SKYWARN Storm Spotter Guides Online

This module compiled with information courtesy of the official NOAA Storm Spotters Guide.

SECTION FOUR:

As in the other sections, you can click on the glossary image wherever you see it, and the glossary will open in another window. Just close that window when you are ready to continue.

In this section, we will go over severe criteria as defined by the National Weather Service and how to determine these things by observation:

The National Weather Service defines a storm as severe if it produces a tornado, hail 3/4 inch in diameter or larger, and/or wind gusts to 58 miles per hour or higher. They also state that it would be desirable to report events associated with a thunderstorm before they reach severe levels.

The following guidelines can be used for reporting weather events:

Report hail occurrences when the hailstones have a diameter of 1/2 inch,
Report wind gusts when their speed reaches 50 miles per hour.
Wall cloud development, especially with rotation.
Obviously, a tornado and funnels should be reported.

HOW TO DETERMINE WIND SPEED VISUALLY:

<1 mph	<1 kts	Calm	Calm conditions, smoke will rise vertically
1 - 3 mph	1 - 3 kts	Light Air	Direction of wind shown by smoke drift not by wind vanes
4 - 7 mph	4 - 6 kts	Light Breeze	Wind felt on face; leaves rustle; vanes move by wind
8 - 12 mph	7 - 10 kts	Gentle Breeze	Leaves and small twigs in constant motion; wind extends light flag
13 - 18 mph	11 - 16 kts	Moderate	Raises dust; loose paper; small branches moved
19 - 24 mph	17 -21 kts	Fresh	Small trees in leaf begin to sway; crested wavelets form on inland waters
25 - 31 mph	22 -27 kts	Strong	Large branches in motion, whistling heard in telephone pole wires; umbrellas used with difficulty
32 - 38 mph	28 -33 kts	Near Gale	Whole trees in motion; inconvenience felt walking against the wind
39 - 46 mph	34 - 40 kts	Gale	Breaks off twigs from trees; impedes progress
47 - 54 mph	41 - 47 kts	Strong Gale	Slight structural damage occurs
55 - 72 mph	48 - 55 kts	Storm	Trees uprooted; considerable damage occurs; damage to chimneys and TV antennas; pushes over shallow rooted trees.
73 - 112 mph			Peels surface off roofs; windows broken; trailer houses overturned.
113+ mph			Roofs torn off houses; weak buildings and trailer houses destroyed; large trees uprooted.

HOW TO DETERMINE RAINFALL INTENSITY FROM OBSERVATIONS:

Light rain / Up to 0.10 inch per hour; maximum 0.01 inch in 6 minutes
Moderate rain / 0.11 inch to 0.30 inch per hour; more than 0.01 inch to 0.03 inch in 6 minutes
Heavy rain / More than 0.30 inch per hour; more than 0.03 inch in 6 minutes

Light rain / From scattered drops that, regardless of duration, do not completely wet an exposed surface up to a condition where individual drops are easily seen.
Moderate rain / Individual drops are not clearly identifiable; spray is observable just above pavements and other hard surfaces.
Heavy rain / Rain seemingly falls to sheets; individual drops are not identifiable; heavy spray to height of several inches is observed over hard surfaces.

ESTIMATING HAIL SIZE VISUALLY:

Pea size - 1/4 inch
Penny size - 3/4 inch
Quarter size - 1 inch
Half Dollar size - 1 1/4 inch

Golfball size - 1 3/4 inch
Tennis Ball size - 2 1/2 inch
Baseball size - 2 3/4 inch
Grapefruit size - 4 inches!

You should refrain from reporting "marble sized" hail, as marbles come in various sizes and could confuse your report. Also, MEASURED hail, such as with a ruler is always desirable, although not always practical.

OTHER REPORTING CONCERNS:

When making a report, you should include the following information:

WHO you are, and the name of your spotter group, and Amateur Radio Callsign if you have one.
WHERE the event is occurring. Use reports from other nearby spotters to triangulate and pinpoint an events location.
WHAT you have seen (the severe weather event, not UFO's).
MOVEMENT of the event. When estimating movement, don't use the motion of small cloud elements for estimation. Instead, observe the whole storm for estimates of motion.
NEED! Is any help needed at that location (i.e. tornado stuck some homes).
Remember to follow this important rule called K.I.S.S. which stands for Keep It Simple Stupid

DISCLAIMER: Storm spotting/chasing has the potential to be a life threatening activity. The material presented here is for educational purposes only. You are strongly suggested to contact someone in your area about getting official SKYWARN training and riding along with someone with spotting/chasing experience before ever attempting to do so on your own. By viewing the material contained within spotterguides.us, you agree that you alone are accept responsibility for what you do with this information.

Site design is Copyright 2003-2024 Dryline Media LLC. All rights reserved. Image copyrights are retained by their respective owners. Please see the CREDITS page for contributors and information about using the material contained within this website.