Indicators for Predicting Severe Weather
Recently we have added CAPE and Gust Maps to help you predict severe weather, and avoid these conditions.
CAPE
CAPE stands for Convective Available Potential Energy and is the amount of fuel available to a developing thunderstorm. More specifically, it describes the instability of the atmosphere and provides an approximation of updraft strength within a thunderstorm. So CAPE is used by weather officials to understand what the potential might be for thunderstorms and how powerful those storms might become if they do materialize.
The standard measurement of energy is represented as Joules Per Kilogram. A high CAPE value might also be expressed by weather experts by using the term “high instability”. When we talk about a highly unstable atmosphere, CAPE values are usually in excess of 2500 J/kg’s which would supply ample energy for strong updrafts and violent thunderstorms, should they develop.
Severe thunderstorms require high CAPE values and the higher the CAPE value, the more energy available to promote thunderstorm growth. However, the CAPE variable is not a “magic number” that will predict the certainty of a thunderstorm. But if a thunderstorm does develop, and the CAPE value is high, then there is a good chance for an “explosive storm”. Below is a typical CAPE Map in the Caribbean. The Yellow/Orange areas show high CAPE values.
The table below is a good guide for Thunderstorm/Lightning.
Gusts
Gusts are sudden, brief increases in the speed of the wind. According to U.S. weather observing practice, gusts are reported when the peak wind speed reaches at least 16 knots and the variation in wind speed between the peaks and lulls is at least 9 knots. The duration of a gust is usually less than 20 seconds.
All sailors know that it is the Gust that can do major damage and make boat control difficult, and often more dangerous than a high average wind strength. It is prudent practise to view the Gust Map, to check the maximum wind strengths you may experience. A large difference between the average wind strength, and the gusts can be very dangerous, especially if you are not prepared. So we advise that you animate your weather routing, over the Gust Maps to check for these situations.
See a typical Gust Map from the North Atlantic. Dark red areas show Wind gusts of over 35 knots. Grey areas over 50 knots.
Rain Squalls
Rain squalls can also affect the wind strength in a dramatic way. These clouds ‘push’ air down to the surface, and so if the cloud was directly upwind, you can expect the wind speed to increase before it passes overhead, and decrease after.
Well done folks ! This is a really useful addition, thanks.
It would be good to be able to download these articles as a pdf so we can read them offline. In this format you can only read them when connected to the internet. Just a thought ……… Thanks
Hi Ellen,
Thanks for the suggestion, we do have offline help in our Offshore software.
In Chrome, Tap CTRL+P and then chose the “save as .pdf” option
Thanks, those wise words of advice have a very practical application 🌀
I LIVE ON AN ISLAND IN THE N. ATLANTIC THAT HAS VERY UNPREDICTABLE WEATHER PATTERNS. I USE THE OCEAN AS A MEANS OF FISHING AND HUNTING. NFLD. HAS THE GULF STREAM AND THE LABRADOR CURRENT MEETING ON OUR DOORSTEP.
This is a very good explanation, of a complex topic
Goor and helpful suggestions. Thanks.
Thanks for the info.
Useful. Keep them coming with with notes on relation to maximizing Predict winds capabilities.
Great job useful information
Thanks and keep up the great work
Awesome, I would love more of these explanations on how to properly read maps, perhaps something about the probability of the wind or how the location of the wind might change slightly or drastically?
Hi Bo,
Have a look at our Help Centre. We have a lot of very useful video and written tutorials. Have a look here.
https://support.predictwind.com/hc/en-us
If you have any further questions contact support@predictwind.com
Very interesting. CAPE is new to me. I guess most people are aware of them, but it might be interesting to do a piece about predicting wind gusts in the lee of high ground.
Very instructive. I follow weather through a number of sites, but this is the most concise presentation I have seen. Thanks much for the insight!
I only race on Long Island Sound. Do you have this service for Long Island Sound?
Hi James,
Yes you can use PredictWind on Long Island Sound. The PredictWind PWG and PWE weather models have 1km and 8km resolution on the Sound.
What you said is very clear. Now I have to remember it!!
thanks , a very intriguing scenery of the different conditions one finds out on the big blue . Will definably be useful & a nother very Important safety tool
A very handy addition to your service thank you.
Will this work on the Great Lakes as this is where I spend much of my time sailing?
Hi Bill,
Yes it will be perfect for the Great Lakes.
It’s a very good idea increase the cultur of weather phoenomena
Very helpfull and informative
Great tips on Weather info..
These look like very useful tools, thanks
very interesting .
Please pubblish more on ruteing.
Hi Michele,
What would you like to see about Weather Routing?
This is one of my favourite written tutorial on how to interpret Weather Routing.
https://support.predictwind.com/hc/en-us/articles/203604734-How-to-Interpret-the-Weather-Routing-Results-
Kind Regards
Nick Olson
Great advice
Thank you. Very informative
Very useful
super
Great new forecasting technology should be speciality very important to Sailboat operators as myself
I have the app on my I pad and find the present Intel. very useful
I sail only greek waters . Ionien and Adriatic. I recognise your meteo services as very useful.
Thank,s for your work
Relatively new to sophisticated weather analysis. I appreciate the explanations to ponder at my leisure. Thanks
Thanks! A most informative presentation.
An excellent tool for sailing the Great Lakes.
looks good
Please send the latest Gust and Cape Maps.
Thanks
Hi Peter,
You will see the Gust and Cape maps updated every 12 hours along with the other forecast parameters.
Could I use CAPE with the OFFSHORE forecast via IRIDIUM ??????
Hi Sergio,
Yes the Cape Parameter can be downloaded in the Offshore App via Iridium GO.
Do you have data for Pacific coast? If answer is yes, how far south from the US border?
Thanks
Hi Victor,
We have full global coverage.
Kind Regards
Nick Olson