Weather 250

Clouds, Precipitation, Storms

Clouds

• Clouds are “water containers”

• Pressure, temperature, moisture and dust are the main ingredients

• The cooler the air, the lower the clouds

• The less the moisture, the smaller the clouds

Clouds and Height

• Three types of clouds

• Stratus-low• Cumulus-mid level• Cirrus-high• All the other parts of

the name signify shape and form

Cloud Gallery

Cloud Gallery 2

How does this relate to weather systems?

• The closer the front, the lower the clouds• As it approaches the clouds get more vertical

What goes up, must come down

How does it form?

• There are typically 1000 condensation nuclei in one cubic centimeter

• Temperature controls the type of precipitation• The exception is hail and it depends on convection

currents in the cloud

What about Hail?

• Hail can range in size from sand grain to softball size

• Accompany cold fronts• Can be associated with

tornadoes or thunderstorms

• Indications of severe weather

When Storms get big

Bang and Boom: thunder

• Electricity in the air• Hotter than the

surface of the Sun• Discharge of

positive and negative charges

How do thunderheads form?

• Thunderheads are called SuperCells

• Large Convection Cells

Hurricanes vs. Tornadoes

• Hurricanes are larger storms 100 km or larger• Hurricanes are basically large rain storms• Hurricanes are warm front products• Tornadoes are cold front products• Hurricanes can be sustained over a month/tornadoes are short events

about an hour• Wet hurricanes/dry tornadoes

Measurement of Hurricanes and Tornadoes

Saffir/Simpson Hurricane Scale

CATEGORY Winds & Effects Tidal Surge1 74-95 mph (64-82 kt) 4-5 ft No real damage to building structures. Damage primarily to unanchoredmobile homes, shrubbery, and trees. Also, some coastal flooding and minor pierdamage.

2 96-110 mph(83-95 kt) 6-8 ft Some roofing material, door, and window damage. Considerable damageto vegetation, mobile homes, etc. Flooding damages piers and small craft inunprotected moorings may break their moorings.

3 111-130 mph(96-113 kt) 9-12 ft Some structural damage to small residences and utility buildings, with aminor amount of curtainwall failures. Mobile homes are destroyed. Flooding nearthe coast destroys smaller structures with larger structures damaged by floatingdebris. Terrain may be flooded well inland.

4 131-155 mph(114-135 kt) 13-18 ft More extensive curtainwall failures with some complete roof structurefailure on small residences. Major erosion of beach areas. Terrain may beflooded well inland. 5 155 mph+(135+ kt) 18 ft + Complete roof failure on many residences and industrial buildings. Somecomplete building failures with small utility buildings blown over or away.Flooding causes major damage to lower floors of all structures near theshoreline. Massive evacuation of residential areas may be required.

FUJITA SCALE FOR TORNADOES

(FO) Gale Tornado (40 - 72 mph)Light damage: some damage to chimneys, breaks branches off trees, pushesover shallow-rooted trees, and damages sign boards.

(F1) Moderate Tornado (73 - 112 mph)Moderate damage: The lower limit (73 mph) is the beginning of hurricane windspeed, peels surfaces of roofs, mobile homes pushed off foundations oroverturned, and moving autos pushed off roads.

(F2) Significant Tornado (112 - 157 mph)Considerable damage: Roofs torn off the frames of houses, mobile homesdemolished, boxcars pushed over, large trees snapped or uprooted, and heavycars lifted off ground and thrown

(F3) Severe Tornado (158 - 206 mph)Severe damage: Roofs and some walls torn off well-constructed houses, trainsoverturned, most trees in forest uprooted, and heavy cars lifted off ground andthrown.

(F4) Devastating Tornado (207 - 260 mph)Devastating damage: Well-constructed houses leveled, structures blown offweak foundations, and cars and other large objects thrown about.

(F5) Incredible Tornado (261 - 318 mph)Incredible damage: Strong frame houses are lifted off foundations and carried aconsiderable distance and disintegrated, automobile sized missiles fly throughthe air in excess of 100 meters, and trees debarked.

(F6+) Inconceivable Tornado (319 - 379 mph)The maximum wind speed of tornadoes is not expected to reach the F6 windspeeds.

Hurricane Gallery

Hurricane HistoryU.S. Hurricanes strikes by State 1900 – 1996

STATE Hurricane Category 1 2 3 4 5 All Major

Florida 17 16 17 6 1 57 24Tex as 12 9 9 6 0 36 15Louisiana 8 5 8 3 1 27 14Mississippi 1 1 5 0 1 8 6Alabama 4 1 5 0 0 10 5Georgia 1 4 0 0 0 5 0South Carolina 6 4 2 2 0 14 4North Carolina 10 4 10 1 0 25 11Virginia 2 1 1 0 0 4 1New York 3 1 5 0 0 9 5Connecticut 2 3 3 0 0 8 3Rhode Island 0 2 3 0 0 5 3Massachusetts 2 2 2 0 0 6 2New Hampshire 1 1 0 0 0 2 0Maine 5 0 0 0 0 5 0

• Over 35 - Red• 25-35 - Orange• 10-25 - Yellow• 8-10 - Green• <8 - Blue• 0 - White

Hurricane tracks 1954-2004

• These are only Hurricanes - category 1-5• In 2004 and 2005 four major hurricanes hit Florida• Massachusetts has had two major hurricanes in the

last twenty years

Tornado Occurrences

• Tornadoes are not always large• Tornadoes often come in clusters of one or

more

Tornado Gallery

Tornado Gallery 2

Nor’easter Feb 12-13 2006

Nor’easters

• Uniquely northeast storm• Generally two merged

lows• Can last for days• Can be hurricane-like• Not always a snow event• Perfect Storm 1991• February 1978• March 1993• January 2005