85 terms

Weather #3


Terms in this set (...)

El Nino and La Nina are associated with
water temps/air circulations over the equatorial Pacific Ocean
Persistent winds in the tropics are also called
trade winds
- "Discovered" by Columbus due to their reliability for trade.
- Trade winds blow northeasterly in N.H. and southeasterly in S.H.
El Nino (The child)
- Near the end of each year, a warm current of water flows southward along coasts of Ecuador and Peru, replacing the cold Peruvian current.

-Normally these countercurrents last for several weeks, but every 3-7 years these warm counter-currents become unusually strong and last for months.

- enhances north-south temp. gradient and thus strengthens the Subtropical jet.
El Nino (the child) means
after the Christ child because it usually appeared during Christmas season.
Characteristics of a switch from normal conditions to El Nino:
1. Surface pressure systems weaken. Surface pressure decreases on the eastern High Pressure area (the High weakens) while surface pressure increases in the western Low (the low also weakens).
2. Because this pressure gradient weakens, the trade winds stop or even reverse.
3. Water in the Eastern Pacific warms. A strong counter current develops and warm water "sloshes back" from Western Pacific Ocean to Eastern Pacific Ocean.
4. Precipitation shifts eastward. The area of upward motion, clouds and precip. normally found in Australia/Indonesia moves eastward to the central or eastern equatorial Pacific.

When these conditions cause sea surface temperature anomalies to be at least 0.5C for 3 consecutive months, an El Nino is said to be in progress.
Jet stream patterns are affected by
weather changes over a large part of the Northern Hemisphere
El Nino can impact weather worldwide by
- U.S. Winter: heavy rains over west coast, particularly California where mudslides are common
- Heavy rains also over the southeast U.S. Midwest
- increased number of east coast winter cyclones.
Dry conditions can cause forest fires over Indonesia in ___________ year
El Nino
1997-1998 El Nino Worldwide weather impacts:
- Indonesia drought in normally wet climate. Brush fires and crop failures occurred.
- Summer monsoon failed to occur in India leading to drought.
- Flooding rains across southern California, Gulf Coast, and Florida.
- Above normal temperatures across
1997-1998 El Nino U.S. economic impacts: some industries gain while other areas lose.
- Department store sales were up by 5-15 percent during the abnormally warm winter in the Midwest, but sales of snow equipment were down by nearly 35 percent.
- Skiing was up in the West but down in the Midwest. In the highly weather sensitive energy sector, households and businesses saved $2-7 billion in heating costs, while energy production and distribution businesses suffered from reduced sales.
- Agricultural losses approached $2 billion, or nearly 1-2 percent of total crop output.
- Property losses were estimated at nearly $2.6 billion.
La Nina
opposite of El Nino, but NOT the normal conditions outside of El Nino events.
- Trade winds are stronger than normal.
- Waters in eastern Pacific Ocean are colder than average.
La Nina impacts are more variable than with El Nino because...
- Occasionally droughts can occur on the central and eastern U.S.
- Greater number of hurricanes can occur in the Atlantic Ocean.
- Rare snows in Pacific Northwest.
- slightly below normal temps and average amounts of precipitation in chicago
Tropical cyclones are the most
destructive storms on Earth.
2005 was a particularly active hurricane season, with 4 hurricanes reaching Category...
5 intensity (Emily, Rita, Katrina, and Wilma).
Loss of life has been greatly reduced in the U.S. due to better
satellite imagery, computer models, warnings, and evacuation procedures.
storm in 1970 killed over 600,000 people in
Hurricane Mitch killed over 11,000 in central America in
central America in October 1998.
Tropical cyclone
generic term for low pressure system that forms over tropical or subtropical areas
Tropical disturbance
Tropical weather system with organized convection, originating in tropics or subtropics, having a non-frontal migratory nature, and maintaining its identity for 24 hours or more
There is no closed circulation.
Tropical Depression
tropical cyclone in which max. sustained surface wind speeds are 38MPH or less. There is a closed circulation.
Tropical Storm
Tropical cyclone in which max. sustained surface winds are greater than 38MPH but less than 74MPH.
T.S. Katrina
A tropical cyclone in which max. sustained surface winds (using the 1 minute average) is 74MPH or greater.
The term hurricane is used for
N.H. Tropical cyclones east of the International Dateline to the Greenwich Meridian.
The term Typhoon is used for
North Pacific tropical cyclones north of the Equator and west of the International Dateline.
The term "cyclone" is used for
South Pacific tropical cyclones.
Super Typhoons
if surface wind speeds reach 150MPH or greater.
Naming storms
- When a tropical depression forms from a disturbance, it is given a number (first, second, etc...) tropical cyclone of the season.(Ex: T.D. 1)
- When the T.D. strengthens to a tropical storm, they are given a name.
Recipe to form hurricanes: 6 things needed
- Sea surface temps of 80F(26.5C) or higher and relatively deep layer of warm water.
- Conditional instability through deep layer in the troposphere.
- Moist air in the mid-troposphere (500mb).
- Weak vertical wind shear above the newly forming tropical cyclone.
- A forming location at least 5 degrees latitude away from the equator.
- A source of cyclonic spin in the lower troposphere.
Even though Atlantic hurricane season is June 1-Nov. 30, the peak months are...
August, September, and October.
Hurricane season peak occurs during second week of September because...
sea surface temperatures are historically at their highest.
Conditional instability
high dew points at lower levels means net condensation occurs after a short ascent.
Mid-tropospheric (500mb) moisture
When a newly forming tropical cyclone mixes dry air in at mid-levels, it enhances evaporative cooling so parcels become more negatively buoyant.
- This causes stronger downdrafts which bring cooler, drier air down which tends to stabilize lower layers.
Weak vertical wind shear
to develop and sustain hurricanes, both directional and speed shear should be light.
For tropical circulations to form
the coriolis effect must be strong enough to deflect the air to the right.
center of the hurricane with relatively light winds.
- inward rush of warm/moist air turns upward and ascends into a ring of cumulonimbus towers. The eyewall is a doughnut shaped wall of intense convective activity surrounding center of the storm.
- Strongest pressure gradients and thus strongest winds occur here.
- Heavy rains occur here as well.
Spiral bands
-arcing lines of showers and thunderstorms peeling away from the hurricane.
-Severe weather often occurs in these bands.
-Strong convergence areas act like fronts.
Storm surge
- Caused by winds piling up water as the hurricane approaches land
- most devastating damage in coastal zone.
- Responsible for 90% of all hurricane related deaths.
- Caused the levees to break in New Orleans with Katrina.
-Worst storm surge occurs in right front quadrant with respect to movement.
Wind damage
Very strong winds occur in the eyewall, particularly in a hurricane's right front quadrant.
- Hurricane Wilma in Oct. 2005
last category 5 hurricane to hit the U.S. Coast. In August 1992
Hurricane Andrew
Inland flooding
Hurricanes weaken rapidly as they move inland but remnants can still cause flooding rains to areas well away from coasts.
occur typically when hurricane makes landfall and are typically in the right front quadrant of the storm.
Hurricane watch
issued for coastal areas where there is a threat of hurricane conditions within 36 hours.
Hurricane warning
when hurricane conditions are expected in 24 hours or less.
Hurricane Katrina (once a category 5 hurricane weakened to a category 3 by the time it made landfall.)
- Killed 1836 people
- Cost more than $90 billion in damage.
- Destroyed much of New Orleans.
- A devastating hurricane strike was predicted years in advance by various scientists since a good portion of New Orleans is below sea level.
-Aging and neglected levee system and a slow response following the disaster resulted in the high loss of life and damage. Many residents did not heed initial warnings to evacuate, putting a severe strain on rescue operations.
- Ultimately 80 percent of New Orleans and large portions of nearby parishes became flooded, and the floodwaters did not recede for weeks.
Hurricane Sandy Oct 2012
- Hurricane that merged into massive extratropical cyclone.
- 286 deaths in seven countries.
- $68 billion damage (surpassed by Katrina).
- After wreaking havoc in Cuba and the Bahamas, Sandy moved north eventually making landfall just north of Atlantic City, New Jersey.
- Major storm surge in coastal New Jersey and Long Island (right front quadrant).
Super Typhoon Haiyan Nov. 2013
- Deadliest Typhoon in Philippines history killing nearly 6000 people.
- Strongest storm ever recorded at landfall (196 MPH).
4th strongest storm ever based on wind speeds.
- Most fatalities were associated with storm surge, but many due to destruction from high winds as well.
Floods are the
#1 weather related cause of property damage in the U.S. and #2 weather related cause of deaths in the world.
geographic area that drains into a river or stream.
height of a river's water surface.
Flood stage
when river rises to a level where it will flood property or farmland.
land that has historically been inundated by the river's floodwaters.
an embankment either naturally created or artificially created to prohibit flow of water onto a floodplain.
Weather factors that determine duration and intensity of floods
- Intensity, duration, and number of rain events that occur in a region.
- Size of rainfall area and its orientation and movement with respect to a river drainage basin.
- Snowmelt, river ice jams, and saturation level of the soil (from previous rains).
Non-weather related factors that determine duration and intensity of floods
- Levees and dams and their effect on drainage.
- Topography (could vary from wide plains to narrow canyons.
- Tsunami.
FEMA (Federal Emergency Management Agency)
enforces local floodplain ordinances pertaining to new and existing development.
- Reduces flood costs by an estimated $1 billion per year.
Widespread Floods
Occur when a large amount of rain falls over a watershed for many days.
Great Mississippi Flood of 1993
- Many "warm side" thunderstorm events occurred in early summer over Upper Mississippi valley.
- Estimated 500 year flood occurrence.
- River in upper basin raised to extreme heights.
- Numerous levee breaches.
- Economic losses $15-20 Billion.
- 30,000 square miles flooded.
"Cold side" weather pattern leading to Widespread flooding
Warm, moist air overruns slow moving or stationary fronts.
"Warm side" weather pattern leading to Widespread flooding.
Clusters of lines of thunderstorms form on warm side of nearly stationary front and move slowing along the front.
Cold side flooding case: Feb. 13-17, 1989
- Some areas in Kentucky received over 13 inches of rain.
- $50 million in economic losses.
- Worst flooding in Appalachian region of eastern Kentucky where water was channeled into valleys enhancing the flooding.
Widespread Flooding compounded by snowmelt
- Rapid melting of heavy snow pack combined with heavy spring rains over frozen ground.
- Leads to massive runoff of water.
- Problem can be compounded by ice jams on rivers.
April 1997 Red River Flood: heavy rains/snowmelt/ice jams.
Several blizzards in 1996-1997 lead to heavy snow pack over Minnesota and Dakotas.
Flooding cleanup-who's responsible?
-Sandbags are used to reinforce levees during widespread flooding events.
- Currently no federal regulations govern this. They ultimately end up in landfills as hazardous materials.
- FEMA has moved thousands of homes/businesses out of floodplains. Government buys floodplain land and converts it to wetland.
Drought is associated with
lack of rain and reduced water supply.
- Drought leads to more deaths worldwide than any other weather phenomenon.
-Spring and summer are key seasons for drought to develop east of the Rockies.
-Winter is the key season for drought to develop in the West.
Meteorological drought
an unusually long period of below normal precipitation.
Hydrological drought
stream and groundwater levels are below normal for an area.
Agricultural drought
period of deficient moisture in the soil layers from which crops and plants draw their water.
Socioeconomic drought
when the moisture shortage is sufficiently large that it impacts people.
Palmer Drought Severity Index (PDSI)
measures moisture deficiency standard to local climate conditions.
Crop Moisture Index
measures moisture in the crop-rooting zone.
U.S. Drought Monitor
Blends different drought indices into a single map published every week.
Drought of 1988
- Affected southern Appalachians/Midwest/northern Plains.
- After wet winter, drought set in during the 1988 spring.
- Less than half the normal precipitation fell during growing season over corn belt.
- Only 3 other growing seasons' months had less rainfall, all during the Dust Bowl years.
Drought of the 1950s
Entire period was not drought. Instead prolonged periods of drought with intermittent periods of normal or above normal precipitation.
1930s Dust Bowl Drought
"Greatest disaster in American history due to weather factors".
Drought was made worse by agricultural, social, and economic factors including its coincidence with the Great Depression.
Heat Wave refers to
an occurrence of unusually high temperatures for a particular region during the warm season.

All time U.S. maximum temperature: 134F Death Valley, Ca in 1913

All time world maximum temperature: 136F El Azizia, Libya in 1922
the number 1 cause of weather related deaths is
heat waves.
Measures of heat stress is
a function of RH or dew point.
The Heat Index
a measure of the apparent temperature, taking into account the air temperature, relative humidity, radiant energy, and wind speed.
Heat Advisory
when a certain threshold of the Heat index is expected to be reached or has been present for 2 or more consecutive days.
Excessive Heat Warning
issued when prolonged periods of a high Heat Index are expected or an extremely high Index is expected for a single day.
Strong surface heating
Occurs when skies are cloud-free.
Urban heat island effect
Asphalt and concrete store greater amounts of heat during the day. This heat is then released into the air at night, keeping minimum temperatures higher than in rural areas.
July 1995 Heat Wave: Chicago and the Midwest
- Short but deadly Heat Wave: July 12th-15th
- 500-1000 deaths attributed. Range is large because heat can aggravate pre-existing illnesses.
- Most deaths occurred in Chicago.
- Prompted better warnings and response systems in major cities.
1930s Dust Bowl Heat Waves
- Hottest decade of the 20th century.
- As opposed to the high dew point scenario of the 1995 - Heat Wave, the 1930s Heat Waves were more of a "dry heat" nature.
- More widespread geographically than 1995.
1936 U.S. Heat Wave worst in the 20th century.