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Title: Marine Weather Course


1
Marine Weather Course
  • NOAA National Weather Service
  • Baltimore/Washington Forecast Office

2
Part I Outline
  • National Weather Service Introduction
  • Baltimore/Washington Forecast Office Operations
    and Marine Area
  • Key Marine Products and Hazards
  • Marine Observation and Forecast Information
  • Marine Safety
  • Marine Reporting

3
NWS Service Delivery Facilities
4
WFO Area of Responsibility
Region is prone to all weather hazards
  • Maryland
  • 13 Counties
  • City of Baltimore
  • West Virginia
  • 8 Counties
  • Virginia
  • 22 Counties
  • 11 independent cities
  • District of Columbia
  • River Basins
  • Potomac
  • Shenandoah
  • Rappahannock
  • Marine Area
  • Tidal Potomac River
  • MD Chesapeake Bay

Approximately 27,000 square miles Serving 9
Million People
5
Operations Services
Spruce Knob, Pendleton County, WV Elevation
4,861 feet
  • Convective
  • - Tornado Severe Thunderstorm
  • Tropical Systems
  • - Hurricanes Tropical Storms
  • Non-Precipitable
  • - Heat Waves
  • - High Wind
  • - Wind Chill/Excessive Cold
  • Hydrological
  • - Flash Floods
  • - River Floods
  • - Small Stream Tributaries
  • Winter Storms
  • Coastal Flooding
  • Wildfire (Red Flag)

6
Operations Services (cont.)
  • Forecasts
  • - Public
  • - Marine
  • - Aviation
  • - Fire Weather
  • - River
  • Support Services
  • - Homeland Security
  • Data Collection
  • - Climate
  • - Cooperative Observers

7
Marine Area
8
Key Marine Products
  • Coastal Waters Forecast (CWFLWX)
  • Special Marine Warnings (SMWLWX)
  • Marine Weather Statements (MWSLWX)
  • Nowcasts (NOWLWX)

9
Coastal Waters Forecast
  • Issued a minimum of 4 times / day
  • Amendments issued as necessary
  • Each CWF goes out 5 days, with each period
    covering 12 hours
  • Used by small pleasure boaters to large
    commercial transport ships.

10
Coastal Waters Forecast
  • Elements
  • Synopsis Short, concise
  • Headlines of long duration hazards Advisories,
    Watches, Warnings
  • Wind from 8 compass points, in knots (kt)
  • Waves wave heights, in feet (ft)
  • Weather thunderstorms, rain, snow and fog
    (significant visibility reduction)

11
Long Duration Hazards
  • Small Craft Advisory (Tidal Potomac and
    Chesapeake Bay) -- the following conditions are
    occurring or expected to begin within the first 3
    forecast periods
  • Sustained winds 18-33 kt
  • Frequent gusts 18-33 kt
  • (frequent refers to lasting gt 2 hours)
  • Waves 4 ft

12
Long Duration Hazards
  • Gale Warning (Tidal Potomac and Chesapeake Bay)
    -- the following conditions are occurring or
    expected to begin within the first 3 forecast
    periods
  • Sustained winds 34-47 kt
  • Frequent gusts 34-47 kt

13
Long Duration Hazards
  • Storm Warning (Tidal Potomac and Chesapeake Bay)
    -- the following conditions are occurring or
    expected to begin within the first 3 forecast
    periods
  • Sustained winds 48-63 kt
  • Frequent gusts 48-63 kt

14
Long Duration Hazards
  • Hurricane Force Wind Warning (Tidal Potomac and
    Chesapeake Bay) -- the following conditions are
    occurring or expected to begin within the first 3
    forecast periods
  • Sustained winds 64 kt or greater
  • Frequent gusts 64 kt or greater
  • Not associated with a tropical system

15
Tropical Hazards
  • Tropical Watches/Warnings
  • Initiated by National Hurricane Center in Miami
  • nhc.noaa.gov
  • Tropical Storm (sustained winds 34 to 63 kt / 39
    to 73 mph)
  • Hurricane (sustained winds gt 64 kt / gt 74 mph)

Isabel, 2003
16
Convective Hazards
  • Severe Local Storm Watches
  • Initiated by Storm Prediction Center in Norman,
    OK
  • spc.noaa.gov
  • Tornado Watch
  • Severe Thunderstorm Watch

17
Coastal Waters Forecast
  • ANZ535-536-231930-
  • /X.EXT.KLWX.SC.Y.0037.051023T1200Z-051023T2200Z/
  • TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD-
  • TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND-
  • 337 AM EDT SUN OCT 23 2005
  • ...SMALL CRAFT ADVISORY NOW IN EFFECT FROM 6 AM
    EDT THIS MORNING THROUGH THIS AFTERNOON...
  • .TODAY...NW WINDS 15 TO 20 KT. WAVES 1 TO 2 FT.
  • .TONIGHT...E WINDS 5 TO 10 KT. WAVES 1 FT OR
    LESS.
  • .MON...NE WINDS 5 TO 10 KT. WAVES 1 FT OR LESS. A
    CHANCE OF
  • SHOWERS.
  • .MON NIGHT...N WINDS 10 TO 15 KT. WAVES 1 FT. A
    CHANCE OF SHOWERS.
  • .TUE...NW WINDS 15 TO 20 KT. WAVES 1 TO 2 FT.
  • .TUE NIGHT...NW WINDS 10 TO 15 KT. WAVES 1 FT.
  • .WED...W WINDS 10 TO 15 KT. WAVES 1 FT.
  • .THU...NW WINDS 5 TO 10 KT. WAVES 1 FT OR LESS.

18
Special Marine Warnings
  • Issued for potentially hazardous over-water
    weather conditions of short duration (2 hours or
    less) and producing winds speeds or gusts 34 kt
    or greater not covered by existing longer fused
    products.
  • Gusty showers/thunderstorms with winds 34 kt or
    greater
  • Waterspouts

19
Special Marine Warnings
  • BULLETIN - IMMEDIATE BROADCAST REQUESTED
  • SPECIAL MARINE WARNING
  • NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON
    DC
  • 621 PM EST SUN NOV 6 2005
  • THE NATIONAL WEATHER SERVICE IN STERLING VIRGINIA
    HAS ISSUED A
  • SPECIAL MARINE WARNING FOR...
  • CHESAPEAKE BAY NORTH OF POOLES ISLAND, MD...
  • CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY
    POINT, MD...
  • UNTIL 745 PM EST
  • AT 621 PM EST...NATIONAL WEATHER SERVICE
    DOPPLER RADAR INDICATED A CLUSTER OF GUSTY
    SHOWERS ABOUT 20 MILES WEST OF BALTIMORE
    HARBOR.... MOVING EAST AT 45 MPH. IN
    ADDITION...GUSTY WINDS ASSOCIATED WITH A COLD
    FRONT WILL PASS OVER THE WATERS JUST AFTER THE
    SHOWERS PASS THROUGH AFTER 7 PM.
  • THIS ACTIVITY WILL AFFECT THE WATERS AFFECT...
  • BALTIMORE INNER HARBOR...
  • HART MILLER ISLAND...
  • POOLES ISLAND...

20
Marine Weather Statements
  • Update/Continue Special Marine Warning
  • Expire/Cancel Special Marine Warning
  • Issued for long term sub-severe hazards lasting
    for longer than 2 hours that will impact marine
    operations

21
Marine Weather Statements
  • MARINE WEATHER STATEMENT
  • NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON
    DC
  • 1045 AM EDT SUN AUG 7 2005
  • ANZ531-071545-
  • /O.CON.KLWX.MA.W.0106.000000T0000Z-050807T1545Z/
  • 1045 AM EDT SUN AUG 7 2005
  • ...A SPECIAL MARINE WARNING CONTINUES UNTIL 1145
    AM EDT...
  • FOR THE FOLLOWING AREA...
  • CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT,
    MD
  • AT 1044 AM EDT...NATIONAL WEATHER SERVICE DOPPLER
    RADAR CONTINUED TO INDICATE A LINE OF
    THUNDERSTORMS...PRODUCING STRONG WINDS OVER 35
    KNOTS FROM CEDAR BEACH TO 9 MILES SOUTHWEST OF
    ROCK HALL...OR FROM 7 MILES WEST OF POOLES ISLAND
    TO 3 MILES NORTH OF SANDY POINT...MOVING
    NORTHEAST AT 15 MPH.
  • OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE
    NOT LIMITED TO HART MILLER ISLAND...CARROLL
    ISLAND...TOLCHESTER BEACH AND ROCKY POINT.
  • MARINERS CAN EXPECT GUSTY WINDS...HIGH
    WAVES...REDUCED VISIBILITIES...DANGEROUS
    LIGHTNING...AND HEAVY RAINS. BOATERS SHOULD SEEK
    SAFE HARBOR IMMEDIATELY...UNTIL THIS STORM
    PASSES.

22
Nowcasts
  • Issued for short term non-severe hazards but
    potentially dangerous conditions, such as with
    winds to 33 kt lasting for 2 hours or less.
  • Sometimes combined with land zones, but
    oftentimes appearing only as a marine Nowcast.

23
Nowcasts
  • SHORT TERM FORECAST
  • NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON
    DC
  • 804 AM EDT FRI OCT 21 2005
  • ANZ530gt537-DCZ001-MDZ005gt007-009gt011-013-014-016gt0
    18-VAZ041-042- 052gt057-211330-
  • ANNE ARUNDEL MD-ARLINGTON/FALLS CHURCH/ALEXANDRIA
    VA-CALVERT MD-CARROLL MD-CHARLES MD-DISTRICT OF
  • COLUMBIA DC-FAIRFAX VA-FAUQUIER VA-HARFORD
    MD-HOWARD MD-KING GEORGE VA-LOUDOUN VA-MONTGOMERY
    MD-
  • NORTHERN BALTIMORE MD-PRINCE GEORGES MD-PRINCE
    WILLIAM/MANASSAS/MANASSAS PARK VA-SOUTHERN
  • BALTIMORE MD-SPOTSYLVANIA VA-ST.MARYS MD-STAFFORD
    VA-
  • CHESAPEAKE BAY FROM DRUM POINT, MD TO SMITH
    POINT, VA-
  • CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT,
    MD-
  • CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT,
    MD-
  • CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH,
    MD-
  • CHESAPEAKE BAY NORTH OF POOLES ISLAND, MD-
  • TIDAL POTOMAC FROM COBB ISLAND, MD TO SMITH
    POINT, VA-
  • TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND,
    MD-
  • TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD, MD-
  • 804 AM EDT FRI OCT 21 2005

24
Marine Product RecapWhats Issued for the Waters?
Coastal Waters Forecast Issued four times daily(4 AM, 11 AM, 4 PM, 11 PM) 5 Day forecast Winds/Waves/Precipitation (Visibility)
NOWCAST Non-Routine, 2-3 hour duration Issued for sub-warning criteria weather Mainly precipitation trends
Marine Weather Statement Non-Routine, 2 hours duration Update/Continue Special Marine Warning Expire/Cancel Special Marine Warning Issued for long term sub-severe hazards lasting for longer than 2 hours that will impact marine operations
Special Marine Warning Non-Routine, 2 hours or less Potentially hazardous weather Showers/thunderstorms with winds 34 kt or greater Waterspouts, or large hail Sudden wind shift
25
NWS Homepage
  • weather.gov/washington
  • weather.gov/baltimore
  • Hazards highlighted on front page
  • Use point and click to view forecasts and
    specific hazard information

26
Coastal Waters Forecast
  • Coastal Waters Forecast
  • Headlines for long fused hazards listed at the
    top of the page
  • Headlines also highlighted at the top of Coastal
    Waters Forecast (Small Craft Advisory, Gale
    Warning, etc)

27
Hazardous Weather Outlook
28
Hazardous Weather Outlook
  • Alerts public to potential hazards and their
    impact
  • Potential hazards over the next 7 days
  • Marine hazards
  • Coastal hazards

29
Marine Weather Message
30
National Digital Forecast Database
  • Graphical depiction of NWS forecast elements
    through 7 days
  • Temperature
  • Weather
  • Sky Cover
  • Many more
  • Program specific sectors
  • Public
  • Marine
  • Tropical
  • Fire Weather
  • Zoom capability to the WFO level

31
National Digital Forecast Database
  • Zoomed into the Tidal Potomac and Chesapeake Bay
  • Marine specific elements highlighted
  • Winds
  • Waves
  • Weather
  • Hazards

www.weather.gov/forecasts/graphical
32
Hydrometeorological Prediction Center
  • http//www.hpc.ncep.noaa.gov/
  • Current Weather Maps and Analyses
  • Surface Pressure Charts
  • Forecast Maps of Surface Features

33
Current Surface Map
  • Isobars (lines of equal barometric pressure)
  • Low Pressure
  • High Pressure
  • Fronts
  • Troughs
  • Updated every few hours

34
Current Radar
  • Accessible through HPC site as a larger regional
    loop OR
  • Local radar viewed at Baltimore/Washington site
  • Detects rain, snow, thunderstorms

35
Current Marine Observations
  • National Data Buoy Center (NDBC)
  • http//www.ndbc.noaa.gov/
  • Contains NOAA/NWS owned observation platforms

36
Current Marine Observations
  • Chesapeake Bay Interpretive Buoy System (CBIBS)
  • NOAA owned/funded
  • Includes buoys which are placed along the
    historic John Smith Trail

37
Current Marine Observations
  • NOAA Tides and Currents (includes PORTS)
  • http//tidesandcurrents.noaa.gov/
  • More wind obs
  • Water level obs
  • Short term wind/water level forecasts

38
NOAA Tides and Currents
  • PORTS Physical Oceanographic Real Time System
  • Graph gives overview of past and current
  • Water levels
  • Winds
  • Pressure
  • Temperature

39
NOAA Tides and Currents
  • High resolution models
  • Forecast of winds (sustained) through 24 hours
  • Forecast of water levels through 24 hours

40
Wind-Wave Correlations
  • WFO Baltimore-Washington forecasts significant
    wave heights in the local Coastal Waters Forecast
    (CWF) product.
  • Significant wave heights are the average heights
    (trough to crest) of the one-third highest waves.
  • For simplicity, significant wave heights are
    termed waves in the WFO Baltimore-Washington CWF.

41
Marine Hazard DisseminationHow Do We Convey the
Message Today?
  • NOAA Weather Radio (NWR)
  • Tone Alarm (SMW) within a minute of issuance
  • All marine products are broadcast on NWR
  • Website (weather.gov/baltimore or
    weather.gov/washignton)
  • Colorful maps on website, click to see text
  • http/mobile.srh.noaa.gov (http-wireless)
  • Recorded Forecast (CWF only)
  • (703) 996-2200 (menu system)
  • Third parties (USCG) retransmit

42
Marine Safety
  • Before going out onto the waterBE PREPARED!!
    Check the latest weather forecasts. Sources
    include
  • NOAA Weather Radio
  • Television Media The Weather Channel or Local
    TV Stations
  • Internet, including our website at
  • WEATHER.GOV/WASHINGTON
  • WEATHER.GOV/BALTIMORE

43
Marine Safety
  • While on the waterSTAY ALERT!! Have a NOAA
    Weather Radio in your boat and continue to
    monitor the latest forecasts.
  • Pay attention to changes in marine forecasts
  • Heed any issued advisories and warnings issued
  • React appropriately to observed changes of marine
    conditions

44
Marine Safety
  • REMAIN ALERT for fast developing / approaching
    thunderstorms. Signs include
  • Dark, threatening clouds increasing in number /
    growing vertically
  • Steadily increasing winds / waves
  • Flashes of lightning
  • Heavy static heard on AM Radio

45
Marine Safety
  • When a thunderstorm approaches
  • Head for shore, if possible
  • While still in the boat, make sure to have on
    your personal flotation device and prepare for
    higher winds and waves
  • When onshore, get out of the boat and seek
    shelter immediately

46
Waterspout west of Crisfield, MD 330 PM EDT
Sunday September 10, 2006
47
  • Waterspout characteristics
  • Short-lived ( usually lt30 min.)
  • Form from small showers or cumulus congestus)
  • Move rapidly if associated with fast-moving
    shower
  • 10- to 100-feet wide move at 5 to 75 mph
  • Visible funnel extends from a few 100 ft up to
    cloud base (2000 ft over the Ches. Bay)
  • Spin either clockwise or counter-clockwise
  • Visible funnel forms from cooling of humid air
    due cooling/expansion (not by sucking the water!)
  • Are called a tornado if it makes landfall
  • Are difficult to detect by radar (little warning)
  • Most common in late summer through the fall
  • DO NOT GO NEAR THEM!!!!

48
  • Waterspout life cycle
  • Dark spot (light inner circle lt100 ft dia.
    surrounded by a larger dark area of more diffuse
    shape/edges (no visible funnel)
  • Spiral pattern alternating light/dark spiral
    bands (vortex growth)
  • Spray ring swirling annulus of sea-spray (min
    winds 50 mph)
  • Mature vortex prominent visible funnel full
    spiral pattern max winds 60-100 mph funnel
    extends to cloud base
  • Decay can occur abruptly when inflow air is cut
    off displays maximum vertical tilt

49
BAD WEATHER ON THE BAY?
  • Report your observations to the National Weather
    Service and help us to improve your Bay forecasts
    through reports of what is really happening.
  • We are interested in winds and wave height
    estimates, current weather conditions, low
    visibilities in fog, and icing.
  • Immediate reports have a direct impact on marine
    forecasts and warnings for you and your fellow
    mariners. However, even old reports are helpful
    as they can be reviewed to help improve future
    marine forecasts.
  • Call our marine report hotline at 1-800-253-7091
    or email us at lwx-report_at_noaa.gov with your
    marine reports!

50
Marine Reporting System
  • 1-800-253-7091
  • Report
  • Location (lat/lon)
  • Wind direction and speed
  • Wave height estimates
  • Weather and obstructions to visibility, if any

51
Part II Outline
  • The Atmosphere
  • The Water Cycle
  • Weather Instrumentation
  • Weather Basics
  • Clouds
  • Fronts and air masses
  • Thunderstorms
  • Lightning
  • Hurricanes

52
Earths Atmosphere
53
Layers of the Atmosphere
  • Temperature is used to define the layers of the
    atmosphere
  • The Troposphere contains all of the weather!

54
Pressure
  • The exertion of force upon a surface by a fluid
    (e.g., the atmosphere) in contact with it.
  • Meteorologists use areas of higher or lower
    pressures to forecast the weather.
  • Low pressure systems usually come with cold
    fronts. High pressure systems usually build
    behind the cold front, allowing pleasant weather
    for a day or two.

55
Measuring Pressure
  • Barometer

56
Wind
  • Air in motion relative to the earth's surface
  • Air moves in 3 dimensions

57
Observing Wind
  • Anemometer
  • Wind sock
  • Weather Vane
  • Described with both distance and speed (mph)

58
Why does the Wind Blow?
  • Pressure Gradient Force
  • Force is due to differences in pressure.
  • Tries to move air to eliminate pressure
    differences by causing air to flow from high
    pressure to low pressure

59
Why does the Wind Blow?
  • 2. Coriolis Force
  • Force is due to the earth's rotation.
  • Causes moving objects (i.e. air, planes, birds,
    etc) to deflect to the right of their motion in
    the Northern Hemisphere

60
Why does the Wind Blow?
  • 3. Friction
  • The earths surface is rough
  • Force that causes air to slow down and spiral
    into lows and out of highs.

61
Temperature
  • A measure of the internal energy that a substance
    contains.
  • This is the most measured quantity in the
    atmosphere.

62
Observing Temperature
  • Thermometer
  • Touch
  • Degrees Fahrenheit (F) or Celsius (C)

63
Dewpoint Temperature
  • Measure of the moisture content in the atmosphere
  • High Dewpoint Temperature means there is high
    water vapor content ? the air is moist or Humid

64
The Water Cycle
  • The continuous movement of water between the
    earth and the atmosphere
  • Four Important Steps are

65
The Water Cycle
  • Evaporation and Transpiration
  • Evaporation ? when a substance changes from the
    liquid phase to the gas phase
  • Water ? Water Vapor
  • Transpiration ? evaporation of water through
    plant membranes
  • How water vapor, which is needed for clouds and
    precipitation, enters the atmosphere.

66
The Water Cycle
  • Condensation
  • Condensation ? when a substance changes from the
    gas phase to the liquid phase
  • Water Vapor ? Water
  • Condensation can be observed in the atmosphere as
    clouds, fog, dew, or frost form.

67
The Water Cycle
  • 3. Precipitation
  • Precipitation ? water, either liquid or solid,
    that falls from the atmosphere to the surface.
  • Clouds are composed of millions of water droplets
    that have condensed. These water droplets grow
    into larger droplets. Eventually, the droplets
    can grow large enough that they will not be able
    to stay suspended in the cloud. When this occurs,
    they fall out of the cloud as precipitation.

68
The Water Cycle
  • 4. Ground Water and Runoff
  • Groundwater ? precipitation is absorbed into the
    ground
  • Runoff ? precipitation flow into streams
    when the ground cannot absorb any more water
  • Some of the runoff will evaporate and some of the
    groundwater will be taken in by plants and then
    transpired.

69
Precipitation
  • The process where water vapor condenses in the
    atmosphere to form water droplets that fall to
    the Earth as rain, sleet, snow, hail, etc.
  • We want to measure what type and how much!
  • The type depends on temperature.

70
Measuring Precipitation
  • Measure LIQUID precipitation in a rain gage.
  • For SOLID precipitation (snow or ice), measure
    with a ruler. You can also melt the snow or ice
    and pour it in a rain gage.

71
Weather Instruments
  • Weather Instruments tell us whats
    happeningespecially for things we cant see.
  • We measure Wind, Precipitation, Temperature and
    Pressure.
  • We use Radar, Satellites, and even Balloons!

72
Doppler Radar
  • Tower is 100 feet tall! The 30 ft. wide white
    ball on top is
  • where the radar dish is.
  • Radar dish inside is 25 feet wide and spins
    constantly. It
  • can see up to 250 miles away!
  • Radar waves sent out hit a storm cloud.
  • Some of the radar wave bounces off the cloud
    back to
  • the radar. More waves are returned to the
    radar if the
  • storm has hail or very heavy rain. It can even
    tell which
  • way the wind is moving!

73
Satellites
  • Satellites are sent high above the earth to take
    pictures of the clouds from above. This is a
    view that people usually dont get to see.

74
Weather Balloons
  • NWS Offices across the US release a weather
    balloon twice a day, once in the morning and
    again at night.
  • The balloon has an Instrument packet that sends
    temperature, wind, and moisture data back to a
    computer.

75
Weather Balloons
  • Data sent back from the Instrument Pack is
    plotted on a graph and sent to large computer
    processors in Maryland to create Numerical
    Weather Predictions

76
Weather-Makers!
  • The basics of Weather help forecasters know
  • What will happen next?

77
Forecasting the Weather
  • In order to forecast the weather, meteorologists
    need to know Whats going on?
  • We look at all of the parts of the weather
    (temperature, wind, pressure, precipitation).
  • Then we look at what is causing the parts to
    behave like they do.

78
Fronts and Air Masses
  • An air mass is a large body of air with generally
    uniform temperature and humidity.
  • Fronts are the boundaries between two air masses.
  • Fronts are classified as to which type of air
    mass (cold or warm) is replacing the other.

79
Clouds
80
Cloud Formation
  • Clouds are made of water, either liquid or solid
  • Clouds typically form when air rises.
  • When air rises, the air's temperature cools and
    may reach its dewpoint temperature, at which
    point it becomes saturated.
  • Once saturated, condensation occurs and the water
    vapor in the air will condense into tiny water
    droplets.
  • As millions of droplets form, a cloud will begin
    to take shape.

81
How to Name that Cloud!
  • Height (High, middle, low, or vertically
    developing)
  • Physical appearance
  • Produce precipitation

82
Naming of Clouds
  • Latin roots
  • cirro ? high, curl of hair
  • alto ? middle
  • stratus ? layer, sheet-like, low
  • cumulus ? heap-like, puffy
  • nimbus ? clouds producing precipitation
  • Combinations can be made of the Latin roots

83
High Clouds
  • Form above 20,000 feet (6000 meters)
  • Composed of ice crystals
  • Typically thin and white, but can be many
    different colors due to the angle of the sun

Examples ? Cirrus, Cirrostratus, Cirrocumulus
84
Mid-level Clouds
  • Bases between 6,500 to 20,000 feet (2000 to 6000
    meters)
  • Composed of either water droplets or ice crystals
    depending on time of year

Examples ? Altostratus, Altocumulus
85
Low Clouds
  • Bases below 6,500 feet (2000 meters)
  • Mostly composed of water droplets
  • May contain some ice particles and snow if
    temperatures are cold enough

Example ? Stratus, Stratocumulus, Nimbostratus
86
Vertically Developing Clouds
  • Span the depth of the troposphere
  • Flat base can grow to heights exceeding 39,000
    feet (12,000 meters)
  • They can contain both liquid droplets and ice
    particles.
  • Can become powerful thunderstorms

Example ? Cumulus, Cumulonimbus
87
Thunderstorms
  • Needed Ingredients for a Thunderstorm Moisture
    (1), Instability (2) and Lift (3)

(2)
(1)
(3)
88
Thunderstorm Hazards
  • Lightning
  • Flash Floods
  • Hail
  • Tornadoes

89
Lightning
  • One of the oldest observed natural phenomena on
    earth, but one of the least understood.
  • A gigantic spark of static electricity
  • Can be seen in volcanic eruptions, extremely
    intense forest fires, heavy snowstorms, large
    hurricanes.
  • Most often seen in thunderstorms.
  • Intra-cloud, Cloud-to-Ground, Cloud-to-Cloud,
    Cloud-to-Air

90
How Much Lightning?
  • 2,000 thunderstorms at any moment
  • Nearly 14.5 MILLION storms each year
  • Lightning flashes about 40 times a second
    worldwide.
  • Satellites help us see lightning around the world.

91
How Lightning is Created
92
Thunder
  • A shock wave starts at each point along the path
    of the lightning bolt.
  • Nearby lightning strikes produce thunder that is
    loud and short.
  • As the shock wave moves away from the strike
    center, it stretches, diminishes, and becomes
    elongated. Then other shock waves from more
    distance locations arrive at the listener.
  • At large distances from the center, the shock
    wave (thunder) can be many miles across. To the
    listener, the combination of shock waves gives
    thunder the continuous rumble we hear. 

93
Tornadoes
  • A tornado is a violently rotating column of air
    descending from a thunderstorm and in contact
    with the ground.
  • Although tornadoes are usually brief, lasting
    only a few minutes, they can sometimes last for
    more than an hour and travel several miles
    causing considerable damage.

94
Hail
  • Hail is precipitation that is formed when
    updrafts in thunderstorms carry raindrops upward
    into extremely cold areas of the atmosphere.
  • Hail can damage aircraft, homes and cars, and can
    be deadly to livestock and people.
  • One of the people killed during the March 28,
    2000 tornado in Fort Worth was killed when struck
    by grapefruit-size hail.
  • La Plata, MD - 4.5 inches diameter on April 28,
    2002
  • Impact at speeds over 100 mph!
  • Sign of a powerful storm .

95
Flash Floods
  • Except for heat related fatalities, more deaths
    occur from flooding than any other hazard.
  • Most flash floods are caused by slow moving
    thunderstorms, thunderstorms that move repeatedly
    over the same area or heavy rains from tropical
    storms and hurricanes.
  • These floods can develop within minutes or hours.

96
Tropical Cyclones
97
Tropical Cyclone Basics
  • Conditions that must be in place before a TC can
    form
  • a) Warm ocean waters (at least 80F) through a
    depth of about 150 feet.
  • b) An atmosphere which cools fast enough with
    height such that it is potentially unstable to
    moist convection.
  • c) Relatively moist air near the mid-levels of
    the atmosphere (10-18 kft).
  • d) Generally a minimum distance of 300 miles
    from the equator.
  • e) A pre-existing near surface disturbance.
  • f) Low values (lt20 kt) of vertical wind shear
    between the surface and the upper troposphere.
    Wind shear is the change of wind speed/direction
    with height.

98
Tropical Cyclone Classification
Stages Sustained wind speeds
Tropical Depression Closed circulation (less than 39 MPH)
Tropical Storm 39-73MPH
Hurricane 74 MPH or higher
99
Saffir-Simpson Hurricane Scale(based on wind
speed alone)
Category Wind Speed (MPH) Damage
1 74-95 Minimal
2 96-110 Moderate
3 111-130 Extensive
4 131-155 Extreme
5 gt155 Catastrophic
100
TC Structure
101
Hurricane Hazards
  • Storm Surge
  • High Winds
  • Flooding
  • Tornadoes

Katrina, 2005 in Louisiana
102
Storm Surge
  • Greatest potential for loss of life related to a
    hurricane is from a storm surge.
  • Storm Surge water that is pushed toward the
    shore by the force of the winds swirling around
    the storm.

103
Generalizations of Storm Surge
  • More intense storms cause higher surges.
  • Highest surges occur usually to the right of the
    storm track.
  • Fast moving storms higher surges along the open
    coast.
  • Slow moving stormsgreater flooding inside bays
    and estuaries.

104
Storm Surge
105
High Winds
  • Satellites, reconnaissance aircraft, and land
    based radars are used to estimate the maximum
    surface wind speed in a hurricane. The intensity
    of a land-falling hurricane is expressed in terms
    of categories that relate wind speeds and
    potential damage. NHC uses the Saffir-Simpson
    Hurricane scale to classify hurricanes. Each time
    you go up a category, the damage goes up roughly
    by a factor of five. So, a category four
    hurricane will produce 25 times more damage than
    a category two hurricane.

106
High winds
  • High rise buildings are also vulnerable to
    hurricane force winds, particularly at the higher
    levels since wind speeds tend to increase with
    height. Recent research suggests that winds
    increase one category as you go up 500 ft.
  • This is why is not uncommon for high rise
    buildings to suffer a great deal of damage due to
    windows being blown out.

107
High Winds
  • Why do winds weaken as you go inland?
  • They weaken due to friction caused by land and
    because hurricanes, once they move inland, lose
    their energy source which is the very warm waters
    of the ocean.
  • A category four hurricane at landfall can weaken
    very rapidly to a category one in just six hours.
    This is because is a function of time and not
    distance, faster moving storms are going to push
    those winds inland more effectively than slower
    moving ones.

108
Damage done by Andrew 1992
109
Wind-blown debris can become deadly projectiles
110
Tornadoes
  • Typically occur on the right side of the storm
    because of an influx of very warm moist air.
  • As the hurricane is making landfall, winds at the
    surface begin to slow down due to friction, while
    winds a mile above the ground are still spinning
    very rapidly creating a favorable wind profile
    for tornadoes to form.

111
Tornadoes
  • When associated with hurricanes, tornadoes are
    not usually accompanied by hail or a lot of
    lightning.
  • Tornado production can occur for days after
    landfall when the TC remnants maintain an
    identifiable low pressure circulation.
  • They can also develop at any time of the day or
    night during landfall.
  • Classified using the Enhanced-Fujita Scale.

112
Inland Flooding
  • Intense rainfall is not directly related to the
    wind speed of tropical cyclones. Some of the
    greatest rainfall amounts occur from weaker
    storms that drift slowly or stall over an area.
  • Inland flooding can be a major threat to
    communities hundreds of miles from the coast.
  • In a study from 1970 to 1999, freshwater flooding
    accounted for more than half (59) of U.S.
    tropical cyclone deaths.

113
Any Questions?NWS Baltimore/WashingtonMarine
Program Leader Contact brandon.peloquin_at_noaa.gov
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