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SKYWARN OBSERVER'S GUIDE
REVISED 11/25/06


SAFETY PRECAUTIONS

When acting as a spotter, always remember that YOUR SAFETY IS MOST IMPORTANT! During a thunderstorm with lightning, stay in your covered vehicle with the windows up and door shut.

DO NOT TRY TO OUTRUN A TORNADO IN YOUR CAR! Get out of your car and curl up into a ball in a ditch or ravine in a location that will be as free of flying debris as you can, but be aware of localized flooding. Keep your head covered and eyes closed.

Above all else, use common sense and DON'T TAKE UNNECESSARY RISKS!

NEVER place yourself in any danger when reporting Severe Weather!
We need you, and thank you for your help!


Please include the following items in all your SKYWARN reports:

WHO: Identify yourself "SKYWARN Spotter" (name plus callsign if amateur radio operator)

WHERE: Report your county and state, and position relative to a known town/landmark ("Seven miles west of Galax"). If the event is not occurring where you are, report your position relative to the event/storm ("Looking three miles north of my location"). If applicable, report the movement and speed of the event being observed.

WHAT: Describe the event/storm (see reporting criteria below)

WHEN: Report the exact time of the event/storm, duration of the event, and if the event still in progress.


WHAT TO REPORT

ONLY REPORT OBSERVATIONS, NOT INTERPRETATIONS

  • Funnel Clouds
  • Tornadoes
  • Wall Clouds (confirmed or suspected)
  • Mama Clouds (mammatus)
  • Roll Clouds
  • Shelf Clouds
  • Report ANY KIND of Thunderstorm Activity During the Winter Months
    • Report time of observation
    • Location
    • Direction of movement
  • Downburst Winds
  • Wind Damage to Buildings
  • Wind Damage to Trees (large limbs broken off)
  • Wind Speeds of 35 mph or Greater
  • In Non-Thunderstorm Events, Report Winds in Excess of 50 mph or Greater
    • Report time of observation
    • Location
    • Estimated wind speed
    • Estimated wind direction
  • Hailstones of Any Size (initial report)
    • Report time of observation
    • Location
    • Size of hailstones - Measure if possible, report largest size, most common size, and depth of coverage. For size reference, use the following table:
       

    HAIL DIAMETER

    DESCRIPTION

    HAIL DIAMETER

    DESCRIPTION

    1/2"

     Dime Size

    3/4" (Severe Criteria) Penny Size

    7/8"

     Nickel Size

    1" Quarter Size

    1 1/4"

    Half Dollar Size

    1 1/2" Walnut or Ping Pong Ball Size

    1 3/4"

    Golf Ball Size

    2" Hen Egg Size

    2 1/2"

    Tennis Ball Size

    Or Report Actual Measurement

  • Lightning Strikes to People
  • Lightning Strikes to Animals
  • Lightning Strikes Causing Building Damage
    • Report time of strike
    • Location
    • What was struck
  • Flooded Streets
  • Standing Water in Buildings
  • Water Over the Banks of Creeks and Streams
  • Rainfall Rates of One (1) Inch Per Hour or Greater
    • Report time of observation
    • Location
    • Depth of standing water (if possible)
    • Actual rainfall rate (if possible)
    • Rainfall totals at the end of a storm event
  • Snow Accumulation of Three (3) Inches - Snowfall Rates of One (1) Inch Per Hour - or Greater
    • Report time of observation
    • Location
    • Depth of snow
    • Actual snowfall rate (if possible)
    • Snowfall totals at the end of a storm event
  • Icing
    • Report any ice accumulation
    • Time of observation
    • Location
    • Measure or estimate thickness of accumulation
    • Damage reports

    Visit NWS Blacksburg's Winter Weather Reporting Procedures page for more information.

  • Weather-related Personal Injury
    • Advise Local Law Enforcement FIRST!
    • Report what person was doing, age, sex, and cause of injury.
  • Any Other Pertinent Reports that may be regarded as a Threat to Life and Property, including power outages.

ALWAYS Record and Report the TIME & LOCATION of Your Observation

ALWAYS IDENTIFY YOURSELF AS A SKYWARN SPOTTER


If a SKYWARN net has been ACTIVATED in your County, report observations to your Net Control Station.

If a SKYWARN net has NOT been activated in your area, report observations by phone to your local emergency management office, law enforcement agency, or the National Weather Service.

The General Public should contact their local emergency management or law enforcement agency during times of severe weather, NOT the National Weather Service.


Notes

When spotting for WALL CLOUDS, FUNNEL CLOUDS, and TORNADOES, the key is always to LOOK FOR ROTATION! Often, scud clouds are mistaken for funnels or tornadoes because they may form beneath the parent thunderstorm and appear to touch the ground. Just remember... with scud there will be no rotation.

When estimating WIND SPEED feel free to use the Beaufort Wind Scale provided in this guide (complete chart below). Study the description of the Effects Observed and choose the appropriate wind speed range from the table. Report the speed in miles per hour or in knots. Do not report the Beaufort Force Number. This will likely send the meteorologists at the National Weather Service scurrying for reference books, wasting valuable time.

ESTIMATING WIND SPEED
25-31 - Large branches moving. Whistling in overhead wires.
32-38 - Whole trees moving. Inconvenience in walking against wind.
39-46 - Small branches (twigs) break. Impedes walking.
46-54 - Slight structural damage. Larger branches, and weak limbs may break.
55-63 - Moderate structural and tree damage.
64 and above - Heavy to severe tree, and structural damage.

When reporting WIND DIRECTION remember that it is ALWAYS the direction the wind is blowing FROM. For example, if you report the winds as Southerly at 10 mph, that means the winds are coming from the south, blowing to the north.

When reporting HAIL, use the common references that are used by the National Weather Service, ranging from dime size (1/2 inch) to softball size (4 1/2 inch)... arggghhhh... let’s hope you never have to report that!!! See the handy hail size table above.

When assessing WIND DAMAGE, remember that most wind damage is done by straight-line winds, not by tornadoes. With straight-line wind damage, all the damage will look like it diverges (moves outwards) from a single point possibly in several directions. With tornado damage, destruction is generally along one direction, debris along the ground is twisted or has spiral characteristics, and often small arcs where the top-soil has been removed are visible.

IF A PERSON IS STRUCK BY LIGHTNING, TAKE APPROPRIATE ACTION TO ENSURE IMMEDIATE AID IS GIVEN! A person retains no electrical charge after being struck, so it is safe to touch that person. This means CPR can be administered immediately if necessary. REPORT the occurrence to LOCAL LAW ENFORCEMENT as soon as possible!


SPOTTER RULES AND CLUES

  1. Always have a safe place nearby to protect yourself from wind and/or hail.
  2. Cars are a safe place from lightning, but NOT from tornadoes.
  3. Moving water is powerful, it only takes a slight current to push a vehicle off the road.
  4. Overshooting tops are an indicator of a very strong storm.
  5. The first gust of wind to reach you from a thunderstorm is frequently the strongest.
  6. A rain free base denotes the storm's updraft area, a place to watch closely.
  7. WALL CLOUDS form on the rain free base often 15 to 20 minutes before the tornado occurs.
  8. Large hail often falls just in advance of a tornado, especially large tornadoes.
  9. Tornadoes usually form in the trailing edge of a thunderstorm.
  10. TORNADOES generally move toward the NORTHEAST at 25 to 35 MPH when associated with fronts, and squall lines but CAN travel as fast as 70 MPH.

THE SPOTTER'S OBSERVATION KIT

Consider keeping the following equipment handy:

  • WEATHER RADIO (It’s nice to be able to keep up with weather warnings.)
  • COMMUNICATIONS RADIO for reporting your observations (When you see severe weather, you’ve got to report it!)
  • RAINCOAT WITH HOOD (Stay dry!)
  • FLASHLIGHT (In case you can’t see when it gets dark!)
  • BINOCULARS (So you can tell whether that cloud is really rotating!)
  • CAMERA or CAMCORDER (So that a permanent record can be made of your observations. Pictures and video are the BEST form of training for other spotters.)
  • COMPASS (For estimating the wind direction -- remember, that’s the direction the wind is coming from!)
  • Your SKYWARN OBSERVER'S GUIDE (So you can remember all this stuff!)

 

Severe Thunderstorm Diagram

Severe Thunderstorm Diagram

At 300mb, a strong jet stream aids in both increasing the wind shear and divergence. This divergence pulls air out of the column and intensifies the surface cyclone, which in turn strengthens the flow around the Low and makes the fronts stronger.
A trough enhances lifting in the mid to upper levels. Think of the trough at 500mb as another lifting mechanism.
Cold dry air from the southwest helps to further increase the wind shear and destabilizes the sounding by making the environment cold in the mid levels. That means that a parcel lifted from the surface will most likely be warmer than the environment and continues to rise on its own.
The low level jet enhances the vertical wind shear (both in speed and direction). Wind shear is a VITAL ingredient in producing rotating thunderstorms. This warm moist air also supports an unstable sounding (warm and moist in the lower levels, cold and dry in the upper levels.
Strong surface cyclone sets up the best environment to get the three ingredients necessary to produce thunderstorms. Well-defined fronts provide a surface lifting mechanism. Surface convergence toward the center of the Low draws warm moist unstable air from the south.

The Beaufort Scale is the oldest method of judging wind force, since it was proposed by Admiral Sir Francis Beaufort in 1806. Separate scales for tornadoes and hurricanes did not come until the 1970's.

BEAUFORT WIND SCALE

Beaufort
Force

Wind Speed

NWS
Description

Effects Observed
On Land

Effects Observed
At Sea

mph

knots

0

< 1

< 1

Calm Calm; smoke rises vertically Sea like mirror

1

1 - 3

1 - 3

Light air Direction of wind shown by smoke drift, but not by wind vanes Ripples with scaly appearance; no foam crests

2

4 - 7

4 - 6

Light breeze Wind felt on face; leaves rustle; ordinary vane moved by wind Small wavelets, crests of glassy appearance and not breaking

3

8 - 12

7 - 10

Gentle breeze Leaves and small twigs in constant motion; wind extends light flag Large wavelets with crests beginning to break, scattered whitecaps

4

13 - 18

11 - 16

Moderate breeze Raises dust and loose paper; small branches are moved Small waves growing larger, numerous whitecaps

5

19 - 24

17 - 21

Fresh breeze Small trees in leaf begin to sway; crested wavelets form on inland waters Moderate waves with greater length, many whitecaps with some spray

6

25 - 31

22 - 27

Strong breeze Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty Larger waves, whitecaps very numerous, more spray

7

32 - 38

28 - 33

Near gale Whole trees in motion; resistance felt in walking against wind Sea tends to heap up, streaks of foam blown from breaking waves

8

39 - 46

34 - 40

Gale Breaks twigs off trees; generally impedes progress Fairly high waves of greater length, well-marked streaks of foam

9

47 - 54

41 - 47

Strong gale Slight structural damage occurs (chimney pots and slate removed) High waves with sea beginning to roll, dense streaks of foam with spray blown higher into air--may cut visibility

10

55 - 63

48 - 55

Storm Trees uprooted; considerable structural damage occurs Very high waves with overhanging crests, sea is white with foam, heavy rolling and reduced visibility

11

64 - 72

56 - 63

Violent storm Widespread structural damage Waves exceptionally high, sea covered with foam, visibility further reduced

12

73 - 82

64 - 71

Hurricane Maximum wind damage Sea completely covered with spray, air filled with foam, greatly reducing visibility

The Fujita (or Fujita-Pearson) Scale for tornadoes was proposed in 1971 by T. Theodore Fujita and Allen Pearson. Thus, the movie Twister was anachronistic when it had Helen Hunt's father warn, in 1965, that they might have an F5 tornado headed toward them. The scale had not been invented yet.

FUJITA SCALE FOR TORNADO INTENSITY

Scale

Category

mph

knots

Expected Damage

F - 0

WEAK

40 - 72

35 - 62

Light - tree branches broken, sign boards damaged

F - 1

 

73 - 112

63 - 97

Moderate - trees snapped, windows broken

F - 2

STRONG

113 - 157

98 - 136

Considerable - large trees uprooted, weak structures destroyed

F - 3

 

158 - 206

137 - 179

Severe - trees leveled, cars overturned, walls removed from buildings

F - 4

VIOLENT

207 - 260

180 - 226

Devastating - frame houses destroyed

F - 5

 

261 - 318

227 - 276

Incredible - structures the size of autos moved over 100 meters, steel reinforced structures highly damaged

Enhanced F Scale for Tornado Damage

An update to the the original F-scale implemented in the U.S. on 1 February 2007.

FUJITA SCALE
DERIVED EF SCALE
OPERATIONAL EF SCALE
F Number Fastest 1/4-mile (mph) 3 Second Gust (mph) EF Number 3 Second Gust (mph) EF Number 3 Second Gust (mph)
0 40-72 45-78 0 65-85 0 65-85
1 73-112 79-117 1 86-109 1 86-110
2 113-157 118-161 2 110-137 2 111-135
3 158-207 162-209 3 138-167 3 136-165
4 208-260 210-261 4 168-199 4 166-200
5 261-318 262-317 5 200-234 5 Over 200

*** IMPORTANT NOTE ABOUT ENHANCED F-SCALE WINDS: The Enhanced F-scale still is a set of wind estimates (not measurements) based on damage. Its uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to the 28 indicators listed below. These estimates vary with height and exposure. Important: The 3 second gust is not the same wind as in standard surface observations. Standard measurements are taken by weather stations in open exposures, using a directly measured, "one minute mile" speed.

Enhanced F Scale Damage Indicators

NUMBER
(Details Linked)
DAMAGE INDICATOR
ABBREVIATION
Small barns, farm outbuildings
SBO
One- or two-family residences
FR12
Single-wide mobile home (MHSW)
MHSW
Double-wide mobile home
MHDW
Apt, condo, townhouse (3 stories or less)
ACT
Motel
M
Masonry apt. or motel
MAM
Small retail bldg. (fast food)
SRB
Small professional (doctor office, branch bank)
SPB
Strip mall
SM
Large shopping mall
LSM
Large, isolated ("big box") retail bldg.
LIRB
Automobile showroom
ASR
Automotive service building
ASB
School - 1-story elementary (interior or exterior halls)
ES
School - Junior or Senior high school
JHSH
Low-rise (1-4 story) bldg.
LRB
Mid-rise (5-20 story) bldg.
MRB
High-rise (over 20 stories)
HRB
Institutional bldg. (hospital, govt. or university)
IB
Metal building system
MBS
Service station canopy
SSC
Warehouse (tilt-up walls or heavy timber)
WHB
Transmission line tower
TLT
Free-standing tower
FST
Free standing pole (light, flag, luminary)
FSP
Tree - hardwood
TH
Tree - softwood
TS

A 95 page PDF file explaining the development and makeup of the Enhanced F-scale is available at the SPC.

Soon after the Fujita Scale was proposed, the Saffir-Simpson Scale for hurricanes was formulated by Herbert Saffir and Robert Simpson.

SAFFIR-SIMPSON SCALE FOR HURRICANE INTENSITY

Category

mph

knots

Surge (ft)

Expected Damage

Tropical
Storm

40 - 73

35 - 63

0 - 3

Slight - Minor roof, tree, and sign damage.

1

74 - 95

64 - 82

4 - 5

Minimal - No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Also, some coastal flooding and minor pier damage.

2

96 - 110

83 - 95

6 - 8

Moderate - Some roofing material, door, and window damage. Considerable damage to vegetation, mobile homes, etc. Flooding damages piers and small craft in unprotected boats may break their moorings.

3

111 - 130

96 - 113

9 - 12

Extensive - Some structural damage to small residences and utility buildings, with a minor amount of curtain wall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain may be flooded well inland.

4

131 - 155

114 - 135

13 - 18

Extreme - More extensive curtain wall failures with some complete roof structure failure on small residences. Major erosion of beach areas. Terrain may be flooded well inland.

5

156+

135+

18+

Catastrophic - Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Flooding causes major damage to lower floors of all structures near the shoreline. Massive evacuation of residential areas may be required.

 


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