JH and a look into the period from T+144, usually

[johnholmes]

just stepping back to today and the current system

this is about the best position and prob track I can give at the moment

Edited January 6, 2008 by johnholmes

[johnholmes]

this chart

fits fairly well with what I suggested just above, certainly deeper than UK Met went for and about fits the GFS early am today predict.

Heavy rain for some with upland snow in the belt just north of the track, estimate about 5-700ft, lying more readily > 1,000ft, perhaps 5-8cm at that height.

Gale force winds to its south(as far as n Wales-Wash I would estimate) and gusts >60mph with prob >70mph in the most exposed spots overnight.

[Cookie]

was just checking the met office website and they have a weather warning out for wales for winds of 70mph.

[johnholmes]

I know

[Cookie]

I didnt say you didnt! I was agreeing with what you put. also thought you didnt like it when people put one liners in your threads?

[Roger J Smith]

John, does this look like being one of those setups that produces very strong downsloping lee waves in northeast England?

I ask that because I haven't seen one myself in the few years that I have been active in UK weather, and I've heard that they can be very strong locally, I suppose the low is a bit weak for this, but still, the tight gradient is impressive at present.

[Roger J Smith]

No worries about the above now, the Irish low tracked due east overnight and left the UK near the Humber estuary, so northeast England probably safe for today from lee downslope effects, Tuesday night may be another story ... the next system looks larger in scale and similar in peak intensity.

The overnight low, at least the part that remained circular and tightly wound, was acting almost like a tropical storm, with similar wind speeds. But it was embedded in a larger low which seems to be absorbing it at this point, so I don't think this little winter hurricane will last much longer as a separate entity.

While most were asleep, I was watching the progress of this across the Irish Sea through south Lancs and into south Yorkshire, at one point winds were gusting to 93 mph at Capel Curig, which I realize is in Snowdonia, but still, that would get anyone's attention, and it was briefly sustained at 60 mph at Aberdaron.

From a few reports on this forum, it seems that the worst of the winds hit Liverpool, some gaps in the Welsh mountains, and probably skipped over parts of the West Midlands to a slight extent before landing on higher terrain of the north central Midlands and now I would expect the east Midlands to take a beating from this for a short while.

Looks like another frontal wave forming over Ireland now with a disorganized squall line extending towards Cornwall and Devon, this may ramp up winds down there soon.

But I'm seeing the genesis of Tuesday's active weather system out around 28 W on satellite imagery, so with this observation I shall hit the sack and wish JH happy viewing today, at least nobody can say this month has been boring, whatever temperature regime you were hoping for.

[johnholmes]

thanks Roger, enjoy your sleep, I'll do an update with where the low ended up after breakfast, some very high winds been reported and probably still some to come.

Quikc check suggests that GFS was nearer the actual than UK Met even at T+24 which is a touch surprising.

Anyway I'll try and look in a bit of detail asap.

[johnholmes]

just a quick look at the short term section

Looking at how the Sunday low was predicted and what the actual showed

This is the Met O predict at T+72

And this is their actual for the same time

This was my take on where I thought it might end up

At T+60 Met showed this

Through it all GFS maintained a very similar idea, different from UK Met all along,

This was one of its later runs (Sunday) but it had always had a second low further south than the initial low, sometimes as a marked trough but usually as a centre crossing somewhere over the far north of England.

At 14z yesterday it appeared to be on this track

And at 23z this was its position

So it tracked about 2-3 degrees further south than Met predicted, about 120-150 miles with GFS having it much closer to its actual track.

I hope this does illustrate just how difficult it can be for any forecaster to get a good ‘hold’ on a situation and go on to give an accurate forecast even at these short time scales. T+72 right down to T+12.

Why the Met O chopped and changed through this spell is something only they could answer. It is rather surprising that GFS guidance was generally much better than the UK Met in this instance.

[Nick F]

Deep low that tracks NE towards and over Scotland Tuesday night has the real potential to bring blizzards across the Highlands and Grampians, UKMO 00z Fax and also the 06z UKMO meso has the low tracking further north, quicker and deeper than 06z GFS, so be interesting to see where it ends up tracking. Cold air will be wrapped around the low, so potential for substantial snowfall over the hills driven on by high winds over Scotland and also N Ireland and far north of England too:

- T+48 fax for 00z Weds

-06z GFS still has low over N of Eire at 00z Weds, so slower than UKMO

[johnholmes]

yes worth watching

so here we go

more differences in the fairly short time scale; Wednesday

UK Met for 00z Wednesday

GFS for same time(from the 06z run)

One over Stornaway the other over Northern Ireland, about 200 miles perhaps a little less. Crucial for wind, ppn type as well.

This is the Extra chart for 06z for wind speeds

and for snow risk by 1200z

a fairly low risk and for areas above about 12-1300ft but still IF it occurred over some of the main trunk routes and with major conurbations edging into those heights.

the snow/rain/sleet chart shows up the same areas

So another check looks to be setting itself up.

Interesting spell of weather even if its not a white out for most!

Edited January 7, 2008 by johnholmes

[johnholmes]

I'm going to keep this one just for longer term data as having two was getting rather complex, to view the short range discussion, please go here

although I cannot find it at the moment; it may just be taking a while to come out on NW

Looking at the attempt to try and predict what may happen a week or more ahead.

updated Monday 07/01/08 at 1723

Taking the GFS products over N America first

a major ridge over/off eastern seaboard, slowly moves east as major trough over central areas swings east shown fromT+24 out to T+168

with major ridge taking its place over western states

this in turn moves everything on in Atlantic sector, thus at T+24

trough off western areas/eastern Atlantic is slowly made more noticeable and becomes anchored over and around UK, see T+168

pressure seems to hold over Russia although its axis and position is changed as can be seen on the two charts above.

the 200mb chart below shows how the ridge/trough set up is over the states/northern Canada

and the chart below for 500mb gives an idea of how NOAA forecasters expect the major ridge/troughs to behave out to mid January

this continues to show major troughing (with –ve anomalies) for our area but is a bit at variance with what is shown above over n America.

this is the 'chat' this morning

909 AM EST MON JAN 07 2008

VALID 12Z FRI JAN 11 2008 - 12Z MON JAN 14 2008

USED THE 00Z OPERATIONAL ECMWF FOR THE MORNING UPDATE PACKAGE. IT

HAS BEEN TOUGH TO BEAT THE ECMWF DURING THE LAST SEVERAL COLD

SEASONS...LIKELY OWING TO ITS 4DVAR SYSTEM AND THE LESS CHAOTIC

ORGANIZATION OF ATMOSPHERIC DISTURBANCES DURING THE WINTER. THE

MODEL IS NOT PERFECT...BUT IT IS CORRECT OFTEN ENOUGH THAT FINDING

FAULT IN ANY PARTICULAR SOLUTION IS A DICEY AFFAIR. IN TODAYS

CASE...THE MODEL HAS THE SUPPORT OF ITS OWN ENSEMBLE MEAN...AS

WELL AS THE GEM GLOBAL MEAN...WITH THE GFS AND ITS ENSEMBLE SUITE

OUT OF SYNC WITH THE OTHER GLOBAL GUIDANCE WITH THE KEY SYSTEMS

DURING THE MEDIUM RANGE PERIOD. IT APPEARS THAT ANOTHER PATTERN

CHANGE IS IN STORE FOR THE NATION...WITH THE LONG WAVE TROUGH

PROGRESSING FROM THE WEST COAST TO THE PLAINS. THE LARGEST

CYCLONE IS FORECAST BY THE ECMWF TO LIFT THROUGH THE EASTERN

STATES DAYS 4 AND 5...WITH A PARTICULARLY STRONG SOUTHERLY

GRADIENT INDICATED IN THE WARM SECTOR EAST OF THE APPALACHIANS.

and the ECMWF(at least for our area of interest-my theory is that if its right over N America then I see no reason why its not going to be near enough correct for our area!). Please discuss.

The summation of all that, in brief, to me is:-

No sign of major blocking developing either in the Greenland or Scandinavia region. A continuing mix of Pm and Tm air with more Pm than Tm in my view and especially so for the northern half of the country. Snow seems likely at elevation, say 500-1,000ft, on occasion. Windy at times and with frost most likely between the continuing major weather systems.

I'll have a look at the pressure/850mb ensembles for those places I showed yesterday.

Obviously, as events over the past month have shown, what seems likely at this range can sometimes be quite different as we get closer to the time.

This is hugely speculative so please do discuss it, but NOT with 1 liners please. I would be very interested to see both Roger and GP post their views on this in here?

Edited January 7, 2008 by johnholmes

[phil nw.]

Thanks John.

Yes looking at all the run`s this evening there`s good agreement for quite a flat pattern and although the PJF is South of the UK no real chance of any Arctic air coming our way at present with this setup.

At least there some interest for the North with some Snow in PM air at times this week.Could be a lot worse-like last Jan.for instance.

[bluearmy]

quick question John:

looking at the cpc prognostic discussion today:

http://www.cpc.ncep.noaa.gov/products/pred...day/fxus06.html

a complete absence of reference to ECM. having read the NOAA discussion, it seems absolutely impossible that ECM 00z run could be ignored in coming to an anomoly forecast chart for North America. this happened for a week or so in early december and its bloody annoying. i assume there to be some kind of political thing going on here with ecm not allowing NOAA to use their data on a publicly available chart. if i were the chaps at NOAA cpc, i'd still use the data and just not reference it in the discussion - after all, i wouldn't want to be wrong.

any thoughts ????

(unless we can verify that the anomoly charts appear to have taken account of ecm data, it seems that they are much diluted as a forecasting tool as they merely represent GEFS/GFS runs which we know from the NOAA discussion can be out of synch with the general NWP)

[johnholmes]

I simply don't know about the situation re ECMWF, its a bit odd if they don't use it as they regularly refer to it in the daily technical discussion, often at the expense of GFS. See my initial post above.

I have only just started saving the 500mb prog charts so have no idea how reliable they are.

Like I said above its a new area for me attempting to use all the data available from both sides of the Atlantic and try to predict what MIGHT happen 10 days or so down the line.

I am still of the opinion that all things suggest a marked trough being in evidence in the upper air over/west/near the UK by the end of the week. This may well last some time. Signs of the Russian high are there but its a long way east at the moment. But that does not mean that in less than 168 hours all will be looking different. We all remember both the high before Christmas and the very rapid development of the last one a few days ago. It went from less than 1018mb to over 1060mb in about 48-60 hours, possibly a bit longer, and there was little that I saw on the GFS/ECMWF charts for the European area ONLY that gave much hint of that beyond T+168 hours.

Edited January 7, 2008 by johnholmes

[johnholmes]

An update on last evenings’ output but just looking out to T+240 or so, and chiefly with GFS although ECMWF is very similar.

Through the next 5-7 days the upper trough will tend to sharpen over/in the vicinity of the UK. This means that the air mass will be of Pm origin, albeit with more of a rPm at times for all parts. Beyond that and both models are showing more amplitude in the upper flow, this will put southern areas into more Tm air than Pm air at times.

The feature causing this is the jet pattern. It has been relatively flat with its axis over/just south of about 50N. During the next 168 hours it becomes more buckled as you can see if you look at either the basic GFS or the Extra charts through that period. With the jet so far south the ability of the Azores high to push north is almost completely absent. By about T+240 this is not the case with either model and the jet over the UK has a definite southerly component to it. This allows, or appears to allow, high pressure over Iberia to begin to edge north with at the same time high pressure entering the western edge of the Atlantic. Remember what the NOAA technical discussion and charts showed last night for the USA/Canada? From about the 20th the jet flow is such that it MAY allow pressure to rise from the south towards our north east. The 06z version even carries it on out to T+360 with a surface high showing to our north west and at the same time the Atlantic high is much more dominant to our west/sw thanks to the positioning of the jet. The 00z output did not have this. By T+384 it has ‘lost’ the nw high but the remnants of the ridge are still there towards Svalbard and into northern Russia.

It is just possible that this ‘window’ roughly 20-23/24 is when we could see a major pattern change.

Far too early to tell just yet but possibly the first concrete sign of this starting.

I’ve not looked at the north American set up this morning. Looking at the ensembles spread as I did last evening once again gives a mixed message. Pressure appears to be on the low side to our north west, but high over Iberia and Russia. So as I say, mixed signals again.

[BLAST FROM THE PAST]

Thansk again John.

I have a little feeling more of this type will show as we go into the next few days. Its taking longer than I thought..it may not happen...but the rumblings are there. As I've mentioned and you have confirmed the jet is pretty south and that is the ground work for 'my' forecast. Good thread this and thanks JH

BFTP

[MAF]

yes, thank you John. the posts are very much appreciated and well worth the read. as ever your unbiased outlook makes for a good read. thank you again

[keithtod43]

An update on last evenings' output but just looking out to T+240 or so, and chiefly with GFS although ECMWF is very similar.

Through the next 5-7 days the upper trough will tend to sharpen over/in the vicinity of the UK. This means that the air mass will be of Pm origin, albeit with more of a rPm at times for all parts. Beyond that and both models are showing more amplitude in the upper flow, this will put southern areas into more Tm air than Pm air at times.

The feature causing this is the jet pattern. It has been relatively flat with its axis over/just south of about 50N. During the next 168 hours it becomes more buckled as you can see if you look at either the basic GFS or the Extra charts through that period. With the jet so far south the ability of the Azores high to push north is almost completely absent. By about T+240 this is not the case with either model and the jet over the UK has a definite southerly component to it. This allows, or appears to allow, high pressure over Iberia to begin to edge north with at the same time high pressure entering the western edge of the Atlantic. Remember what the NOAA technical discussion and charts showed last night for the USA/Canada? From about the 20th the jet flow is such that it MAY allow pressure to rise from the south towards our north east. The 06z version even carries it on out to T+360 with a surface high showing to our north west and at the same time the Atlantic high is much more dominant to our west/sw thanks to the positioning of the jet. The 00z output did not have this. By T+384 it has 'lost' the nw high but the remnants of the ridge are still there towards Svalbard and into northern Russia. It is just possible that this 'window' roughly 20-23/24 is when we could see a major pattern change.

Far too early to tell just yet but possibly the first concrete sign of this starting.

I've not looked at the north American set up this morning. Looking at the ensembles spread as I did last evening once again gives a mixed message. Pressure appears to be on the low side to our north west, but high over Iberia and Russia. So as I say, mixed signals again.

Please can you explain why the heavy rain forcaste for 9am this morning never materialised this morning,has not materialised this morning in swales,had to do a full days work outside.

[johnholmes]

this thread is for events which occur beyond 5 days ahead?

Nowhere in the text you have copied do I talk about today or even tomorrow!

nothing to add this evening to the earlier comments but will do an update if it seems necessary on Wednesday

Edited January 8, 2008 by johnholmes

[johnholmes]

Update on Wednesday at 11am

Just a fairly quick update for this morning.

The past 2-3 runs from the 2 main models show less of the ‘window’ I talked about 20-23 January. There is a suggestion on the 06z GFS in the period several days earlier, 16-18 January, when something similar is being progged. High pressure to our south trying to link with rising values to our north west. But it’s a transient feature or seems to be, and its only one run.

Overall right through to T+384 GFS has a similar pattern to what we are in. The major feature is a long wave trough in the vicinity of the UK, with smaller features running through it. Occasionally they elongate it into the continent, and at other times there is a temporary receding of the main trough westwards (allowing milder air back into some districts).

The 500mb prog from NOAA still shows signs of a major trough over the period just west and over the UK.

Over North America, out to T+180, then the pattern there is for the ridge, which was(at 500mb) just off the eastern seaboard to move further east with a trough over the west to swing east with the trough line, with minor features changing its position briefly, for it to set up over the eastern half of the Sates. This of course simply reinforces the pattern we have.

In summary then, a brief colder spell with winds from north of west for most but essentially much the same as we have had for the past week seems likely out to 12 days or more ahead. Only if the jet starts to show a longer term tendency to oscillate more is there the probability of any marked change in pattern. Not showing over the past 24 hours other than the comment around 16-18th.

[Lord of the clouds]

Thanks for the above Summary John, very informative as is usual! No doubt many people on here will be righting off Winter now, even thought we are only in January!! There's still pleny of time for things to change, it aint over until the Fat Lady sings....

[BLAST FROM THE PAST]

The past 2-3 runs from the 2 main models show less of the ‘window’ I talked about 20-23 January. There is a suggestion on the 06z GFS in the period several days earlier, 16-18 January, when something similar is being progged. High pressure to our south trying to link with rising values to our north west. But it’s a transient feature or seems to be, and its only one run.

other than the comment around 16-18th.

[PB22]

Thanks John, certainly further signs tonight of some changes as we go into the second half of the month. However, there's no sign of any height rises occuring towards Greenland at the moment. Indeed the pressure ensemble for Iceland shows a trend towards falling pressure as we go into the later part of the month:

Pressure is showing a tenacy to rise over eastern and northeastern Europe later:

Meanwhile, the Berlin 850hPa ensemble does show a few colder members showing, suggesting an easterly may set up later in the month:

So it may well be that we have to look towards the northeast again. We may get some brief northerly incursions across the UK, but for anything longer and more sustained I think we will need to rely on our friend the Siberian/Scandinavian High to develop and build westwards. Whether that will happen remains open to question. In the meantime, enjoy the unsettled weather!

[MAF]

a quick question John. (or anyone who wishes to answer) when was the last time a sustained Scandi High was prevalent over the UK. Seems that the westerly flow has dominated the winters for what feels like a lifetime