Short range model discussion - into 2018

[chrisbell-nottheweatherman]

4 hours ago, knocker said:

Time to relax and enjoy a relaxing day tomorrow before the defibrillators get whipped into action at the end of the week as the transient ridge promises a reasonable day.

In fact Wednesday may well be not a bad day either for most to start with but heavy rain and strong southerly winds will slowly take over as the front associated with the major trough to the west struggles east.

A similar story on Thursday although the strong winds will abate apart from the north east.

Still unsettled on Friday but changes are afoot with the trough to the west becoming negatively tilted (forcing the jet south as Interitus mentioned earlier in a much more detailed and complex post ) whilst the high cell amplifies in the north east.

 

 

With the jet heading south of the longwave trough and a south-easterly flow establishing itself over the UK, it would only take a reajustment of the trough orientation to being elongated on an east-west axis for an easterly draw to verify (not that I want cold conditions at this point).

[knocker]

Today, once the patchy rain associated with the low in the south east and the occlusion to the west has fizzled out, will be dry and fairly sunny in most areas, particularly the west with maybe just the isolated shower, as the ridge sidles in from the west.This will continue to be the state of play overnight for most areas but through the night cloud and rain will encroach from the west as a front associated with the complex area of low pressure to the west, courtesy of a deep upper trough, tracks east. It will also become increasingly windy in the west. (Do not look at the fax chart if you are of a nervous disposition)

Wednesday continues to be dry and fairly sunny for many areas to the east, albeit with a southerly wind increasing in strength but cloud and rain, sometimes heavy, will continue to encroach from the west as a low associated with the aforementioned low pressure area deepens and tracks slowly NNE to be 956mb by 1800. But at the same time a glance at the 500mb chart indicates that things are-a-changing with high pressure building to the NE and the trough adjusting alignment.

Eventually overnight and through Thursday the front struggles across the country taking patchy rain with it but the strong winds do abate apart from in the north east. But aloft the pattern is still evolving with the trough to the west increasingly becoming negatively tilted and another trough swinging south west to the east bringing much colder air.

Friday sees a SW/NE split as the upper pattern continues to adjust with showery rain pertaining in the south west but a strong south easterly wind bringing wintry conditions to the north east with snow showers on the high ground as temps start to plummet.

Saturday it becomes colder for all of the UK as the wind backs easterly and strengthens with snow showers and perhaps longer periods in eastern and central areas. This is compounded by the GFS developing an upper low in the Denmark area and tracking it west overt the UK by 00 Sunday.

There is a caveat vis the end of the week as last evening's fax charts are not as doom laden as the GFS and do not totally agree albeit the general prognosis is still rapidly downhill

Edited March 13, 2018 by knocker

[knocker]

11 hours ago, knocker said:

The ecm evolution this evening is quite intriguing, It forms a small upper low over Denmark at T108 and develops it and tracks it west to be over south east England by T120 where it is still intensifying and phasing with the main trough. Will this key development repeat at midnight.

The short answer is yes which doesn't of course mean that it will transpire. If so could concentrate snow showers in the east/central;/south areas later on saturday

[knocker]

A welcome satellite image at 0545.

[knocker]

Classy 1130 high res. MODIS  courtesy DSRS and the midday analysis. Cracking day in these parts.

[knocker]

The 0600 GFS has delayed the onset of the colder air on Saturday/Sunday and adjusted it's direction of travel further south. This is quite likely inter run variations

The 1200 analysis

 

 

[phil nw.]

A nice mild interlude today until Thursday but after a brief drier spell today the next set of fronts from an approaching Atlantic low slowly head in to the west tomorrow and ease further ne on Thursday so more rain for many by then.

Thurs midday

Then it's starts to get interesting(for coldies anyway) as the much heralded cold spell starts to show it's hand to the east as pressure builds over Scandinavia.

Friday is looking like changeover day as the cold from the east starts to move this way as the Atlantic fronts stall and start to move back west.

The T84hrs fax

We can see on the medium range NW model the leading edge of the colder uppers showing up to the north east by Friday midday.

This model shows that by Saturday midday the cold has made further advances west across much of the UK with snow showers developing in the bitter flow,especially down the eastern side.Snow fall forecasts not to be taken too seriously at this stage as we know and anyway further developments make well occur on that front in subsequent runs.

 

what is notable is the depth of cold expected within such a short range now given the lateness of the season.

[knocker]

Actually Phil vis depth I was looking at a forecast sounding earlier and within this time frame certainly not comparable with the earlier bitter cold with a cap on convection.  Of course outside the time frame...................

[knocker]

The 1500 geostationary (courtesy DSRS) showing the complex low/frontal area to the west.

[ptow]

21 minutes ago, knocker said:

Actually Phil vis depth I was looking at a forecast sounding earlier and within this time frame certainly not comparable with the earlier bitter cold with a cap on convection.  Of course outside the time frame...................

And in laymans terms Knocker if you wouldn't mind

[phil nw.]

17 minutes ago, knocker said:

Actually Phil vis depth I was looking at a forecast sounding earlier and within this time frame certainly not comparable with the earlier bitter cold with a cap on convection.  Of course outside the time frame...................

Yes i don't think we are looking at -15C uppers this time Malcolm but sub 10-12c are showing on all the models up to now(pre-12z runs)so cold enough for the time of year methinks!

As for snow fall maybe flurries to start with i think but an eye to the east as the upper cold pool moves across the south  later on Saturday and into Sunday-timing uncertain as is it's final track.The high may be further south as will any instability in that case.

ECM T120hrs for example

may give something more.

[knocker]

21 minutes ago, ptow said:

And in laymans terms Knocker if you wouldn't mind

The big inversion at 850mb and very dry air thereafter would indicate no great vertical extent of convection/clouds. Effectively puts a lid on it. The colder air from the east is undercutting, cold air advection, the warmer air aloft. Of course as the colder air gets established later then this would change.

Edited March 13, 2018 by knocker

[knocker]

25 minutes ago, phil nw. said:

Yes i don't think we are looking at -15C uppers this time Malcolm but sub 10-12c are showing on all the models up to now(pre-12z runs)so cold enough for the time of year methinks!

As for snow fall maybe flurries to start with i think but an eye to the east as the upper cold pool moves across the south  later on Saturday and into Sunday-timing uncertain as is it's final track.The high may be further south as will any instability in that case.

ECM T120hrs for example

may give something more.

Ah that little upper low

Edited March 13, 2018 by knocker

[Polar Maritime]

Chance of gales tomorrow mainly Western/coastal areas and high ground I would think.

[knocker]

And quite wet

[knocker]

The ecm has the upper low feature running west through the Channel Saturday evening to be over Cornwall/Brest by 00 Sunday. Snow associated with itskirting and just affecting the south coast but the heavier accumulations in the Channel and NW France.

[knocker]

Satellite at 2020 showing the frontal cloud edging in to the west

 

[knocker]

The main problems over the next 36 hours or so are going to be rain and strong winds associated with the fronts and complex low pressure system just to the best of the UK. This will mainly affect the south west, Wales and N. Ireland, where gales are possible as the rain is quite slow moving so some quite high totals are likely in places. Elsewhere sunny intervals but the wind will pick up during the day. During this evening  and overnight the rain will gradually move north east clearing the south west by morning

Through Thursday the rain will continue to affect the north east, perhaps some snow in eastern Scotland, leaving brighter conditions in it's wake but later a low associated with the aforementioned complex low pressure are will drift into the south west bringing more showery rain. Temps still a little above average but breezy.

By midday Friday the pattern change is well under way with the upper trough to our west becoming negatively tilted as high pressure surges to the north east with another trough and much colder air swinging south west around the latter. On the surface the low changes tack into Ireland and a fresh south easterly wind  is introduced to the north east.and much lower temps.

The new pattern continues to become established over Saturday with strong easterly/ south easterly winds affecting all of the UK and much colder with snow showers quite likely in the east and south with a dying cold front moving slowly west.

Sunday feeling very bitter in the strong easterly wind with the possibility of snow showers in the east and central areas and perhaps some more persistent snow in the S/SE as the cold pool associated with the upper low tracks west and swings into France. Still to be decided.

 

 

Edited March 14, 2018 by knocker

[knocker]

It's obviously far too early to attempt to call the possible snow event in the south on Sunday but for the record this morning the ecm has the cold pooll/upper low a little more north and west than the GFS. At 00 Sunday it is in the eastern Channel  Over the next 12 hours the main snow belt remains in the Channel as it moves west but the norther edge would impact the south coast. But the main point is the temp which will not get above freezing in many places and in the strong easterly wind the wind chill be very nasty indeed.

Edited March 14, 2018 by knocker

[knocker]

The updated morning fax's through Friday/Saturday and the indications of snow showers  on Saturday. What one would call the morning clarification

Edited March 14, 2018 by knocker

[knocker]

The 0600 surface analysis

[Derecho]

Cheers Knocker, I think this page will become useful with all the bickering in the MAD thread. However I wonder if the cold pool could actually end up missing us or we get a dry easterly for many? 

[knocker]

13 minutes ago, Quicksilver1989 said:

Cheers Knocker, I think this page will become useful with all the bickering in the MAD thread. However I wonder if the cold pool could actually end up missing us or we get a dry easterly for many? 

Well as you know the gfs does just that and looking at forecast sounding in France cold and very dry are the operative words

 

[knocker]

The 0800 geostationary (Courtesy DSRS) says it all really

[chrisbell-nottheweatherman]

2 hours ago, knocker said:

Well as you know the gfs does just that and looking at forecast sounding in France cold and very dry are the operative words

 

I'k=m pretty useless at reading skew-t outputs, but even I can work out that it's a dry flow from that!