What are Extreme Weather Warnings?
Sam Bullock avatar
Written by Sam Bullock
Updated over a week ago

Experienced sailors know the key indicators that could signal extreme weather. These indicators include the following:

  • Lightning Index

  • Cape Index

  • Rain Squalls

  • Extreme Gusts

  • Wind against current

When doing a quick check on the weather forecast, it is easy to miss these key indicators, which can often signal extreme weather, even when the averaged forecasted conditions are benign. So to make sure you do not miss these extreme weather events, we now have the following warnings in the interface.

How to view the Extreme Weather Warnings

Daily Briefing - Warnings will be displayed on the daily briefing card if any of the forecast time-steps within a Daily Briefing card meet the warning requirements.

Forecast Tables - Warnings will be displayed in a new warning row at the top of the Tables. If any of the forecast conditions meet the warning criteria for an individual timestep, a warning will be shown at the top of that column. Click/Tap on the warning to see what kind of warning has been triggered. We suggest you then dig into the forecast variables that are causing the warning to get a clear picture of what is likely to happen.

Weather Routing/Departure Planning - Warnings are now displayed on both the Weather Routing Maps and Weather Routing Tables. When conditions along the route trigger a warning, a warning icon will be displayed on the map. If consecutive points have warnings, the map will consolidate these into a single warning. When you Click/Tap on the icon, the section of route that there are consecutive warnings for will be highlighted in orange, and a description of the warnings will be displayed in a popup.

In the Weather Routing Tables, warnings will not be consolidated, every row that has warning conditions will display a warning. You can click/tap on the warning to see its description. Also, click/tapping on the individual description of a warning will take you to the relevant table tab which displays the raw data.

What conditions trigger the extreme weather warnings?





If gust is 50% or more, greater than the 10 m wind speed

If 10 m wind is less than 12 knots, the warning will not be triggered.

If Gust is greater than 40 knots, the warning will always be triggered.

Rain Squall

If rain is 3mm/hour or more AND gust is 25 knots or more.


If (temp < 20deg) CAPE 1000+ triggers warning

if (20deg < temp < 30deg) CAPE 2000+ triggers warning

if (temp > 30deg) CAPE 3000+ triggers warning

Wind Chill

if wind chill is less than 8 degrees Celsius


Any Lightning value greater than 0

The unit for lightning strikes is how many strikes per square 100kms surrounding your location.

So any number above 0 could mean some lightning. The bigger the number the greater the potential.


Any Fog value greater than 0.25 AND less than 0.75

Fog & Rime

Any Fog value greater than 0.75

Weather Routing Warnings




> 4 deg Roll

Vertical Acceleration

> 0.2g's Vertical Acc

Slamming Incidence

> 50% Slamming Inc

Wind Against Current

When current direction and wind direction are less than 60 degrees apart (wind & current direction convention is opposite) & Wind is more than 12 knots & Current is more than 1 knot

Note: The warnings are only available for the Basic, Standard and Professional Forecast Subscriptions.

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