Storm Station 247

The Field Book/Vol. IX, The Station/FB-STN-001

How to read a warning

A warning is a product with a fixed anatomy: a headline naming the hazard, an area, a time it ends, what is happening and what it will do, what to do, and a line of code that lets a machine track the same event from the first issue to the last.

Plate FB-STN-001Warning doctrineRevision 1, 2026-09-24Status draftAlso called warning product, VTEC, P-VTEC, H-VTEC, impact based warning, watch, advisory, statement

The parts of a severe thunderstorm warning, numbered on an invented example: the VTEC code line, the headline, the issuing office and time, the counties covered, the time it ends, where the storm is and how it moves, the hazard, its source and its impact, what to do, the polygon's corners, and the storm's position and motion for machines.1122334455667788AABBCCDDEESTORM STATION 247THE FIELD BOOKPLATE FB-STN-001-AAN EXAMPLE SEVERE THUNDERSTORM WARNING, WITH AN INVENTED OFFICE AND COUNTY; NOT A REAL WARNINGFIG. A THE ANATOMY OF A WARNING/O.NEW.KXXX.SV.W.0412.260924T2100Z-260924T2145Z/1BULLETIN - IMMEDIATE BROADCAST REQUESTEDSevere Thunderstorm Warning2National Weather Service, example office KXXX3400 PM CDT Thu Sep 24 2026* Severe Thunderstorm Warning for... Example County in the example state...4* Until 445 PM CDT.5* At 400 PM CDT, a severe thunderstorm was located6 near Exampleton, moving east at 25 mph. HAZARD...60 mph wind gusts and quarter size hail.7 SOURCE...Radar indicated.8 IMPACT...Hail damage to vehicles is expected.9 Expect wind damage to roofs, siding, and trees.PRECAUTIONARY/PREPAREDNESS ACTIONS...10For your protection move to an interior room onthe lowest floor of a building.LAT...LON 3510 9745 3520 9720 3495 9715 3485 974011TIME...MOT...LOC 2100Z 270DEG 22KT 3503 973712MAX HAIL SIZE...1.00 INMAX WIND GUST...60 MPH$$INSET THE POLYGON OVER ITS COUNTY, PLANEXAMPLE COUNTYNEXTCOUNTYSTORM AT 2100Z, 270° AT 22 KT1112N22.8 km (14.2 mi)READ IT IN THIS ORDER1 Is it a watch or a warning? The headline.2 Is it here? The area, or the polygon.3 Until when? The end time.4 How bad, and seen or only indicated? HAZARD, SOURCE.5 What will it do? IMPACT.6 What to do. The actions.TITLEHow to read a warning, the anatomy of a warningVOL. IX THE STATION · WARNING DOCTRINETYPEDOCUMENTSCALENOT TO SCALEREVREV 1 DRAFT SHEET 1 of 2DATE2026-09-24IDFB-STN-001-ADRAWN AS linework on paperSOURCES NWS
Fig. A The anatomy of a warning. An example severe thunderstorm warning, with an invented office and county; not a real warning NOT TO SCALE The sheet, SVG, 11 by 17
  1. The P-VTEC line, for machines
  2. The headline, the event name
  3. Who issued it, and when, in local time
  4. The area it covers
  5. The time it ends
  6. Where the storm is, and where it is moving
  7. HAZARD, what it brings
  8. SOURCE, how it is known
  9. IMPACT, what it will do
  10. Precautionary and preparedness actions
  11. LAT...LON, the corners of the polygon
  12. TIME...MOT...LOC, position and motion

What it is

A warning is a product. The Weather Service issues it in a fixed format, so that a person, a broadcaster, a phone and a machine can each find the same parts in the same places. Read it in order and it answers six questions: what, where, until when, what is happening, what it will do, and what to do.

Every alert on this site, from a Tornado Warning to a Frost Advisory, is built the same way. Fig. A numbers the parts on an invented example.

  1. The headline names the event: a phenomenon, then a significance. Tornado Warning. Flood Watch. Wind Advisory.
  2. Who issued it, and when, in the local time of the office.
  3. The area: counties and zones by name, or, for a warning drawn around one storm, a polygon.
  4. The time it ends. A warning is only in force until then, unless it is extended.
  5. What is happening: where the storm is and where it is moving. In a storm warning this becomes three tagged lines: HAZARD (what it brings), SOURCE (how it is known: radar indicated, or observed) and IMPACT (what it will do to people and things).
  6. What to do: the precautionary and preparedness actions.
  7. The code: a line of VTEC for machines, and for a storm warning the polygon's corners and the storm's motion.

What it is not

A warning is not a forecast. A forecast says what the weather will be. A warning says a hazard to life or property is happening, is about to, or is likely, in this area, until this time.

A watch is not a weaker warning. It is a different product with a different job: it is issued before anything is happening, over a large area and for several hours, when conditions favour the hazard. Its job is to make people ready. The warning is the call to act.

An advisory is not a warning for a smaller place. It is for a less serious hazard: one that causes significant inconvenience, and that could threaten life or property if people are careless. A statement follows up a product in force, or covers a hazard below the others.

A Special Weather Statement is none of these. It carries no VTEC code. Forecasters use it for a storm just below the severe threshold, or for a hazard with no product of its own.

Lookalikes

Watch
Not a weaker warning. A watch is issued before anything is happening, for a large area and several hours, so that people are ready when the warning comes.
Outlook
A forecast of risk days ahead. It warns of nothing.
Special Weather Statement
Carries no VTEC code and no watch or warning. It is used for a storm near the severe threshold, or for a hazard with no product of its own.

The machine

The code is what lets one event be followed from its first issue to its last. The P-VTEC string, drawn dimensioned in Fig. B, reads:

/O.NEW.KXXX.SV.W.0412.260924T2100Z-260924T2145Z/

  • O is the product class: operational. T is a test, E experimental.
  • NEW is the action. The same event is later CON (continued), EXT (extended in time), EXA (extended in area), EXB (extended in area and time), UPG (upgraded), CAN (cancelled early) or EXP (expired). COR corrects a product and ROU is routine.
  • KXXX is the issuing office, four letters. This example's office is invented.
  • SV is the phenomenon, severe thunderstorm. The Book's index lists every code.
  • W is the significance: W warning, A watch, Y advisory, S statement.
  • 0412 is the event tracking number. Each office keeps one series for each phenomenon and significance, begun again each January 1, so the number and the office together name one event for the year.
  • The two times are when the event begins and ends, always in UTC.

Flood products carry a second line, the H-VTEC, which names the forecast point on the river, the flood severity (minor, moderate or major), and its immediate cause: excessive rainfall, snowmelt, an ice jam, or a dam or levee failure among them.

The polygon comes after the text. LAT...LON lists its corners in hundredths of a degree. TIME...MOT...LOC gives the time, the direction the storm is moving from in degrees, its speed in knots, and where it was.

The damage threat

Since impact based warnings, a severe thunderstorm warning can carry a damage threat. Considerable means hail of 4.4 cm (1.75 in) or wind of 31 m s⁻¹ (70 mph). Destructive means hail of 7.0 cm (2.75 in) or wind of 36 m s⁻¹ (80 mph), and it sets off a Wireless Emergency Alert on phones in the polygon. A tornado warning's threat can be considerable, and at the top it becomes a Tornado Emergency.

Above, the P-VTEC string of an example warning dimensioned field by field: product class, action, office, phenomenon, significance, event tracking number, and the begin and end times in UTC. Below, a time strip of one event: a watch issued for several hours over a large area; inside it a warning issued as NEW, continued as CON with a statement, and ended as EXP when it runs out or CAN when it is cancelled early.1122334455667788AABBCCDDEESTORM STATION 247THE FIELD BOOKPLATE FB-STN-001-BTHE CODE DIMENSIONED FIELD BY FIELD, AND ONE WARNING'S LIFE FROM ISSUE TO EXPIRYFIG. B THE VTEC LINE, AND THE LIFE OF ONE EVENT/O.NEW.KXXX.SV.W.0412.260924T2100Z-260924T2145Z/1PRODUCT CLASS2ACTION3OFFICE4PHENOMENON5SIGNIFICANCE6EVENT NUMBER7BEGINS AND ENDS, UTCO.NEW: A NEW OPERATIONAL EVENT. LATER ISSUES OF THE SAME EVENT READ CON, EXT, EXA, EXB, UPG, CAN OR EXP, WITH THE SAME NUMBER.1800Z1900Z2000Z2100Z2200Z2300Z0000Z0100Z0200ZUTCSEVERE THUNDERSTORM WATCH SV.A 1800Z TO 0100Z, MANY COUNTIESSV.W 0412 NEW 2100ZEXPCON, A STATEMENTSV.W 0413 NEW, THE NEXT COUNTY DOWNSTREAMEXPSV.W 0414 NEW 2300ZCAN 2325Z, THE STORM WEAKENED8910TITLEHow to read a warning, the VTEC line, and the life of one eventVOL. IX THE STATION · WARNING DOCTRINETYPETIME STRIPSCALENOT TO SCALEREVREV 1 DRAFT SHEET 2 of 2DATE2026-09-24IDFB-STN-001-BDRAWN AS linework on paperSOURCES NWS
Fig. B The VTEC line, and the life of one event. The code dimensioned field by field, and one warning's life from issue to expiry NOT TO SCALE The sheet, SVG, 11 by 17
  1. Product class, O for operational
  2. Action, NEW for a new event
  3. Issuing office
  4. Phenomenon
  5. Significance
  6. Event tracking number
  7. Begins and ends, UTC
  8. The watch, hours over a large area
  9. The warning, minutes over a polygon
  10. The event ends, EXP or CAN

Ingredients

  • A hazard: something happening or about to happen that threatens life or property
  • A forecaster who has seen it, or a clear signal that it is coming
  • A product: the fixed format the Weather Service issues it in, so every reader and every machine can find the same parts in the same places

Scales

time
minutes (a storm warning) to days (a winter storm or flood warning)
horizontal
a polygon around one storm, or whole counties and zones
vertical
not applicable, a warning is drawn on the ground
orlanski
not applicable

Signatures

headline
the event name; phenomenon then significance; such as Tornado Warning
code
the P-VTEC string: /k.aaa.cccc.pp.s.####.yymmddThhnnZ-yymmddThhnnZ/; flood products add an H-VTEC line naming the forecast point, the flood severity and its cause
text
the area; the time it ends; HAZARD, SOURCE and IMPACT in a storm warning; precautionary and preparedness actions
machine
LAT...LON, the polygon's corners; TIME...MOT...LOC, where the storm was, and how it moves

The numbers

QuantityValue, and the kind of number it is
WarningA hazard is occurring, imminent or likely, and threatens life or propertyStandard, Watch
WatchConditions favour the hazard; its occurrence, place or timing is still uncertainStandard, Watch
AdvisoryA less serious hazard that causes significant inconvenience, and could threaten life or property without careStandard, Watch
StatementA follow up to a product in force, or information on a hazard below the othersStandard, Watch
Storm based warningDrawn as a polygon around the threat, not whole counties; among them the severe thunderstorm, tornado, flash flood, snow squall, extreme wind and special marine warningsStandard, Directive 10-511
Life of a severe thunderstorm or tornado warningCommonly 30 to 60 minutesTypical, Directive 10-511
Considerable damage threatSevere thunderstorm: hail 4.4 cm (1.75 in) or wind 31 m s⁻¹ (70 mph)Standard, Directive 10-511
Destructive damage threatSevere thunderstorm: hail 7.0 cm (2.75 in) or wind 36 m s⁻¹ (80 mph); sets off the Wireless Emergency Alert on phonesStandard, Directive 10-511
VTEC timesAlways Coordinated Universal Time (UTC), written yymmddThhnnZStandard, Directive 10-1703
Event tracking numberFour digits, one series for each office, phenomenon and significance, begun again each January 1Standard, Directive 10-1703

How the station sees it

The alerts page reads every alert in force from the Weather Service every two minutes. It draws each on the counties it covers, filled for a warning, hatched for a watch, washed for an advisory and outlined for a statement, and draws the polygon of a storm warning over them as a heavy line. The card for each alert prints its headline, when it ends, the area, the severity, urgency and certainty the Weather Service gives it, and the full text with what to do.

What it adds is this book. Each card carries the plates that explain the machine behind its hazard, under "Read the plates", and this plate on every one.

How it is warned

The order of reading is the order of acting. The headline tells whether the product is a watch, to get ready, or a warning, to act. The area tells whether it is you. The end time tells how long. The HAZARD, SOURCE and IMPACT lines tell how bad, and whether it has been seen or only indicated on radar. The actions tell what to do, and they are written by the forecaster for this event.

An expired warning has not always ended the danger. A storm can leave one polygon and enter the next: the next warning is a new event, with a new number, for the area downstream. Read the one in force where you are.

See also

Sources

  1. National Weather Service. Watch, Warning, Advisory definitions.
  2. National Weather Service. Directive 10-511, WFO Severe Weather Products Specification.
  3. National Weather Service. Directive 10-1703, Valid Time Event Code (VTEC).
  4. National Weather Service. Directive 10-922, Weather Forecast Office Hydrologic Products Specification.
  5. American Meteorological Society. Glossary of Meteorology.

Definition after the Watch, Warning, Advisory definitions. Plate FB-STN-001, revision 1, 2026-09-24. The number is permanent; cite it.