Storm Station
Sign in

Field Book/Vol. VI, Events/FB-EVT-133

Extreme cold

Extreme cold is air, or wind on bare skin, cold enough to bring frostbite and hypothermia. It is warned by an Extreme Cold Warning, watched for by an Extreme Cold Watch and advised by a Cold Weather Advisory, each at the air temperature or wind chill its own office sets.

Plate FB-EVT-133Heat, cold, air, dust and fireRevision 1, Status draftAlso called Extreme Cold Warning, Extreme Cold Watch, Cold Weather Advisory, dangerous cold, bitter cold, dangerous wind chill

The Weather Service's wind chill chart as a table: the wind chill for each air temperature from 40 to −45 degrees Fahrenheit and each wind from 5 to 60 miles an hour, each figure worked by the 2001 index, and the cells shaded by the time in which bare skin can freeze, 30, 10 or 5 minutes, as the Weather Service's chart shades most of each cell. The cell for 0 degrees in a 15 mile an hour wind, a wind chill of −19 and frostbite in 30 minutes, is outlined.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKPLATE FB-EVT-133-ATHE WEATHER SERVICE'S WIND CHILL CHART, EACH FIGURE COMPUTED BY THE 2001 INDEX, AND THE TIME IN WHICH BARE SKIN CAN FREEZE AS THE CHART SHADES ITFIG. A THE WIND CHILL CHARTAIR TEMPERATURE, °FWIND, MPH, AT 33 FT4035302520151050−5−10−15−20−25−30−35−40−455363125191371−5−11−16−22−28−34−40−46−52−57−63103427211593−4−10−16−22−28−35−41−47−53−59−66−72153225191360−7−13−19−26−32−39−45−51−58−64−71−7720302417114−2−9−15−22−29−35−42−48−55−61−68−74−812529231693−4−11−17−24−31−37−44−51−58−64−71−78−843028221581−5−12−19−26−33−39−46−53−60−67−73−80−873528211470−7−14−21−27−34−41−48−55−62−69−76−82−89402720136−1−8−15−22−29−36−43−50−57−64−71−78−84−91452619125−2−9−16−23−30−37−44−51−58−65−72−79−86−93502619124−3−10−17−24−31−38−45−52−60−67−74−81−88−95552518114−3−11−18−25−32−39−46−54−61−68−75−82−89−97602517103−4−11−19−26−33−40−48−55−62−69−76−84−91−98BARE SKIN CAN FREEZE IN:30 minutes10 minutes5 minutesWind chill = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275TV^0.16; each cell shaded as the Weather Service’s chart shades most of it.123TITLEExtreme cold, the wind chill chartVOL. VI EVENTS · HEAT, COLD, AIR, DUST AND FIRETYPECLASSIFICATIONSCALENOT TO SCALEREVREV 1 DRAFT SHEET 1 of 3DATE2026-10-17IDFB-EVT-133-ADRAWN AS linework on paperSOURCES NWS
Fig. A The wind chill chart. The Weather Service's wind chill chart, each figure computed by the 2001 index, and the time in which bare skin can freeze as the chart shades it NOT TO SCALEMaximizeThe sheet, SVG, 11 by 17
  1. The cell the Weather Service's own text names: 0 °F (−17.8 °C) in a 15 mph (6.7 m s⁻¹) wind, −19 °F (−28.3 °C), frostbite in 30 minutes
  2. The air temperature, across; the wind at 33 ft (10 m), down
  3. The coldest and windiest, −98 °F (−72.2 °C), frostbite in 5 minutes

What it is

Extreme cold is cold that harms people and animals: air cold enough, or wind on bare skin strong enough, to bring frostbite and hypothermia. It comes most often with arctic air carried south behind a cold front, and it is worst where that air settles over snow on a clear, calm night.

The Weather Service warns it with an Extreme Cold Warning when the air temperature or the wind chill reaches the warning criteria its office has set, watches for it with an Extreme Cold Watch when those conditions are possible but not yet certain, and advises with a Cold Weather Advisory for dangerous cold short of the warning. Each office sets its own figures, because the same cold that is ordinary in one place is dangerous in another, where people and buildings are not made for it. In the lower 48 the warning criteria run from −40 °F (−40 °C) in parts of Minnesota, Montana, the Dakotas and Wyoming to 20 °F (−6.7 °C) in parts of California, Arizona, Florida and Texas; Fig. B draws every forecast zone.

What it is not

It is not a frost or a freeze, Frost, freeze and hard freeze FB-EVT-092: cold that kills plants in the growing season. A freeze is warned for the plants; extreme cold is warned for people.

It is not a cold wave, Cold wave and arctic outbreak FB-EVT-132: the days of arctic air that bring the cold. Extreme cold is the danger to people within it.

It is not a blizzard, Blizzard FB-EVT-081, though a blizzard's wind brings dangerous wind chills. A blizzard is warned for the snow and the visibility.

Lookalikes

Frost and freeze
Cold that kills plants in the growing season, Frost, freeze and hard freeze FB-EVT-092. Extreme cold is cold that harms people and animals.
Cold wave
The days of arctic air that bring the cold, Cold wave and arctic outbreak FB-EVT-132; extreme cold is the danger to people within them.
Blizzard
Wind and snow that hide the way, Blizzard FB-EVT-081. Its wind brings dangerous wind chills, but it is warned for the snow and the visibility.

Machine

Arctic air, and a clear night

The coldest air in North America forms over the far north in winter, where the sun is low or absent and snow-covered ground loses heat to space through the long nights. A strong area of high pressure carries that air south behind an arctic front. Under the high the sky clears and the wind falls, and through the night the snow loses still more heat. The air just above it cools fastest, and the coldest air lies in a shallow layer at the ground, colder than the air a few hundred feet above it. Valleys collect it. The lowest temperatures come around dawn.

Wind on bare skin

The body keeps a thin layer of warm air next to the skin. Wind strips it away and carries heat off faster than still air would, so a cold wind makes bare skin lose heat as it would at a much lower temperature in calm air. The wind chill is that temperature. The Weather Service's index, introduced in 2001, works it from the air temperature and the wind, by the equation below. It is built on a model of a human face, reckons the wind at 5 ft (1.5 m), the height of an adult's face, from the anemometer's reading at the standard 33 ft (10 m), and assumes no sun: a clear night sky. Bright sunshine may raise the wind chill by 10 to 18 °F (5.6 to 10 °C). The index is defined only at or below 50 °F (10 °C), and for winds above 3 mph.

At 0 °F (−17.8 °C) in a 15 mph wind, the wind chill is −19 °F (−28.3 °C), and bare skin can freeze in 30 minutes. Fig. A sets out the Weather Service's whole chart, with the time bare skin takes to freeze in each cell: 30 minutes, 10 or 5. Fig. C draws a face in a 25 mph wind at −5 °F (−20.6 °C), where the wind chill is −31 °F (−35 °C).

What wind chill is not

Wind chill applies only to people and animals. A car's radiator or a water pipe in the wind cools faster, but only to the air's own temperature: at −5 °F, the radiator in Fig. C cools no lower than −5 °F, though the wind chill is −31 °F. In the same way, frostbite needs the air itself below freezing. A wind chill below freezing on a day when the air is above it cannot freeze the skin, though it can still bring on hypothermia.

Frostbite and hypothermia

Frostbite is the freezing of the skin and the tissue beneath it; the parts most prone to it are uncovered skin and the hands and feet. Hypothermia comes when the body loses heat faster than it can make it, and in extreme cold a person can succumb to it in minutes; with prolonged exposure it can come even in cold short of the warning. The Weather Service's examples of each product name both: "Frostbite and hypothermia will occur if unprotected skin is exposed to these temperatures."

Plan of the lower 48 states and Alaska, each public forecast zone shaded by the air temperature or wind chill at which its office issues an Extreme Cold Warning, as the Weather Service's national guidance gives them: from −40 degrees Fahrenheit across Minnesota, Montana, the Dakotas and Wyoming to 20 degrees in California, Arizona, Florida and south Texas, and as cold as −70 in Alaska. Ten places are numbered with their warning and advisory criteria: Seattle 10 and 25, International Falls −40 and −30, Rochester −25 and −15, Chicago −30 and −20, Denver −25 and −15, Washington −10 and 0, Los Angeles 20 and 35, Phoenix 20 and 30, Dallas 0 and 10, Miami 20 and 35.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKPLATE FB-EVT-133-BEXTREME COLD WARNING CRITERIA IN EVERY FORECAST ZONE OF THE LOWER 48 AND ALASKA, AS THE NATIONAL GUIDANCE GIVES THEM; ALBERS EQUAL AREA, ALASKA DRAWN SMALLERFIG. B THE NATIONAL GUIDANCEALASKA, DRAWN SMALLER0500 mi(805 km)Albers equal area, true to scalealong 29.5° and 45.5° N0500 mi(805 km)12345678910WARNING CRITERIA, °Fair temperature or wind chill−70 to −55, Alaska only−40 to −30−25 to −15−10 to 05 to 1520PLACEWARNADV.1 Seattle10252 International Falls−40−303 Rochester−25−154 Chicago−30−205 Denver−25−156 Washington−1007 Los Angeles20358 Phoenix20309 Dallas01010 Miami2035Each office sets its own, and maytailor it with public health officials.The advisory is most often 10 °F(5.6 °C) warmer than the warning.As the guidance stood on September 28, 2026.TITLEExtreme cold, the national guidanceVOL. VI EVENTS · HEAT, COLD, AIR, DUST AND FIRETYPEPLANSCALE500 mi (805 km) BAR AS DRAWNREVREV 1 DRAFT SHEET 2 of 3DATE2026-10-17IDFB-EVT-133-BDRAWN AS linework on paperSOURCES NWS
Fig. B The national guidance. Extreme Cold Warning criteria in every forecast zone of the lower 48 and Alaska, as the national guidance gives them; Albers equal area, Alaska drawn smaller 500 mi (805 km) BAR AS DRAWNMaximizeThe sheet, SVG, 11 by 17
  1. Seattle: warning 10 °F (−12.2 °C), advisory 25 °F (−3.9 °C)
  2. International Falls, Minnesota: warning −40 °F (−40 °C), advisory −30 °F (−34.4 °C)
  3. Rochester, New York: warning −25 °F (−31.7 °C), advisory −15 °F (−26.1 °C)
  4. Chicago: warning −30 °F (−34.4 °C), advisory −20 °F (−28.9 °C)
  5. Denver: warning −25 °F (−31.7 °C), advisory −15 °F (−26.1 °C)
  6. Washington: warning −10 °F (−23.3 °C), advisory 0 °F (−17.8 °C)
  7. Los Angeles: warning 20 °F (−6.7 °C), advisory 35 °F (1.7 °C)
  8. Phoenix: warning 20 °F (−6.7 °C), advisory 30 °F (−1.1 °C)
  9. Dallas: warning 0 °F (−17.8 °C), advisory 10 °F (−12.2 °C)
  10. Miami: warning 20 °F (−6.7 °C), advisory 35 °F (1.7 °C)
Elevation, heights to scale, of a clear night at −5 degrees Fahrenheit with a 25 mile an hour wind: the anemometer measuring the wind at the standard 33 feet (10 metres), the wind slower nearer the ground, a person whose face, at 5 feet (1.5 metres), is where the index reckons the wind and feels a wind chill of −31 degrees, and a parked car whose radiator cools only to the air's −5 degrees and no lower.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKPLATE FB-EVT-133-CELEVATION OF A PERSON AND A PARKED CAR ON A CLEAR NIGHT AT −5 °F (−20.6 °C) IN A 25 MPH (11.2 M S⁻¹) WIND; HEIGHTS TO SCALEFIG. C A FACE IN THE WINDA CLEAR NIGHT: THE INDEX ASSUMES NO SUNBright sunshine may raise the wind chill by 10 to 18 °F (5.6 to 10 °C).33 ft (10 m)THE ANEMOMETER: THE WIND IS MEASUREDhere, at the standard 33 ft (10 m)THE WIND, 25 MPH (11.2 M/S) AT 33 FT,slower nearer the ground5 ft (1.5 m)THE FACE, 5 FT (1.5 M): THE INDEX RECKONSthe wind here, at an adult’s faceIT FEELS −31 °F (−35 °C)THE CAR’S RADIATOR COOLS TO −5 °F(−20.6 °C), the air’s own temperature, and nolower: wind chill is for people and animalsAIR −5 °F (−20.6 °C)Frostbite needs the air itself below freezing.12345TITLEExtreme cold, a face in the windVOL. VI EVENTS · HEAT, COLD, AIR, DUST AND FIRETYPEELEVATIONSCALEHEIGHTS TO SCALEREVREV 1 DRAFT SHEET 3 of 3DATE2026-10-17IDFB-EVT-133-CDRAWN AS linework on paperSOURCES NWS
Fig. C A face in the wind. Elevation of a person and a parked car on a clear night at −5 °F (−20.6 °C) in a 25 mph (11.2 m s⁻¹) wind; heights to scale HEIGHTS TO SCALEMaximizeThe sheet, SVG, 11 by 17
  1. The anemometer, at 33 ft (10 m)
  2. The wind, slower nearer the ground
  3. The face, at 5 ft (1.5 m): a wind chill of −31 °F (−35 °C)
  4. The radiator: −5 °F (−20.6 °C), the air's own temperature
  5. A clear night, the sky the index assumes

Ingredients

  • An arctic air mass carried south from high latitudes behind a cold front
  • Wind, which carries heat away from bare skin faster than still air
  • A clear, calm night, which lets the ground lose its heat to space
  • Snow on the ground, which loses heat readily and keeps the air above it cold

Scales

time
hours to days; the coldest around dawn, after a clear, calm night
horizontal
a region under an arctic air mass, hundreds to more than a thousand miles across
vertical
the coldest air lies in a shallow layer at the ground, under a temperature inversion
orlanski
macro-alpha to macro-beta for the air mass that brings it

Equations

The wind chill

Twc=35.74+0.6215 T−35.75 V0.16+0.4275 T V0.16T_{wc} = 35.74 + 0.6215\,T - 35.75\,V^{0.16} + 0.4275\,T\,V^{0.16}
TwcT_{wc}
the wind chill temperature, °F
TT
the air temperature, °F
VV
the wind speed at the standard 33 ft (10 m), mph

Assumes The National Weather Service's 2001 index, defined only at or below 50 °F (10 °C) and for winds above 3 mph. It is built on a model of a human face and the heat it loses to the wind, reckons the wind at 5 ft (1.5 m) from the reading at 33 ft (10 m), and assumes no sun, a clear night sky. It applies to people and animals only.

Working form At 0 °F (−17.8 °C) in a 15 mph (6.7 m s⁻¹) wind, the wind chill is −19.4 °F (−28.6 °C), which the Weather Service's chart prints as −19: bare skin can freeze in 30 minutes. At −20 °F (−28.9 °C) in a 25 mph (11.2 m s⁻¹) wind it is −50.8 °F (−46.0 °C), and bare skin can freeze in 10 minutes.

Signatures

surface
the temperature falling through a clear; calm night; a north or northwest wind behind an arctic front; a very low dew point
satellite
clear sky over snow cover behind the front; the cold air too dry and shallow for cloud
radar
nothing; the air is clear and dry
sounding
a shallow; very cold layer at the ground under a strong inversion

Numbers

QuantityValue, and the kind of number it is
Extreme Cold WarningAir temperatures or wind chill values reaching or exceeding locally defined warning criteriaStandard, Directive 10-515
Extreme Cold WatchConditions favorable for air temperatures or wind chill values to meet or exceed local Extreme Cold Warning criteriaStandard, Directive 10-515
Cold Weather AdvisoryAir temperatures or wind chill values reaching or exceeding locally defined advisory criteria, but not exceeding warning criteriaStandard, Directive 10-515
The national guidanceNot a strict set of rules; each office is encouraged to work with local public health officials and other partners to tailor its criteriaStandard, Directive 10-515
Warning criteria in the lower 48From −40 °F (−40 °C) to 20 °F (−6.7 °C), air temperature or wind chill, across 3,850 forecast zonesStandard, National Weather Service Guidance for Extreme Cold Warnings and Cold Weather Advisories
The coldest criteria−40 °F (−40 °C) in parts of Minnesota, Montana, the Dakotas and WyomingStandard, National Weather Service Guidance for Extreme Cold Warnings and Cold Weather Advisories
The warmest criteria20 °F (−6.7 °C) in parts of California, Arizona, Florida and TexasStandard, National Weather Service Guidance for Extreme Cold Warnings and Cold Weather Advisories
Advisory criteria10 °F (5.6 °C) warmer than the warning in 3,575 of the 3,818 zones of the lower 48 given bothStandard, National Weather Service Guidance for Extreme Cold Warnings and Cold Weather Advisories
Warning criteria in AlaskaAs cold as −70 °F (−56.7 °C), in 21 of its 119 zonesStandard, National Weather Service Guidance for Extreme Cold Warnings and Cold Weather Advisories
Rochester, New YorkWarning at −25 °F (−31.7 °C) or below; advisory from −15 to −24 °F (−26.1 to −31.1 °C)Standard, Wind Chill Temperature Index (2001)
Wind chill indexDefined only at or below 50 °F (10 °C) with wind above 3 mph (1.3 m s⁻¹)Standard, Wind Chill Temperature Index (2001)
The wind it usesReckoned at 5 ft (1.5 m), the height of an adult's face, from the reading at 33 ft (10 m)Standard, Wind Chill Temperature Index (2001)
Bright sunshineMay raise the wind chill by 10 to 18 °F (5.6 to 10 °C)Standard, Wind Chill Temperature Index (2001)
FrostbiteOnly when the air itself is below freezing, whatever the wind chillStandard, Wind Chill Temperature Index (2001)
Where frostbite strikes firstUncovered skin and the extremities, such as the hands and feetStandard, Cold Weather Safety
HypothermiaThe body losing heat faster than it can produce it; in extreme cold it can come in minutesStandard, Cold Weather Safety
What wind chill does to thingsCools them only to the air temperature, faster; a car's radiator at −5 °F (−20.6 °C) cools no lower, though the wind chill is −31 °F (−35 °C)Standard, Wind Chill Temperature Index (2001)

How the station sees it

Every place on this site gives what the weather feels like, and at or below 50 °F that is the wind chill, worked by the same 2001 equation from the temperature and the wind the page gives beside it. The airport stations report both every minute, so the wind chill they give follows each gust. Where an office has an Extreme Cold Warning, Watch or Cold Weather Advisory in force, the place's page carries it, and each alert has its own report.

  • Airport weather stations: the temperature and the wind every minute, from which each place's feels-like figure is worked
  • Every station on the map: all the instruments that report temperature, ranked on how well they report
  • Severe Alerts: every Extreme Cold Warning and Watch and Cold Weather Advisory in force, each with its own report

How it is warned

An Extreme Cold Warning is issued when the air temperature or the wind chill is expected to reach the office's warning criteria; an Extreme Cold Watch when those conditions are possible but their occurrence, location or timing is still uncertain; a Cold Weather Advisory for dangerously cold conditions that are not expected to reach the warning. The directive's national guidance is not a strict set of rules: each office is encouraged to work with local public health officials and other partners to tailor its criteria.

Most often an office's advisory sits 10 °F (5.6 °C) above its warning: it does in 3,575 of the 3,818 forecast zones of the lower 48 that are given both. In Rochester, New York, a warning is issued when the temperature, with or without wind, is expected to fall to −25 °F (−31.7 °C) or below, and an advisory when it is expected to fall between −15 and −24 °F (−26.1 and −31.1 °C). Duluth's office, where the warning criteria are −40 °F (−40 °C), gave its warning for wind chills "as low as 45 to 50 degrees below zero"; Denver's office, where the advisory criteria are −15 °F (−26.1 °C) and the warning −25 °F (−31.7 °C), gave its advisory for "very cold temperatures as low as 20 below zero".

During extreme cold, avoid going outside. If you must, dress in layers, cover every bit of bare skin with a hat, a face mask and gloves, and make sure someone knows where you are. Check on older relatives, friends and neighbors, and bring pets indoors. Use portable heaters correctly, and never run a generator or a grill indoors. To keep pipes from freezing, wrap them, drain them or let them drip slowly. Keep at least half a tank of fuel in the car.

VTECPhenomenonThe alerts that carry it
CWcold weatherCold Weather Advisory
ECextreme coldExtreme Cold Warning; Extreme Cold Watch

Every alert in force now

See also

Sources

  1. National Weather Service. Directive 10-515, WFO Non-Precipitation Weather Products Specification.
  2. National Weather Service. National Weather Service Guidance for Extreme Cold Warnings and Cold Weather Advisories, Directive 10-515 Appendix B.
  3. National Weather Service. Wind Chill Temperature Index (2001).
  4. National Weather Service. Understanding Cold Weather Alerts.
  5. National Weather Service. Cold Weather Safety.

Definition after the Directive 10-515, WFO Non-Precipitation Weather Products Specification. Plate FB-EVT-133, revision 1, 2026-10-17. The number is permanent; cite it.