Temperatures and Temperature Patterns
- Measured in: Fahrenheit, Celsius, Kelvin (no negatives)
- Should be above ground (5ft, ~1.5 meters), natural surface, and shaded
- Normal ≤ 30years worth of data
Influences/Factors: LOCALS
- Latitudes
o Variations in solar angle and day length depend on latitude
o Increased latitude = increased range
o Related to net radiation
§ Net gain – tropics and subtropics
§ Net loss – poleward of 38°
- Ocean currents
o Warm vs. cold
- Cloud cover
o Daily range is dependent on humidity and cloudiness (less clouds = more range; more clouds = less range)
- Altitude
o Decrease temperature, air pressure, and ______
o On average, temp decreases at 6.5°C/km in the troposphere. Therefore, it’s expected to be cooler at greater heights.
- Land & water, proximity to water
- Surface type
2/12/14
Thunderstorms and Severe Weather
Wedge tornado = a tornado that is wider than it is tall
Thunderstorm = a localized storm produced by a cumulonimbus cloud and always accompanied by lightning and thunder
Thunderstorms are most common in Florida because it is a peninsula.
Ingredients for Thunderstorms
Moisture
- Typical source is from the large bodies of water (Atlantic ocean, Pacific ocean, Gulf of Mexico)
- Measurements: dewpoint (TD) and relative humidity (RH)
Lift
- Topography
- 
Air density
- Drylines
- Outflow boundaries
Instability
- Warm moist air at the surface and cold air above that
- 
CAPE = potential energy of a storm
- Warm air rises
Severe Thunderstorms:
To be severe, you have to have...
- Winds >= 58mph
- Hail 1” +
- Tornado
Stages of Thunderstorm Development
- Cumulus Stage
o Dominated by updraft
o Bergeron builds precipitation supported by updraft
- Mature Stage
o Side-by-side updraft and downdraft
o Downdraft has heavy rainfall, cold pool
o Most severe stage
- Dissipating Stage
o Downdrafts dominate
o Light precipitation
Severe Weather:
- 1” hail
- Wind gusts ≥ 58mph
- Tornado
Types of Thunderstorms
- Single Cell (Air Mass)
o Commonly form in warm mT air masses during the summer
o Short lived (less than 30mins)
o Weak
o Rarely produce severe weather
- Multicellular
o Single cells lumped together
o Squall line forms ahead of a cold front as a line of thunderstorms
o MSC – Mesoscale Convective Systems
§ Thunderstorm complex about the size of the state of Iowa
§ Flood and severe weather producers
§ Tend to dominate summer months in U.S.
o Often more intense than single-cells
- Squall-line
- Supercell
o Rotating updraft
o Speed + directional shear
o Produce damaging winds, grapefruit size hail, and tornadoes
Lightning
- Electrical discharge between 2 charge centers
- Can be within a cloud
- Travels at the speed of sound (1000ft/s, 1 mile every 5 seconds)
- Distance = time(sec)/5
- Average temp is hotter than the surface of the sun
Bow Echoes and Derechos
- Strong winds and downdrafts
- Last a long time and cover large areas
Hail
- Ice
- Forms by recycling up into the updraft
Tornadoes
- Violently rotating column of air descending from a thunderstorm and in contact with the ground
- Most are brief, lasting only a few minutes. Sometimes last for more than an hour
- On average 100 people a year are killed by tornadoes (30yrs average of 65)
- 45% of all fatalities occurred in mobile homes
- Most rotate counter-clockwise
- Typical diameter is 300-2000 ft
- Usually move SW to NE
- Winds rage 75-250mph
- Can consist of one or multiple vortices
- Fujita Intensity Scale
Why does the south have a disproportionate number of fatalities?
- More tornadoes during nighttime hours
o between sunset and sunrise
o more difficult to spot
o days are shorter à more likely to occur at night
- More forest cover
- Strong tornadoes
- Storm move faster (stronger wind shear)
- Lower base clouds
- Higher population density
- Lack of a focus on “tornado season”
o Complacency
- More mobile homes/weak frame housing structure (reduce visibility)
- Other
o Education
o Coping styles
o Warning distribution systems
Instability = CAPE (has the potential to be unstable) more CAPE, mean more instability
Lift = convergence, low pressure, mountains
Wind Shear = speed/direction (between0 & 6km if >= 35knots+ you’re going to get supercells)
Floods
Tropical Weather
- Occurs between 0 and 23.5 degrees N & S
- Differs from midlatitue weather:
o No major air mass differences (lots of heat & humidity)
o Easterly winds
o Not much temperature differences
Hurricane
- An intense storm of tropical origin with sustained winds exceeding 74mph
- Conditions for development
o >27C or 80F (june through November)
o Convergence
o Forms 5-20degrees latitude
- Will not form 0-5degrees N & S of equator
- Cannot pass through the hemisphere
- DO NOT LIKE WIND SHEAR
- Stages of development
1. Tropical disturbance
2. Tropical depression
3. Tropical storm
4. Hurricane
- Weakening
o Move over cooler water
o Move onto land
o Move into very strong wind shear
- Official season June – November
- Peaks: Aug, Sep, Oct (80% of Hurricanes)
- Saffir-Simpson Intensity Scale
- Hazards
o High wind speed
o Flooding
o Storm surge
o Tornadoes
- Most destructive side is the right (wind speed, storm surge tornadoes)
- WATCH issued 24-48hrs prior to landfall
- WARNING issued within 24hrs prior to landfall
