Warning Levels - a guide

M.T. Cranium

As to levels and what they imply, would take this as a rough guide --

LEVEL ONE -- For rainfall, local amounts in the 20-40 mm range, minor flooding possible, issued so that residents and motorists in affected regions will have some advance notice that rainfalls will be sufficient to create minor flooding potentials.

For wind speeds, local gusts in the 55-65 knot range and in regions used to strong winds, minor wind damage likely. Risk of some brief power outages.

LEVEL TWO -- For rainfall, local amounts in the 40-60 mm range, some fairly severe flooding possible, more widespread disruption implied if a level two impacts larger urban areas.

For wind speeds, local gusts in the 65-79 knot range and in some cases not in areas that often see strong winds, would imply widespread minor damage and isolated disruption to road or other forms of travel. About the level of most strong winter storms encountered last year.

LEVEL THREE -- For rainfall, torrential downpours that total 60-100+ mm and produce severe local flooding that could be life-threatening. As far as I can recall, we have never issued a level three rainfall advisory here, something like the legendary flooding in the 1980s might warrant this.

For wind storms, gusts over 80 knots would prompt such a warning. We had one out for the violent wind storm last (12th) February in Munster. Severe and widespread wind damage could be expected.

Boards readers should note that the levels are chosen by thread starters and can be upgraded by moderators in consultation with our forecasting personnel (which in the past has meant Maq, Weathercheck and/or myself). On some occasions a poster may choose level 2 and see that downgraded to level one or even no level of alert. We try to balance the level chosen with overall impacts but the system is not entirely meant to be population-oriented, in borderline cases we would probably go with the lower of two possible levels bearing in mind how many people might be affected. In all cases, any given alert level carries no implied national warning, in other words, the alert level is not meant to be a guarantee that you, the reader located in Ireland, will see these conditions in your local area. It would always be necessary to follow the thread and any maps provided to understand what regions are expected to see alert conditions. It would be a given in most cases that a level two alert would carry with it some peripheral level one alert conditions and that a level three alert would carry level two and possibly level one conditions in various regions (and all levels could also be associated with no alert level in some regions).

File this away for future reference and if you're inclined to start threads with an alert level, use this as a rough guide to what level to choose. Duration of either heavy rainfall or strong winds will also be a factor. Sooner or later, there is bound to be some freak local tornado situation that pops up without an alert, as there probably is on several occasions each year but going un-noticed in general as these very local events impact an isolated area. That kind of wind damage potential is not going to come with an alert but you can be aware of the potential for it by following severe weather thread discussions and tools such as the Estofex warning levels. Be aware that most level one tornado alerts generally verify in terms of one isolated cell that may only be identified days after the fact by its local tree damage signature. As I'm saying, sooner or later one of these will choose to visit a residential area of some town and we'll be asked to explain why there was no alert, but unless widespread significant wind damage is expected (a situation not seen very often in Ireland from severe thunderstorms) there probably would not be an alert unless somebody was carefully watching radar and saw a reason to issue an alert for a specific location. Here again, the ratio of "looks bad on radar" comments to actual damage is fairly large. Meso-scale heavy rainfall warnings are more likely to come to pass as their radar signatures are both larger and longer lasting.

We have not issued alerts for lightning alone, usually in cases where frequent intense lightning is expected, the thread title will just reflect that situation, or there would be an associated rainfall alert. Neither have we ever (to my knowledge) issued an alert for dense fog but if a situation develops with widespread disruption potential, we might easily have a thread without an alert level. Snowfall amounts for alert levels would be something like 5-15 cm level one, 15-30 cm level two and 30+ cms level three. Here again, the scale of disruption would be a factor, likely if it was a widespread 5-15 cm with one county or location expecting 15-30 cm, the alert level chosen would be level one, whereas if it were 15-30 for greater Dublin in that same situation, it might be level two. These levels are always going to contain a subjective element and we need to set them in advance. We had quite an active discussion last February about whether to stay at level two or upgrade to level three and that discussion persisted longer than the strong winds too.

delw

Should be stickyed IMO
Cheers MT

M.T. Cranium

Thanks, a moderator wisely removed this post which I had originally placed in the current rainfall (level one) thread. Keep in mind, we prefer the term "alert" to "warning" here on Boards in view of the implied responsibility of Met E and other agencies to issue official warnings. The term "alert" probably carries less impact than warning, if you wanted to get more technical, level one alerts are actually alerts in the generally accepted meteorological usage and level two or three alerts are warnings. The term "watch" is used in North America ahead of an actual warning to give advance notice that a warning might be needed later. I don't think that term is used much in Europe and alert might suggest the same thing.

People should realize that this system on Boards developed over time and some of us have inherited it without necessarily having any or much input into how it operates. Perhaps someone can give us a better historical perspective, it seems to me that these alert levels go back quite a way and before I started forecasting here at all. I stay out of the question of how to design an alert system mostly because I don't live in Ireland and you have a much better understanding of what terms might mean to readers, so in fact you'll find that I seldom originate these tagged threads although on a few occasions I have started one, and on a few other occasions I have lobbied for a change in level (not always up as you might have suspected ).

The basic idea would seem to be, level one don't be caught entirely unaware that some significant weather is approaching, level two, you might want to take some precautions if you think the forecast affects your interests directly, and level three, something big this way cometh.

I believe we are doing something useful with our alerts. In many cases (not all) they are mirror images of Met E warnings and simply extend the reach of those warnings to Boards readers who might not have noted (or might never note) the official warnings. In other cases we may have come up with somewhat different "takes" on various situations and it goes without saying that there would be a scatter of results ranging from less effective to more effective. You can probably see why we would be especially aware of the need to avoid downplaying official warnings although on a few occasions this concept can be inferred by the reader from comments from "the usual suspects." It would be worse to have a serious error in downgrading than vice versa, and it helps our credibility if we happen to catch one or two situations that turn out a bit more severe than otherwise forecast.

The reason that I say that I feel this is generally effective can be found in posts (and quite a few PMs that I get and probably others get as well) along the lines of "read your forecast, moved my car, tree feel in that very spot" and to balance against that with negatives is difficult, I suppose if somebody cancelled a lucrative venture they might lose a similar amount, but if somebody moves a car and the tree does not fall (but might have) then that's not really a loss, just a waste of one minute and perhaps you would miss the annoying phone call as a bonus.

Who knows what the actual results of our level 3 alert last February may have been? And we know going into situations like that, some people in marginal areas will over-estimate their impacts and come away perhaps perceiving an over-forecast, but in this sort of thing, you're mainly concerned with assisting those in actual danger and would prefer to be very helpful to a few as opposed to avoiding a minor inconvenience to many, if you see my drift. Hopefully we will all see some drifts this winter (myself included as we also had a snow no-show last winter, basically).

Video

February 12th was the strongest winds i've ever seen in my lifetime level three was justified for sure.. it passed over fairly quickly but was very intense for what we're used to but anyways I'm sure a lot of the newbies will appreciate this post being a sticky.

Villain

Why not use the colour system that is in use by Met Eireann? seems odd to use numbers when people are used to colours?

M.T. Cranium

Good point, I think our three levels come out with the appropriate colour on screen but we could add two words (code ___ ) after the level (number).