How Our Event Guidance Fared: Mar-Jun 2019
In the past four months, we’ve provided guidance individually for a variety of exciting events, via climatological data and expert weather pattern insight.
We take a look back at when these hit home with precise predictions and when we narrowly missed the mark… & how that real weather impacted spectator and participant experience…
ACCURATE IN ADVANCE: 8th February for Cheltenham Festival 2019 12th-15th Mar (Range: 32-35 Days)
“The best estimate for the conditions leading up to the festival is one of drier than usual weather mid-late Feb giving way to wetter or snowier weather by the closing days of the month, which then persists through at least early March, [meaning…] a heavy or soft going is more likely than a firm going.”
Going was ‘good to soft, soft in places’, far closer to ‘soft’ than ‘firm’ in the spectrum, much as I suggested over a month in advance.
Figure 1: Charts showing the amount of rainfall compared to average observed during each of 10th-25th Feb (left) and 1st-15th Mar (right).
GOING STILL GOOD: 11th March for Grand National 6th April (Range: 26 Days)
“It’s more likely than not that the predominant pattern during the fortnight preceding the Grand National will be one with high pressure located over or a little east of the UK, [meaning…] the going at the is most likely to be between ‘good to soft’ and ‘good to firm’.”
According to this article in the Liverpool Echo, the going was assessed as being ‘good, good to soft in places’. This is all within the range of conditions that I suggested to be most likely.
Figure 2: Chart showing the mean 500 hPa Geopotential Height (GPH) for the fortnight preceding the Grand National 2019, compared to the long-term average. GPH is proportional to surface pressure, so where it’s above normal, there’s more high pressure than usual (and vice versa).
AND AGAIN…: 4th April for Hay Festival 23rd May – 2nd June (Range: 49-60 Days)
“A high chance of one or two wet days occurring during the Hay Festival 2019 […] you’d be lucky not to see a very wet day at some point, especially within the opening four days.”
Significant rainfall (i.e. 1 mm or more) was observed during the afternoon of 27th May (lasting into the early hours of 28th) and during the morning of 29th. As luck would have it, that makes for two days, as I suggested was likely.
“If you’re camping out, packing for cold nights will likely prove a good idea[…] Sweltering conditions at the Hay Festival 2019 are possible, but only have an outside chance.”
As anticipated, there were chilly nights to contend with, especially those when temperatures fell close to 5°C. There was also a lack of particularly hot conditions by day (though 1st June reaching 23.8°C is not bad going for the location and time of year!)
IN IT FOR THE LONG RUN: 19th April for London Marathon (Range: 9 Days)
“Good temperatures for running look the clear favourite […] be that with dry weather or spells of rain. It looks unlikely that the event will be affected by either soaring temperatures or thunderstorms – or both!”
My ‘clear favourite’ temperature-wise did arise, with a daytime maximum in the mid-teens. Meaning runners’ need for cooling rain would have been far outweighed by spectator desire for dry skies. Fortunate, then, that the potential showers didn’t materialise across London that day!
THINGS GOT CLOSER: 7th June for Glastonbury 26th-30th June (Range: 19-23 Days)
“There’s a good chance more than one day will see enough rain to increase the amount and wetness of muddy conditions at the festival.”
This was a close one; showery weather took place during the preceding weekend, and continued into the early hours of the first day (26th), but then it turned dry and increasingly warm.
“I have the impression that the wet weather will most likely be part of a ‘breakdown’ to a spell of warm or hot weather during the preceding week. Meaning there could be thunderstorms, bringing a risk of torrential downpours, lightning and strong wind gusts.”
We certainly saw the ‘warm or hot weather’, with temperatures climbing to near 30°C on 28th for example. There was a very real possibility that this hot weather would be brought to an end by thunderstorms (model simulations were strongly suggesting this about a week prior to the event!), but this didn’t come to pass. Such weather was instead a good way southwest of the UK (see Figure 3, left).
Figure 3: Charts showing departures from the long-term average, in (left) the amount of rainfall and (right) the mean temperatures, for 26th-30th June 2019.
PRACTISE MAKES PRECISION, STAYING RECEPTIVE: 13th June Looking for Drier & Warmer Weather
“It looks like it will be at least 21st June before any widespread dry and warm weather becomes established that has a chance of lasting more than a couple of days”
I’m particularly satisfied with how this one played out. It was based on guidance tools and observation data pointing toward a strengthening of the global pattern response to the El Niño event.
Figure 4: Charts showing departures from the long-term average, in (left) the amount of rainfall and (right) the mean temperatures, for (top) 15th-20th June 2019 and (bottom) 21st-26th June 2019.
This change had originally been expected to occur by the start of June (making for a drier Cricket World Cup; see ‘Post-Script’ below). When it comes to long-range guidance, it’s the timing of changes that affects accuracy far more than the nature of the atmospheric response.
You see, the tools that guide us with respect to such changes are prone to being too quick or slow with the processes behind them. Thankfully, more often than not, past experience enables meteorologists such as myself to identify when these tools make such mistakes, and adjust outlooks accordingly.
A Quick Note on Environmental Erraticism:
8th May for Cricket World Cup (Range: 22-39 Days)
Long-range guidance using ‘analogue’ years* is a developing area of meteorology that’s still prone to some hiccups. I’m not going to hide the fact that the Cricket World Cup (CWC) was an example this year.
Figure 5: Charts showing the means of the ‘analogue’ (i.e. most comparable on the global scale) years (left) with the observed conditions in 2019 (right), for the 1st (top) and 2nd (bottom) ten-day periods of the Cricket World Cup.
May-June 2019, the upper atmosphere was the warmest on record. It behaved in ways never before observed at this time of year. Meanwhile, there was an unusually weak global response to an ongoing El Niño event in the tropical Pacific Ocean.
This duality of peculiar phenomena was surprising to the meteorological community.
‘This duality of peculiar phenomena was surprising to the meteorological community […] The response to these atmospheric anomalies stayed surprisingly weak, especially in relation to the expected strength of a weather pattern response.’
Unusually warm upper atmosphere temperatures encourage extremes of weather (such as the western European heatwave of late June and the Alaskan heatwave of early July).
But… The response to these atmospheric anomalies stayed surprisingly weak during the CWC. The change did, however, manifest for the final week of June. Then, rainy conditions did indeed move to the southwest of the UK… as seen in my Glastonbury review.
James Peacock MSc
Head Meteorologist at MetSwift
* These are historical years (1950-2018) in which Earth’s atmosphere has been found to have behaved most similarly to how it’s expected to in 2019.