materials are wool, which naturally wicks away moisture, and fleece, a synthetic material that maintains its insulating ability even when wet and that spreads the moisture out so the material dries quickly. Compare to: foulies.

PostHeaderIcon Barometric Pressure

the atmospheric pressure as measured by a barometer. Changes in barometric pressure are used to forecast changes in weather. Some rules of thumb include the 1-2-3 rule. If pressure drops 1-2 millibars an hour over a 3-hour period, be alert. The weather is worsening. There is also the 4-5-6 rule. A drop of 4-5 millibars in 6 hours suggests that significantly worsening weather, such as a gale—or worse—is approaching. Barometric pressure is measured in force per unit; e.g., pounds per square inch, millibars, or inches of mercury. The current barometric pressure and predicted future pressures are shown as isobars on synoptic charts.


About the author:
Bob Roitblat is an avid sailor, writer and professional speaker. If you have any comments about this blog, or you are interested in having Bob to speak at your club, contact the author here: bob@sailorspeak.com

You may also be interested in Bob’s other blog, At The Helm, that is focused on the owners of small-to-medium sized closely-held businesses.

PostHeaderIcon Cumulonimbus

a vertically developed cumulus cloud that extends through all altitude levels. It has a dark base and is often capped by an anvil-shaped cirriform cloud. Also called a thunderstorm cloud, a cumulonimbus is frequently accompanied by heavy showers, lightning, and thunder, and is sometimes accompanied by hail, tornadoes, or strong, gusty winds. Cumulonimbus clouds are heavy, dense clouds made up of water droplets in their lower portions and ice particles in their upper portions. The cumulo prefix suggests that the cloud is bumpy and unstable, while the nimbus part suggests that the cloud contains rain.

PostHeaderIcon Mistral

a brutal wind that develops when two air masses collide over the Alps. Cold air is drawn in from North and accelerates through the Rhone Valley to the Gulf of Lion and France’s Mediterranean Coast, where winds can build to hurricane force.

PostHeaderIcon Warm Front

the leading edge of an advancing synoptic-scale warm-air boundary that is replacing a retreating, relatively colder air mass. Generally, with a warm-front passage, the temperature and humidity increase, and the barometric pressure rises. Although there is a wind shift—usually from the southwest to the northwest in the Northern Hemisphere—it is less pronounced than with a cold front passage. Precipitation, such as rain, snow, or drizzle, as well as convective showers and thunderstorms are generally found ahead of the surface front. Fog is common in the cold air ahead of the front. Although clearing usually occurs after a warm front passes, some conditions may produce fog in the warm air.

PostHeaderIcon North Pacific High

a semi-permanent center of high atmospheric pressure located over the North Pacific Ocean between 30 and 40 degrees North latitude and between 140 and 150 degrees West longitude. The North Pacific High has a major influence on boats competing in any of the trans-pacific races, including Transpac, Pacific Cup and Vic-Maui. See also: slot cars.

PostHeaderIcon Geostrophic Scale

a graphical device used in estimating pressure gradient wind speeds from the isobar (lines of constant pressure) spacing on a synoptic chart. Wind speed is estimated by measuring the perpendicular distance between the isobars on the weather chart and plotting this against the geographic latitude on the wind scale. Also known as a geostrophic wind scale.


About the author:
Bob Roitblat is an avid sailor, writer and professional speaker. If you have any comments about this blog, or you are interested in having Bob to speak at your club, contact the author here: bob@sailorspeak.com

You may also be interested in Bob’s other blog, At The Helm, that is focused on the owners of small-to-medium sized closely-held businesses.

PostHeaderIcon Virga

precipitation that falls from a cloud then evaporates in the dry air beneath the cloud before it reaches the ground. Virga resembles streaks of water that extend downward from a cloud. Typically, virga falls from altocumulus, altostratus or high-based cumulonimbus.

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