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Model output discussion - the beast arrives


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Evening Guys  Officially signing off for the winter from my window - still all but 5 inches on the ground - have a great year ! Current   favourite   See

First rule of GFS model watching. Never trust a dartboard low....... But especially in this type of set up.

See you next Saturday then, Steve?

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ECM 12z 120hs becomes messy. Appears to produce a secondary low over Iberia. Uppers remain low enough given the continental flow.

ECM1-120.thumb.gif.056309a6e7b2f3bf8dca4a7ab9dac6cb.gif

This is becoming less clear cut than we were yesterday!

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12 noon on Friday on the ECM - a (warm/occluded?) front lies from north central Wales to Kent producing snow.

Edit: That low at day 6 close to the South-East produces some wintry precipitation in the SE too as it passes by.

Edited by mulzy
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ECM0-96.GIF?25-0 ECM0-120.GIF?25-0

Really interesting how the milder air moves on this run; because the main low becomes so compact and heads so far west while the broader trough becomes distorted by small disturbances (cold air interacting with milder air on small spatial scales) and stretched to the east, the main 'thrust' is to the east-northeast giving all but perhaps the far SE corner a miss. 

The only real pull of milder air across the UK is the wrap-in to the circulation, but that circulation is also wrapping in the deeply cold continental air which is why we're looking at a major snow-maker.

Edit:

ECM1-144.GIF?25-0

Ah okay, so the much more eastward 'thrust' does end up sending the next low in a more useful direction. 850s near zero SE but the airmass a continental-maritime hybrid so not clear what form precipitation would take. The plot thickens!

Edited by Singularity
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Last weekend most models had a ‘wobble’ for everything to fall apart( cold heading further south), come the new week everything then got back on track. ( upgrades galore)

Now I’m not saying this will happen tomorrow but after tonight’s UKMO I feel this may happen again. Call it a ‘gut’ feeling.

Either way, if this does/doesn’t happen enjoy the next few days!!! 

MNR

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Interesting to see the Met Office issue Advisories for Thursday with low likelihood but High impact.

“There is a slight chance that roads may become blocked by deep snow”

To me it is very unusual for such terminology to be used especially this far out, they also stressed the massive uncertainty which is clear going by the model difference and that even small changes can make huge localised impact differences.

ECM now trundling out, and while not perfect for keeping cold conditions looks better than this morning’s run for keeping out the milder weather from the South West.  

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So I checked the details on that US site and for a large swathe of S England right down to within about 10 miles of the south coast, there is a heavy spell of snow on Thursday morning, then a drier afternoon before some light snow into Friday night. This then turns to freezing rain in the early hours, which becomes heavy for a time around 3 am but then transitions back to heavy snow by dawn!

I expect that last part is thanks in part to the disturbance in the Channel helping to mix out the less cold air, and in part to some good old fashioned evaporative cooling via intensity of precipitation.

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For what I see the ECM 12z will have produced some of the largest snow totals of all the runs so far.

Exceptional chart, the hardest hit being the Dublin area receiving almost 65cm of snow between Thursday and Saturday. Whilst most other places looking in excess of 20-25cm.

5a93043bf17e2_snowaccumulation.thumb.jpg.d61e1af2cc7e745d5a7a906c951cf800.jpg

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ECM at T192, look how closely balanced this thing is now, with T850s just holding on below freezing, and absolute mayhem from the pressure charts :

ECM0-192.GIF?25-0

ECM1-192.GIF?25-0

Admittedly posted with a nimby aspect to it!

Edited by Mike Poole
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1 minute ago, Ben Sainsbury said:

For what I see the ECM 12z will have produced some of the largest snow totals of all the runs so far.

Exceptional chart, the hardest hit being the Dublin area receiving almost 65cm of snow between Thursday and Saturday. Whilst most other places looking in excess of 20-25cm.

5a93043bf17e2_snowaccumulation.thumb.jpg.d61e1af2cc7e745d5a7a906c951cf800.jpg

They are complete nonsense at this range and often at any range. They aren't indicative of anything much and are almost always completely wrong. Take this years PM air streams for an example of why these are nothing but eye candy.

Edited by parrotingfantasist
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2 minutes ago, Ben Sainsbury said:

For what I see the ECM 12z will have produced some of the largest snow totals of all the runs so far.

Exceptional chart, the hardest hit being the Dublin area receiving almost 65cm of snow between Thursday and Saturday. Whilst most other places looking in excess of 20-25cm.

5a93043bf17e2_snowaccumulation.thumb.jpg.d61e1af2cc7e745d5a7a906c951cf800.jpg

Those snow depth charts are completely inaccurate. No idea what algorithm they use but it's nonsense!

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2 minutes ago, Nick L said:

Those snow depth charts are completely inaccurate. No idea what algorithm they use but it's nonsense!

 

4 minutes ago, parrotingfantasist said:

They are complete nonsense at this range and often at any range. They aren't indicative of anything much and are almost always completely wrong. Take this years PM air streams for an example of why these are nothing but eye candy.

Agreed, merely eye candy as all precipitation is accounted for in its accumulation. 

As inaccurate as these snow depth charts normally are, my intention was just a case of showing how well the ECM has delivered (snow depth wise) compared to other models/previous runs.

 

Edited by Ben Sainsbury
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36 minutes ago, radiohead said:

ECM follows the GFS with an intense low!

ECU1-120.GIF?25-0

ECM also being progressive with this low pressure system suggests that the GFS bias to blowing up LPs isnt the case

Edited by Paul
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