Model Output Discussion - 2nd March Onward

[Barking_Mad]

Paul Hudson blog:

[...]it doesn’t come as too much of a surprise that wintry weather looks set to return into next week, with cold air pushing across most parts of the UK from the Northeast.

This will lead to a risk of snow, not just over high ground but perhaps at some lower levels as well.

It’s still a way off, so timings for the onset of winter’s return vary depending on which computer model you look at – indeed the American forecast model is much earlier with the colder air, introducing it later in the weekend.

But the message is clear: don’t pack away your snow boots and thermals just yet.

http://www.bbc.co.uk/blogs/paulhudson/posts/Dont-pack-away-the-snow-boots-just-yet

[HammerJack]

Sorry if this should be in a different forum. I am getting a flight from Liverpool early Monday mornig. What do people think the chances currently are of disruption?? I know its difficult to say at the moment, but just based on current charts what do people think?

Not even the professionals could tell you 100%. It's best to stay tuned to NW & MO updates and closer to the time (over the weekend) things will become a lot clearer. Edited March 6, 2013 by LeighD

[shaky]

If the GFS and ECM verified I would be very surprised to see a repeat of the end of February easterly. The two set ups are miles apart.

This to me looks much more condusive to convection so I'd expect to see some disruptive snowfall, the UKMO however is much drier, its been wrong all week so lets hope it suddenly hasn't found some consistency!

to be honest it might have!!just had a look at the cfs and it looks very much like the ukmo!!so cant discount it just yet!!

[Tamara]

in april 2008 i think we had snowfall on the southcoast sorry mods if this is of topic but what was the upper air temps on this event ?

They were a bit higher than the suggested uppers for the cold spell which is currently being modelled So by way of perspective if we also take into account the fact the April 2008 snow event occured about three weeks later then we can see the potential early next week suggests. I'm not sure that precipitation is going to be modelled accurately at this distance but the ingredients look different to a couple of weeks or so ago (except the depth of cold is maybe even better than then)

Edited March 6, 2013 by Tamara Road

[Froze were the Days]

One more final chance to be led up the garden path all the way to the door of number 63 'Snowmaggedon' only to be turned away (again)?

[BLAST FROM THE PAST]

Heavy snow moving towards the sw at 216. The E and SE back in -10c air...

Nice little turn up Steve to keep you in 'the pot' as it were on the forum? I'm Very hopeful for area this time too

BFTP

[sunnijim]

in april 2008 i think we had snowfall on the southcoast sorry mods if this is of topic but what was the upper air temps on this event ?

We did,my weather log confirms a temperature of 3c on the sunday at 1pm,this dropped to 0c at 3pm as the snow arrived in Hastings.

The snow settled readily on the beach and by nightfall there was 2 inches and a severe night frost. The thaw kicked in the following day but snow was on the grou d for 24hrs.

I think a polar low was responsible for that outbreak,it worked its way down the centre of the UK then swung SE into SE England on a West NW flow.

Edited March 6, 2013 by sunnijim

[nick sussex]

These are IMO the most fraught times if you're a cold and snow lover because you can almost smell the snow but its not a sure thing yet.

For March the synoptics are superb, I remember saying a while back how you need to tap the coldest source of air to mitigate against the slush factor this late into the season.

The ECM and GFS deliver the absolute best you could wish to see in terms of cold for March in the UK, almost perfection because you have Arctic air flooding south crossing western Scandi so less modification then heading back sw'wards across the North Sea to pick up some nice moisture. For this reason I'm in absolutely no mood to see this watered down and certainly do not want the UKMO to verify.

As SM mentioned earlier these are incredibly rare synoptics, even if you get just a 36 to 48 hr window of convection its real quality because of the low dew points and deep cold upper air.

[Gibby]

Good evening. Here is the report of the 12z output from GFS, UKMO and ECM for today Wednesday March 6th 2013.

All models show a slack SE flow with troughs embedded (mostly weak) meandering North over the UK at times. Cloud cover will be extensive with rain and drizzle at times in most places but more especially in the South and West at first. Over the weekend the parent Low drifts East towards SW Britain then further East into the Low Countries with a NE flow steadily becoming established over the UK with increasingly wintry weather spreading South in response to High pressure near Greenland pushing cold and strong Northerly winds South towards then over the UK.

GFS shows High pressure moving slowly South down the Atlantic just to the West of the UK with a slack and cold Northerly flow over the UK for much of next week. Some sunny intervals could be expected but sleet and snow showers too especially over the East and through the day. Through FI tonight the UK stays very much on the cold side with some dry but cold and frosty conditions for a time late next week giving way to unsettled weather with rain, sleet or snow at times for the rest of the run, the sleet and snow mostly in the North.

The GFS Ensembles show the cold weather arrives late in the weekend the cold weather only slowly relaxes it's grip with many colder options maintaining cold out to the end of the run. However, as usual late in the output the mean for the pack level off close to the mean for mid March.

The Jet Stream continues to show a East moving flow well to the South of the UK with the ridging I mentioned this morning continue to feature later next week although the main body of the flow remains well South, especially over Europe.

UKMO for the late weekend and early next week shows Low pressure moving away East from the English Channel over Sunday and Monday with a cold and raw NE flow with rain, turning to snow for a time clearing away SE early in the week. By Tuesday High pressure has largely taken control from the North though with scattered wintry showers for some areas and widespread sharp night frosts.

ECM continues to show the best chance for sustained longevity of cold with cold air swamping the UK from Sunday with sleet and snow widely early in the week before a drier spell with scattered snow showers occurs through the middle of the week followed by the chance of a real March blizzard which is shown to be feasible from Friday's chart with Low pressure in the Western English Channel threatening heavy snow for Southern Counties before a return to snow showers in very chilly uppers with variable winds and frosty nights.

In Summary the weather is going to take a steep turn for the worse after the first shoots of Spring have been shown over the last few days. Low pressure crosses through the South at the weekend opening the door for a strong blast of cold NE winds followed by a Northerly flow as pressure becomes High over Greenland. Coupled with a Jet stream which looks like holding well South of the normal position the continuation of wintry synoptics could continue for some considerable time, even though it is now March.

[Frosty.]

The Gfs & Ecm 12z have the WOW factor about them, very significant cold spell heading towards the uk and arriving during the weekend and then staying next week and some areas are in for a lot of snow with drifting in the sometimes strong bitter winds, the ecm and gfs indicate reloads of cold to keep the generally very cold upper air intact, so it looks like widespread sharp frosts, snow showers, longer periods of snow, near ice days or actual ice days and high windchill, really remarkable weather for early/mid march, just want the ukmo to join the party tomorrow and it will be a full house. Seeing the 510 dam line visit the uk is rare even in winter but in mid march

Here comes the freeze.......

Edited March 6, 2013 by Frosty039

[Cheese Rice]

The ECM goes for 850's of -12/-13. SST's over the North Sea around 6.c. A good 19.c temperature difference;

If this come to fruition then expect some serious convective potential. Widespread sub zero maxes due to just the sheer number of snow showers piling in leaving a short gap between each one.

Edited March 6, 2013 by Cheese Rice

[Barking_Mad]

Looking at the charts with my limited knowledge it certainly looks like snow is possible in many places but to varying degrees. Dew points look at the moment to be forecast very close to zero, Might be sleety in places

[snowking]

So then, heres what I was referring to earlier

^^ this sort of setup has support in the extended range from the ensemble mean height anomalies

Here they were as of 0z this morning:

With the GEM more bullish on more of an Atlantic influence slowly mixing out the coldest air and probably leaving a bit of a messy mix in situ across the UK.

12z's:

As we can see, the GEM swinging around a bit too much, but the GFS steadfast on its projection for a continued cyclonic NEly influence on the UK into the extended range - though we are lining up here for a potential Atlantic v Scandinavian trough battle once again - so the channel low type scenario is one that would have some support on this basis

SK

[Barking_Mad]

Temps from March 2012!

[nick sussex]

Looking at the charts with my limited knowledge it certainly looks like snow is possible in many places but to varying degrees. Dew points look at the moment to be forecast very close to zero, Might be sleety in places

All talk of sleet is currently banned from the forum!

The North Sea is at its coldest now so less problems for coastal areas, what you perhaps lose in the gradient you make up for in less marginality.

If the ECM/GFS verify you're likely to see some large drops in temps during the showers with downdrafts, its one of the more interesting aspects of spring snow with the increase in solar energy adding a bit more spice to things.

But we're not there yet because T96hrs with this type of set up is still too far out especially when you've got the UKMO hanging around ready to tell us all that Santa Claus doesn't exist!

[MR EXTREMES]

all models suggest reload but ukmo dont wanna know.

jma t180

ecm t192

gfs t180

gem t192

nogaps t180

they all scream reload incredible stuff.

[Cheese Rice]

Another reason why this spell is even more interesting is that it seems like we are still in winter, the synoptics are so good that it feels like we are in mid Jan not mid March!

[nick sussex]

Actually no disrespect to the UKMO because its normally my second favourite model but I hope its server crashes for the next 24hrs so that it can't dish out any more Scroogelike output!

But as is the way with these models one minute they can go from zero to hero and the other way aswell.

[Timmytour]

I love Gibbo's summaries which to me are always a no-nonsense look at what the models are actually showing.

And I love the 3 day difference in his ECM outlook.

From the 3rd March

ECM shows an unsettled weekend next weekend with Low pressure close by or over Southern Britain bringing rain at times here. Colder weather already over the North will ease South to all areas early in the week that follows with some outbreaks of rain clearing South to be replaced by NE winds and wintry showers in places to end the run.

...and tonight

ECM continues to show the best chance for sustained longevity of cold with cold air swamping the UK from Sunday with sleet and snow widely early in the week before a drier spell with scattered snow showers occurs through the middle of the week followed by the chance of a real March blizzard which is shown to be feasible from Friday's chart with Low pressure in the Western English Channel threatening heavy snow for Southern Counties before a return to snow showers in very chilly uppers with variable winds and frosty nights.

[fergieweather]

All talk of sleet is currently banned from the forum!

The North Sea is at its coldest now so less problems for coastal areas, what you perhaps lose in the gradient you make up for in less marginality.

If the ECM/GFS verify you're likely to see some large drops in temps during the showers with downdrafts, its one of the more interesting aspects of spring snow with the increase in solar energy adding a bit more spice to things.

But we're not there yet because T96hrs with this type of set up is still too far out especially when you've got the UKMO hanging around ready to tell us all that Santa Claus doesn't exist!

The only saving grace is our expectation for daytime RST's in many low-lying areas to rise sufficiently to mitigate against prolonged lying snow, but with threat of substantial nocturnal accumulations. It's knifedge regarding regional/localised potential for disruption and UKMO will hold fire on early warnings until better continuity on coldest solutions and then some understanding of how RST's will respond (and thus how much any snow could accumulate to become troublesome).

[fergieweather]

Actually no disrespect to the UKMO because its normally my second favourite model but I hope its server crashes for the next 24hrs so that it can't dish out any more Scroogelike output!

But as is the way with these models one minute they can go from zero to hero and the other way aswell.

GM hasn't been followed in raw guise for some 2 days now. Public forecasts based on raft of modifications.

[chionomaniac]

The only saving grace is our expectation for daytime RST's in many low-lying areas to rise sufficiently to mitigate against prolonged lying snow, but with threat of substantial nocturnal accumulations. It's knifedge regarding regional/localised potential for disruption and UKMO will hold fire on early warnings until better continuity on coldest solutions and then some understanding of how RST's will respond (and thus how much any snow could accumulate to become troublesome).

I suspect that if we see any snow forecast for around evening rush hour then that is where the trouble will begin. People not getting home and getting stuck when it starts to get dark. Another forecasting conundrum for the meto.

[fergieweather]

I suspect that if we see any snow forecast for around evening rush hour then that is where the trouble will begin. People not getting home and getting stuck when it starts to get dark. Another forecasting conundrum for the meto.

Exactly summarises the problem. And there's no pressing rush to issue early advisories given lack of coherent PPN prognosis at this juncture.

[nick sussex]

The only saving grace is our expectation for daytime RST's in many low-lying areas to rise sufficiently to mitigate against prolonged lying snow, but with threat of substantial nocturnal accumulations. It's knifedge regarding regional/localised potential for disruption and UKMO will hold fire on early warnings until better continuity on coldest solutions and then some understanding of how RST's will respond (and thus how much any snow could accumulate to become troublesome).

Thanks Ian F, I hope you haven't taken any criticisms of the UKMO raw output by myself too personally, put it this way if the GFS had been so unreliable during the last week it would have suffered a lot worse!

As you've probably seen over the winter the GFS normally gets most derided by myself and others. Yes its a difficult set up for the UKMO forecasters because even with that cold air temps especially in cities and towns should creep above freezing but in any showers could well plummet to freezing or below.

Nighttime of course looks the greater concern for those out and about.

[Frosty.]

Here is the chart I forgot to post, really remarkable weather on the way, severe for a time and very bad news for farmers doing their lambing, the 17.5c 64f yesterday and 15c today are going to be a dim and distant memory by next monday.

Edited March 6, 2013 by Frosty039