Cold Spell Media Forecasts and Model Output (General Chat)

th3 s1aught3r wrote: »

Scotland, parts of Northern Ireland having worse snow for 20 years :eek:

yes. it's the worst snow in northern ireland for 25 years. i think higher parts of northern ireland will see close to 18 inches of snow if this were to continue untill Saturday morning.

BEASTERLY wrote: »

M.T says south bearing the brunt AGAIN!:D

Hope folks in the north and west are enjoying there mickey mouse dusting.

I'm happy with my measly dusting:D. who knew it was such a competitive sport:pac:

nacho libre wrote: »

I'm happy with my measly dusting:D. who knew it was such a competitive sport:pac:

It must be tough, my scraps left from 3 weeks are probaly deeper than what you have now, i feel for ya.:D

Only takin the piss;)

ciaranm wrote: »

Can I ask, what does M.T. know, or claim to know, that the rest of you weather boffins don't?

I'm quite new to all this. I drop in for extreme weather. Drizzle doesn't excite.
Is M.T. at a different level to everyone else... a cut above?

Sorry, I'm not trying to ruffle any feathers. Just to get a handle on what to expect.

Hes a climatologist... :rolleyes:

Why was the post about N.Ireland removed ?

Opr

Why was the post about N.Ireland removed ?

Having posted it , I moved it to the other thread, as it is not really about model output.

I'm getting beers in preparation for the 18z, it's bound to look epic after them !

Sorry, I've been lurking, reading, checking model runs, trying to stay awake, and wondering about that offer I heard on the radio while waiting for my one minute interview, something about a car I could have from Germany for only a million euros. Sounds good, I may get a picture of it first though.

Anyway, I was stressing southeast Ireland on the radio and have been in my forecasts from tomorrow on, and I think we can look back at previous forecasts to establish that today's snow in north and west has been well predicted. Even there, reports on this forum tend to range from 3 cms to 20 or more cms in Connacht which shows that any given regional forecast number is an average which your local situation may exceed or fall short.

I will be updating the forecast soon, after reviewing all the model runs and trying to make sense of what's currently unfolding. I think that the models are having more trouble than is worth describing here but I do feel that you can get a sense of the overall evolution and then decide from there what details are most likely to verify. Otherwise, I am stuck saying it's going to be cold and there could be snow if snow develops sort of a thing, which I think would be a waste of the reader's time since that is already obvious to anyone who is already interested in the weather.

Looks to me at present that the feature moving south into Ulster is the reflection of the polar vortex and should move generally SSE then SE next 12 to 18 hours. This should bring in a period of accumulating snow to the east and southeast. Will be somewhat conservative on the update for amounts with this (in those regions). The activity still moving in from the west may become steady-state, weaken a bit, then redevelop tomorrow as the PV arrives and begins to split in terms of upper and surface features.

From that point on, it's mainly a question of how strong the almost daily cycle of low pressure formation to the southwest tracking around south of Ireland will prove to be -- here's where the models are having all sorts of trouble. Some models look fairly robust on this energy and this is why I mentioned the potential for 10-15 cm snowfalls but as that radio interview was so shortened, I wasn't able to chat about details and would have said these are totals for different events that might peak in different places, also the snow will tend to be low-density and easy to compact, so even where some place sees several falls, the cumulative effect will be less than just adding the daily amounts, it will settle and the further snowfalls would weigh down the layers underneath. In that way, you could theoretically see 10 cms a day for three days but only have 12-15 cms at the end of the three days.

I'm sure that's more than enough for most people, and clearly this is all somewhat speculative, however, I have to say that I see a spectrum of possibilities that also includes an all-out major snowstorm, sooner or later with a frontal boundary like this established near 48-50 deg N, that New Years 1979 setup could show up in the mix. I saw some potential for a storm of that intensity during this 3-5 day period and if not, the current model runs are also suggesting potential for a major storm around 25-27 Dec now. As I thought, the GFS has totally abandoned the milder track for the weekend and kept the weekend lows in the Channel.

Okay, heading over to update the forecast after one last look at radar. Enjoy what you get, as JB says (we chatted once in 1979, a frightening experience for both of us, I think). :cool:

M.T. Cranium wrote: »

I'm sure that's more than enough for most people, and clearly this is all somewhat speculative, however, I have to say that I see a spectrum of possibilities that also includes an all-out major snowstorm, sooner or later with a frontal boundary like this established near 48-50 deg N, that New Years 1979 setup could show up in the mix. I saw some potential for a storm of that intensity during this 3-5 day period and if not, the current model runs are also suggesting potential for a major storm around 25-27 Dec now. As I thought, the GFS has totally abandoned the milder track for the weekend and kept the weekend lows in the Channel.
:

it would be absolutely incredible if a snowstorm were to happen. just a quick question M.T. how many snowdances would one have to do to make it happen? :pac:

Nacho libre, you've already had a snowstorm so you must know the right moves.

Yes, I would say downgrade of forecast for southeast but not to the extent of saying no significant snowfalls, just removing the heaviest amounts from the table, would still be quite significant at even 5-10 cms a day.

Situation is clearly "fluid" and any snow that does occur can quickly become heavy as we've seen in the north and northwest. One factor is that this snow has low water ratios, meaning you get roughly twice the snow depth for the amount of available moisture, compared to average for snow. It's a fairly light, powdery snow that's being reported. Will settle to more compact depths in some places after a few hours.

By the way, let me know if you measure any snow to water ratios at your own locations. I would find it helpful, just to explain what I mean here, normally 10 cms of snow would melt down to 10 mms if you had a rain gauge, took the snow inside and let it melt. That would be the average. This kind of snow might melt down to only 5 mms of liquid. So it has a 20:1 ratio instead of 10:1 as perhaps last time with the streamers. On the other hand, a heavy wet snowfall that you sometimes get, might leave 15 mms for the 10 cms of snow. That would be more like a 7:1 ratio. We get those here sometimes and they are killers to shovel. The dry stuff you can sweep away sometimes. Those heavy lake effect storms are often 20:1 or higher ratios.