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12-02-2020, 15:23   #16
Oneiric 3
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I know of and much appreciate your more technical and methodical methods (which I do not call into question) my point is more that those snow charts, as unreliable as they may be, are still reflective of what each model that produces them are showing based on all of the 'upper' conditions that they either use as a starting point or what they forecast. You are spot on about GFS having a colder bias with regards upper temps etc, but regarding conditions on the ground, it wasn't too far off as far as I can tell, and neither was the ECMWF in fairness.

Anyway, I don't want to saturate this thread with pointless charts, but here is what both the GFS and ECM forecast for Tues (yesterday) morning on the 10th with regards 850 temps over Ireland.




GFS is the colder of the two for sure on a more synoptic scale, but this may be down to its lower resolution.
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12-02-2020, 15:57   #17
Gaoth Laidir
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I think each model generates those snow charts differently, taking into account things such as soil temperatures, etc. I do remember the ECM showing a larger "snow depth" at one point but as I said, I take those with a pinch of sea salt. I'm not sure that anywhere below 200 m had any snow lying for any appreciable length of time yesterday. Knock Airport did report hourly depths up to 7 cm this morning but it was only described as patchy wet snow covering less than half the ground.

But on a larger scale the GFS does and always has tended to get thicknesses woefully low. These were the thickness values versus the ECM 36-hr forecast (red dashed line ending at 20W). Around 700 km of a difference between the easternmost extent of the 516 dam line at 12Z yesterday. It turned out to be close to 520 dam in the end.

ECM


GFS
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12-02-2020, 16:49   #18
Oneiric 3
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I don't know what is wrong with my computer, but I can't see your images (which I assume you included given your headings).

But yes, I don't disagree regarding the 'thickness' forecasts, but that wasn't really my point, but no matter.

Thickness forecasts from Monday 00z for Tuesday 06z.



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12-02-2020, 17:21   #19
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Much clearer charts than mine anyway so you're not missing much!
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12-02-2020, 18:09   #20
Nqp15hhu
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Quote:
Originally Posted by Danno View Post
You need a direct airflow from Greenland to give proper snow here like late December 2000 and middle February 1994 (IIRC).
These events gave series of squall dumping several cms of snow in minutes.
Anything else from west of north is too moist and marginal.
Northwesterlies can deliver snow here.
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12-02-2020, 18:09   #21
Nqp15hhu
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Quote:
Originally Posted by RobertKK View Post
There has been lying snow on the hills in Kilkenny since early Monday morning, all the showers since were snow showers and every night the snow got topped up, so there is snow here for the third day in a row. It must have been about 6-7cm or so.
You weren’t affected by the warm low which came down from the north.
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12-02-2020, 19:22   #22
sryanbruen
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Quote:
Originally Posted by Danno View Post
You need a direct airflow from Greenland to give proper snow here like late December 2000 and middle February 1994 (IIRC).
These events gave series of squall dumping several cms of snow in minutes.
Anything else from west of north is too moist and marginal.
Mid-January 1984 Danno mid-February 1994 was an easterly.
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13-02-2020, 11:39   #23
Mortelaro
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Quote:
Originally Posted by Nqp15hhu View Post
I was looking forward to getting some snow out of this cold spell. I analysed the charts and it was looking quite good for Ulster.

I honestly expected a covering out of this.

Tuesday, today was progged to have 516dam, -8c 850pha and 300m freezing levels which should surely yield snow at sea level, even at the coast.

Instead, what we have got is 2/3c at sea level, slightly negative dew points but positive wet bulb. So showers are sleety and barely of snow.

The only lying snow of note is above 300m, everything below that level is of a slushy mess.

The cold spell a few weeks ago, which was of -6c 850pha produced sea level snow cover with warmer atmospheric conditions. So why is this cold spell so marginal?

I study all of this and I am fairly interested in it. I can’t establish why colder atmospheric conditions would yield more marginal conditions for snow. Surely a freezing level at 300m would guarantee sea level snow?

Is the atmosphere warmer than predicted?

One thing I notice is that the dew points rise within the shower and drop afterwards. Could this be limiting snowfall?
More eloquently explained by GL,your issue was marine layer
The last 1000ft or so between cloud and ground
Its effects dissipate as you move inland or uphill
Better with both
Marine layer for you being too near the north Atlantic trumped uppers
Its another example of imperfect modeling I think as its affects should have shown
Thankfully that's why we have human forecasters
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13-02-2020, 22:46   #24
Danno
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Quote:
Originally Posted by sryanbruen View Post
Mid-January 1984 Danno mid-February 1994 was an easterly.
It wasn't 1984 - too young to remember that!

Perhaps it was 1990:

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