Warning Levels - a guide

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.