This Sunday, as you’re walking down the Reading streets en route to a Hallowe’en-themed party, or dressing up and terrorising the neighbourhood for their sweets, you have probably tried your hardest to look really scary (unless you’re lucky enough to naturally be like that). You might have decided you would try a witch costume. The stereotype would include a long hat and broomstick, and perhaps a black cat. If you really wanted the full scary effect, though, wouldn’t a full moon be perfect for lighting your way? But what about the weather? Picture a stereotypical spooky scene: high cloud drifting past a full moon, perhaps some mist or fog, and cold temperatures. How much of this can we expect this Sunday night in Reading? If it’s not possible in Reading, where would be the scariest place – in terms of weather – this Hallowe’en?
Moon and high cloud
Unfortunately, there will be a half-moon this Hallowe’en, meaning we’ve already got a less-than-ideal backdrop to Hallowe’en. It will also rise around midnight, meaning you’ll have to risk an ASBO to trick-and-trick in the moonlight this year. Fortunately, the GFS model hints that there will be a break in the low cloud around midnight for Reading, through which some sparse, high cloud may be seen drifting ominously…
Ignoring the Moon, which is going to be similar in phase and moonrise time wherever you are, you can maximise your chances of visible high cloud somewhere near Fort William in the Scottish Highlands. GFS suggests a zero chance of low or mid-level cloud on Sunday night in NW Scotland, but that an advancing warm front should bring plenty of cirrus and other high-level cloud.
The GFS predicts visibilities of between 5 to 12 km overnight, which dismisses hope of some light mist (defined as less than 2 km visibility). The break in cloud is not long enough to allow the Earth’s surface to cool to saturation, which is required before any fog or mist can form. Light winds and plenty of moisture from the week’s low pressure systems are other essential ingredients that are present, so perhaps mist is not too far away?
Turning to the GFS model again, it is difficult to find somewhere obvious in the British Isles with the indications of fog or mist, i.e. close to saturation, low visibility. Areas near Newcastle and King’s Lynn have hints, but nothing worth travelling for (you are taking this blog seriously, right?). It was difficult to be sure, too, that the areas with low visibility and high saturation were a signal of fog and not heavy rain. SW Finland was a good candidate, with the added bonus of shorter days at this time of year. GFS suggested <1 km visibility and low cloud bases. But what is Finnish for Hallowe’en?
A good Hallowe’en demands a chill down the spine in more ways than one. Reading will only just nudge into single digits on Sunday night, warmed by the intermittent low cloud acting as a blanket (albeit a very threadbare one) to trap the day’s remnant heat. Fortunately, the Scottish Highlands again appear to be the place to be, with lows of -2ºC forecast before 6am by the GFS model. If that’s not good enough, may I refer you to WCD’s Friday presentation on Antarctica. The slight problem, however, is the lack of people to scare.
Although it would be rather difficult to find a howling wind and still expect mist formation in Reading, I found a good example here, in Liverpool, Nova Scotia, Canada. Granted, this was the weather for yesterday and today, but an example nonetheless. It appears the existence of both simultaneously is due to the relatively warmer waters off the coast of Nova Scotia in autumn. When cold, dry, polar air flows across the water, evaporation increases and the air reaches saturation. This fog is advected into the coastal area by the strong winds – a ready-made spooky scene!
I will leave the decision of the ‘scariest place’ to you! Also, what other meteorological factors can contribute towards an appropriate Hallowe’en scene? Have you ever encountered a place on Earth that seemed spooky because of the atmospheric conditions?