Kasim Awan
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Posts posted by Kasim Awan
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@Met4Cast I do think another bout of amplification is possible. Often cold snaps tend to repeat synoptically around 3-5 weeks after. I can think of countless examples. So from a predictive statistics perspective I think a northerly spell is very possible into February at some point. Probably watered down by the strong signal for Iberian heights though.
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I don't agree with the posts writing off February. Give it time there is a chance of another cold spell.
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Interestingly winds here are a lot lighter than Isha. Goes to show how orographic Isha was.
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In terms of warnings the only issue for me was the late red warning which made no sense because high resolution output agreed on the 90mph+ swathe a lot earlier. There was no lower confidence 24 hours earlier.
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This storm due to the wind direction was very orographically and topographically modulated which is why away from Glasgow area, areas affected by the sting jet and and low elevation parts of Northern Ireland, low level gusts rarely increased above 55mph. There are a few reasons for this. First is wind direction, southwesterlies reduce the >850mb vorticity over the West Midlands, Cheshire, greater Manchester, Sheffield and Leeds area. Manchester airport rarely gusted above 40mph, Leeds rarely above 50mph which is a lot lower than predicted. This direction also increases gusts over high ground and on the east coast due to the relative magnitude of atmospheric wavelengths at higher wind speeds. Basically stronger 700mb mean winds increase the wavelength for orographic modulation meaning effects of wind strengthening were felt further east so along the coast as opposed to central eastern areas. Higher ground areas though still experience usual strengthening with altitude plus acceleration. This is why 100mph was recorded at 500m asl Yorkshire and over 70mph on the east coast. The sting jet over Northern Ireland and Scotland was there but fairly widespread and it absorbed a significant amount of the pressure differential potential therefore reducing wind gusts over England. 106mph in Orkney indicative of a big absorption. These mechanisms both worked to reduce gusts over low level England. The orographic effects influential over northern England and the differential absorption further south.
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1 minute ago, ANYWEATHER said:
I really don't think 5 mph is either here or there! Its like saying that the predictions for 100mms of rain and been downgraded to 95 mms, in situations like this models give us a jist of the expected gusts ,irrelevant really as the storm still is intensifying. .......
Not if you look at it this way. 55mph typical for inland areas vs 70mph had it further upgraded. The differences are noteable when comparing output from 24 hours ago.
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4 minutes ago, Mapantz said:
Either there's a delay in this system, or wind speeds are not as strong as forecast for down here..
I think wind speeds have reduced a fair bit for inland central / southern England, 5-8mph. I know this is an unpopular statement however if you compare the last few icon wrf harmonie charts it's quite clear. Still talking 55-65mph for a short time with 70mph locally in squalls.
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Harmonie gusts are around 5mph lower for central England than 06z. Will be interesting to see the gusts across low level central England later.
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3 minutes ago, Jo Farrow said:
The likelihood of the (already mentioned) HIGH impacts would have to move from Low through Medium to High, I wonder if they can be that certain of where & when? Amber is out, people who are going to listen should be heading home, it's Sunday evening/night. Different time of day, then yes there would be room to upgrade. Who knows
Dependant on reactivity in Exeter I think the only way a red would be achieved given the low likelihood of high impact is if observations noted a sting jet with 90mph+ surface gusts. That should push up likelihood of high impact into high zone.
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Caenarfon airport now 81mph - likely benefiting from some downslope acceleration still significant for lower levels.
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2 minutes ago, Man With Beard said:
I don't know which model you are referring to for this downgrade, though, GFS has been fairly stable for a few days.
Re: AROME high gusts: I saw this model attempt such streaks in the last storm near me, didn't materialize. But one to watch.
The northwards push through England was evident on icon runs probably a 10mph reduction through England. Likely associated with the sting jet absorbing some of the pressure differential as this increases winds over Scotland.
All very normal slight adjustments. Still looking at 55-70mph through inland central southern England considering the icon is now at the lower end of projections. The sting jet is probably slightly more likely than not. Been years since a proper one.
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Just now, Polar Maritime said:May be a good idea to keep your devices charged up tonight.
Oh come on the banter isn't that good.
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Just now, Man With Beard said:
Almost every spot south of Glasgow with a gust above 60 mph
Very rare to see that. The magnitude and extent of this storm is probably a one in 6+ year event.
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3 minutes ago, Derecho said:
Well that's incorrect, higher pressure has higher air density. If you look at the horizontal and vertical wind equations
You can see that air density is used in the equation to calculate the zonal and meridional components
Climate - Pressure, Wind, Air | Britannica
WWW.BRITANNICA.COM
Climate - Pressure, Wind, Air: Atmospheric pressure and wind are both significant controlling factors of Earth’s weather and climate. Although these two physical variables may at first glance appear to be...
Understanding Air Density and its Effects | Coast Flight
IFLYCOAST.COM
Understanding air density and its effects By Jack Williams, USATODAY.com In simple terms, density is the mass of anything – including air – divided by the volume it occupies. In the metric system, which...Quote from the above:
Increasing the pressure increases the density. Think of what happens when you press down the handle of a bicycle pump. The air is compressed. The density increases as pressure increases.
The pressure gradient force is what is most important
Your post is theorerically correct however ignores the fact that deep cyclogenesis is unlikely at 1030mb etc. Have you ever seen a 50mph average wind at 1030mb? Probably not, because gradients tent to reduce at higher pressure.
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3 minutes ago, Nick123 said:
As soon as you said it 5mph has been knocked off my highest gust!
I wont bother again now.
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After watching every single UK severe weather event with close detail since around 2010 I can say this with reasonable confidence.
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15 minutes ago, Derecho said:
If the low was further north then yes but the Iberian heights alone won't lead to downgrades in gusts. A 5mph difference is minor when it comes to a storm this big. I saw these kind of differences when I was on shift in the lead up to storm Eunice hitting.
Your post shows a lack of attention to detail. The Iberian heights can reduce winds over England because the gradient at higher pressures produces less severe winds.
Not once did I say 5mph wasn't minor. It is minor but the observation that forecast pressure has increased over England is correct. A northwards push in Iberian heights would only increase pressure if the storm met it with an equal force from the southwards movement, however this storm is moving north east so any northwards push in high heights would result in a northwards push of the pressure gradient rather than a tightening of it if the storm was moving southwards such as in this example.
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3 minutes ago, Derecho said:
Yup the increase in Iberian heights would lead to an increased pressure gradient if the storm was in the same position and was just as deep.
That is wrong. This is a deepening low so higher pressure would push the more severe gusts north.
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1 minute ago, Jo Farrow said:
This may be a post more for model discussion rather than the reality of severe and stormy weather incoming to a good part of the UK tonight.
How is high resolution output on a storm irrelevant to a thread about that storm? Additionally did I once say the spell would not be severe or stormy - just that we have seen slight 5mph downgrades in the past 36 hours which is typical of strong storms with high wind speeds.
2 minutes ago, Astral Goat Juice said:5mph is absolutely nothing - Batten down the hatches, some places will experience 90mph gusts tonight.
Exactly, it is a nonsense that my post is somehow stating the storm will be less severe. Ok fine if quantitative correct analysis is unwanted, good day!
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6 minutes ago, Nick123 said:
Hopefully the start of downgrades?
Countrywide or is that your location?
Pretty much for the entire storm, but in particular central and southern England. It has been downgrading since Friday. To do with increases in the strength of the Iberian high.
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ICON pushes wind gusts down by 5mph.
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Just now, Thunders said:
strongest gust here is 4.5 mph, this will increase within the next 4 hours
I've just had 51mph.
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Strangely the area excluded from amber is the area I would've upgraded first this morning.
The WRF has a batch of 40mph average winds / 70mph gusts into this area.
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Model Output Discussion - Spring Has Sprung
in Forecast Model Discussion
Posted · Edited by Kasim Awan
I'm not buying into anything just saying it's possible. It's mid winter it's possible every year, though probably lower this year compared to most.