A few people have been commenting how we seem to be stuck in Autumn. Certainly the wet and windy, often stormy weather is a major feature of Autumn. Plenty of lows have continued to rattle in bringing gales, heavy rains and flooding, the SW winds bringing mild-ish conditions. There have only been tiny bits of snow (away from Scottish mountains where there has been some). Ice is becoming more of a problem now that the earth is cooling down properly with the lack of sunlight over the past month. But no real cold spell, no standstill UK snow, no real pictures on the evening news of people stuck in their cars all night on the M-whatever. No ‘there will be grit shortages’ stories.
Winter did come late last year (2013). I lived in NE Scotland, the snowiest county in the UK and it did snow every day in February. At first I was all excited, posting snow pics on social media to make my fellow southern weather forecasters jealous. Then it was just, look outside, Oh snowing again. February and March were the cold snowy winter months. People were saying, “is it ever going to end, will Spring come?” So there is still time this year.
The indigenous people of Australia name their seasons after types of weather or nature’s response, so the dry season, the rainy season or looking for migration, or appearance of wildlife. For the Aboriginals, the rainy season comes when it rains. So just because it the calendar month of December, why do we assume it should be snowing in the UK.
Daylight has a lot to do with it, the shortest day, the UK is furthest away from the sun. Less actual heating each day, colder nights. January and February are actually the coldest months, due a lull in the heat loss from our surrounding seas. Also the UK maybe an island/s, but in weather terms nobody is an island. The air flows around the earth and what is going on over Europe or N.America has a knock on effect for us.
The extreme cold and heavy snowfall in the US have been in the news recently. This has helped amplify the strength of the Jetstream. The Jetstream that affects us (the polar jet) is fed by the temperature gradient across Polar and mid latitude regions. The N.America cold polar air, has been intense, giving a greater temp. change to the milder air of Atlantic and southern states. That has given the whole westerly flow more oomph than normal. There was a mild December and a milder than average first half of January and England has already been very wet for 2014. Thanks to the strong Jetstream bombarding the UK with low after low.
What we need is something to stop all this. A High pressure, does anybody have a high pressure? We get our coldest weather when the winds blow from the northeast or east. To our north is a lot of sea, that doesn’t get extremely cold. Siberia on the other hand does have that reputation.
Last week there were murmurings and shrieks of a cold spell and snow from the East, for this week’s forecast. That didn’t come to bear. It was always a wavering situation. The next possible spell looks like being end of Jan into start of Feb.
It’s not just the Jetstream. The Pacific is not experiencing an El Nino or La Nina event, so the worldwide neutral conditions are not a factor for this winter. The stratosphere (been in the news with the Polar Vortex) has been in a strong westerly phase of the QBO (quasi-biennial oscillation). This 14 month ish phase looks set to end in next few months and could allow some changes. So far it has been enhancing the westerly flow across the Atlantic. Bit of sudden stratospheric warming, to stir things up, the Polar Vortex eases up a bit and blocking is more likely. Blocking= a big high in the way, forcing the Jetstream south and a different wind direction for the UK. See the Strat. thread http://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/
Last weeks ‘excitement’/desperation came from a High developing over NW Europe, the Scandinavian high (Scandi High on the forum). If there is really cold air tucked around this, then it can deliver. The thickness charts 1000-500hPa are ideal to show where the air is coming from, dark blue drawn from Siberia or green/yellow in the easterly coming from SE Europe or the Med. Once a high is established then it takes a while to move its big lumbering self, the blocking can go on and on.
So even if you spot a hint of cold air, high pressure etc in the beyond day 5 charts, hold your horses. The problem with forecasting this, is that the UK is often at the edge of cold pushing out from Europe and at the front line of the Atlantic bombardment. That pushing and shoving borderline area can often lead to disappointment. Or, we can view it as another of weather forecasting’s challenges that keeps us so interested in the weather in the UK.
If it snowed every day for 3 months, what would we discuss?