FI Charts ( T120+ onwards) Winter 2024/2025 **READ MOD NOTE IN FIRST
Comments
-
-
-
-
-
Atlantic in full control right out to the end of the 00Z run.
It does turn cooler overall, and even cool enough for some snow across northern hills. Typical weather for this time of year. At least with a W to NW based zonal flow after this initial mild and wet spell, there are opportunities for sunny spells, showers and some inland overnight frosts.
Nothing to get excited about though.
5 -
Advertisement
-
-
-
Despite a largely bright and sunny Saturday, the current spell of unsettled weather looks set to continue into the opening days of March.Ireland remains in an Atlantic zonal setup with low pressure systems to our west and high pressure to our south resulting in rain and strong winds at times.
Sunday will bring strong to gale force winds and heavy rain that will clear to scattered showers on Sunday afternoon.
Next week will bring higher than average precipitation amounts while temperatures will be slightly above the seasonal average at 8-11c.
More widespread rain is expected on Wednesday and Thursday, but there will be good dry spells during Monday, Tuesday and Friday.
Next weekend into the beginning of March looks more unsettled with higher than average precipitation levels and above average temperatures.Western and northwestern counties likely to see the heaviest rainfall and strongest winds over the next two weeks.The below graph shows air temperatures, pressure and precipitation levels for the next 16 days.
www.weatheire.com
8 -
-
-
Advertisement
-
-
-
-
-
-
-
The GFS is not letting up on the prospect of colder air in the polar stratosphere becoming displaced by the end of next week, which, if such an outcome were to verify, would deliver colder conditions to mid-latitude regions like Europe, USA and Eurasia.
With just 3 days to go until the beginning of the meteorological spring, the last thing you want to see in long range weather model output is the possibility of a Polar Vortex (PV) split or Sudden Stratospheric Warming (SSW).
The PV is a band of strong westerly winds that forms in the stratosphere between about 10km and 50km miles above the North Pole every winter. When the vortex weakens, shifts, or splits, the polar jet stream often becomes extremely wavy, allowing warm air to flood into the Arctic and polar air to flood south. In the case of the the latest GFS output, two lobes of cold air sink south into the mid-latitudes.
A SSW refers to a swift jump in polar stratospheric temperatures. The warming is preceded by a slowing then reversal of the westerly winds in PV. Such disruptions of the PV can lead to cold air outbreaks in the mid-latitudes, in place like Eurasia, Europe and the United States.
Despite there having been an estimated 25 major SSW events during the past 40 years, a relatively small number have led to a severe cold outcome in Ireland. For example, a major SSW around February 10th, 2018, produced the infamous Beast From The East of late February and early March that year. A SSW in January 2019 had little impact on Ireland's weather, which, in fact, remained relatively mild for the rest of the meteorological winter. Another SSW in January 2021 produced cold conditions in Ireland and Britain, but it was much less severe that the 2018 outcome.
Should the latest output from the GFS model verify, it would take another 2 to 3 weeks for the impact of a PV split and any accompanying SSW to be felt in the mid-latitudes. By then, we are looking at a risk of cold weather after mid-month into early April, an outcome nobody wishes to see materialise.
www.weatheire.com
6 -
-
-
-
Advertisement
-
-
-
That is the case indeed for the east coast where we often feel the legacy of winter with a slow time lag in the Irish Sea warming up.
However, there have been plenty of cases of very warm easterly winds as early as April for much of the country. In April 2003 for instance during the Easter period, parts of the west had 4 consecutive days of 23C or above. Belmullet reached 24.2C on 17th April, Holy Thursday. The chart for that day shown below. In fairness though, the airmass beneath the ridge was very warm too so even on the east coast we got highs of 18C away from the immediate coastline which are significantly above the April average.
Yes, whilst the stratospheric polar vortex tends to hibernate through mid to late spring and not return until late August, its state during the spring can have an effect on the North Atlantic Oscillation phase of the succeeding summer. A slow descent or gradual final warming tends to either be more favourable of a positive NAO which is better for dry and warmth in summer though no guarantee (2024 last year being a prime example) whilst a more rapid final warming will be more favoured to producing a negative NAO which normally translates to more unsettled conditions and sometimes cool. There was a very dynamic final stratospheric warming through the second half of April 2019 which led into a record breaking May -NAO producing similar effects to a major mid-winter warming and this persisted through the summer giving an unsettled season though a warm, dry July inbetween.
Ideally if we are to see any major SSW that it will occur early and or a final SSW to be non-dynamic. An early final warming does not necessarily spell bad news for summer. 2022 had an early final warming in March and with the exception of a changeable May/June, the March-August period of 2022 produced a lot of fine settled weather.
If anybody is interested, here's the paper discussing the effects of the state of the stratospheric polar vortex through the spring on the summer NAO.
Skillful predictions of the Summer North Atlantic Oscillation
Photography site - https://sryanbruenphoto.com/
8 -
-
