Published 17 October 2021.
Changes in sea temperature
Sea temperatures in the Northern Hemisphere Atlantic and North Sea are significantly generally warmer than climatology for the time of year.
Tropical Atlantic is above average and is forecast to remain warmer than average through to at least Spring 2022 (See Met Office graphic below).
The East Pacific has larger cold anomalies than last month. Forecasts suggest that tropical Pacific Sea Surface Temperatures are likely to cool further to a significant La Nina state for the Winter before approaching a neutral state in Spring/Summer 2022. Meanwhile the Indian Ocean, W and SW Pacific have well above average temperatures for the time of year.
The North Atlantic Oscillation index (500hPa index shown below) turned negative more or less as forecast in late September and is forecast to remains negative for the next two weeks though with reducing confidence and strength. The negative NAO is consistent with a blocked or non mobile pattern which can be anticyclonic or cyclonic over the UK depending on the location of the “blocked” high and low pressure centres but it might also relate to less deep low pressure systems across the North Atlantic.
The UK at present is heading towards a more mobile Atlantic pattern more like a positive phase of the NAO although this may not last.
For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation
Recent Climatology – SW England
October up to the 17th has been warmer and perhaps slightly drier than average (1981-2010) with near or a little above average sunshine. Temperature anomalies are around 2 deg C so far..
2021 UK Met provisional Temperature and Rainfall anomalies for July to September 2021 are shown below: Temperature has been mostly above average although the South of England was colder in August. Rainfall deviated from the long term average (1981-2010) across the W of Scotland which was drier than average with parts of the south of England being wetter than average.
To illustrate the difference between 1981-2010 (top row) and 1990-2020 (lower row) in the 30 year climate periods, both are shown in the graphic below. Temperature and rainfall anomalies for September 2021 and the year to September are shown below.
UK River flows in September 2021 were near average and ground water remains above average in the East of the region. Details can be found in the September 2021 Hydrological Summary
Data as of 17th October show near normal river values across of the SW but with some locations (in orange) showing below average values.
Reservoir levels, according to SW Water, were fairly high across SW England as of 10th October 2021.
Global Flood Awareness (updated to version 3) October forecast for the period October to January 2022 indicate average flood risk for SW England. River flow forecast shown are blue for above normal river flow and grey near average.
2021 Atlantic hurricane season Started 22 May 2021. Data from Wikipedia as of 17th October 2021.
Wikipedia data summary: Total depressions 20, Total storms 20, Hurricanes 7, Major hurricanes (Cat. 3+) 4.
Estimates for total fatalities 159 total and damage $69.5 billion (2021 USD) which may be the fourth costliest tropical cyclone season on record. Global (Pacific and Indian Ocean) fatalities amounted to 518.
A: 1: Stratosphere
North polar stratospheric circulation is changed to “winter” mode as shown by the 50hPa and 10hPa analysis for the 16th and the T+24 hour forecast. The polar stratospheric vortex is forecast to become unstable due to stratospheric warming.
In the Southern Hemisphere there is a strong and fairly stable stratospheric vortex with a well established Ozone “hole”. Data shows the size of the “hole” is currently above average with large scale ozone depletion having taken place.
2: Upper Troposphere
CFSv2 200hPa contours (top row) and CFSv2 anomaly (middle) and NMME (lower row) for November 2021 to February 2022. There is a hint from CFSv2 data for a less mobile patterns across the Atlantic for November and December followed by a more zonal type.
B: Lower Troposphere:
Selection of model solutions for November 2021 to February 2022 using October data, are shown below.
Top row temperature anomaly and lower row precipitation anomaly.
Source Data WMO low resolution super ensemble for the winter December 2021 to February 2022.
Top row temperature anomaly and lower row precipitation anomaly. Left image three month mean then individual months.
Individual members of the WMO super ensemble
Full graphics for the November can be viewed at http://www.weather-info.co.uk/wxsvc/seaslatest.html
C: Comparing the output of seasonal models for July August and September based on June 2021 data for the UK and Ireland.
For graphics and details see Verification review July August September
Summary – 19 June 2021 –
Temperature most likely near normal or slightly above normal for the three month season. Scotland and Ireland more likely normal and highest chance for above normal in S/SE England.
Rainfall for the season probably below average in the S/SE of UK, in terms of rain days, and normal in the N and NW. Some indication for a wetter than average September especially in the north. Overall rain total for the three month may end up near average perhaps below in the south but thundery showers unlikely to be predicted by seasonal models and can easily tip the balance to wetter.
Comment: Temperature was above average but the north had stronger anomalies than the south and the south was below average in August. Rainfall gridded for UK and countries show below average rain but due to rainfall in July some spot locations were above normal.
Scoring will attempt to state good, fair, poor or no signal.
TEmperature marked fair if monthly lower value for August no shown otherwise most have above average and NCEP text uses 1991-2020 hence normal = above normal in previous 30 year period.
Comment: Looking for above average temperatures, below average rain and above average pressure.
1. Russia (WMO): Temp good . PPN .
2. USA – CFS2 : Temp fair. PPN .
3. UKMO Contingency: Temp fair . PPN fair .
4. UKMO : Temp fair . PPN fair . PMSL fair
5. USA – IRI : Temp no signal . PPN poor .
6. KMA APCC : Temp fair . PPN no signal.
7. JMA : Temp fair . PPN poor. PMSL fair (WNW)
8. NMME : Temp good. PPN fair .
9. WMO multi : Temp fair. PPN fair.
10. BCC : Temp fair. PPN fair .
11. NASA : Temp fair. PPN poor .
12. Brazil: Temp poor . PPN poor .
13. CanSips : Temp fair . PPN fair.
14. IMME : Temp poor. PPN poor .
15. Copernicus Temp poor . PPN fair . PMSL poor
16. CMCC Temp good . PPN fair . PMSL poor
17: DWD Temp poor . PPN poor . PMSL poor
18. EC Temp fair . PPN poor . PMSL fair
19 JMA Temp poor . PPN poor . PMSL poor
20 UKMO Temp good. PPN good . PMSL fair
21. MF Temp poor . PPN poor . PMSL poor
22 NCEP Temp poor . PPN poor . PMSL poor
23 ECCC Temp: good. PPN fair . PMSL poor
Remainder of Autumn 2021 (November).
Near normal or slightly milder than average temperatures seem likely with near normal or slightly below normal rainfall.
Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November average around 9 or 10 Celsius. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. November totals range from around 80mm east of the moors to over 200mm over the moors.
Winter 2021 / 22 (December January February)
Temperatures across SW England are likely to be slightly milder than average this winter although December may see values close to average which would be a change from recent months. Rainfall probably above average overall but December could be drier than average with January and February wetter than average. Below average snowfall is most likely, which mostly limits snow to the Moors although December has a slightly increased risk of snow showers.
Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.
Spring (2022 March April May)
Overall milder than average temperatures but with lower anomalies in May. Rainfall for the season probably close to average values but some longer drier spells are possible although models do not agree which month could be drier.
Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset
Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.
The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary
SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579
IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.
UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/
NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1
GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.
‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu
International seasonal monthly data from WMO
Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin
Climate data from The Met Office UK and NCEP USA
Contains public sector information licensed under the Open Government Licence v3.0.