Meteorology 1050 Exam 4 Aldrich

Weather Forecasting

Predicting how the present state of the atmosphere will change over a period of time

Nowcasting

Present - 6 hours

Short Range Forecasting

1 - 3 Days

Medium Range Forecasting

3 - 5 days

Long Range Forecasting

5 - 10 days

Extended Forecasting

Up to 90 days

Persistence Forecasting Tech.

What happened yesterday will likely happen today

-Accuracy will depend on the weather patterns and your location

Climatology Forecasting Technique

The long term average of weather conditions are used to predict weather for a given day.

While weather does change a lot, climatology can be accurate fairly often.

Trend Method Forecasting Technique

Assumes that the speed and direction of a weather system will not change.

-Based on nearby observations

Analogue Forecasting Technique

Find a date in the past where the weather maps look exactly as it does now

-An okay method as patterns are repeatable, but exact evolution is not always the same

-Works best with severe/winter weather

Numerical Modeling Technique

Numerical equations exist to calculate the future state of certain variables

-Pressure, Temp., Winds, Humidity, Clouds, Precip.

-Predictions come from computer models

Computer Models

Work by dividing the atm. into 3D boxes called grids.

-The point in the middle is called the grid point

-All the mathematical equations are solved at each grid point

Station Model

A "cluster" of current weather data for one particular weather reporting site.

Thunderstorms

Must contain lightning or thunder

-Strong gusty winds

-Precipitation

-Hail - All sizes

Ordinary (pop-up) Thunderstorm

Most common type of thunderstorm

Form in areas with weak wind shear

Self-Extinguishing

-They actually "kill" themselves with colder, downdraft air

Short lifetime

-Almost always under an hour

Multi-Cell Thunderstorm

Clusters of t-storms that form in different stages in one area

The updrafts are stronger and support more continuous convection than a "pop-up" storm

Squall-Line Thunderstorm

Organized line of thunderstorms

-The most intense rainfall is at the leading edge, then tapers off behind the linear

-May form along or ahead of a cold front

-If a portion of the leading edge jumps out ahead of the rest of the line, it's called a bow echo and likely will produce damaging winds

-Gusty winds huge downdrafts

-Heavy rain, winds and hail

Supercell Thunderstorm

Some of the most dangerous storms

-A t-storm with a rotating updraft

-The rotating updraft is the difference between a multi-cell storm and supercell storm

-The most organized and long-lived type of t-storm

Severe Thunderstorm

Winds greater than 58mph

Hail larger than 1"

Presence of a tornado or possible rotation

Flanking Line (Beaver Tail)

Updraft/food supply for the mesocyclone

Rear-Flank Downdraft

Rear portion of the mesocyclone's downdraft

Storm Inflow "Suck Zone"

Influx of moisture rich air into a mesocyclone

Mesoscale Convection Systems

Large grouping of multiple storms that move together and last for hours

-Circular

->Covers many states

->Can produce severe weather

-Linear

->Very strong winds

->isolated, quick tornadoes

Gust Front

Leading edge of cold air coming from a large, severe thunderstorm.

"Shelf Cloud"

Microburst

A very localized column of sinking air, producing damaging straight line winds at the surface.

Usually located in a strong downdraft area and produces extremely strong straight-line winds.

Derechos

A widespread and long-lived, violent windstorm that is associated with a fast-moving band of severe t-storms usually taking the form of a bow echo.

Usually associated with a very buoyant, warm air mass.

Occur most often in the summer

Lightning

A discharge of electricity in a mature thunderstorm

-Heats the air over 50,000 degrees Fahrenheit

-5 times hotter than the sun

How does lightning work?

Charge separation occurs in the cloud.

Negative charges are found near the cloud base.

Positive charges are higher up in the cloud and at the ground.

The buildup of negative charges at the cloud base will eventually overcome the insulation of the air and "electricity" is created.

Stepped Leader

Initial "spark" of lightning leaves the clouds base.

Very faint and almost invisible

As it approaches the ground, a positive charge starts upward and meets the negative charges

Return Stroke

The upward flow of current that we see as lightning

-This process happens quick. Around 1/10000 of a second

Sheet Lightning

Lightning that occurs within a cloud, and is obscured by other clouds

It appears as a luminous white sheet

Heat Lightning

Distant lightning that illuminates the sky, but is too far away for thunder to be heard.

Has nothing to do with "summer-time heat"

Ball Lightning

A luminous sphere that appears to "float" in the air, or zip around for a few seconds

Ribbon Lightning

When the wind blows a stepped leader horizontally

Thunder

Heating and expansion of the air creates a shock wave.

Sounds like a crack followed by a bang when we're close to the lightning strike.

Rumbles when we're farther away because the sound bounces off various surfaces before reaching the ear

Tornadoes

A rapidly rotating column of air whose rotation reaches the ground.

Characteristics:

Diameter: 100yards

Path length: 2 - 4 miles

Lifespan: 5 to 10 min.

Wind: 80 to 300 mph

Forward Speed 30 mph

Waterspouts

Similar to tornadoes, only over water and with much slower speeds.

Occur in coastal waters and are associated with weal convection t-stroms

Funnel Cloud

A funnel-shaped cloud of condensed water droplets, associated with a rotating column of air.

Extend from the base of a cloud but do not reach the ground

Tornado Dust-Whirl Stage

Dust swirling upward form the grounds and grows towards the funnel cloud in the sky

Tornado Organizing Stage

Downward extend of funnel and "connection" with dust-whirl on the ground

Tornado Mature Stage

Tornado on the ground

Tornado Decaying Stage (Roping Out)

Stretched into a thin funnel shape -rope

Tornado "Time Schedule"

Most occur in the late afternoon due to daytime heating.

Most common month are March, April, May, June and July

Mesocyclone

A large rotating vortex inside a supercell t-storm that will sometimes produce tornadoes

Suction Vortices

Stronger winds than the overall tornado that produces significant damage

-Mini tornadoes inside the main tornado

Doppler Radar

A specialized weather radar that "sees" wind (velocity) and precipitation (reflectivity).

Red: Wind blowing away from the radar

Green: Wind blowing towards the radar

Measuring the Strength of Tornadoes

Meteorologist examine the damage done by tornadoes and the winds are estimated based on damage produced

The Fujita Scale

EF-0 Weak 65-85mph

EF-1 Moderate 86-110 mph

EF-2 Significant 111-135 mph

EF-3 Severe 136-165 mph

EF-4 Devastating 166-199 mph

EF-5 Incredible 200 mph

EF-0 to EF-1 74%

EF-2 to EF-3 25%

EF-4 to EF-5 1%

Tornado Direction and Duration

Most tornadoes travel form southwest to northeast.

Some tornadoes change direction and path

-Some have even traveled backward and made complete circles

Warning Signs

Strong persistent rotation in clouds.

Circulating dust and debris.

Hail and then rapid quietness.

A very loud roar with heavy rain

Tornado Watch

Watch out for t-storms that could produce tornadoes

Thunderstorm Watch

Watch out for severe t-storms

Tornado Warning

A tornado is occurring now - or soon will

Thunderstorm Warning

Severe thunderstorms are occurring now - or soon will.

Thickness charts help forecasters

​Predict whether falling precipitation will be rain or snow.

A weather warning indicates that

Hazardous weather is either imminent or occurring within the forecast area.

The ASOS system is designed to provide nearly continuous information about wind, temperature, pressure, cloud-base height, and runway visibility at various airports.

True

False

TRUE

​____ tend to steer the movement of surface pressure systems.

Winds aloft

There are many techniques involved in creating a weather forecast. Which of the following do not belong?

Numerical Modeling, Persistence, Farmer's Almanac

According to the National Weather Service, the subjective term "fair" implies a rather pleasant weather situation.

True

False

TRUE

Seasonal forecasts make specific predictions of rain or snow. (In this case, specific refers to exact amounts of rain/snow and on what dates)

True

False

FALSE

An analysis is a

Surface or upper-level chart that interprets the present weather patterns.

A blocking high is a

​high pressure system and accompanying ridge that persists in the same location for many days.

For ____ to occur, separate regions containing opposite electrical charges must exist within a cumulonimbus cloud.

Lightning

Squall lines generally do not form

Behind a cold front

The wind shear associated with several major airline crashes is believed to have been caused by​

Microburst

An ordinary thunderstorm​:

​is a scattered/isolated storm and normally not severe.

Large hail is more common in Kansas than in Florida.​

True

False

TRUE

Distant lightning that is so far away you cannot hear the thunder is called​

heat lightning

The most likely time for an ordinary thunderstorm to form is​

Late Afternoon

Thunderstorms are a common phenomenon in areas dominated by subtropical highs.

FALSE

Opening windows during a tornado decreases the pressure on the opposite wall and therefore decreases the chances that the building will collapse.​

FALSE

To help distinguish a storm's air motions, a Doppler radar can display ____​

wind velocities in color

Tornadoes have occurred in every state, including Alaska and Hawaii.​

True

False

TRUE

According to the Enhanced Fujita Scale, an ____ tornado causes only minimal damage, whereas an ____ completely demolishes a house and sweeps it off its foundation.​

EF0; EF5

To an observer on the ground, the first sign that a supercell may give birth to a tornado is the sight of ____.​

​rotating clouds at the base of the storm

Damage from a tornado is normally most severe during the ____ stage.​

​mature

If a downdraft is too ____, it may inhibit the lifting needed for tornado formation.​

cold and strong