D generally clear skies are replaced by cloudiness

d) Generally clear skies are replaced by cloudiness and precipitation at front.
D. Lifecycle
1. Cyclogenesis

a) Origin to maturity typically takes 3-6 days, and another 3-6 days to dissipate.
b) Cyclogenesis—birth of cyclones.
c) Most common cause is likely upper-air conditions near polar-front jet stream.
d) Most begin as waves along polar front.
e) Often bring heavy rain or snowstorms to NE U.S. and SE Canada.
2. Occlusion
a) After cyclonic circulation is well developed, occlusion begins.
b) After occluded front is fully developed, cyclone dissipates.
c) Occlusion is the death of a midlatitude cyclone.
VI. Midlatitude Anticyclones
A. Midlatitude anticyclone—large migratory midlatitude H-pressure cell.
B. Characteristics
1. Typically larger than a midlatitude cyclone, but also moves W to E.
2. Travels at same rate, or little slower, than midlatitude cyclone.
a) Prone to stagnate or remain over same region (while cyclones do not).
(1) Can cause concentration of air pollutants.
(2) Los Angeles, CA; you often hear about smog in LA, which is result of air
pollution and anticyclonic conditions
3. Cyclones and anticyclones alternate with one another in an irregular sequence.
VII. Nor’easters
A. Nor’easter: strong area of L pressure, named for winds that blow in from NE.
B. Nor’easters form between October and April, when cold air & moisture are plentiful.
1 . There are 2 components:
a. Gulf Stream L-pressure (c-clockwise winds)
b. Arctic H-pressure (clockwise winds)
2. 2 Types of Nor’easters:
a. Offshore forming – storms in news because dump snow on metro areas
like Washington, D.C., NYC, Boston, etc;
b. Onshore forming – less exciting; move west of major cities; produce rain
3. Nor’easters are notorious for producing heavy snow, rain, oversized waves/storm
surge, beach erosion,
structural damage, cold temperatures, winds up to 50mph
4. Famous Nor’easters:
a) Blizzard of 1888 – killed 400 people; 200 boats grounded and 100 sailors died;
snow drifts up to 50’ high, 40-50” of snow and winds up to 50mph; sometimes
called the Great White Hurricane; transportation issues initiated creation of NYC
underground subway; $25 million damage
b) Ash Wednesday Storm of March 7, 1962 – 1 of 20 worst storms in U.S. in 20 th c.;
killed 40 people; AKA Five High storm b/c it lasted through 5 high tides; called
Ash Wed. storm because worst damages sustained that day; waves reached 40’
and winds were over 60mph
c) Groundhog Gale of 1976 –max winds up to 102mph (Cat. 2 hurricane); Bangor,
ME – water rose 12’ in 15 min; Oswego, NY got 56” of lake-effect snow in 2 days.
d) Blizzard of 1978 – winds up to 65mph; snowed for 36 hrs straight; snow drifts up
to 15’; 54 died including child who disappeared in snow only feet from his front
door, but they had to wait until snow melted to find him
e) Halloween Storm of 1991 –meteorological abnormality; nor’easter met up with
Hurricane Grace remnants; storm moved backward; large waves Maine to Puerto
Rico; winds over 100mph; 50’ mean wave height; rogue waves over 100’; 12
deaths (6 on Andrea Gail - The Perfect Storm ); almost $1 billion in damage;