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As promised yesterday in our update on the potential cold spell outbreak next week and after overwhelming feedback from our followers I will be providing a daily update on the possible incoming colder period of weather which is set to arrive next week.

Giving forecasts regarding will it snow next week and what day is still to far out as many thing need to fall into placesand we also need to move into a better timeframe to see what could possibly lie ahead.

Sudden Stratospheric Warming

First we will look at the Sudden Stratospheric Warming which has occurred over the first week of January 2021 and how it can eventually effect out weather in the weeks ahead. A SSW sees cold air descending above the Arctic, resulting in warming by as much as 50°C. This is in association with a significant weakening or reversal of westerly winds circulating around the North Pole between 10 and 50 km above the ground – the stratospheric polar vortex. Normally with a SSW it increases the risk of the zonal winds reversing with a higher chance of a easterly or northeasterly airflow this time of year which can result to colder conditions moving out of Arctic like we seen back at the end of (February 2018 the beast from the east). A SSW increases the risk of more prolonged and significant snowy and cold spell.

During these events the vortex can break down completely, and when this happens the disruption in the stratosphere can trigger a shift from westerly to easterly winds which can be followed by lower-altitude winds shifting in the same direction. On average 70% of occasions see this switch to easterly conditions at ground level, with the resulting cold and easterly shift in our weather.

Forecasting the colder weather was much easier back near the start of February 2018 but this time its much more complex with many factors having to fall into place.

Latest weather model outputs today (Tuesday 12th January 2021)

The 3 forecast models we will be looking at is the ECMWF, GFS, GEM

Below you can see the latest outputs from the 3 forecast models this evening

Charts attached show upper air temperatures at 850hPa which is the temperature at about 1.5 km which is generally above the atmospheric boundary layer. The 850 hPa temperature' is used to locate and identify warm fronts and cold fronts.

GFS

ECMWF

GEM

The 3 different model outputs are from this evenings 12z run which shows colder air from around the 19th of January onwards. All 3 forecasting models charts above are for the 21st of this month.

The chart below now shows 7 different weather model outputs for the 20th of this month with them all showing some sort of cooler or colder weather.

GREENLAND HIGH

Some of the forecasting models shows a Greenland high pressure system and blocking pattern which could open the doors for something rather cold but this is 50/50 at this stage. Chart below shows the Greenland high.

Many will remember the famous 2010 cold spell in latter part of November that year when northern blocking established over Greenland which resulted in the Jet Stream moving south, allowing cold air to flow in from the north and east.

Snowfall

At this stage its is yet too early give much detail about snow especially when and where it will snow. However in such colder spells of weather there is the chance of snowfall and that can come in many ways depending on the wind directions and where the cold sits.

EASTERLY FLOW (Can be colder air coming across from the continent or down from the arctic)

Under a northeast or easterly flow we are likely to see the coldest conditions this way would also increase the chance of sea streamer and some big snowfalls across the eastern half of Ireland.

NORTHERLY FLOW (arctic maritime air)

Under a northerly air flow you would also see very cold temperatures with the risk of snow coming from sea streamers again which is showers moving in from the sea. You also can get what we call a polar low moving down from the north to south which can give longer spells of snow and stormy weather. We are likely to see a northerly airflow to start next week

NORTHWESTERLY FLOW (Polar Maritime air)

In winter this air mass will lead to a mixture of rain, hail, thunder and even snow over some western and north parts, Showers in this airflow is are fairly frequent. Showers would be less across the eastern half of Ireland and the UK.

WHAT ARE SEA STREAMERS?

Typically sea streamers snow will develop in narrow bands, sometimes called streamers. The streamers tend to align with the wind direction. They are produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water or sea water . The lower layer of air, heated up by the lake water or sea water picks up water vapor from the lake or sea and rises up through the colder air above the vapor then freezes and is deposited on the leeward downwind shores. This also is known as lake effect snow.

**SEA STREAMER OR LAKE EFFECT SNOW FORMATION**

POSSIBLE OUTCOME NEXT WEEK

So to finish with this a cold spell does look likely next week with no massive changes in the forecast models today and to say how cold it will get is to soon to say but yes it looks like it will get cool and colder but to say it will get significantly colder at the moment cant be answered as its to far out but the trends are there. It will be the end of this week into the weekend before we have any real idea of how cold it could get.

As mentioned above snow showers look possible for some areas next week most likely across the northern half of Ireland first next week particularly over higher ground areas. Much harder to say for lower levels yet as some of the colder air to start will be modified. There is a chance of colder air moving in after midweek next week but there is uncertainty yet. One outcome that we could see later next week is areas or a area of low pressure moving up across Ireland leaving the warmer air to the south and up over the colder air sitting over Ireland leading to some falls of snow in places and this looks likely to be the highest chance of seen any good covering but this is uncertain.

Anyone posting charts forecasting snowfall for any day next week at this stage are just fooling themselves as I mentioned in my update last night its way to far out and we can only look at snowfall at around 1 to 3 day out before really forecasting a outcome due to the amount of parameters which have to fall into place.

If you liked this update make sure to give it a like and let us know what you think in the comments

Regards Kenneth

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