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WIND VECTORS …
NWS Surface Observations: Wind and Temps and more …
SEE ALSO …
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SEVERE WEATHER WARNINGS
High Wind Watch
A High Wind Watch is issued when the following conditions are possible:
1) sustained winds of 40 mph or higher for one hour or more
OR
2) wind gusts of 58 mph or higher for one hour or more.
High Wind Warning
A High Wind Warning is issued when the following conditions are occurring or imminent:
1) sustained winds of 40 mph or higher for one hour or more
OR
2) wind gusts of 58 mph or higher for one hour or more.
Wind Advisory
A Wind Advisory is issued when the following conditions are expected for 3 hours or longer.
1) sustained winds of 31 to 39 mph
AND/OR
2) wind gusts of 46 to 57 mph.
Extreme Wind Warning
An Extreme Wind Warning is issued for surface winds of 100 knots (115 MPH) or greater associated with non-convective, downslope, derecho (NOT associated with a tornado), or sustained hurricane winds are expected to occur within one hour.
Severe Thunderstorm Watch
A Severe Thunderstorm Watch is issued when severe thunderstorms are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.
Severe thunderstorms are defined as follows:
1) Winds of 58 mph or higher
AND/OR
2) Hail 1 inch in diameter or larger.
Severe Thunderstorm Warning
A Severe Thunderstorm Warning is issued when severe thunderstorms are occurring or imminent in the warning area.
Severe thunderstorms are defined as follows:
1) Winds of 58 mph or higher
AND/OR
2) Hail 1 inch in diameter or larger.
Tornado Watch
A Tornado Watch is issued when severe thunderstorms and tornadoes are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.
Severe thunderstorms are defined as follows:
1) Winds of 58 mph or higher
AND/OR
2) Hail 1 inch in diameter or larger.
Tornado Warning
A Tornado Warning is issued when a tornado is imminent. When a tornado warning is issued, seek safe shelter immediately.
Special Marine Warning
A warning of potentially hazardous weather conditions of short duration (up to 2 hours) affecting areas included in a CWF that are not adequately covered by existing marine warnings and producing one or more of the following:
1) Sustained marine convective winds (showers/thunderstorms) or associated gusts of 34 knots or greater
AND/OR
2) Hail three quarters of an inch or more in diameter
AND/OR
3) Waterspouts
Small Craft Advisory (Sterling Virginia)
Small Craft Advisories are issued for the Tidal Potomac River and the Chesapeake Bay when one or both of the following conditions is expected to begin within 36 hours:
1) sustained winds of 18 knots to 33 knots
OR
2) frequent gusts (duration of two or more hours) between 18 knots and 33 knots.
OR
3) waves of 4 feet or higher
NWS Winter Terms
nws.noaa.gov/os/winter/ww.shtml
WINTER WARNINGS
Blizzard Warnings are issued for frequent gusts greater than or equal to 35 mph accompanied by falling and/or blowing snow, frequently reducing visibility to less than 1/4 mile for three hours or more. A Blizzard Warning means severe winter weather conditions are expected or occurring. Falling and blowing snow with strong winds and poor visibilities are likely, leading to whiteout conditions making travel extremely difficult. Do not travel. If you must travel, have a winter survival kit with you. If you get stranded, stay with your vehicle and wait for help to arrive.
Winter Storm Warnings are issued for a significant winter weather event including snow, ice, sleet or blowing snow or a combination of these hazards. Travel will become difficult or impossible in some situations. Delay your travel plans until conditions improve.
Ice Storm Warnings are usually issued for ice accumulation of around 1/4 inch or more. This amount of ice accumulation will make travel dangerous or impossible and likely lead to snapped power lines and falling tree branches. Travel is strongly discouraged.
Wind Chill Warnings are issued for a combination of very cold air and strong winds that will create dangerously low wind chill values. This level of wind chill will result in frostbite and lead to hypothermia if precautions are not taken. Avoid going outdoors and wear warm protective clothing if you must venture outside. See the NWS Wind Chill Chart.
Lake Effect Snow Warnings are issued when widespread or localized lake induced snow squalls or heavy showers are expected to produce significant snowfall accumulation. Lake effect snow usually develops in narrow bands and impacts a limited area. These bands can produce very heavy snow with sudden restrictions in visibility. Driving conditions may become hazardous at times.
In the absence of weather systems causing wind, daytime periods are more likely to be windy compared to night time periods.
Wind is the result of a combination of meteorological processes that involve the sun’s heat, the rotation of the earth including the variety of diameters of the sphere of the earth and differential speeds at different diameters, and other factors in the atmosphere.
Diurnal Winds
The sun heats the Earth’s surface during the day. The air above the ground warms up and begins to rise (convection), which creates an area of low pressure under the rising air. Cooler air from surrounding regions involves higher air pressure, and moves toward the low-pressure area, which creates wind toward the low pressure.
The process of heat rising is also known as “thermal convection.”
Differential Heating occurs because the sun heats the Earth unevenly because of a variety of land colors that absorb heat differently, cloud shadows, and terrain shadows. Also, land areas gain heat faster than water bodies because of the difference in the physics of heat capacities in land compared to water, which has a higher heat capacity. The differential heating leads to pressure differences, which affect wind as the atmosphere seeks equilibrium.
The study of thermodynamics begins with the concept that ‘nature abhors a vacuum’. Every space needs to be filled with something because empty spaces (especially spaces devoid of molecules) are unnatural in the earth’s atmosphere.
Because the sun’s heat occurs during the day, these heat differentials are more pronounced during the day, compared to night time hours. Also, more intense the sunlight cause greater temperature differences, which cause stronger winds.
At night, when the sun no longer causes thermal convection, the heat differentials that cause wind diminish — situation known by meteorologists as a “nocturnal lull.”
Weather systems, weather fronts, geographical features (such as mountain ranges), adiabatic processes, and larger climate patterns, can influence also wind. Some conditions result in stronger winds continuing or beginning at night.
In areas of large water bodies near a long shoreline, such as the ocean or a very large lake, specific daily variations can occur from the thermal convection differences of the air above land compared to the air above water.
Sea Breezes or Lake Breezes (from water to land) occur because land heats up faster and causes more thermal convection above land than above water. Again, warm air rises, creates a low-pressure area, and draws in cooler, high-pressure air from the air over the water body.
Land Breezes (from land to water) occur because land cools down faster than the water body. The cooler air over the land creates a high-pressure area, and the physics equilibrium draws air or pushes air from above the land toward the warmer, lower pressure air above the warmer water.
For Deeper Thinking, Consider Adiabatic Definitions to consider how air pressure and humidity are related to wind …
Adiabatic
Changes in temperature caused by the expansion (cooling) or compression (warming) of a body of air as it rises or descends in the atmosphere, with no exchange of heat with the surrounding air.
Adiabatic Lapse Rate
The rate of decrease of temperature experienced by a parcel of air when it is lifted in the atmosphere under the restriction that it cannot exchange heat with its environment. For parcels that remain unsaturated during lifting, the (dry adiabatic) lapse rate is 9.8°C per kilometer.
Adiabatic Process
A process which occurs with no exchange of heat between a system and its environment.
Dry Adiabatic Lapse Rate
The rate at which the temperature of a parcel of dry air decreases as the parcel is lifted in the atmosphere. The dry adiabatic lapse rate (abbreviated DALR) is 5.5°F per 1000 ft or 9.8°C per km.
Dry-adiabatic
1. An adiabatic process in a hypothetical atmosphere in which no moisture is present. 2. An adiabatic process in which no condensation of its water vapor occurs and no liquid water is present.
Moist Adiabatic Lapse Rate
(abbrev. MALR)- The rate at which the temperature of a parcel of saturated air decreases as the parcel is lifted in the atmosphere. The moist adiabatic lapse rate (abbreviated MALR) is not a constant like the dry adiabatic lapse rate but is dependent on parcel temperature and pressure.
Moist-adiabatic
(Also known as saturation-adiabatic process.) An adiabatic process for which the air is saturated and may contain liquid water. A distinction is made between the reversible process, in which total water is conserved, and the pseudoadiabatic or irreversible moist adiabatic process, in which liquid water is assumed to be removed as soon as it is condensed.
