Short Term Model discussion 03/01/19 onwards

[knocker]

The major winter storm to impact the east coast this weekend is forecast to give a lot of snow, It is relevant to some discussion here recently

An interesting blog post on it by Jack Sillin

https://blog.weather.us/major-winter-storm-to-impact-the-east-coast-this-weekend/

 

Edited January 18, 2019 by knocker

[knocker]

With some reference to the above

 

[knocker]

outlook - becoming colder with increasing snow risk

The 500mb and surface analysis for midnight and the 0300 WV image

Most of England will start the day cold and cloudy but largely frost free. A different story in northern Scotland where there is quite severe frost in the clearer air. This is much the story for the day; cloudy and dry over much of the country with perhaps some patchy rain and a few light snow flurries early on in the east of England but in the south west a continuation of quite heavy showers, This regional variation also reflects the temps today

Tonight remaining cloudy over England, with the showers lingering in the south west, but a clearer colder night in Ireland and Scotland before some rain (snow on the higher ground), associated with the cold front arriving from the north west in the early hours tomorrow.

This will then track slowly south east through Sunday, albeit weakening as it goes, but it does introduce some colder air in it's wake with some wintry showers in the north west. Further south still quite cloudy with some sunny intervals.

The cold front duly clears the south east by midnight but there is a lot of activity to the west. The much discussed storm has appeared over the eastern United States whilst another trough has tracked east into the Iceland area, and the cold front associated with this will bring rain, snow on the higher ground, into the north west early Monday which will track south east through the day and overnight into Tuesday

The front will clear into the North Sea in the early hours of Tuesday as the upper trough sinks south east, leaving the country in a brisk north westerly with frequent heavy showers which could be of rain, hail or snow.

The amplification of the subtropical high in mid Atlantic and the alignment of the upper trough over the UK is still causing problems so on Wednesday I'll stick to the fax chart. Thus another cold showery day with troughs embedded in the circulation.

[Cymro]

5 hours ago, knocker said:

outlook - becoming colder with increasing snow risk

The 500mb and surface analysis for midnight and the 0300 WV image

Most of England will start the day cold and cloudy but largely frost free. A different story in northern Scotland where there is quite severe frost in the clearer air. This is much the story for the day; cloudy and dry over much of the country with perhaps some patchy rain and a few light snow flurries early on in the east of England but in the south west a continuation of quite heavy showers, This regional variation also reflects the temps today

Tonight remaining cloudy over England, with the showers lingering in the south west, but a clearer colder night in Ireland and Scotland before some rain (snow on the higher ground), associated with the cold front arriving from the north west in the early hours tomorrow.

This will then track slowly south east through Sunday, albeit weakening as it goes, but it does introduce some colder air in it's wake with some wintry showers in the north west. Further south still quite cloudy with some sunny intervals.

The cold front duly clears the south east by midnight but there is a lot of activity to the west. The much discussed storm has appeared over the eastern United States whilst another trough has tracked east into the Iceland area, and the cold front associated with this will bring rain, snow on the higher ground, into the north west early Monday which will track south east through the day and overnight into Tuesday

The front will clear into the North Sea in the early hours of Tuesday as the upper trough sinks south east, leaving the country in a brisk north westerly with frequent heavy showers which could be of rain, hail or snow.

The amplification of the subtropical high in mid Atlantic and the alignment of the upper trough over the UK is still causing problems so on Wednesday I'll stick to the fax chart. Thus another cold showery day with troughs embedded in the circulation.

Great forecast but can I ask you kindly not to forget us in Wales! 

[johnholmes]

One thing for folks to note is the consistency for 12z Monday, two Fax charts issues on different days but the overall position of the cold front is very similar. Perhaps shows just how little time they spend looking at the GFSoutputs!

[knocker]

High res sat image 1230. Some very impressive Cbs in these parts this morning

[knocker]

As mentioned above

[knocker]

A quick look at Monday/Tuesday with the fax and ecm. By 1800 Monday the rain is into the north west and it's borderline here with the temp hovering around 1-3C so snow on the higher ground  And this applies further south as the front tracks south east with the dew point hovering around 0C. The front certainly introduces colder air, or rather the occlusion following on does, with widespread severe frost Wednesday morning. The snow, sleet or rain issue to be decided later

Edited January 19, 2019 by knocker

[knocker]

Outlook - cold with periods of rain, sleet and snow

The 500mb and surface analysis for midnight and the 0400 UK chart

Quite a cold start to the day, particularly in north east Scotland , but mainly cloudy in England and Wales with plenty of low cloud and mist around. This will remain during the day with maybe the odd break here and there and still quite but the cold front encroaching from the northwest will bring a band of rain, sleet and snow, the latter on the higher ground, into north west Scotland and Northern Ireland by 0700. This front will track south east during the day, weakening as it goes. with showers over western Scotland in the clearer air behind

This evening and overnight much of southern England and Wales (mustn't forget Wales knocker ) will keep the low cloud with patchy drizzle whilst the north will be clearer with the odd shower still over western Scotland.

The good news is the cloud over England Wales will tend to break through Monday so some sunny intervals but from around 1400 more extensive cloud will reach western parts with a band of heavy rain and strengthening winds, associated with another cold front, impacting N. Ireland and north west Scotland. This will then track and with snow down to quite low levels. Temps varying around the average.

Through Monday evening and into Tuesday the front will clear east, closely followed  by another, as a shallow wave forms on them and the rain, sleet and snow will eventually clear leaving a cold day with squally wintry showers in western regions.

By Wednesday the waving front is well to the east leaving the country with a mainly dry, but cold day, perhaps the odd wintry shower over north west coasts as the subtropical high amplifies to the west

A not dissimilar day on Thursday but cloud and rain later in western regions as a warm front edges in associated with a low tracking around the top of the ridge. And again this is where the gfs and the fax start to differ so be aware.

And the NH profile at T120

 

[knocker]

I should have included in the above widespread frosts Wed/Thurs

[knocker]

This morning's update on Monday's front

Edited January 20, 2019 by knocker

[Skyraker]

2 hours ago, knocker said:

This morning's update on Monday's front

Oh dear, those FAX show only rain.

Never mind, onwards and upwards eh.

[The Enforcer]

I have come out of reverse-hibernation too soon.

 

It is rather damning that the potential snow event that was identified from a week away, now within 48 hours is shown as 'rain only' when the following factors apply:

1/ 850's at least -7C (for Oxfordshire)

2/ below average 2m temperatures ahead of the cold front

3/ core period of winter (how many times does one read "if only this had been in January"?)

4/ front crossing overnight

5/ active front - some heavy precipitation

I have this weird hunch that the conditions look more favourable for this than the 10th December 2017 rain to snow event (unforecasted for here by at least half of the hi-res models even at T+6), which gave as much snow here as the entire March easterly.

 

[knocker]

The high res at 1130. The odd shower down here this morning

Edited January 20, 2019 by knocker

[knocker]

The latest look at tomorrow afternoon

As the band of rain, sleet and snows moves east around midday blizzard conditions could exist for a time over higher ground in northern Scotland as winds pick up quickly ahead of the front, The wind will drop quickly after the passage of the front, Thereafter any snow restricted to the higher ground as the front moves ESE clearing most of the country by  midnight

Edited January 20, 2019 by knocker

[knocker]

An interesting evolution from the gfs as it develops a wave on the front Tuesday morning and deepens it quite rapidly. This, with other factors, slackens the flow leading to a widespread frost Wednesday morning

[knocker]

The ecm has two centers on the deconstructing front and a widespread frost Wed morning

[knocker]

Outlook - cold but predominately dry

The 600mb and surface analysis for midnight and the 0400 surface chart

As can be seen a cold start in most areas with mist and some freezing fog around. This will clear this morning and for most of the day England and Wales will have broken cloud and sunny intervals/ But further north a cold front will bring a belt of heavy rain into north west Scotland and N. Ireland by 1400 with some very strong winds reaching gale force around the Hebrides and other exposed areas. And as the precipitation will fall as snow on the higher ground some quite nasty conditions for a while. The front will track slowly ESE during the afternoon with some snow on high ground in the NW of England.

The front will continue it's slow progress through this evening and overnight with some snow on the high ground in Wales and possibly the moors of the south west and maybe even  a few flurries on the back edge as it clear the south east. Behind the front squally wintry showers which could well give some accumulations of snow in places. And with a widespread frost, ice could be a problem in the morning.

With the front well out of the way Tuesday will be cold day with wintry showers in the brisk north westerly wind

A not dissimilar day on Wednesday as the showers tend to die out as the front fragments in the North Sea and the subtropical high amplifies in the west. Another cold day

A quiet cold day on Thursday but cloud and some light rain may encroach western regions later as systems running around the northern flank of the high push an associated warm front east

By Friday there is a deep surface low 968mb just east of Iceland and the ridge has been suppressed which has made the movement of the warm front east somewhat problematic but it has introduce warmer air over the southern half of Britain

The NH profile at T120

Worth noting again a marked disagreement between the gfs and the fax on the analysis for Midday Friday

Edited January 21, 2019 by knocker

[knocker]

An illustration of the cold unstable air tomorrow lunchtime. A forecast sounding for the north west with cold air and the tropopause down to 450mb and convection up to it

[Joneseye]

On 20/01/2019 at 11:38, The Enforcer said:

I have come out of reverse-hibernation too soon.

 

It is rather damning that the potential snow event that was identified from a week away, now within 48 hours is shown as 'rain only' when the following factors apply:

1/ 850's at least -7C (for Oxfordshire)

2/ below average 2m temperatures ahead of the cold front

3/ core period of winter (how many times does one read "if only this had been in January"?)

4/ front crossing overnight

5/ active front - some heavy precipitation

I have this weird hunch that the conditions look more favourable for this than the 10th December 2017 rain to snow event (unforecasted for here by at least half of the hi-res models even at T+6), which gave as much snow here as the entire March easterly.

 

I'm down the road from you in Newbury and have a sneaky suspicion of back edge snow overnight. Not long to wait and find out. 

Also liking the look of those convective charts posted by Knocker and the high res model predictions of shower activity tomorrow.

[knocker]

Outlook - unsettled and cold becoming quieter and a tad warmer

The 500mb and surface analysis for midnight and the Castor Bay sounding

The cold front is currently still clearing the south east but the rest of the country is in the cold, unstable airstream following on behind.(see the Castor Bay sounding)  So an icy start to the day in many places and wintry showers are already effecting western regions, more concentrated  in the north west at first but becoming more widespread as troughs track east within the circulation. These showers a mix of rain, sleet and snow. the latter initially on the higher ground, but then to lowers levels and there could be a fair accumulations in areas of shower concentration. A cold day

The wintry showers will continue in the north and west this evening and slowly dying out as the wind drops and thus with clear skies a widespread frost by Wednesday morning. The front, now an occlusion, is waving in the North Sea as the upper trough slips south east over Britain.

Wednesday, with the occlusion still to the east, will be a dry but very cold day with the odd shower in the north and west/east coastal regions

Whilst all this has been going on the Atlantic high pressure has been steadfast but it is now coming under increasing pressure and deepening troughs are swinging around into Iceland and an associated warm front has pushed east to be over Ireland by midday Thursday, Thus some cloud and patchy rain along with warmer air creeping into western regions later on on what generally has been a cold and dry day

Pressure on the ridge continues and by midday Friday there is a deep surface low 974mb south of Iceland with winds picking up over Scotland. The movement of this has pushed the aforementioned warm front across the country, thus a cloudy day with some patchy rain and temps, for a change, a little above average

By Saturday the process is again well underway with the subtropical high amplifying in the Atlantic and the upper trough slipping south whilst on the surface the cold front is slipping south east across the country, Thus the cloudy warm sector will shrink during the day as the belt of light rain introduces clearer and cooler air

The NH profile at T120

[Paul]

I've split out the last few posts in this thread and posted them into the focused model thread, as this thread is merging into that one. 

Will be locking this now.