Gale, fresh or strong?

Confronted with a weather forecast predicting any sort of a gale, the first instinct of a true-born Green-Gymmer is to shrug off the warning: “What’s a bit of breeze?”

Earlier reports had suggested we would get the benefit of a window of good weather, as the remnants of Hurricane Gonzalo made landfall on Britain.  As the event drew closer, the forecasters seemed more certain about the timetable: sunshine Tuesday morning, but windspeeds peaking too.

What the experts were not sure of was just how strong those winds were going to be.  The Chief Forecaster’s Assessment (issued by the Met Office 1626 on Mon 20 Oct 2014) was undeniably true, but not awfully helpful for anyone planning a work session in the great outdoors:

“some damage to trees is possible, given that many are still in full leaf.” 

Anything is ‘possible’.  What a planner would like to know is, how probable it is!

It is, after all, not that long ago that in unusually warm sunshine for the season I found a day-flying moth most improbably basking on my front door.

At least I think it was a day-flying moth.  If I have correctly identified it as a Small White Wave (Asthena albulata: small wingspan, < 2 cm), it was outside its normal habitat.  For it normally lives in broad-leaved woodland rather than a housing estate.  Perhaps it only comes and poses on my door when it spots the opportunity to be well camouflaged in between visits from the window cleaners.

In defence of forecasters: it has subsequently been pointed out to me, by someone who’d know, that ‘possible’ has two different meanings:

1. probability greater than zero    
2. probability something like a quarter

Meaning #2 is what you get when a forecaster presents results in words rather than numbers.  Furthermore – scientist observes – “very small scale weather forecasting is extremely difficult unless you put in tremendous resources, which you can do if it is a very important spot such as an airport.  I am not sure your Green Gym location would count for that”! 

As it happens, we are near a spot to which more weather-forecasting resources are allocated (RAF Benson), but can only access their information in the same Janet-and-John format as any other members of the public.  With the geography here, an accurate forecast for the air-station can be U/S for a location only a couple of miles away.

To return to the tale of today’s non-Green Gym:

Cue translate mph into knots, and look up Beaufort Scale.  Target fell neatly between Force 8 (which wouldn’t put off our volunteers) and Force 9 (which would, or at least should, especially when we’re scheduled to be working under trees):

8: Fresh Gale 

Moderately high waves, of greater length.  Edges of waves begin to break into spindrift; foam is blown in well marked streaks along the direction of the wind.  Considerable airborne spray.

Some twigs broken from trees.  Cars veer on road.  Progress on foot is seriously impeded.

9: Strong gale

High waves whose crests sometimes roll over.  Dense foam is blown along wind direction.  Large amounts of airborne spray may begin to reduce visibility.

Some branches break off trees, and some small trees blow over. 
Construction/temporary signs and barricades blow over.

No mention in the Beaufort Scale of wheelie bins overturning!

Add the observation from someone who would know, that there are lime trees at the site which have a track record of shedding large limbs, and alas, as ‘C’ – and the one who sat through 6 hours of TCV risk-assessment training – it fell to me to make the unpopular call and say, “No, we can’t do it: if we know there are trees which are liable to drop big branches, and if we know that the first high winds of this autumn are forecast to peak during the session, it would be irresponsible of us to proceed.” 

Which may have been right, but was terribly boring.