Terms in this set (171)
air moves away from high pressure and towards low pressure
measured in millibars or inches of mercury
High pressure system
Low pressure system
causes air around high pressure system to move clockwise and around a low counterclockwise
electrical storm associated with lightning and thunder; accompanied by heavy rainfall, strong winds, and occasionally hail and tornadoes; flash flooding, blizzards/ice storms, dust storms
Ingredients for thunderstorm
fuel-water vapor, instability, lifting mechanism
stages of a thunderstorm
cumulus stage, mature stage, dissipating stage
conditions are favorable for severe thunderstorms to develop in the area
severe weather has been reported
lightning, hail, tornadoes, downbursts, derechos, dust storm, blizzards and ice storms
powerful electrostatic discharge produced during a thunderstorm- charge separation
types of lightning
intra-cloud lightning, cloud to ground, anvil to ground, cloud to cloud
produced in tall, vertical clouds. water droplets bounce around above and below the freezing level
formation not well understood.
peak season april through june.
SKYWARN- not a network of storm chasers.
classified using enhanced Fujita Scale, estimates wind speeds based on damage. EF5 winds in excess of 200mph
region where tornadoes occur more often
weather conditions favorable for tornado formation
tornado observed by a trained spotter or Doppler Radar
strong downdraft that produces dangerous and potentially damaging winds; occur in very unstable storms; occurs in mostly Great Plains, western US
cause significant damage (often confused with that of a tornado); downbursts in excess of 60-100 mph; usually associated with a stationary front; form in thunderstorms that are bow or spearhead shaped; major threat to starting and landing aircrafts
downburst derecho damage
both produce damage from straight line winds, which is often mistaken for tornado damage
caused by gust fronts from a thunderstrom; can move up to 50mph, common in southwest US
winter storm associated with heavy snowfall and strong winds
produced by sleet and freezing rain; ice coats all objects; especially dangerous because they induce power outages in freezing temperatures (risk of hypothermia)
weather system movement
over North America, weather systems typically move West to East due to prevalent westerly winds
air pressure and elevation
as elevation increases, air pressure decreases. common units in the US to measure pressure are inches of mercury and millibars.
change in pressure
the most basic change in pressure is the twice daily rise and fall due to the heating from the sun. other fluctuations occur as a result of the migrating weather systems. Northern half of US has most dramatic air pressure change.
change in wind speeds and/or direction with height
large body of air with uniform temperature and humidity
prinicpal air masses
polar latitudes, continental, maritime, and tropical. most weather occurs along the periphery of air masses.
most frequently occur in the southeastern US. Florida has the highest number of thunder days.
Warm moist air from GofM and Atlantic most readily available. SE has access to 2 moisture sources.
require moisture, instability, lifting mechanism for formation
higher in warm ocean currents and puts more moisture into air than cool currents at same latitude
when is air unstable
considered unstable if it continues to rise when given a nudge upward or sink if given a nudge downward. if bubble or parcel of air forced upward, it will continue to rise on its own. as parcel rises, it cools and water vapor condenses to form tall cumulonimbus thunderstorm cloud.
cooler air denser than warm air. the number of atoms and molecules that make up the layers of the atmosphere changes based on elevation. the first 18,000 feet of the atmosphere contains 1/2 of the air molecules.
wind chill temperature index
reflects body's perception of cold temperatures when exposed to wind
what can give air upward lift?
differential heating; fronts, drylines and outflow boundaries; terrain
indicated by presence of winds, temperature differences, pressure differences. boundary between two air masses of different temperatures and different air densities. Cold fronts move faster than warm fronts.
thunderstorm life cycle
lasts 30 minutes, towering cumulus stage, mature cumulus stage, dissipating stage
types of thunderstorms
ordinary cell, multi cell cluster, squall line, supercell
responsible for most of the US's significant tornadoes. only 20 to 25% of supercells produce tornadoes. only 15 to 20% of those produce significant tornadoes. ideal conditions when winds are veering or turning clockwise with height; entire cloud rotates, giving a striated or corkscrew appearance to the storm's updraft.
formed when updrafts carry raindrops upward in cold areas of the atmosphere. NM, CO, and WY have the most hail storms. cross sections of hail stones are not uniform and exhibit layers of ice.
severe weather hazards
can also produce hail, lightning, strong winds (derechos, downbursts, tornadoes) and winter storms (Nor'easter, blizzards, ice storms)
TV, NOAA weather radio
sources for receiving timely and accurate warning info
severe weather accounts for 1/3 of the nation's major disasters; flooding and hurricanes make up for the most damage
one of the deadliest hazard types with heat and winter weather
derecho and downburst hazards
derechos similar damage to that of tornadoes. both are aviation hazards, delta L1011 aircraft crashed during runway approach from downburst
warnings only 10 to 15 minutes beforehand. risks higher for immobile/disabled, mobile home residents, people unaware of warnings, people staying in exterior rooms with windows
deadliest tornado since 1950
2011 tornado season
327 deaths, triggered by presence of La Nina, state of Alabam activated Emergency Operations center before a single tornado touched down thanks to National Weather Service
person forwarding tornado info to the national weather service
mid-lat cyclone with prevailing winds from NE
Storm of the Century 1993
caused all major airports along the US east coast to be closed for the first time ever. Had wind speeds of Cat 3 hurricane
compared to 2007, communication was lacking in emergency management
movement of moisture and air
300mph wind is 9 times as strong as a 100 mph wind
develops over the tropical or subtropical waters, has an organized circulation. hurricanes NOT associated with fronts. draws energy from latent heat (MAIN ENERGY SOURCE)
what weakens a hurricane
wind shear, friction, cool water
hurricane favorable conditions
warm ocean waters, an atmosphere that cools fast enough with height such that it is potentially unstable to moist convection i.e. upward rush of cooling air. low values of vertical wind shear
tend to develop off NAfrican coast and move westward
West African Disturbance Line
line of convection which forms over west Africa and moves into Atlantic ocean
Hadley cell- tropical circulation pattern with rising air near equator and downward air flows in subtropical zone.
3 major circulation cells- Hadley, Ferrel, Polar
earth's global circulation patterns exhibit no seasonal movement
purpose of cyclones
to take heat stored in oceans and transfer it to the upper atmosphere where the upper level winds carry that heat to the poles, warming the poles and cooling the tropics.
suck heat out of water, lowering water temp.
regulate earth's temperatures
may have organized cloud systems but NO ORGANIZED CIRCULATION.
winds of 38mph or less
winds greater than 39mph, given a name
hurricane Cat 1
winds of 74-95 mph
hurricane Cat 2
winds of 96-110 mph
hurricane Cat 3
winds of 111-129 mph
hurricane Cat 4
winds of 130-156 mph
hurricane Cat 5
winds greater than 157 mph.
Saffir-Simpson Hurrican Wind Scale
national hurricane center removed storm surge and central pressure data to avoid confusion, scale only accounts for wind speed.
however, from a tropical wave to a tropical storm, central pressure of system continually drops.
air spirals in toward the center in a counter-clockwise pattern in the northern hemisphere (clockwise in the southern hemisphere)
calmest part of the storm, cloud free due to descending air flow
strongest winds and heaviest rains
curved bands of clouds that trail away from eye in spiral fashion
longest lifespan, strongest Atlantic Basin hurricane
National weather service started naming in 1953.
Letters Q, U, X, Y, Z ommitted
storm surge, rainfall, flooding, tornadoes
shallow slope, shallow water, high tide, low central pressure allow greater surge
investments made to minimize impacts from natural disasters yield $4 for ever $1 spent
Nor'easter, doesn't form over tropical waters
primary source of energy is release of laten heat through condensation, E stored by evaporated water
hurricane weakened by wind shear, cool water, land, cut off from fuel source
warm ocean current in the GofM, assumed that this current is a source for rapid intensification of storms
net winds strongest at right-front quadrant because of combo of storm's winds plus forward motion of the storm itself. At quadrant, hurricane with sustained winds of 150 and forward motion of 30= 180mph winds
controlling factors: wind belts, pressure systems, frontal weather systems
june 1 to november 30
female names in Atlantic started in 1953, male names added in 79 by WMO
hurricanes observed by buoys, satellites, aircraft, RADAR, ships
issued if conditions likely to threaten an area within 36 hours.
Forecasts by using ensemble runs of computer models by National Hurricane Center
Galveston Hurricane (1900)
Category 4, over 8000 deaths
Katrina 3 (2005)
Costliest hurricane over $80 billion
Ike 2 (2008)
Great Galveston Hurricane 1900
no ability to monitor storm, barrier island no protection from surge, no sea well yet, densely populated, disastrous impact
how was Galveston improved after 1900 hurricane?
what did authorities do with dead bodies after 1900 hurricane?
cremated them (too many)
1928 Okeechobee Hurricane
topping of levees like Katrina.
Florida's forgotten storm.
Vulnerable population group migrant farm workers.
Structural mitigation resulted- construction of Herbert Hoover dike around Lake Okeechobee became the US Army Corp's first major flood control project.
1935 Labor Day Hurricane
one of only 3 Cat 5's.
Cat 5 at landfall, first 5 to hit US as of August 2010.
408 dead, 250 WWI veterans working in the Keys, not evacuated in a timely fashion.
1938 Long Island Express
referred to as "stealth" storm because after passing Bahamas, the storm moved out of sight of forecasters.
like 1900 Galveston Island Hurricane, lack of timely detection of the storm off-shore.
hurricane tracking tools at the time= barometric pressure readings, wind speed measurements, rainfall measurements.
park in Long Island destroyed by 40 ft wave, registered as an earthquake at Fordham U.
Hurricane Andrew 1992
FL at Cat 5
Revealed deficiencies in building codes and enforcement, situational awareness, coordination and response problems.
Today Florida has the best building codes of any state. Took Homestead, FL 10 years to get back to normal
Hurricane Katrina 2005
Cat 3 at landfall.
Bay St. Louis, MS 28 ft storm surge.
Fictitious computer modeling 2004 in BR of Hurricane Pam showed how a storm would impact NOLA.
Nola had flood plan prior to Katrina, experienced only Cat 1.
Height of failed levee 8-9 feet.
Storm surge highest in right front quadrant in Mississippi, was 30 ft.
Katrina costliest disaster in US history.
why was katrina so bad?
underestimation of social vulnerability by officials, evacuation issued too late, failure of government planning, preparation, response and coordination at all levels.
Hurricane Isaac first mandatory evacuation in Nola.
LA wetlands vanishing at 40sqmi/yr
What were the Cat 5 hurricanes to hit the US?
1935 Labor Day Hurricane
All US regions but central at risk from hurricanes
cost 2.4 billion a year
kill roughly 200 people per year, mainly deaths caused by flash flooding
Are floods rare?
NO, almost every US county has experienced major flooding
the speed at which water moves through a channel at a given point. the rate of water flow is measured in feet per second
the volume of water passing a given point in a river per unit of time in cubic feet per second
the gauged height of the water level in a river
any predefined stretch along a river
any branch of a river
the slope of a river between two defined points
the vertical distance between water surface and stream bed
the movement of water from land to the oceans, generally through rivers, lakes, and streams. generated through precipitation
NOT ALL RIVERS GENERATE RUNOFF
area surrounding a river within which runoff is drained into that river
boundary that separates runoff from one stream to another. usually highest elevation point between two channels.
first order streams
in the upper reaches of sub-basins, headwaters are highest point of elevation, water flows downhill
becomes inundated when the river floods
high frequency floods with minor flooding have an interval of say, 5 years. 5% annual chance of occurring is a 20 year flood.
diagrammatic representation of discharge over time
rising river represented by rising limb on hydrograph.
river reaches peak discharge, shown as crest.
crest followed by decreasing discharge and downward slope.
crest doesn't necessarily occur with storm. first, storm, next crest because it takes time for runoff to collect in a river.
hydrographs for levees
hydrograph for community downstream from levee looks the same as hydrograph for urban community
river with numerous channels
factors that influence damage amount
flood depth, velocity of waters, duration, amount of sediments in waters
riverine, storm surge, ice-jam flooding
types of floodin
riverine (weather systems, snow melt), dam and levee failure, flash floods, coastal flooding, ice-jam flooding, storm surge flooding
natural influences on floods
topography, soil texture (frozen/saturated), vegetation, season, amount of precipitation
human influences on floods
urbanization, agriculture, forestry, flood control
impact of urbanization
runoff from urbanized areas delivered quicker to streams and rivers, less water intercepted by vegetation, so RUNOFF INCREASED
urban hydrograph has higher crest, and is steeper due to decrease in time it takes to flood
urbanization and floodplain
floodplain development and loss of riparian vegetation leads to widening floodplain.
construction of dams/levees, collection of more/new data may also lead scientists to change flood designations/magnitude estimates for a flood event.
elements considered- number of years of record, rank of individual flow within recorded years.
flooding magnitude and frequency not easy to predict (lack of historical records, drastic changes to land use)
x-year flood has probability of 1-in-x chance of occurring annualy based on annual recurrence of flood with a SPECIFIC MAGNITUDE.
there is a 26% chance of flooding over the life of a 30 year mortgage for a 100 year flood even though annual chance of occurring is 1%.
only required for homes and buildings in high risk areas, not the whole flood plain.
National Flood Insurance Program gave building code requirements for floodplain development.
Losses have been transferred to the taxpayer and not the insured.
use of retention ponds decreases peak discharge.
levees- increase extent of flooding downstream since flood waters can't expand into upstream floodplain. NO UNIFORM BUILDING CODES.
1993 Mississippi River Flood
Bigger than the 1973 flood and recurrence interval exceeded 100 years
local land use policies
allow homeowners to build behind dams and in flood plains
can occur at any time of the year, anywhere, at any time of day or night
1927 Mississippi River Flood
in 1926, army corps of engineers declared levee system along MS river would prevent future floods.
effected area the size of New England.
African american refugees herded onto the levee and guarded to keep them from fleeing or finding work elsewhere.
Dynamiting of Poydras levee south of city unnecessary.
Impetus for 1928 Flood Control Act
1993 Midwest Floods (MS River)
largest most significant flood in US history.
contributing factors: heavy snowfall previous winter, lots of snowmelt, intense summer rains that summer.
Flood areas on satellite image dark blue to black.
Lasted may through september, few months
20 of 275 of federal levees topped, 767 of 1091 of non-federal levees topped.
Flood crest 19 ft at St. Louis.
Many homeowners relocated as gov offered buy outs.
2008 Midwest Flooding
along MS river
2011 Midwest and MS river floods
as bad as 1927 in terms of discharge.
opened Morganza, Bonnet Carre, and Birds Point floodways (Birds point last opened in 1937, earthen levee)
failure of south fork dam
town 15 miles downstream.
took 5 years to recover
1976 Big Thompson Canyon Flash Flood
climbing to higher ground best way to escape flash flood.
12 inches of rain in 4 hours equivalent to rainfall for a whole year.
144 lives lost, 850 saved by US army off of roof tops, etc.
major impetus nationwide for creating early warning systems for flash floods in mountainous cities and recreation areas
larimer county implemented reverse 911
deficiency in precipitation over an extended period of time. conceptual definition does NOT help to ID severity/beginning, middle, end.
caused by changes in general circulation over an area, and semi-permanent high pressure systems.
factors that control drought
temperature, evaporation, soil type, vegetation type, percent vegetation cover, antecedent soil moisture conditions.
only primary source of water input into the system
constant exchange of water with the Earth's hydrosphere. Driven by solar energy balance. Precipitation, evapo-transpiration, horizontal transport of water vapor, runoff, infiltration, groundwater discharge/flow
measured by tipping bucket rain gauge, standard rain gauge
combo of water evaporated out of a system and water that is transpired out of leaves of plants
Water balance equation
Precipitation= runoff+ evapotranspiration+ change in storage
Simplified water balance equation
positive difference= soil begins to store water
negative difference= soil loses water, drought
types of drought
meterological- below normal precipitation
agricultural- soil moisture insufficient for crops and pastures
hydrological-surface and subsurface water supplies fall below normal water levels
socioeconomic-water shortages impact society
Palmer Drought Severity Index
smaller numbers=more extreme the drought.
Useful for monitoring drought impact.
Crop Moisture index
assess short-term drought conditions
society's vulnerability to drought determined by physical and social factors, such as demographic trends and geographic characteristics
Normalized Difference Vegetation Index algorithm
measures and maps density of green vegetation across Earth via satellite imaging
US Drought Monitor
primary mandate to assess the current state of drought in the US, map released every Thursday
Drought vs. other natural disasters
slow rate of onset, broad impacts, underestimates of severity, deadly in developing countries
increased fire hazard, damage to wildlife and fish, unemployment
dust storms, wild fires, heat waves
tend to have greater effect on children and elderly.
the hotter the body gets, the more blood the heart pumps and the more blood vessels get dilated.
Air temp above body temp=heat gain
relationship between air temp and humidity and skin temp
health effects of heat
heat cramps, heat exhaustion, heat stroke
forecast and warning
heat warning- heat values forecast to meet/exceed warning criteria for at least 2 days
heat advisory- hazardous conditions have begun or will begin within the next 36 hours
heat watch- conditions favorable for heat to meet or exceed local warning criteria in 12-24 hours
1930s Dust Bowl
PDSI below 3.
Four drought periods, farmers unable to recover from preceding droughts.
Drought loosened soils-topsoil carried away (dust storms)
Black Sunday April 1935
Massive dust storm, many thought that the world was ending
extensive farming, poor land management practices, aftermath of the Great Depression.
Mass exodus to California.
Lessons learned from Dust Bowl
reservoirs built or enlarged and domestic water systems improved, new insurance and aid programs, sensitive agricultural lands taken out of production, changed farming techniques
Drought of 1988-1989
costliest drought in US History
Chicago Heat Wave of 1995
record high of 106 F
Hot weather emergency plan only 1.5 pages long.
739 dead in excess mortality.
Urban heat island effect
asphalt and concrete store heat longer and gradually release heat at night.
age (old, young), poor, male workers, homeless
Why such high mortality in Chicago Heat wave?
no warnings until the end of the heat wave, power failures, opening of hydrants dropped water pressure and doubled city's water consumption, lack of resources.
Parallels with Katrina- population vulnerability, failure of governmental preparations and respondence.
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