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 105̊F but less than 115̊F for less than 3 hours per day, or nighttime lows above 80̊F 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 1995Chicago 1995 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 (5/8 statute Light: Visibility is 1 km (5/8 statute
mile) or moremile) or more Moderate: Visibility less than 1 km Moderate: Visibility less than 1 km
but not more than ½ km (5/16 but not more than ½ km (5/16 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 2-5 mm in diameterabout 2-5 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 3-5
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 ≥ 35 mph, falling or ≥ 35 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 1959-2000
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 1950U.S. phonetic alphabet in 1950 1953: Women’s names in U.S.1953: Women’s names in U.S. 1978: Eastern North Pacific both genders1978: Eastern North Pacific both genders 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 5 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
35-64 kts (39-73 mph); Given name35-64 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 (2005)Named Storms: Maximum 30 (2005) Named Storms: Minimum One (1914)Named Storms: Minimum One (1914) Hurricanes: Maximum 15 (2005)Hurricanes: Maximum 15 (2005) Hurricanes: Minimum Zero (1907, 1914)Hurricanes: Minimum Zero (1907, 1914) Major Hurricanes: Maximum Seven Major Hurricanes: Maximum Seven
(1950, 2005)(1950, 2005) 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, 1935, 892 mb, Cat. 51. Florida Keys, 1935, 892 mb, Cat. 5 2. Camille, 1969, 909 mb, Cat. 52. Camille, 1969, 909 mb, Cat. 5 3. Katrina, 2005, 920 mb, Cat. 33. Katrina, 2005, 920 mb, Cat. 3 4. Andrew, 1992, 922 mb, Cat. 54. Andrew, 1992, 922 mb, Cat. 5 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,
2,500-3,0002,500-3,000 3. Katrina, 2005, Cat. 3, 1,500+ 3. Katrina, 2005, Cat. 3, 1,500+
(1,836?)(1,836?) 4. Louisiana, 1893, Cat. 4, 1,100-1,4004. Louisiana, 1893, Cat. 4, 1,100-1,400 5. South Carolina/Georgia, 1893, Cat. 5. 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, $26.5 billion2. Andrew: FL and LA, $26.5 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 5. Charley: FL, NC, and SC, $15 billion5. Charley: FL, NC, and SC, $15 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