Cold hunt - models and chat

[kold weather]

1 minute ago, feb1991blizzard said:

The dark blues are only of use if surface pressure is above 1000, preferably >1015 if you want brutal cold, never think the dark blues are good if in the centre of a low, you probably need the purples to suffice and even that might not do.

Yeah.

For those who don't know, to work out thicknesses you need to find out the geopotenial heights (that would be the colours on the meteociel charts for example, same with wetterentrale), lets say 528 for example here of the top of my head.

Then for you either add or subtract from that based on the pressure above or below 1000mbs.

So for example, with a low pressure of 970mbs, that actual thickness is 558, which would actually be high. In contrast if the surface pressure is 1020, the thickness would be 508, which would actually be very cold. Broadly anything below 520 is going to be snow in all but the most exceptional chances. 533 will be rain, except again in exceptional circumstances.

[southbank]

10 hours ago, kold weather said:

I've never seen snow from a NW, trust me, I'd remember if I had (I've been on here for 15 years, never happened to me, you must be lucky to be on the 'flight' path of a Chesire streamer then! They always used to miss me when I lived in Essex, though I often saw the convective cloud tops.

And no I never dismissed anything, indeed I said that the timing would be important and that the longer it lasted the better the chances for snow would be, especially in the east of the region. It was never really on for my region unfortunately due to it coming a little too early.

If I'm critical its only bwcause I know that plenty of areas are going to get snow, and I will get 0 from this set-up, call it jealousy I spose!

Then again Daniel, I do hope I wrong! Prove me wrong NW!

like you said a very rare event,  but during the Dec 2010 there was a cheshire gap streamer that did indeed make it all the way down to London (SW) certainly and gave a quick covering that caused traffic chaos , but in 47 years that is my only memory of snow from NW 

[Tim Bland]

8 minutes ago, Ed Stone said:

Once the big low gets away, slider heaven awaits?

What could possibly go wrong? I’ll get my sledge

Edited January 24, 2019 by Tim Bland

[kold weather]

2 minutes ago, frosty ground said:

The low has brought the milder air further north

Looks quite similar to the ECM in the way its handling that LP coming out of the states between 120-144hrs. Probably a snow-rain for the south on this run, but how far that line extends will be interesting to see, especially if the LP shifts its center.

[shaky]

5 minutes ago, frosty ground said:

The low has brought the milder air further north

Has it lol!!from what i can see its better!!

[Weathizard]

Just look how much that Canadian vortex segment is draining away, regardless of anything else this is simply the best news of the winter so far. The 144 chart looks messy but I would take it in a heartbeat for chances in Feb, looks primed although we may have to deal with the pain of it expelling energy into the Atlantic, temporarily.

[kold weather]

Good 06z run, we could do with that LP being a solid 10mbs weaker BUT the trend for a possible snow event is still there for Jan 29-31st period. The ECM ensembles have been onboard this for the last 3 days now, so worth watching. Given the low is still shifting from run to run, we still have plenty of time for adjustments.

On this run verbatim, N.Midlands is probably the snow line, though just about everywhere would get leading edge snow at least. On that snow line you'd be looking at 6-9 inches probably.

Edited January 24, 2019 by kold weather

[swfc]

Upgrade at 162 hours.Heigths better into Greenland and good nhp!!!!

[feb1991blizzard]

Just now, swfc said:

Upgrade at 162 hours.Heigths better into Greenland and good nhp!!!!

And a more favourably orientated trough giving a right UK dumping.

[frosty ground]

Shaky it's just a little slower and its not a major change but the milder air is further north Look at Ireland and see where the centre of the low is

[kold weather]

Also worth noting that 8 out of 10 times these sorts of LPs adjust southwards, that is where the likely margin of error will be, especially if the models are a little too strong with this feature (though well within the range of what is possible).

[Tim Bland]

A very rate chart with multiple lows floating around the uk in a predominantly northerly sources airstream. As said cold enough for snow midlands north and higher ground further south 

Edited January 24, 2019 by Tim Bland

[Trom]

1 hour ago, Altostratus said:

The ECM more or less follows the mean up to day 7 and the envelope is pretty tight. Thereafter, there is some divergence as expected, although that is well outside any semi reliable time frame. It's worth remembering how useless the ensembles have been so far this winter, so probably wise not to go looking for any trends beyond 120hrs as they are likely meaningless. 

Yes, the operational is very close to the mean for 7 days out.  Recent runs the op and ensemble means haven't been.  Does this herald some consistency and perhaps less volatility on the ECM in future runs?  Time will tell.

[chionomaniac]

This chart is truly unbelievable. Off the scale cold into the heart of the USA. ( >-35C 850 hPa  temps)

[Methuselah]

Looking good - if a tad marginal, south of the M4 corridor - for next Wednesday.

[Weathizard]

Just now, chionomaniac said:

This chart is truly unbelievable. Off the scale cold into the heart of the USA. ( >-35C 850 hPa  temps)

Remarkable, not normally a good sign for slowing down the jet out of the eastern seaboard is it? 

[shaky]

Brilliant 06z midlands north!!snow from 78 hours all the way to 192 hours so far!!big 12zs coming up i feel!!

[Tim Bland]

2 minutes ago, chionomaniac said:

This chart is truly unbelievable. Off the scale cold into the heart of the USA. ( >-35C 850 hPa  temps)

Doesn’t bode well for a cold feb for us does it? Will fire up the jet stream 

[kold weather]

1 minute ago, chionomaniac said:

This chart is truly unbelievable. Off the scale cold into the heart of the USA. ( >-35C 850 hPa  temps)

I've been  hearing some US mets say that is one of the most intense PV they have seen, the cold is also very impressive for sure!

[swfc]

Close to linking up here with the artic high.wondering if the block to the east will prevent it?Great run so far tho

[frosty ground]

1 minute ago, Weathizard said:

Remarkable, not normally a good sign for slowing down the jet out of the eastern seaboard is it? 

The fact its the central USA that is getting the cold rather than eastern is better i would have thought.


Artic high is really showing its hand now.

[Paul_1978]

12 minutes ago, southbank said:

like you said a very rare event,  but during the Dec 2010 there was a cheshire gap streamer that did indeed make it all the way down to London (SW) certainly and gave a quick covering that caused traffic chaos , but in 47 years that is my only memory of snow from NW 

Seem to remember significant snow in Yorkshire in January 1984 that came from a north westerly?

06z GFS for next week looks wonderful (unless I'm mistaken) for snow potential with Yorkshire again hopefully getting a fair bit?

[Mike Poole]

32 minutes ago, Stu_London said:

Seems to me that a lot of people still get sucked in by the darker blues and purples in use on the metociel site. Just because there graphics look more impressive for cold doesn’t make the event any less marginal

I think the more likely explanation is that people make assumptions about temperature from the blue colours on the 500 hPa heights chart, rather than checking them on the T850 chart.  Meteociel does use the full range of colour on its charts, whereas most others use more pastal shades, this is one reason I like them, makes them much easier to read.

[mountain shadow]

3 minutes ago, Weathizard said:

Remarkable, not normally a good sign for slowing down the jet out of the eastern seaboard is it? 

We want that PV digging as far South in the US as it helps the jet buckle more and pull the Azores High Westwards and Northwards. 

[kold weather]

Wow, that PV lobe develops a central pressure of 950mbs, that's VERY low for the core of the PV, I'd imagine the thicknesses there must be truly insane!

Azores high won't last long against that sort of pressure but we already are on the right side of the cold so that may not be a total disaster, but we will see. That 2nd lobe to our north will probably induce a +ve NAO type pattern eventually given the strength of that PV/jet combo to our east.