Polar low watch

Quantum
Advanced Member Topic Starter

28 January 2019 14:32:25

So the models seem to have picked up on the possibility of a polar low forming and hitting the NW of scotland. The most spectacular example of this was the 0Z ARPEGE on the 27th which produced a Catogary 2 hurricane landfalling in the outer hebridies. Although no other run has been anywhere near as dramatic as that, there is now more of a consensus building about the chance of a PL forming.

For example the WRF is showing a PL near the Orkney isles early wednesday.

Polar lows are formed out of baroclinic disturbances in the arctic or antartic regions but they are unique in that, unlike normal depressions, they intensify through barotropic processes namely surface heat fluxes and latent heat fluxes which can reach magnitudes comparable to regular tropical cyclones. They also have many similarities to Medicanes and subtropical cyclones with a deep cold core supporting a shallow warm core.

Polar lows are very hard to predict, they are tiny features (even smaller than medicanes) but they can have gusty winds, snow, soft hail and lightning on them making them potentially hazadous features. However they do not survive long inland so really the only places likely to be impacted by the PL are the extrema of NW scotland or possibly N Ireland. Its also possible it may make its way into the Irish sea and cause problems on the Isle of Man or even NW England.

Quick caveat regarding these model outputs. I know from my time medicane watching that the models do love to overblow these features. I've seen many examples of record breaking medicanes being predicted by WRF and but not many actual record breaking medicanes (although to be fair it did actually happen earlier this year). Obviously there isn't going to be a catogary 2 hurricane but gale force gusty winds, heavy snow or hail is still a possibility. And it is likely to be without any real warning as no model is going to predict these well at all.

Edited by user 28 January 2019 14:34:03 | Reason: Not specified

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Quantum
Advanced Member Topic Starter

28 January 2019 14:36:12

#2

9Z ICON you can just about see it in the top left corner at +30h.

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Gray-Wolf
Advanced Member

28 January 2019 15:02:36

#3

Thanks for the heads up Q'!

I'm surprised to hear you say the Irish sea has a chance of it visiting? I'd have thought the North Sea would have been more open to its travels ( should it form?)

I had been noting the positive sst's around the UK for a while now so any incursion of uber cold was always going to be fun ( lake effect snow showers for the windward coasts?)

I'd plumped for a snowy Fylde coast/Liddypool for the end of the week?

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The Beast from the East
Advanced Member

28 January 2019 15:05:29

#4

Thanks Q

Have you any historic charts of previous polar lows?

Purley, Surrey, 70m ASL

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Quantum
Advanced Member Topic Starter

28 January 2019 15:06:48

#5

Thanks for the heads up Q'!

I'm surprised to hear you say the Irish sea has a chance of it visiting? I'd have thought the North Sea would have been more open to its travels ( should it form?)

I had been noting the positive sst's around the UK for a while now so any incursion of uber cold was always going to be fun ( lake effect snow showers for the windward coasts?)

I'd plumped for a snowy Fylde coast/Liddypool for the end of the week?

Originally Posted by: Gray-Wolf

Most of the model runs are predicting it moves down the west side of the UK. If it does reach the irish sea it will be weakening by then. It could go into the north sea but if it does I suspect its unlikely to affect land and will also weaken quickly.

25/26 (850hpa temp) 11 days snow/sleet falling

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Quantum
Advanced Member Topic Starter

28 January 2019 15:08:44

#6

Thanks Q

Have you any historic charts of previous polar lows?

Originally Posted by: The Beast from the East

Not any particular examples that I'm aware of other than the nowegein sea example I gave in the MO thread which was the strongest ever recorded. I do recall they do hit scotland from time to time, its probably happened a handfull of times or more in the last decade or so. I think you'd struggle to see some of the weaker ones on analysis charts as they are such tiny features although they will show up on FAX charts or in satellite imagery.

25/26 (850hpa temp) 11 days snow/sleet falling

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Gray-Wolf
Advanced Member

28 January 2019 15:12:31

#7

'Tallyho 83' just linked the MetO forecast for today up ( short term snow potential) and they appear to show your feature hitting the far NW of N.I. during weds P.M. ?

Koyaanisqatsi

ko.yaa.nis.katsi (from the Hopi language), n. 1. crazy life. 2. life in turmoil. 3. life disintegrating. 4. life out of balance. 5. a state of life that calls for another way of living.

VIRESCIT VULNERE VIRTUS

Chunky Pea
Advanced Member

28 January 2019 15:14:10

#8

PL event which I spoke of in the MO thread. Jan 29th 2015:

If I remember correctly, it system had an 'eye' before making landfall. Had a Hi Res sat animation of it but can't find it at the mo in my archives.

Patrick,

East Galway, Ireland.

Hade Edge Snowman
Advanced Member

28 January 2019 15:17:08

#9

Thanks Q

Have you any historic charts of previous polar lows?

Originally Posted by: The Beast from the East

Didn't a Polar Low form in early January 2010?

Hade Edge Snowman

Holmfirth

West Yorkshire

1070 feet/326 metres ASL

Quantum
Advanced Member Topic Starter

28 January 2019 15:26:52

#10

ICON 12Z.

25/26 (850hpa temp) 11 days snow/sleet falling

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Quantum
Advanced Member Topic Starter

28 January 2019 15:32:24

#11

ARPEGE has a much deeper storm (not 27/0Z armagedon though) and takes it in a completely different direction (moving ENE rather than SSW). This is all starting to feel like the Medicane thread where you have no idea where the thing will end up even 24 hours before it happens!

ARPEGE also keeps it off shore so it has a longer lifespan and presumably causes more snow in NE scotland.

Edited by user 28 January 2019 15:33:55 | Reason: Not specified

25/26 (850hpa temp) 11 days snow/sleet falling

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Chunky Pea
Advanced Member

28 January 2019 15:32:32

#12

Had a Hi Res sat animation of it but can't find it at the mo in my archives.

Originally Posted by: Chunky Pea

One I captured earlier that day:

Patrick,

East Galway, Ireland.

Quantum
Advanced Member Topic Starter

28 January 2019 15:35:24

#13

Thing is if the polar low ends up as part of the circulation in the depression on Tuesday it could make the thing even more unpredictable than it already is, could spawn another front somewhere or just add energy to the system.

25/26 (850hpa temp) 11 days snow/sleet falling

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Quantum
Advanced Member Topic Starter

28 January 2019 15:38:05

#14

In fact actually the polar low does, according to the ARPEGE, seem to inject some heat into the main low which, by thursday manifests itself as an occluded front across NW scotland. This occluded front could pass south on Friday giving more snow which has, thus far, been unpredicted.

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Quantum
Advanced Member Topic Starter

28 January 2019 15:44:51

#15

The PL (or what will become the PL) already exists as a swirl of cloud to the SE of Iceland.

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Quantum
Advanced Member Topic Starter

28 January 2019 15:51:11

#16

Metoffice models not interested though?

This could cause some forecasting errors if the other models are right.

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Quantum
Advanced Member Topic Starter

28 January 2019 16:08:58

#17

We can see it up close on the ARPEGE now.

Depth of 972mb, warm core is evident even at 500mb! That's really impressive. Possibly TC like rather than subtropical like. In fact the warm core is so pronounced on the ARPEGE its going to be rain, not snow!

25/26 (850hpa temp) 11 days snow/sleet falling

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KevBrads1
Advanced Member

28 January 2019 16:15:14

#18

PL event which I spoke of in the MO thread. Jan 29th 2015:

If I remember correctly, it system had an 'eye' before making landfall. Had a Hi Res sat animation of it but can't find it at the mo in my archives.

Originally Posted by: Chunky Pea

We got snow from that here

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KevBrads1
Advanced Member

28 January 2019 16:19:18

#19

Timelapse of that 29th/30th January 2015 event

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polarwind
Advanced Member

28 January 2019 16:28:12

#20

Thanks Q

Have you any historic charts of previous polar lows?

Originally Posted by: The Beast from the East

I remember a really good one for Derby, in Feb 1969. Some 200mm snow in 5 hours - windy too.

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Dave,Derby

Gandalf The White
Advanced Member

28 January 2019 16:31:47

#21

We got snow from that here

Originally Posted by: KevBrads1

Surely if it's got frontal troughs then it's not a polar low? By definition they don't have.

Location: South Cambridgeshire

130 metres ASL

52.0N 0.1E

Chunky Pea
Advanced Member

28 January 2019 16:39:48

#22

Timelapse of that 29th/30th January 2015 event

http://www.youtube.com/watch?v=tMcCns47qbU

Originally Posted by: KevBrads1

Amazing video KevBrads

What looks like an almost 180 degree turn in the wind direction there shortly after midnight in your location, which would make sense given that the low would have drawn much closer to your region at around that time.

This was the location of the low at 11pm that evening (sorry, have no similar images for after that or for the UK region)

Patrick,

East Galway, Ireland.

Bolty
Advanced Member

28 January 2019 17:33:22

#23

Yes I remember the 29-30 January 2015 polar low too. It was pretty heavy for a time, though it didn't last very long from what I remember (it snowed for no more than 30-45 minutes?). I'm sure I've got a video on YouTube somewhere, will try and find it.

Scott

Blackrod, Lancashire (4 miles south of Chorley) at 156m asl.

My weather station