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Summer 2020 update 2

Latest indicators


11/05/2020

This is our second look at what the seasonal forecasting models and background signals are suggesting about the weather prospects for summer 2020. The first summer 2020 forecast indicators issued on 23rd April remain online to read. The TWO summer forecast will be issued in late May.

Fine weather in summer

By by simonwakefield [CC BY 2.0], via Wikimedia Commons

Seasonal model overview

A range of seasonal models are available. However it is important to remember that their skill level (accuracy) for the UK is low.

Model Temperature Rain
GloSea (UKM) Above average No signal
ECM Slightly above average in the south - slightly below in the north Below average
Meteo France Above average in the east No signal
DWD Above average Slightly below average
CS3 Above average No signal
Beijing Climate Center Above average Below average
CanSIPS Slightly above average Slightly below average
CFSv2 Above average Below average
Table 1: Forecast temperature and precipitation anomalies, June, July and August

 

The notable things at this stage are:

i) All models show temperatures above the average taken over the 3 month summer period as a whole in the south of the UK. ECM favours below average temperatures in the north.

ii) Most models are forecasting either no signal or below average levels of precipitation.

Note: Since the first summer forecast indicators discussion GloSea has updated and now seems to be favouring warmer conditions more strongly. 



Anomalies masking the outcome

The anomalies in the table may not be telling the complete story. They are for the meteorological summer as a whole and there is a chance that extreme swings are cancelling each other out to an extent. For example hot and dry periods may be offset by cool and wet ones leading to a close to average outcome overall. 

ENSO conditions

The state of the El Niño Southern Oscillation (ENSO) has significant impact on temperature and rainfall patterns around the globe. Nonetheless its link to the UK summer is thought to be weak.

Latest forecasts suggest there a 60% chance of ENSO-neutral lasting through the Northern Hemisphere summer. It remains the most likely outcome for the autumn too. Therefore ENSO is not expected to favour a particular outcome.

Note: The probabilities have not changed since the first summer forecast indicators discussion.

Atlantic Hurricane season

Several forecasts for the 2020 Hurricane Season have been issued. They range from suggesting slightly below to slightly above levels of activity. At this stage none of them go for an anomalously active or quiet season. 

Colorado State University is predicting 16 named storms, 8 hurricanes.

Accuweather is predicting 14 to 18 tropical storms of which 7 to 9 are forecast to become hurricanes.

The predictions possibly favour an increased chance of settled weather in the UK during the late summer.

Summary

1) Seasonal models suggest above average temperatures and below average rainfall levels taken over the June, July and August period taken as a whole.

2) El Nino is not expected to strongly favour a particular outcome.

3) The latest 2020 Atlantic Hurricane season forecasts perhaps point to an increased chance of settled weather relative to the average in the late summer.

At this stage a summer with above average temperatures is thought probable. The signal for rainfall is weaker but it favours drier than average conditions.

A drier and warmer than average season suggests the possibility of some very high maximum temperatures being recorded in the UK but it does not ensure them. It could instead mean long warm or very warm periods like those in summer 2018 rather than the record breaking heat spikes we experienced in summer 2019.

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