Thundersnow
Encyclopedia
Thundersnow, also known as a winter thunderstorm or a thunder snowstorm, is a relatively rare kind of thunderstorm
with snow
falling as the primary precipitation
instead of rain
. It typically falls in regions of strong upward motion within the cold sector of an extratropical cyclone
. Thermodynamically, it is not different from any other type of thunderstorms but the top of the cumulonimbus are usually quite low.
One unique aspect of thundersnow is that the snowfall acts as an acoustic suppressor of the thunder. The thunder from a typical thunderstorm can be heard many miles away, while the thunder from thundersnow can usually only be heard within a two to three mile radius from the lightning. In the United States
, March is their peak month of formation, and on average, only 6.3 events are reported per year.
Thundersnow, while relatively rare anywhere, is more common with lake effect snow
in the Great Lakes
area of the United States
and Canada
, the midwestern U.S., and the Great Salt Lake
. Thundersnow also occurs in Halifax, Nova Scotia
, sometimes several times per winter season. Bozeman, Montana
also sees thundersnow more often than average with these storms typically occurring in April or May. The British Isles
and other parts of northwestern Europe
occasionally report thunder and lightning during sleet or (usually wet) snow showers during winter and spring. It is also common around Kanazawa
and the Sea of Japan
, and even around Mount Everest
. When such storms happen at ski areas, these mountains are often evacuated for safety.
aloft passes by, which steepens the lapse rate
s between the lake temperature and the temperatures aloft. A difference in temperature of 45°F (25°C) or greater between the lake temperature and the temperature around 5000 feet/1500 meters (the 850 hPa level) usually marks the onset of thundersnow if surface temperatures are expected to be below freezing. However there are several factors affecting its development and other geographical elements. The primary factor is convective depth; this is the vertical depth in the troposphere that a parcel of air will rise from the ground before it reaches the equilibrium (EQL) level and stops rising. A minimum depth of 0.9 mi (2.5 km) is necessary and an average depth of 1.8 mi (3 km) or more is generally accepted as sufficient. Wind shear
is also a significant factor, linear snow squall bands produce more thundersnow than clustered bands, thus a directional wind shear with a change of less than 54° between the ground and 1.2 mi (2 km) in height must be in place, any change in direction greater than 54° through that layer will tear the snow squall apart. A bare minimum fetch
of 30 mi (50 km) is required in order for air passing over the lake or ocean water to sufficiently saturate with moisture and acquire thermal energy from the water. The last component is the echo top or storm top temperature, which must be at least −22°F (−30°C). It is generally accepted that there is no longer any super cooled water vapor present in a cloud at this temperature but rather ice crystals suspended in the air. This allows for the interaction of the ice cloud and graupel pellets within the storm to generate a charge and create lightning or thunder as a result.
. Thundersnow can also be located underneath the TROWAL, a trough of warm air aloft, which shows up in a surface weather analysis
as an inverted trough extending backward into the cold sector from the main cyclone. In extreme cases, thunderstorms along the cold front are transported towards the center of the low pressure system and will have their precipitation change to snow or ice once the cold front becomes a portion of the occluded front. The Superstorm of 1993 and White Juan
were such cases.
when a shortwave aloft moves into the region. The shortwave will steepen the local lapse rates, allowing for a greater possibility of both heavy snow at elevations where it is near or below freezing, and occasionally thundersnow.
or blizzard
. Winds of above tropical storm force
are frequent with thundersnow. As a result, visibilities in thundersnow are frequently under 1/4 mile. Additionally, such wind creates extreme wind chill
s and may result in frostbite
.
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
with snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
falling as the primary precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
instead of rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
. It typically falls in regions of strong upward motion within the cold sector of an extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
. Thermodynamically, it is not different from any other type of thunderstorms but the top of the cumulonimbus are usually quite low.
Formation
There are usually four forms of thundersnow:- A normal thunderstormThunderstormA thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
on the leading edge of a cold frontWeather frontA weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. In surface weather analyses, fronts are depicted using various colored lines and symbols, depending on the type of front...
or warm frontWarm frontA warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient...
that can either form in a winter environment or one that runs into cool air and where the precipitation takes the form of snow. - A heavy synopticSynoptic scale meteorologyThe synoptic scale in meteorology is a horizontal length scale of the order of 1000 kilometres or more. This corresponds to a horizontal scale typical of mid-latitude depressions...
snowstorm in the comma head of an extratropical cycloneExtratropical cycloneExtratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
that sustains strong vertical mixing which allows for favorable conditions for lightningLightningLightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
and thunderThunderThunder is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, thunder can range from a sharp, loud crack to a long, low rumble . The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within...
to occur. - A lake effect or ocean effect thunderstorm which is produced by cold air passing over relatively warm water; this effect commonly produces snow squalls over the Great LakesGreat LakesThe Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
. - A cold frontCold frontA cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
containing extremely cold air aloft, steepening lapse rates and causing strong vertical movement which allows for favorable conditions for lightning and thunder to occur
One unique aspect of thundersnow is that the snowfall acts as an acoustic suppressor of the thunder. The thunder from a typical thunderstorm can be heard many miles away, while the thunder from thundersnow can usually only be heard within a two to three mile radius from the lightning. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, March is their peak month of formation, and on average, only 6.3 events are reported per year.
Thundersnow, while relatively rare anywhere, is more common with lake effect snow
Lake effect snow
Lake-effect snow is produced during cooler atmospheric conditions when cold winds move across long expanses of warmer lake water, providing energy and picking up water vapor which freezes and is deposited on the leeward shores...
in the Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
area of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, the midwestern U.S., and the Great Salt Lake
Great Salt Lake
The Great Salt Lake, located in the northern part of the U.S. state of Utah, is the largest salt water lake in the western hemisphere, the fourth-largest terminal lake in the world. In an average year the lake covers an area of around , but the lake's size fluctuates substantially due to its...
. Thundersnow also occurs in Halifax, Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
, sometimes several times per winter season. Bozeman, Montana
Bozeman, Montana
Bozeman is a city in and the county seat of Gallatin County, Montana, United States, in the southwestern part of the state. The 2010 census put Bozeman's population at 37,280 making it the fourth largest city in the state. It is the principal city of the Bozeman micropolitan area, which consists...
also sees thundersnow more often than average with these storms typically occurring in April or May. The British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
and other parts of northwestern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
occasionally report thunder and lightning during sleet or (usually wet) snow showers during winter and spring. It is also common around Kanazawa
Kanazawa, Ishikawa
is the capital city of Ishikawa Prefecture, Japan.-Geography, climate, and population:Kanazawa sits on the Sea of Japan, bordered by the Japan Alps, Hakusan National Park and Noto Peninsula National Park. The city sits between the Sai and Asano rivers. Its total area is 467.77 km².Kanazawa's...
and the Sea of Japan
Sea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...
, and even around Mount Everest
Mount Everest
Mount Everest is the world's highest mountain, with a peak at above sea level. It is located in the Mahalangur section of the Himalayas. The international boundary runs across the precise summit point...
. When such storms happen at ski areas, these mountains are often evacuated for safety.
From lake effect precipitation
This type of thundersnow occurs after a cold front or shortwaveShortwave (meteorology)
A shortwave or shortwave trough is an embedded kink in the trough / ridge pattern. This is the opposite of longwaves, which are responsible for synoptic scale systems, although shortwaves may be contained within or found ahead of longwaves and range from the mesocale to the synoptic scale...
aloft passes by, which steepens the lapse rate
Lapse rate
The lapse rate is defined as the rate of decrease with height for an atmospheric variable. The variable involved is temperature unless specified otherwise. The terminology arises from the word lapse in the sense of a decrease or decline; thus, the lapse rate is the rate of decrease with height and...
s between the lake temperature and the temperatures aloft. A difference in temperature of 45°F (25°C) or greater between the lake temperature and the temperature around 5000 feet/1500 meters (the 850 hPa level) usually marks the onset of thundersnow if surface temperatures are expected to be below freezing. However there are several factors affecting its development and other geographical elements. The primary factor is convective depth; this is the vertical depth in the troposphere that a parcel of air will rise from the ground before it reaches the equilibrium (EQL) level and stops rising. A minimum depth of 0.9 mi (2.5 km) is necessary and an average depth of 1.8 mi (3 km) or more is generally accepted as sufficient. Wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
is also a significant factor, linear snow squall bands produce more thundersnow than clustered bands, thus a directional wind shear with a change of less than 54° between the ground and 1.2 mi (2 km) in height must be in place, any change in direction greater than 54° through that layer will tear the snow squall apart. A bare minimum fetch
Fetch (geography)
The fetch, often called the fetch length, is the length of water over which a given wind has blown. It is used in geography and meteorology and is usually associated with coastal erosion. It plays a large part in longshore drift as well....
of 30 mi (50 km) is required in order for air passing over the lake or ocean water to sufficiently saturate with moisture and acquire thermal energy from the water. The last component is the echo top or storm top temperature, which must be at least −22°F (−30°C). It is generally accepted that there is no longer any super cooled water vapor present in a cloud at this temperature but rather ice crystals suspended in the air. This allows for the interaction of the ice cloud and graupel pellets within the storm to generate a charge and create lightning or thunder as a result.
From synoptic forcing
Synoptic snow storms tend to be large and complex with many possible locations and factors affecting the development of thundersnow. The best location in a storm to find thundersnow is typically on the northwest side, within what is known as the comma head of a mature extratropical cycloneExtratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
. Thundersnow can also be located underneath the TROWAL, a trough of warm air aloft, which shows up in a surface weather analysis
Surface weather analysis
Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations...
as an inverted trough extending backward into the cold sector from the main cyclone. In extreme cases, thunderstorms along the cold front are transported towards the center of the low pressure system and will have their precipitation change to snow or ice once the cold front becomes a portion of the occluded front. The Superstorm of 1993 and White Juan
White Juan
White Juan is the unofficial name given to the Atlantic Canada blizzard of February 2004, a strong nor'easter that affected most of Atlantic Canada between February 17 and 20, 2004—only five months after Hurricane Juan devastated central Nova Scotia and Prince Edward Island.The storm dropped...
were such cases.
From upslope flow
Similar to the lake effect regime, thundersnow is usually witnessed in terrain in the cold sector of an extratropical cycloneExtratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
when a shortwave aloft moves into the region. The shortwave will steepen the local lapse rates, allowing for a greater possibility of both heavy snow at elevations where it is near or below freezing, and occasionally thundersnow.
Hazards
Thundersnow often produces snowfall rates in the range of 2 to 4 inches per hour. Snowfall of this intensity may limit visibilities severely during even light wind conditions. However, thundersnow is often a part of a severe winter stormWinter storm
A winter storm is an event in which the dominant varieties of precipitation are formed that only occur at low temperatures, such as snow or sleet, or a rainstorm where ground temperatures are low enough to allow ice to form...
or blizzard
Blizzard
A blizzard is a severe snowstorm characterized by strong winds. By definition, the difference between blizzard and a snowstorm is the strength of the wind. To be a blizzard, a snow storm must have winds in excess of with blowing or drifting snow which reduces visibility to 400 meters or ¼ mile or...
. Winds of above tropical storm force
Beaufort scale
The Beaufort Scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort Wind Force Scale.-History:...
are frequent with thundersnow. As a result, visibilities in thundersnow are frequently under 1/4 mile. Additionally, such wind creates extreme wind chill
Wind chill
Wind chill is the felt air temperature on exposed skin due to wind. The wind chill temperature is always lower than the air temperature, and the windchill is undefined at the higher temps...
s and may result in frostbite
Frostbite
Frostbite is the medical condition where localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas...
.
See also
- Lake-effect snow
- Wind shearWind shearWind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
- SnowSnowSnow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
- ThunderstormThunderstormA thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
- LightningLightningLightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
- Severe weather terminology (United States)Severe weather terminology (United States)This article describes the United States National Weather Service severe weather terminology. The NWS defines precise meanings for nearly all its weather terms. This article describes NWS terminology and related NWS weather scales...
- Blizzard warningBlizzard warningA Blizzard Warning is an advisory issued by the National Weather Service of the United States which means sustained winds or frequent gusts of 35 mph / 15 m/s or greater with heavy snow is forecast for a period of 3 hours or more. A blizzard tends to reduce visibilities to 1/4 of a mile or...
- Severe thunderstorm warningSevere thunderstorm warningA severe thunderstorm warning is issued when trained storm spotters or a Doppler weather radar indicate a strong thunderstorm is producing dangerously large hail or high winds, capable of causing significant damage. In the United States, it does not account for lightning or flooding...
External links
- What causes thundersnow?
- Straight Dope staff report: Why don't snowstorms produce lightning?
- Research on Convective Snow from University of MissouriUniversity of MissouriThe University of Missouri System is a state university system providing centralized administration for four universities, a health care system, an extension program, five research and technology parks, and a publishing press. More than 64,000 students are currently enrolled at its four campuses...