April Showers here to stay? 20C on the way?

As the clocks have gone forward unironically the weather has sort of gone backwards; with polar air moving south across UK and Western Europe. Courtesy of stronger sun which is now comparable strength to late summer, we often see in spring, 'April showers' the surface heating from the sun, causes air close to surface to rise as less dense than cooler air this condenses into shower clouds Cumulonimbus. Often days with long sunny spells in Spring and Summer, can be interrupted into afternoon as heating of the day peaks and we see sharp and brief torrential showers. This will be the story over the next few days.

A rash of torrential showers with hail/thunder poss across S/SE England Wednesday PM

Distinctive towering Cumulonimbus

Overnight tonight there will be a widespread air frost across UK and Ireland a cold night for April however not unheard of.

Do watch out for icy patches first thing following showers of today.

Minimum temperature at 0600 Wednesday widely freezing temperatures

Into tomorrow we see low pressure offshore east coast of Scotland back west and very slowly move SSW down Britain this will bring organised precipitation with weather fronts to Scotland and Northern England with significant snow for hills as much as 20cm possible. Most of the country will see a continuation of sunny spells and showers, some lucky areas may avoid them altogether the greatest risk areas will be in the south and east.

Following a showery regime another cold night with icy stretches possible for central and northern areas a little less cold in the south and east. Into Thursday, again a rather similar picture with a continuation of sunshine and showers these are possible anywhere. With a rather gusty wind it will feel particularly cool on already cool temperatures.

From Friday we see the beginning of a change with temperatures recovering nearer to normal with rain limited to west although remaining blustery with a cool wind off continent.

Into weekend it is looking dry for many however a slight chill with easterly flow this could result in cloud bubbling up for areas in east England close to the North Sea; with brightest and warmest conditions in the west.

Into the new week a continental flow will continue as it is April it will not be as remotely cold as it would have been in winter months - we would have seen very cold conditions from this then. We may see lows come in from east off North Sea which may bring organised rainfall most sheltered areas being those further south and west, likely not nicest of weeks in east with Stratus cover possible a persistent feature with cool sea.

Further outlook: Very uncertain nonetheless the first half of April is very unlikely to bring anything warm with a southerly tracking jet stream deflected south by regions of blocking (high pressure) to north. I do sense it may be quite a struggle this month, however greater chance of drier and warmer conditions in the second half of April, perhaps it will not be May or late April until we truly see the weather settle down and lose its changeable nature.

An early taste of spring followed by winter's last hoorah?

First of all I'd like to apologise for the lack of content that's life for you, but let's just get into it; this blog post will look at spring-like conditions this week and beyond with these conditions unlikely to hold, is winter finished with; or is there a sting to its tail? Read on to find answer. After a lacklustre winter promising so much background signals et al, although, I'm sure many in Southern Central England enjoyed witnessing biggest snowfall since 2010 despite no impressive cold and in situ and of NW origin. Attention increasingly draws to Spring; easter bunnies and all that shenanigans with gathering warmth of sun's rays for many comes as a relief as we move away, from often, dark and dreary season that is winter.

After a very unsettled period of weather in which we were bombarded by low pressure barrelling across Atlantic with only second named Storm Eric which brought widespread gales and drenching rains, although rather tame. In contrast winter 13/14 had over twelve major wind storms, notable has been clear absence of stormy weather courtesy of subtropical ridges from Azores extending unusually north. With polar jet shifted to north of UK and has derailed several easterly cold spells despite macro-pattern being good.

Storm Erik approaching the British Isles at 0600 UTC 07/02/18 imagery from Meteosat-SEVIRI

After a rather cool feeling Monday with a weak northerly airstream, we lose the chilly wind with Azores high poised to move in imminently, cutting of chilly flow with positive heights anchored over Central Europe this week. Bringing the first unseasonably mild conditions of 2019 to Europe most anomalous mild conditions to be seen in northern Europe on Friday GFS has 850hPa temps this is roughly 1500 meters up, 16C above norm in south of Finland.

This ridge of high pressure will introduce much 'warmer' airmass however will not remotely carry characteristics of a 'Spanish plume' with southerly winds prevailing this week. In summer time temperatures would have soared to low 30s in south of England alas it is far too early for that. However, there will be plenty of sunshine in which it will feel quite warm across England and Wales but do note early in day likely to be chilly with frost risk. Generally temperatures will range from 11-13C perhaps 14C in the capital. Areas further N and W Scotland, NI and Ireland will be more vulnerable to cloud and drizzly conditions with more of a moist southwesterly component. The foehn effect is likely to result in highest temperatures in mountainous regions of North Wales and North Scotland where a localised 16C is achievable. The peak of this mild spell countrywide is expected on Thursday.

Although do make the most of it this proper taste of spring is unfortunately expected to be fleeting, a breakdown from W will initiate on Saturday first across N/NW parts and by Sunday all areas will be subject to a more cyclonic westerly flow. With much more in way of cloud and temperatures nearer to seasonal norm although still quite mild perhaps it won't feel it.

The expectation into next week is for weather to start more unsettled with the spring-like conditions of this week a far cry although by no means is a wet period being signalled just less in the way of high pressure. Something which has grabbed my interest is current sea surface temperature anomalies (SSTs) through Atlantic basin; this winter, waters south of Greenland have been cold. This has recently reversed there are papers which show a greater correlation with -NAO with above average SSTs in this region, this means an area of blocking high pressure to north of UK which deters milder airflows and more often than not UK can see colder conditions, notably so in the case of 2018 infamous beast from the east. What's been notable this winter is clear lack of -NAO despite background signals/NWP suggesting otherwise. I would say there is great scope going into March for a wintry pattern -NAO pattern, although be aware of a lesser significance than mid winter. Furthermore what can be drawn, it seems going into spring a greater emphasis for a more southerly tracking storm track/ jet stream this is not good if you are after settled Spring.

I am of the opinion the weather will turn more settled mid week so a short period of wet and blustery weather for NW parts especially. With another blocking high likely to fill in vacuum but this may bring decidedly different weather at first it may be mild but it is conceivable we could see a cooling trend. A blocking high to north/northeast has been glanced at NWP and does reflect with pacific forcing which has an influence on our weather, MJO phase 8 this is a cold blocked phase for NW Europe the below chart is representative of what's possible.

Low risk for now but the possibility of drawing in much cooler east winds in final week of February into March. I do see a cold spell in next few weeks certainly not forecasting something exceptional, although with a chance of settling snow possibly anywhere. Atlantic intrusions may deliver more substantial snow to lower levels. I do not think winter is quite done with us even if it seems it never turned up.....

In recent years spring has testified winter weather can easily strike in this transitioning period from winter to spring. There are roughly 3 to 4 weeks remaining in which widespread swathes, can see a wintry pattern you may be fearful to know and indeed it is premature to say winter is over. Although a sizeable chunk of mild weather to get through first if so. We may have passed the point of temperatures remaining below freezing and continuous lying snow cover away from high ground. The arctic itself is its coldest early March its time of year where we see maximum arctic sea ice extent. Well into spring northerly airstreams can be potent exemplified in 2016 the capital had some flakes at end of April some of the latest snow I can remember, with the frequency of E/N/NE winds is greatest in spring it's not so surprising. And I wouldn't be so surprised if we winter has a final encore.

Cheers,

Dan

'A Cold Hearted Winter' - winter forecast 2018/2019

At this time of year increasingly thoughts draw to what may lay ahead in the upcoming winter months, will there be snow? With seemingly helpless task in finding direction in the atmospheric ‘chaos’ which never stands still, ebbs and flows in global circulation is which drives what weather we see. In this winter forecast blog post I’ll try make sense of multitude of teleconnections these list from: the ENSO state (El Nino and La Nina); the QBO (Quasi Biennial Oscillation); Stratospheric Developments: Solar Activity and more. Some of these drivers are more dominant to one another whereas some drivers can work destructively with another accessing their weight is a very difficult task but I'll give it a go.

Forecast summary:

A turbulent winter season with a highly meridional jet stream strong chance of significant cold and snow but also much milder/unsettled conditions.

Risk of significant disruption to Polar Vortex from mid Dec with ‘fallout’ seen in January possibly precipitating in much colder conditions. I am however expecting first cold spell later December but more intense cold spell in January. It is very unlikely to be continuous from December. I’d expect pattern to relax with westerlies taking hold and then for pattern to reamplify. As of now zonal winds at 10hPa are stronger than normal indicating a stronger than average stratospheric PV. Compelling signs into December for a strong weakening of zonal winds. Thus, continuing the disconnect with troposphere the lower atmosphere where weather happens, a strong PV often propagates vertically into troposphere; greatly increasing, risk of a stronger jet stream and milder conditions therefore these potential developments, make colder, blocked weather patterns more likely during the first half of winter. Late winter period in contrast to winter 2017-2018 expecting it to be relatively mild and this goes against grain of others winter forecasts and many seasonal models.

Temperatures; for winter 2018-2019 statistically unremarkable while tempted to go for an overall colder winter I do have hesitation with some variables such as Atlantic SSTs and W-QBO. However, do not let overall picture deceive you, these can hide extremes of significant cold in which I’d say is likely to feature and similarly much milder, wetter conditions.

December– near normal to touch above; very mild start offset by drier, possibly much colder second half possibly with the first snowfall esp. E courtesy of easterly winds.

January– coldest month of the winter, perhaps well below average long overdue.

February– near normal, cold weather is likely but possibly early spring like conditions.

Rainfall; likely to be above average across England and Wales this is needed following a very dry summer; owing to a southerly tracking jet stream, drier conditions possible for Scotland nearest to blocking highs and displaced storm track. Although I expect certainty won’t be immune to multiple bouts of wet and very windy weather.

Forecast drivers:

QBO

First of what is it? The QBO is in essence the directional flow of upper winds on fringe of atmosphere above equator which flow either westerly or easterly we pretty much know from November where QBO will be for winter making it a very useful winter forecast indicator of being constant. An easterly phase increases chance of cold weather patterns and increased chance of disruption to PV you may have heard about SSW (Sudden Stratospheric Warming) in the run up to ‘Beast From The East’ 2018, while westerly vice versa, strong jet & increased winter rainfall. Currently we are in descending negative phase (westerly) and through winter 2018-2019 this will only ‘strengthen’ – this could possibly mean a backloaded winter is unlikely contrary to last winter 2017-2018 which also featured an E-QBO.

ENSO state

This winter we face a weak El Nino a climate cycle in Pacific Ocean which covers 30% of Earth’s surface. As a result, its sea surface temperature (SST) pattern configuration, has a great influence on weather and climate around the world. During La Nina conditions we see colder than normal SSTs dominate equatorial parts of Pacific whereas in El Nino conditions which are being seen this winter vice versa. The ensemble guidance above are indicating a weak to moderate El Nino with magnitude peaking at roughly +1 to +1.5 there are indications El Nino will weaken even further towards spring, some word around Twitter is that El Nino has already peaked. It’s quite possible it will not be particularly influential this winter not being overly ‘strong’. In winter 2010-2011 in which saw the coldest December since 1890 we had a record strength La Nina historically this favours a cold start to winter with milder conditions seen late winter. Some argue it was this which led to that winter burning out. Presumably on the face of it the ENSO state this year favours a backloaded winter, although I am doubtful it will be strong enough to have much of an imprint on atmospheric circulation in UK and Europe this winter.

What is El Nino? This Met Office video is a good introduction.

https://youtu.be/WPA-KpldDVc

Solar Activity

spotless sun 1/12/18

There is emerging and recognised evidence that low solar activity years tend to correlate with more frequent high latitude blocking events and a more meridional jet stream for reasons not well understood. Thus, increasing the chance of cold blocked weather patterns. Currently we are at end of weakest solar cycle 24 and we are approaching the next solar minimum – the least active part of a solar cycle. What is very interesting the last time we had an inactive sun with El Nino conditions was in winter of 2009-2010 - a cold and snowy winter in UK, I do see this winter having some similarities. Low solar activity this winter and winters following 18/19 are going to be an exciting time for theory to be well tested in digital age.

Northern Hemisphere snowpack

Northern Hemisphere snow cover & sea ice 30/11/18

Research studies suggest that a healthy snowpack in Northern Hemisphere during the autumn can be a valuable tool to predict subsequent winter with a feedback mechanism in HLB and cold and snow in Eurasia and U.S. Dr Judah Cohen theory looks particularly at region below 60N during month of October being the critical month, October 2018 featured a very slow build in snow cover however towards the end of the month the snowpack exploded. Therefore, giving mixed signals, currently Northern Hemispheric snowpack is above average, this is good for winter prospects in UK. A deeper, extensive snowpack results in formation of colder and denser air-masses through albedo, fresh snow cover can reflect as much as 90% of incoming solar radiation. Already I have noticed unusually low 850hPa temperatures given the time of year in NH. And as such the cold air ‘reservoir’ this winter may be colder than normal increasing risk of UK seeing significant cold and snow.

Conclusion

Unfortunately due to time constraints I have not been able to really scratch surface but I tried, a winter of discontent for 'coldies' I absolutely do not see, you may have got an impression from above I'm optimistic and indeed I am. With midwinter statistically coldest time of year my main area of interest, December should not be dismissed too for wintry weather. I hope you liked this winter forecast my first official one following a successful summer forecast, in experience these forecasts either go spectacularly wrong or right, no in between - will review later. Cheers :-)

Dan