One inch and 58 miles an hour, quoted from the notice that set them, and why no course can tell you your own office's reporting threshold.

In this lesson you will

  • State the current severe hail threshold and its effective date.
  • State the severe wind threshold in both miles per hour and knots.
  • Report hail by diameter or a fixed reference object, and avoid the discouraged comparisons.
  • Distinguish measured from estimated magnitudes and identify reportable wind damage indicators.

The notice that set both numbers

Both national severe criteria come from one service change notice, and it is worth seeing in the original because it does two things at once: it changes the hail number and states explicitly that the wind number is not changing.

EFFECTIVE TUESDAY...JANUARY 5 2010 AT 0001 COORDINATED UNIVERSAL
TIME...ALL NWS WEATHER FORECAST OFFICES...WILL OPERATIONALLY CHANGE
THE MINIMUM HAIL SIZE CRITERION...FROM 3/4 INCH /PENNY/ DIAMETER OR
LARGER HAIL TO 1 INCH /QUARTER/ DIAMETER OR LARGER HAIL. NO CHANGE IS
BEING MADE TO THE...WIND CRITERION OF WIND GUSTS EQUAL TO OR IN
EXCESS OF 50 KNOTS /58 MPH/.

NWS Service Change Notice 09-52, abridged at the ellipses as marked. The capitals are the original product format, not emphasis.

Learn these two and nothing else
Severe hail is 1.00 inch, quarter size, or larger.Severe wind is 58 mph, or 50 knots, or greater. The wind figure has not moved. The hail figure moved once, on 5 January 2010, and the old three-quarter-inch penny threshold is the most commonly repeated outdated number in spotting. If you learned the penny, relearn the quarter.

Severe is national. Reportable is local.

Those two criteria decide what is severe, everywhere in the country, and they do not move. They do not decide what is worth reporting, which is a different question with a different answer in every forecast area. Each office publishes its own list of what it wants to hear about, and the lists genuinely differ.

The one thing to do after this lesson
Find your own forecast office's "submit a storm report" page and read it. It takes two minutes, it is the authority for your area, and no course can substitute for it. The examples below are illustrations of what such a page looks like and how much offices vary, not the criteria for wherever you are standing.

Hail is the easy case, because most offices ask for it the same way. This is the wording used by the Mobile and Pensacola office, which is typical:

Hail: Specify the size, location, and time of occurrence.

NWS Mobile/Pensacola, "Submit a Storm Report", read 11 September 2026. One office's wording, quoted as an example of the pattern.

There is no minimum size in that sentence, and there usually is not. Report all hail, whatever size it is, and let the office decide what crosses a threshold. Pea-sized hail in a place with no radar coverage is a useful data point; it is just not a severe report.

Wind, where the offices diverge

Wind is where a "please report at least" figure would be useful and where the country is least consistent. Some offices publish a number below the severe criterion so that they hear about sub-severe gusts. Others publish none at all and ask for damage instead.

What an office may publishWhat that asks of you
A "report gusts of at least" figure below 58 mphCall in measured or estimated gusts at or above it, even with no damage. Figures in the 40 to 50 mph range are in circulation at various offices.
No numeric figure, damage wording onlyReport the damage. "Any structural damage, downed trees, downed power lines" is one office's entire published wind criterion.
Nothing you can findFall back on the national rule: report damage, and 58 mph is the severe criterion. Then ask the office.

The middle row is the live wording from the Mobile and Pensacola page, which publishes no mph figure anywhere. That is a real office-to-office difference rather than an omission, and it is why this course prints no single national "please report" wind number: there is not one.

So carry two rules, not one
Report wind damage, whatever the speed. That works everywhere and no office objects to it. And 58 mph, or 50 knots, is the severe criterion, which is the number that matters when you have an actual measurement or are asked whether a storm met criteria. Anything your own office adds on top of those two sits between them.

Describing hail so the number survives

  1. Give a diameter if you measured one. A number in inches beats every reference object there is.
  2. Otherwise give a fixed reference object. Coins are ideal: everybody has one and they do not vary. Quarter, half dollar, golf ball, hen egg, tennis ball, baseball.
  3. Never use an object whose size varies. Marbles, pebbles, mothballs, balloons. NWS guidance names marbles specifically, and module 5 lesson 2 shows the awkward fact that an NWS reference table still carries a legacy marble row anyway.
  4. Say measured or estimated. This becomes a tag in the record and it is the difference between a data point and an impression.
  5. Report the largest stone, and say it is the largest. "Mostly pea size with a few quarters" is a better report than either half of it alone.

The full NWS size chart is reproduced verbatim in module 5 lesson 2, along with the measurement procedure and the reason a photograph beside a coin turns your estimate into somebody else's measurement. It is not reprinted here.

Describing wind when you have no anemometer

Most wind reports are damage reports, because most spotters do not have a calibrated instrument and the ones who do are often measuring in a sheltered back garden. So describe the damage, concretely, and let the survey assign a speed.

  • Trees. Limbs down, and roughly what diameter. Trees snapped. Trees uprooted. These are three different things and they mean three different wind speeds.
  • Power. Lines down. Poles snapped or leaning. A pole broken off is a much stronger statement than a line down.
  • Structures. Roof material lifted, shingles, decking, a wall, an outbuilding. Say what moved and roughly how far.
  • Objects. Anything heavy that was moved, and how far. The May 2025 survey recorded a barbecue smoker thrown twenty to thirty yards; that sentence does real work.
Where the speed comes from
You describe, the survey rates. Trapp and colleagues documented how unreliable estimated wind speeds are in the severe wind record, and module 5 lesson 5 covers why your own estimate is probably high and probably a multiple of five. A precise description of what broke is worth more than an imprecise number, and it is something you can actually deliver.

Check yourself

You measure a hailstone at 0.9 inches with a ruler. What is the correct report?

  1. Report it, giving 0.9 inches measured, and note that it is below severe criteria
  2. Do not report it. Below one inch it is not severe and therefore not reportable
  3. Report it as one inch, since it rounds up and is close enough to the criterion
  4. Report it as severe. The old three-quarter-inch threshold is exceeded
Hint

The local office asks for hail without naming a minimum size, and the national criterion answers a different question.

Answer

Report it, giving 0.9 inches measured, and note that it is below severe criteria

The office asks you to specify size, location and time, with no minimum. Reportable and severe are different questions: 0.9 inches measured is a good report that happens not to meet criteria. Rounding it up would put a false severe report in the record, and the three-quarter-inch threshold was replaced on 5 January 2010.

Sources

  1. NWS Service Change Notice 09-52: the one-inch hail severe criterion, operational 5 January 2010 at 0001 UTC
  2. NWS Mobile/Pensacola, "Submit a Storm Report"
  3. NWS Weather Spotter's Field Guide
  4. Trapp et al. 2006, Wea. Forecasting 21(3), 408–415: buyer beware, some words of caution on the use of severe wind reports
  5. NWS Mobile, 10 May 2025 severe weather event and damage surveys
  6. NWS New Orleans and Baton Rouge, "Estimating Hail and Wind"