FI Charts ( T120+ onwards) Winter 2022/2023 **READ MOD NOTE IN FIRST POST**
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Sudden stratospheric warming (SSW) is the overall umbrella to describe all warming events of the stratosphere. Major is when the zonal mean zonal winds at 60N 10hPa reverse from westerly to easterly (i.e. <0 m/s). If it doesn't reverse then it's a minor event no matter how significant the colours look on the charts that are posted everywhere. I've explained these time and time again in-depth in my annual stratosphere watch threads - least up until this year when I haven't done. Here's the most recent one if you would like to know more: https://www.boards.ie/discussion/2058216087/stratosphere-watch-2021-22/p1.
Many of our cold spells from years past were in part due to some effect from the stratosphere, it doesn't necessarily need to be a major SSW event. As we seen in December just gone, we got a case of a "bottom up split" (a non-official term for your information) where the troposphere was blocked and resulted in warming in the lower stratosphere whilst the upper stratosphere was very much cold and the stratospheric polar vortex at 10hPa was running rampant. This was the case in the late 2010 too. Meanwhile in the 2009-10 winter, we seen a significant deceleration of the zonal mean zonal winds at 60N 10hPa in mid-November which led onto a split in the lower to mid stratosphere in December which could have explained the extreme negativity of the Arctic Oscillation in that winter which had the most negative AO of any modern winter on record with mid-December to mid-January 2009/10 and mid-February 2010 especially being blocked. Notable examples of a major SSW event leading to cold spells pre-2013 include but not limited to February 2001, January 1985, December 1981 and January 1960. Pre-1952 stratospheric records are very sparse and there is no way to tell the likes of 1947 were caused by major SSWEs.
The below is a brilliant figure from Lee (2022) and it shows the D3-D30 NAO index and Northern Hemispheric MSLP anomaly (as per ERA5) following all the respective major SSW events since 1981 (1979 is an error). As can be seen 2018 was an extreme example and vast majority don't go as extreme as that. The more negative the NAO index, the more it's likely a very blocked pattern with deeper low pressure around the Azores and high pressure over Greenland. See how sometimes the NAO even goes positive following a major SSW event with February 2008 being the most recent example of this. These typically occur from non-downward propagation SSW events (nSSW) but can happen from downward propagation events (dSSW) too if the vortices end up in the wrong locations, this happens a lot with displacements.
The 2018 event was an extreme case scenario where we had an ideal evolution of a PV split with a warm core around Greenland and the other side of the Arctic Circle whilst the vortex broke into two in perfect locations to creating a massive blocking area of high pressure. Split events have a tendency for quicker tropospheric responses and 2018 was very quick. We started to see evidence of Scandinavian high pressure by 22nd February 2018, this was 10 days after the zonal mean zonal winds at 60N 10hPa (I'll refer to as U-60N from this point on in the post) had reversed to easterly on 12th February. We need to get this idea out of our heads, if we haven't already after the 2019 and 2021 events, that a major SSW = blocked and cold for Europe guaranteed and will always get a beast from the east scenario. 2018 was the exception, not a benchmark. 2013 was a strange one, a very major warming in early January followed by a cold spell with no significant blocking - Ireland often on the periphery - then the lower stratosphere to the troposphere never really recovered from it and in fact blocking just got much more extreme as time went on resulting in one of the coldest Marches on record. This happened whilst the upper strat had well and truly recovered back to norm or stronger than normal U-60N aloft. It's pretty incredible really how we could feel the aftermath effects of the SSW still by early April, 3 months after it occurred.
We have yet to see anything out of the ordinary shown on any of the models for January 2023. There has been zero signal of a major SSW or even a significant enough minor SSW that would warrant attention. The U-60N has been forecast to only really go back closer to average and even that is a stretch. What the GFS has been showing is a standard minor PV displacement that occurs a few times almost every single winter. If you're wanting to see a significant risk of high latitude blocking in northern Europe to result in a cold easterly flow towards Ireland from a stratospheric warming, you sure as hell would be hoping for better to appear on models than what has been shown.
Photography site - https://sryanbruenphoto.com/
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5 inches of rain forecast for the southwest over the next 15-16 days. 31MM recorded so far for the first three days of January 2023.
Valentia only recorded 76mm for all of January 2022. The LTA is around 173mm.
www.weatheire.com
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A very wet 7 to 10 days to come at the very least with the Atlantic really stepping on the gas, a mid winter Atlantic trainwreck. Far out in FI there is a small chance we may get a day or 2 of settled weather with maybe a frost, but it turns unsettled again after this.
If we are going to get some cold weather this month, it will most likely be around the end of the 3th or 4th week of the month and unlikely to last very long as the Atlantic is going to need something major to stop it's onslaught.
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Bleak. January is to winter like what August (excl. 2022) is to summer.
At least I won't feel too guilty wasting evenings over the next week and a half binging on boxsets when it's dark, wet and windy outside.
Weekend of 14th/15th looks outdoors enticing on the current 12z rolling out:
a pet day or two no doubt.
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Agree, we all know very well that when this type of rot sets in it’s a very very long way back to anything cold other than some occasional Pm shots.
I wonder where they get their water from in Iberia? The winters there seem to be very dry every year. I presume it’s spring rainfall that fills the reservoirs?
I presume it can get quite wet down there in spring when the NAO goes neg and our winter begins.
Post edited by Elmer Blooker on1 -
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After a windy and wet week ,ECM leaning towards colder weather by next weekend on the latest runs, other models leaning that way too apart from the GFS showing the cold to arrive a couple of days later, that small area of LP in the last frame would be a snow maker but I wont hold my breathe 😀 , currently everything looks quite transitionary atm.
Plenty of windy spells next week, will have to wait further to see if one deepens and hits the target, very wet too coming in off the Atlantic especially along the Atlantic Seaboard.
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Latest ECM currently suggesting a heavy frontal snow event in parts of Connaught and Leinster (possibly very northern parts of Munster too) although even this far out, it's pretty knife edged stuff and I'm currently in no way convinced.
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