Model Output Discussion - 17th Oct Onwards

[Frosty.]

I think something is brewing in nov/dec/jan/feb/march...CFS shows a lot of lovely cold on the way. :-)

[Zenarcher]

Here are the differences between the GFS, ECM, UKMO, GEM, JMA and NAVGEM.

 

 

Most at the moment don't show a strong low. The UKMO shows the deepest low but none of the other models are showing that, as for the ECM it sends the low a lot further South down into France.

[BLAST FROM THE PAST]

Well, let's see what models bring tomorrow....I'm sure it will be different 

 

BFTP

Edited October 22, 2013 by BLAST FROM THE PAST

[radiohead]

Wel ,let's see what models bring tomorrow....I'm sure it will be different 

 

BFTP

 

We have the 18Z GFS to go first. Looks like the low might be back on this run.

[BLAST FROM THE PAST]

We have the 18Z GFS to go first. Looks like the low might be back on this run.

Indeed that will be this one

 

[radiohead]

18Z. Up to 65 knots sustained off the southwest coast.

 

[Geordiesnow]

Although hard to pin down the specific details, the trend does look like once the polar air starts to flood through Canada and starts interacting with the jet stream, it will intensify the jet stream which does bring the risk of a deep depression occuring but what we are also seeing is a more active Atlantic but this time, with winds coming from a cooler Westerly direction so it looks like the mild spell will be replaced by more average temperatures if not even a little below average. 

 

Interesting output for sure. 

Edited October 22, 2013 by Geordiesnow

[Timmytour]

Can't help thinking that the volatility of model output is consistent with what a "traditional" autumn should bring us. Furthermore I think there is an increasing trend for the seaons to be more "traditional"....winters with wintry weather, summers with the occasional spell of hot weather without it being enduring, springs that don't disappear in the blink of an eye or start in early Feb and autumns with a bit of good old fashioned wet and windy weather.

So why is our weather pattern reverting to type? I blame global normalisation

[radiohead]

From a quick look over the 18Z GFS ensembles, it seems around 9 show a storm of 965mb or lower, 4 of those 955mb or lower.

 

Should be interesting to see how things look in the morning.

[Mark Neal.]

GFS 00Z. Monday morning, Low pressure.

 

GEM 00Z. Monday afternoon, low cuts across uk..

 

 

UKMO 00Z.  2am on Monday morning..

 

 

Just looking at the 3 models which show a deep area of low pressure through Monday, i know the timing of the three is different. But just trying to show the low pressure coming through the UK.. 

Edited October 23, 2013 by Mark N

[VillagePlank]

Re: Sun/Mon storm,

 

Still there on the 00z GFS ,

 

 

GEFS 18z shows the range of possibilities (for Heathrow),

 

 

With the interesting numbers, which are skewed to the high values (so it's more likely that the pressure will be from the mean toward the high value than the low value)

 

 

This is supported by GFS cluster analysis. Here, we find two clusters, each consisting of 30% of the ensemble members, and together containing, obviously, 60% of the members,

 

 

Here's the associated dendrogram, (clusters above are the right two)

 

 

You'd have to go with windy, that's for sure: storm of the century ala Daily Express? I don't think so: well, at least, that's not what the probable forecast is.

 

Edited October 23, 2013 by Sparkicle

[Frosty.]

The GEFS 00z mean is showing a cooler blast early next week with the very mild / warm s'ly / sw'ly winds veering to a much chillier nw'ly for a time, followed by a midweek ridge which would bring a touch of frost, especially to rural areas but soon followed by a flattening out of the pattern with lows sweeping in off the atlantic and temps returning to the mild category but not as mild as currently. Further on, the mean indicates a pressure rise from the south/se which forces the PFJ to retreat further north with lighter winds and benign weather spreading north across southern britain with sunny spells by day but overnight / early morning fog, but continuing unsettled & windier across northern britain throughout with spells of rain interspersed by sunny spells and showers and temperatures around average.

Edited October 23, 2013 by Frosty.

[Biggin]

Can I ask do the models show whether the low deepens or fills as it crosses the UK.

[radiohead]

0Z GEM looks quite severe. Violent storm force at sea, with storm force/gales along coasts.

 

[VillagePlank]

Can I ask do the models show whether the low deepens or fills as it crosses the UK.

 

The probabilistic cluster analysis reckons it doesn't really cross the UK, it skirts across the very North (so maybe touching Scotland) It deepens mainly to the west of Norway. Of course, this is still early days, with plenty of time for change.

 

Edited October 23, 2013 by Sparkicle

[Nick F]

Can I ask do the models show whether the low deepens or fills as it crosses the UK.

 

GFS shows the low deepening as it crosses the UK, the centre 968mb over northern England at 06z Monday, then 965mb over central N Sea at 12z Monday.

 

However, long way off from getting the track nailed, notice ECM slower with the low and takes it on a much more southerly track deepening it up the English Channel.

 

Although the track isn't nailed, a strong 160mph+ jet streak racing across the N Atlantic over the weekend, a trough developing in the strong upper flow will likely allow a surface depression to develop and rapidly deepen given divergence aloft - it's just a question over where it exactly it will track for now.

Edited October 23, 2013 by Nick F

[Biggin]

Thanks guys

[Frosty.]

The Ecm 00z op run shows yet another surge of warmth pumping up from the south on friday, along with a spell of heavy rain and strengthening winds pushing northwards through the whole of the uk by the end of friday, the very mild air is then chased away southeastwards during saturday and the generally unsettled and sometimes very windy spell persists throughout the run with just a weak atlantic ridge during the middle of next week separating us from the next depression, although the southeast corner could have a fine day or two towards the end of next week as an anticyclone builds across the near continent. Another feature of next week is a rapid alternation in the airmasses between tropical maritime and a much cooler north atlantic oceanic airflow, they chop and change throughout next week but on balance it's much cooler next week compared to the current exceptionally mild spell, when it's mild next week it will be a pale imitation of the current conditions. There is a strong hint that by T+240 hours we are going to see a strong surge of high pressure from the south beyond that point.

[johnholmes]

picking up where Nick has left off the UK Met idea is shown on the Fax chart T+96 and 120, deepening it from something less than 1008mb around 43N 50W to a touch below 985mb at 51N 20+W at 12z Sunday. This is rather deeper than their own model shows on the 00z run, although not by much,  this of course came out after the T+120 Fax was issued, position looks about the same. This then tracks the low (still deepening to about 970mb) over northern England. As Nick says the actual track will slowly begin to be clearer from the 3 main models over the next 48 hours. ECMWF seems too far south. It will deepen for sure looking at how the jet is predicted to behave in the period as it moves from 50 west toeast of the meridian. Very strong winds with gales on its southern flank seem inevitable, just how strong again we need to wait for later runs to firm up on this. Severe gale force gusts seem quite likely over exposed areas. How much rain, and where, will not be clear until even closer to the event.

Fax chart link

http://www.netweather.tv/index.cgi?action=fax;sess=

 

jetstream (GFS) link

http://www.netweather.tv/index.cgi?action=jetstream;sess=07ffcb4b739052c16b3ea2ef3f5894ab

 

And in the longer term 6-15 days or more=little change, strongish 500mb westerly type flow remains the pattern to end of October, who knows possibly beyond into early November. At some point it will change but when is not something showing yet on the anomaly charts and not really anything else as far as I can see.

Edited October 23, 2013 by johnholmes

[Tom Quintavalle]

As Nick states above, the exact track of this deepening low will be hard to forecast until much nearer the event and therefore the area which is likely to be affected by the strongest winds.

Another factor to consider is after the warm Autumn to date, a lot trees have retained most of their leaf cover and will be prone to damage, with presenting a more solid barrier to the strongest winds that occur, one of the factors that caused so much tree damage in October '87. Hopefully this storm will be nowhere near as violent.

 

Tom.

Edited October 23, 2013 by Kentish CZ

[Summer Sun]

Latest from Gibby

 

All models continue to programme unsettled weather for the reliable future with the next three to four days agreed upon by all output. The mild SSW flow of recent days is replaced by a fresher Westerly flow, still somewhat showery but less heavy and thundery than of late. A ridge is then shown to move up across the UK tonight and tomorrow with a window of dry and bright weather for all tomorrow. By Friday a new Low will be showing it's hand towards the South and West with cloud and heavy rain moving NE across England and Wales through the day. This then becomes absorbed by a large Atlantic depression up to the NW to make way for a very windy and unsettled weekend with showers or longer spells of rain in near gale West or SW winds for all and temperatures back down to average levels or maybe a little below in the North where it may become chilly enough by the beginning of next week for some hill snow over Scotland.

 

GFS then shows a small but vigorous Low crossing East over Britain early next week with gales and heavy rain for all, severe on Western coasts for a time. This then is followed by a temporary rather chilly showery NW flow before a weak ridge moves East across the UK around midweek and in turn followed by a return to cloud and mild SW winds with rain by the end of the week. This then paves the way for the rest of the run as Northern and Western areas become most prone to strong winds and rain at times while the South and East close to higher pressure over Europe sees only occasional rain on weakening cold fronts as they pass through. It would be relatively mild over the UK but not as mild as recently.

 

UKMO looks very disturbed this morning for early next week with a chilly and strong NW flow next Tuesday following a potentially stormy spell for a time early in the week. Most areas would see some sunshine but squally showers and with temperatures much lower than of late some snow over Northern mountains would be likely.

 

GEM today brings back it's vicious little Low crossing England and Wales early next week with potential gales, possibly damaging in places buffeting Wales and Southern England for a time along with heavy rain. As it clears the weather becomes showery and then calms down briefly under a transient ridge before further Low pressure and attendant rain and showers take over for all again before the end of next week. Temperatures would be near or perhaps a little below for a time in the NW flow in the wake of the Low early next week but all this is academic in the strength of the wind as it would feel chilly everywhere.

 

NAVGEM is also very disturbed next week with trough and Low pressure streaming over the UK through the week with spells of rain alternating with showers. It would be windy with gales at times though without the storm system shown by some other output nothing out of the ordinary is shown by NAVGEM. Temperatures would be close to normal overall, perhaps rather cold in the North at times.

 

ECM brings the disturbance next week just that bit further South which would take any real strong winds down over France. However, it is close enough to provide a lot of rain following a wet weekend for the South. Later in the run pressure rises somewhat over the South with the strongest winds left for Scotland while Southern areas though rather cloudy and damp will see some drier interludes in much less wind than previously. Near average temperatures look likely for all from ECM next week.

 

The GFS Ensembles show an oscillating pattern between the members suggesting a mobile pattern alternating between mild and wet weather with cooler and showery weather through the next few weeks. There is a more definitive dip in temperatures early next week, which proves short-lived when rainfall is at it's peak. Thereafter the rainfall will not be quite as pronounced in the South with some drier interludes in between the rain. Winds from most members are shown to be fresh to strong for most of the UK for much of the run.

 

The Jet Stream shows the flow currently to the South of the UK moving North over the coming days to the UK where it continues to blow over in an oscillating fashion for the foreseeable future.

 

In Summary today the outlook remains disturbed, often windy and potentially stormy for a short while. All models bring in some sort of disturbance early next week which ranges from a damaging storm to just a wave depression running East in the flow with no more than a band of wind and rain. Which is right is hard to call at the moment but the potential is there for something rather nasty and will need to be watched in future outputs as the time draws nearer. Outside of that there is plenty of wind, rain and showers for all and with the recent unseasonal warmth behind us we can all expect to feel colder without it ever being very cold. Some output suggests a rise of pressure to the SE which as always in these situations is possible and would send the Jet Stream further North along with the depressions to bring some dry and mild weather back across the SE at times. Having said that it is just one of several options we are likely to see in the output over the coming days as the very volatile situation over the Atlantic continues.

 

http://www.norton-radstockweather.co.uk/Model-Analysis%282859336%29.htm

Edited October 23, 2013 by Summer Sun

[Yarmy]

As Nick states above, the exact track of this deepening low will be hard to forecast until much nearer the event and therefore the area which is likely to be affected by the strongest winds.

Another factor to consider is after the warm Autumn to date, a lot trees have retained most of their leaf cover and will be prone to damage, with presenting a more solid barrier to the strongest winds that occur, one of the factors that caused so much tree damage in October '87. Hopefully this storm will be nowhere near as violent.

 

Tom.

 

It's the length of day that determines when trees start to lose their leaves, not the warmth. The temperature, amount of sunlight, and moisture determine the intensity of display. 

[Tom Quintavalle]

It's the length of day that determines when trees start to lose their leaves, not the warmth. The temperature, amount of sunlight, and moisture determine the intensity of display. 

 

Thank you Yarmy for that, I didnt realise that was the case. 

 

Tom.

[lightningsprite]

It's the length of day that determines when trees start to lose their leaves, not the warmth. The temperature, amount of sunlight, and moisture determine the intensity of display.

Actually not entirely true...some species rely on the length of the day while others on the temperature. .which is why there are variations in Autumn as to when the trees start to lose their leaves...otherwise all the leaves would drop at the same time each autumn!

[Yarmy]

Actually not entirely true...some species rely on the length of the day while others on the temperature. .which is why there are variations in Autumn as to when the trees start to lose their leaves...otherwise all the leaves would drop at the same time each autumn!

 

Well, I'll defer to your greater knowledge.  However, according to this:

 

http://www.usna.usda.gov/PhotoGallery/FallFoliage/ScienceFallColor.html

 

"Because the starting time of the whole process is dependent on night length, fall colors appear at about the same time each year in a given location, whether temperatures are cooler or warmer than normal."