Atmospheric HazardsAtmospheric HazardsPart IIPart II

Heat Waves, Winter Storms, Heat Waves, Winter Storms, and Hurricanesand Hurricanes

Session 8Session 8

Air MassAir Mass

Large body of air (usually > 1000 Large body of air (usually > 1000 miles +/- in diameter) that exhibits miles +/- in diameter) that exhibits relatively homogeneous properties of relatively homogeneous properties of temperature and moisturetemperature and moisture

Source RegionsSource Regions

Locations where air masses developLocations where air masses develop Classification from temperature and Classification from temperature and

the characteristics of the ground the characteristics of the ground surfacesurface

Temperature can be Arctic, Polar, or Temperature can be Arctic, Polar, or TropicalTropical

Surface type can be Continental or Surface type can be Continental or MaritimeMaritime

Source Region TypesSource Region Types

Maritime (ocean) surface (m); Maritime (ocean) surface (m); provides very moist airprovides very moist air

Continental (land) surface (c) ; Continental (land) surface (c) ; provides dry airprovides dry air

High (polar) latitudes; source of cold High (polar) latitudes; source of cold airair

Low (tropical) latitudes; warm air Low (tropical) latitudes; warm air sourcesource

Air Mass RegionsAir Mass Regions

Letter DesignationLetter Designation

Lower case = nature of the surfaceLower case = nature of the surface Upper case = temperatureUpper case = temperature

Basic Air Mass TypesBasic Air Mass Types

MaritimeMaritime ContinentalContinental

Maritime (m)Maritime (m)

Maritime Polar (mP)Maritime Polar (mP) High latitudesHigh latitudes Cool and MoistCool and Moist Humid all year, mild or cold, mild Humid all year, mild or cold, mild

temperatures may have low clouds in temperatures may have low clouds in winter, cold storms like a Nor'easter, found winter, cold storms like a Nor'easter, found in North Pacific, Northwest Atlanticin North Pacific, Northwest Atlantic

More MaritimeMore Maritime Maritime Tropical (mT)Maritime Tropical (mT) Low latitudesLow latitudes Warm and MoistWarm and Moist Warm and humid year roundWarm and humid year round Gulf of MexicoGulf of Mexico

Continental (c)Continental (c)

Continental Polar (cP)Continental Polar (cP) High latitudesHigh latitudes Cold and dryCold and dry Found in Interior Canada and Alberta, Found in Interior Canada and Alberta,

dry entire year, cold in winter, cool in dry entire year, cold in winter, cool in summer, cold waves in wintersummer, cold waves in winter

Associated with “Lake Effect” snows Associated with “Lake Effect” snows around Great Lakesaround Great Lakes

Continental Arctic (cA)Continental Arctic (cA)

Polar and Arctic LatitudesPolar and Arctic Latitudes Extremely cold and extremely dryExtremely cold and extremely dry Arctic Basin and Greenland Ice Cap, Arctic Basin and Greenland Ice Cap,

very stable air mass all year, very stable air mass all year, produces cold waves in winterproduces cold waves in winter

Continental Tropical (cT)Continental Tropical (cT)

Low latitudesLow latitudes Extremely hot and extremely dryExtremely hot and extremely dry Hot, dry, and unstable; cloudless Hot, dry, and unstable; cloudless

skies, occasional drought as in Great skies, occasional drought as in Great PlainsPlains

What are Fronts?What are Fronts?

Fronts are a boundary between Fronts are a boundary between dissimilar air massesdissimilar air masses

Different densities, temperature and Different densities, temperature and moisture (humidities)moisture (humidities)

Why are Fronts Important?Why are Fronts Important?

Mark the beginning of a major Mark the beginning of a major change in weatherchange in weather

Produce areas of convergence and Produce areas of convergence and divergence aloft thus forcing vertical divergence aloft thus forcing vertical motion fields in their vicinitymotion fields in their vicinity

TypesTypes

Frontal types are determined by the Frontal types are determined by the type of thermal change in air mass type of thermal change in air mass charactercharacter

1. Cold front1. Cold front 2. Warm front2. Warm front 3. Occluded front3. Occluded front 4. Stationary front4. Stationary front

Symbols for FrontsSymbols for Fronts

Cold FrontCold Front Marks the leading edge of a colder air Marks the leading edge of a colder air

mass moving into a regionmass moving into a region Cold front usually found in a low pressure Cold front usually found in a low pressure

troughtrough Drawn as a solid blue line with the Drawn as a solid blue line with the

triangles along the front showing its triangles along the front showing its direction of movementdirection of movement

Cold Front FeaturesCold Front Features

In the Northern Hemisphere, winds In the Northern Hemisphere, winds ahead of the cold front at the surface ahead of the cold front at the surface (warm side) will be generally from a (warm side) will be generally from a southerly direction (can also range southerly direction (can also range from SE to SW) and shift to a more from SE to SW) and shift to a more westerly direction (could range from W westerly direction (could range from W to N) behind the front (in the cold air)to N) behind the front (in the cold air)

One of the best ways to determine the One of the best ways to determine the time of frontal passage is in time of frontal passage is in recognizing the abrupt wind shiftrecognizing the abrupt wind shift

Warm FrontWarm Front

Marks the leading edge of a warmer Marks the leading edge of a warmer air mass moving into a regionair mass moving into a region

Solid red line with semicircles Solid red line with semicircles pointing in direction of movementpointing in direction of movement

Usually found in a troughUsually found in a trough

Warm Front FeaturesWarm Front Features

Winds are generally from an easterly Winds are generally from an easterly direction ahead of the front at the direction ahead of the front at the surface (on the cold side) while surface (on the cold side) while shifting to a more southerly direction shifting to a more southerly direction behind the front in the warm airbehind the front in the warm air

Occluded FrontOccluded Front

Occurs when a cold front (that typically Occurs when a cold front (that typically moves faster than a warm front) catches moves faster than a warm front) catches up and Merges with a warm frontup and Merges with a warm front

Purple line with alternating cold-front Purple line with alternating cold-front triangles and warm-front semicircles triangles and warm-front semicircles pointing in the direction toward which the pointing in the direction toward which the front is movingfront is moving

Occlusion CharacteristicsOcclusion Characteristics

Cold occlusion: cold front takes over Cold occlusion: cold front takes over a warm or stationary front (cold air in a warm or stationary front (cold air in back)back)

Warm occlusion: warm front Warm occlusion: warm front overtakes a cold or stationary front overtakes a cold or stationary front (cold air in front)(cold air in front)

Stationary FrontStationary Front Boundary between dissimilar air masses that Boundary between dissimilar air masses that

moves very slowly back and forth so that over moves very slowly back and forth so that over a relatively long period of time, it appears not a relatively long period of time, it appears not to be moving at allto be moving at all

Winds generally from the south ahead of the Winds generally from the south ahead of the front at the surface (on the warm side) while front at the surface (on the warm side) while northerly behind the front in the cold airnortherly behind the front in the cold air

Drawn as alternating red and blue line with Drawn as alternating red and blue line with semicircles facing the cold air on the red line semicircles facing the cold air on the red line and the triangles pointing towards the warmer and the triangles pointing towards the warmer air on the blue lineair on the blue line

Heat WavesHeat Waves

“A period of abnormally and uncomfortably hot and unusually humid weather. Typically a heat wave lasts two or more days.”

Definition from National Weather Service

Location Dependent

Heat AdvisoryHeat Advisory

Issued within 12 hours of the onset of the following conditions: heat index of at least 105̊DF but less than 115̊DF for less than 3 hours per day, or nighttime lows above 80DF for 2 consecutive days

Threshold value is expected or has been present for two or more consecutive days

Excessive Heat WarningExcessive Heat Warning

Prolonged periods are expected or extremely high indices are expected for a single day

Heat IndexHeat Index

"Apparent Temperature" is an accurate measure of how hot it really feels when the Relative Humidity (RH) is added to the actual air temperature

How it really feels like to an individual

Heat ExhaustionHeat Exhaustion

Mild form of heat stroke, characterized by faintness, dizziness, and heavy sweating

Heat StrokeHeat Stroke

Condition resulting from excessive exposure to intense heat, characterized by high fever, collapse, and sometimes convulsions or coma

Heat Index CategoriesHeat Index Categories

Heat Wave CausesHeat Wave Causes

Absence of polar air masses (jet stream further north of area; strong ridge)

Strong heating of the surface (sinking of atmosphere, high pressure, leads to a warm air dome)

Additional Causes of Heat WavesAdditional Causes of Heat Waves

Dry ground (lack of soil moisture) Amount of vertical mixing of air

(vertical mixing near surface is weak or confined to shallow depth, little mixing of drier air aloft to reach surface and mix with warm, moister air near ground)

Urban Heat IslandUrban Heat Island

Heat is often worse in cities compared to rural areas

It can be very noticeable at night and difficult sleeping without air conditioning

Heat Wave Case StudiesHeat Wave Case Studies

Chicago 1995̊Chicago 1995̊ United States 2006United States 2006

Midlatitude CyclonesMidlatitude Cyclones

Source of most stormy weather in Source of most stormy weather in the United Statesthe United States

Does not include “garden variety” Does not include “garden variety” thunderstorms or tropical cyclonesthunderstorms or tropical cyclones

PhenomenaPhenomena

Severe thunderstormsSevere thunderstorms TornadoesTornadoes Severe winter stormsSevere winter storms BlizzardsBlizzards Heavy SnowHeavy Snow High windsHigh winds FloodsFloods

CyclogenesisCyclogenesis

Development or strengthening of a midlatitude cyclone

Source RegionsSource Regions

Major areas in the United States for cyclogenesis

Eastern slopes of Rocky Mountains Great Basin Gulf of Mexico Atlantic Ocean off of North Carolina

SnowSnow

Precipitation composed of white or Precipitation composed of white or translucent ice crystals, chiefly in translucent ice crystals, chiefly in complex branch hexagonal form and complex branch hexagonal form and often agglomerated into snowflakesoften agglomerated into snowflakes

Intensity characterized as light, Intensity characterized as light, moderate, and heavymoderate, and heavy

Snow IntensitiesSnow Intensities

Light: Visibility is 1 km (5̊/8 statute Light: Visibility is 1 km (5̊/8 statute mile) or moremile) or more

Moderate: Visibility less than 1 km Moderate: Visibility less than 1 km but not more than ½ km (5̊/16 but not more than ½ km (5̊/16 statute mile)statute mile)

Heavy: Visibility less than ½ kmHeavy: Visibility less than ½ km

Snow GrainsSnow Grains

Precipitation in the form of very Precipitation in the form of very small, white opaque particles of icesmall, white opaque particles of ice

Solid equivalent of drizzleSolid equivalent of drizzle Also called granular snowAlso called granular snow Similar to snow pellets in Similar to snow pellets in

appearance, but more flattened and appearance, but more flattened and elongated with diameters < 1 mmelongated with diameters < 1 mm

Neither shatter or bounce when they Neither shatter or bounce when they hit hard surfacehit hard surface

Snow PelletsSnow Pellets

Precipitation consisting of white, opaque, Precipitation consisting of white, opaque, approximately round (sometimes conical) approximately round (sometimes conical) ice particles having a snowlike structure ice particles having a snowlike structure about 2-5̊ mm in diameterabout 2-5̊ mm in diameter

Crisp and easily crushedCrisp and easily crushed Rebound when they fall on a hard surface Rebound when they fall on a hard surface

and often break upand often break up Often fall in a shower before or with snow Often fall in a shower before or with snow

and when the surface temperature is at or and when the surface temperature is at or slightly below 0slightly below 0° C° C

Freezing RainFreezing Rain

Falls as liquid but freezes after Falls as liquid but freezes after hitting the surfacehitting the surface

Surface is below freezing while Surface is below freezing while atmosphere is warmeratmosphere is warmer

Winter Storm OutlookWinter Storm Outlook

Major storm expected in next 3-5̊ days

Winter Storm AdvisoryWinter Storm Advisory

Mixed precipitation (snow, sleet, freezing rain) expected but not warning in 12-24 hours

Winter Storm WatchWinter Storm Watch

Heavy snow, sleet, blizzard conditions, significant accumulations of freezing rain or drizzle, or combination of types within 24-48 hours

Winter Storm WarningWinter Storm Warning

Winter precipitation expected in 12-24 hours, may include “near-blizzard” conditions

Ice StormsIce Storms

Usually freezing rainUsually freezing rain Can cause significant hazards such

as ice on roads, power lines, and fallen trees

BlizzardsBlizzards

Sustained winds Sustained winds ≥ 35̊ mph, falling or ≥ 35̊ mph, falling or blowing snow, visibilities at or below blowing snow, visibilities at or below ¼ mile, and lasting a minimum of ¼ mile, and lasting a minimum of three hoursthree hours

Blizzard FormationBlizzard Formation

Occur within circulation of extra-tropical cyclones as the cyclones provide wind and snow

North American geography has favorable environment for blizzard formation due to north-south orientation of Rocky Mountains

Three ingredients (cold air, strong winds, and moisture) are necessary to form a blizzard

Blizzard StatisticsBlizzard Statistics

11 blizzards on average per year in the continental United States

40 states in continental United States had at least one blizzard between 195̊9-2000

Blizzards per Season 1959-2000Blizzards per Season 1959-2000

Blizzards by County 1959-2000Blizzards by County 1959-2000

Blizzard ProbabilityBlizzard Probability

Case StudiesCase Studies

1998 Northeast Ice Storm1998 Northeast Ice Storm January 2007 North American Ice January 2007 North American Ice

StormStorm Midwest Blizzard of 1978Midwest Blizzard of 1978 March 1993 Superstorm aka “Storm March 1993 Superstorm aka “Storm

of the Century”of the Century”

Tropical CyclonesTropical Cyclones

International agreement for all International agreement for all hurricane-type stormshurricane-type storms

Western North Pacific: TyphoonWestern North Pacific: Typhoon Indian Ocean, Australia: CycloneIndian Ocean, Australia: Cyclone Eastern Pacific and North Atlantic Eastern Pacific and North Atlantic

Basin: HurricaneBasin: Hurricane

Tropical Cyclone LocationsTropical Cyclone Locations

Hurricane ImpactsHurricane Impacts

High windsHigh winds Storm surgeStorm surge Heavy rainHeavy rain Inland floodingInland flooding Possible tornadoesPossible tornadoes

NamesNames

Originally in West Indies after specific Originally in West Indies after specific “saints day” closest to storm in 19“saints day” closest to storm in 19thth CenturyCentury

Australians assigned women’s names Australians assigned women’s names late 19late 19thth Century Century

U.S. phonetic alphabet in 195̊0U.S. phonetic alphabet in 195̊0 195̊3: Women’s names in U.S.195̊3: Women’s names in U.S. 1978: Eastern North Pacific both 1978: Eastern North Pacific both

gendersgenders 1979: Both genders in all U.S. areas1979: Both genders in all U.S. areas

2011 2012 2013 2014 2015 2016

ArleneBretCindyDonEmilyFranklinGertHarveyIreneJoseKatiaLeeMariaNateOpheliaPhilippeRinaSeanTammyVinceWhitney

AlbertoBerylChrisDebbyErnestoFlorenceGordonHeleneIsaacJoyceKirkLeslieMichaelNadineOscarPattyRafaelSandyTonyValerieWilliam

AndreaBarryChantalDorianErinFernandGabrielleHumbertoIngridJerryKarenLorenzoMelissaNestorOlgaPabloRebekahSebastienTanyaVanWendy

ArthurBerthaCristobalDollyEdouardFayGonzaloHannaIsaiasJosephineKyleLauraMarcoNanaOmarPauletteReneSallyTeddyVickyWilfred

AnaBillClaudetteDannyErikaFredGraceHenriIdaJoaquinKateLarryMindyNicholasOdettePeterRoseSamTeresaVictorWanda

AlexBonnieColinDanielleEarlFionaGastonHermineIanJuliaKarlLisaMatthewNicoleOttoPaulaRichardSharyTobiasVirginieWalter

Hurricane SeasonHurricane Season

North Atlantic Basin: June-NovemberNorth Atlantic Basin: June-November

The Yearly CycleThe Yearly Cycle

FormationFormation Pre-existing regions of low pressurePre-existing regions of low pressure Ocean surface temperatures > 79Ocean surface temperatures > 79° F (26° C)° F (26° C) Surface layer of warm water must be deep,

typically 200' of greater (around 60 meters) Winds in the atmosphere must not change

direction substantially with height (wind shear)

Location 5̊ degrees north or south of Equator

Evolution of HurricaneEvolution of Hurricane Tropical Wave: unorganized cluster of Tropical Wave: unorganized cluster of

thunderstorms with weak surface circulationthunderstorms with weak surface circulation Tropical Disturbance: Slight circulation with Tropical Disturbance: Slight circulation with

organized group of thunderstorms, organized group of thunderstorms, maintains identity for 24 hours, sustained maintains identity for 24 hours, sustained winds up to 19 kts (23 mph)winds up to 19 kts (23 mph)

Tropical Depression: Several closed isobars Tropical Depression: Several closed isobars as storm increases in strength with as storm increases in strength with sustained surface winds of 20-34 kts or up sustained surface winds of 20-34 kts or up to 39 mph; Number for identificationto 39 mph; Number for identification

Continuing EvolutionContinuing Evolution

Tropical Storm: Sustained winds from Tropical Storm: Sustained winds from 35̊-64 kts (39-73 mph); Given name35̊-64 kts (39-73 mph); Given name

Hurricane: Winds greater than 64 kts Hurricane: Winds greater than 64 kts (74 mph)(74 mph)

Major Hurricane: Category 3 or Major Hurricane: Category 3 or Higher on Saffir-Simpson Scale (96 Higher on Saffir-Simpson Scale (96 kts or 111 mph)kts or 111 mph)

Decay CriteriaDecay Criteria

Strong vertical wind shearStrong vertical wind shear Reduced source of heat and moistureReduced source of heat and moisture Dry, cool air transported into systemDry, cool air transported into system High pressure aloftHigh pressure aloft

Saffir-Simpson ScaleSaffir-Simpson Scale

Average SeasonAverage Season

18 Named Storms18 Named Storms 11 Tropical Storms11 Tropical Storms Six HurricanesSix Hurricanes Two Major HurricanesTwo Major Hurricanes

Record SeasonsRecord Seasons Named Storms: Maximum 30 (2005̊)Named Storms: Maximum 30 (2005̊) Named Storms: Minimum One (1914)Named Storms: Minimum One (1914) Hurricanes: Maximum 15̊ (2005̊)Hurricanes: Maximum 15̊ (2005̊) Hurricanes: Minimum Zero (1907, Hurricanes: Minimum Zero (1907,

1914)1914) Major Hurricanes: Maximum Seven Major Hurricanes: Maximum Seven

(195̊0, 2005̊)(195̊0, 2005̊) Major Hurricanes: Minimum Zero Major Hurricanes: Minimum Zero

(Several)(Several)

Most Intense Hurricanes to U.S.Most Intense Hurricanes to U.S.

1. Florida Keys, 1935̊, 892 mb, Cat. 5̊1. Florida Keys, 1935̊, 892 mb, Cat. 5̊ 2. Camille, 1969, 909 mb, Cat. 5̊2. Camille, 1969, 909 mb, Cat. 5̊ 3. Katrina, 2005̊, 920 mb, Cat. 33. Katrina, 2005̊, 920 mb, Cat. 3 4. Andrew, 1992, 922 mb, Cat. 5̊4. Andrew, 1992, 922 mb, Cat. 5̊ Note: Wilma set record of 882 mb Note: Wilma set record of 882 mb

before landfallbefore landfall

Deadliest U.S. HurricanesDeadliest U.S. Hurricanes

1. Galveston, 1900, Cat. 4, 8,000+ 1. Galveston, 1900, Cat. 4, 8,000+ (8,000-12,000)(8,000-12,000)

2. Lake Okeechobee, 1928, Cat. 4, 2. Lake Okeechobee, 1928, Cat. 4, 2,5̊00-3,0002,5̊00-3,000

3. Katrina, 2005̊, Cat. 3, 1,5̊00+ 3. Katrina, 2005̊, Cat. 3, 1,5̊00+ (1,836?)(1,836?)

4. Louisiana, 1893, Cat. 4, 1,100-1,4004. Louisiana, 1893, Cat. 4, 1,100-1,400 5̊. South Carolina/Georgia, 1893, Cat. 5̊. South Carolina/Georgia, 1893, Cat.

3, 1,000-2,0003, 1,000-2,000

CostliestCostliest

1. Katrina: LA, MS, AL, FL, several other 1. Katrina: LA, MS, AL, FL, several other states, $81.6 billionstates, $81.6 billion

2. Andrew: FL and LA, $26.5̊ billion2. Andrew: FL and LA, $26.5̊ billion 3. Wilma: FL, $20.6 billion3. Wilma: FL, $20.6 billion 4. Ike: TX, several states, $19.3 billion4. Ike: TX, several states, $19.3 billion 5̊. Charley: FL, NC, and SC, $15̊ billion5̊. Charley: FL, NC, and SC, $15̊ billion 6. Ivan: FL, AL, several other states, 6. Ivan: FL, AL, several other states,

$14.2 billion$14.2 billion

Case StudiesCase Studies

KatrinaKatrina IkeIke