Short range model discussion - into 2018

[johnholmes]

1 hour ago, knocker said:

Anyone for a convergence zone? The 1200 Geostationary

Compare the sat picc to the Fax. How on earth does the senior man justify 7 of them. Talk about stand in the corner, the senior lecturer at the Met O College, in my time, would have had a fit if confronted with that!

[swebby]

8 minutes ago, johnholmes said:

Compare the sat picc to the Fax. How on earth does the senior man justify 7 of them. Talk about stand in the corner, the senior lecturer at the Met O College, in my time, would have had a fit if confronted with that!

8 if you include the one over Denmark.  Certainly one over the bristol channel first thing but that died away by lunchtime. 

Edited February 28, 2018 by swebby

[Interitus]

2 hours ago, johnholmes said:

How is Sidney with all that white stuff, best make sure doors and windows are tight shut or he may appear at your dinner table!

 

Just hope the conditions don't get so bad that he appears on the dinner table!

Brutally cold for much of the UK this evening, temperatures pretty much universally sub-zero, accompanied widely by winds between 20-30 mph

Edited February 28, 2018 by Interitus

[knocker]

23 minutes ago, Interitus said:

Just hope the conditions don't get so bad that he appears on the dinner table!

Brutally cold for much of the UK this evening, temperatures pretty much universally sub-zero, accompanied widely by winds between 20-30 mph

A quick glance here confirms that.and a severe frost in morning and wind chill

https://wow.metoffice.gov.uk/

Sid's okay

Edited February 28, 2018 by knocker

[chrisbell-nottheweatherman]

2 hours ago, knocker said:

Anyone for a convergence zone? The 1200 Geostationary

Given our heavy, prolonged snow around that time, I'm not going to argue with the trough over Norfolk...

[knocker]

The ecm has light snow around 0600 along the south west coast spreading north during the day with main wodge Cornwall, Devon, Somerset and into central South Wales Turning to rain in Cornwall by the evening. The lighter snow further NE/E.Then a pause in the proceedings before the next front arrives Friday morning

[knocker]

1 hour ago, knocker said:

The ecm has light snow around 0600 along the south west coast spreading north during the day with main wodge Cornwall, Devon, Somerset and into central South Wales Turning to rain in Cornwall by the evening. The lighter snow further NE/E.Then a pause in the proceedings before the next front arrives Friday morning

The updated fax charts 1200 Thurs >00 Saturday

 

 

 

Edited February 28, 2018 by knocker

[Ice Man 85]

33 minutes ago, knocker said:

The updated fax charts 1200 Thurs >00 Saturday

 

 

 

Please tell me there's some hope for an improvement in temperatures! Not looking good from the det. runs!

[ItNeverSnowsInWindsor]

Well the GEFS ensembles don’t show any heavy precipitation for London tomorrow ☹️ Hope they’re way off the mark! 

[knocker]

Similar story to last night vis the anomalies. Upstream some ridging in the Hudson Bay area with the secondary vortex near north west Greenland and sill a strong westerly jet exiting the south east US en route to Iberia. The main vortex over northern Russia with an associated trough orientated across the UK into the eastern Atlantic.

Regarding the UK the pattern it smacks of a sense of inertia with a light W/WSW drift into the south from a flow originating in N. Canada. It portends a slack low pressure area over, or adjacent to, the UK and unsettled weather with the temps still below average.

[knocker]

Out of interest had a quick look at the midday sounding at Albermarle. You wont see many midday soundings on the last day of Feb, in the UK

[johnholmes]

2 minutes ago, knocker said:

Out of interest had a quick look at the midday sounding at Albermarle. You wont see many midday soundings on the last day of Feb, in the UK

True and with the energy available even with a dry bulb of ).0 C then it is no wonder thunder snow occurred, TWS has just commented that there were, I think he quoted, 4 separate METARS from Newcastle airport reporting this.

Truly a very memorable few days. It seems pretty unlikely that this will repeat itself very soon in February coming years.

february here, a quick check, suggests it is the coldest since I began weather observations in January 1997!

 

[Nick F]

Synoptic analysis Thursday to Saturday – update 21z 28/02/2018

Tonight

T+00 fax chart for 6pm today shows a 1051mb surface high over Scandinavia, low pressure system between the Azores and Iberia and low pressure over Black Sea combine to drive a long-fetch very cold and dry easterly flow across much of Europe, including the UK.

A 500mb low / cold pool moved over the North Sea and across northern Britain today, impressively low temperatures and thicknesses with this feature.

500mb temperatures below -40C, 500-1000mb thickness of 502 dam on Abermarle (NE England) radiosonde ascent. The steep lapse rates on the radiosonde all the way up to 500mb is generating vigorous convection which is producing widespread frequent heavy snow showers across northern England, southern and eastern Scotland. The central belt will act to funnel and merge these heavy showers westward – so prolonged heavy snow – combined with strong to gale force easterly wind will cause drifting of large accumulations reaching 20-30cm and locally 40cm. Hence the Red Warning issued by the Met Office valid between 15z today and 10z Thursday morning.

The strong easterly wind will blow in further snow showers across eastern parts of England overnight too, perhaps giving further slight accumulations on top of what’s already on the ground. Drifting of the powdery snow in the strong winds.

Thursday

Further frequent snow showers blowing in across northern England and eastern Scotland on Thursday, adding to already significant accumulations across NE England, central and eastern Scotland. Further south, attention turns to Storm Emma, which will be centred over NW Iberia Thursday noon, but will send an upper warm front north well ahead of the low pressure system, the moisture advection behind this warm front upgliding over still bitterly cold sub-zero air air at the surface over southern UK will bring some snow from the south during the morning. Some divergence between the models, even at less than 24 hours out, over how far east the snow will move north. GFS west of Isle of Wight and London, while ECMWF and ARPEGE further east with the snow moving north. Heaviest falls look to be reserved for SW England, Wales and later on southern Ireland – bringing 10-20cm widely by the end of the day, perhaps up to 40cm over the SW Moors, drifting of snow in the strong to gale force wind will be a problem over higher routes – hence Met Office Amber Warnings. Snow generally looks to be lighter further east across England, but needs monitoring.

 

Friday

Storm Emma drifting north across the Bay of Biscay tomorrow afternoon, evening and night will then swing northwest toward SW Ireland on Friday, deepening as it does so. This deepening and change in direction is associated with the 500mb upper low cold pool crossing the UK today ending up to the SW of UK and Ireland on Friday and engaging Emma into its circulation, surface lows tending to follow the 500mb contour. An occluding cold front associated with Emma will move N and NE across southern England and Wales on Friday afternoon and evening bringing another band of snow – likely heavier more widely, as the low moves NW toward Ireland.

 

 

The occluded front on Saturday looks like stalling and weakening over central or northern England and Wales – models diverge again. Bitterly cold easterly flow still entrenched across much of the UK on Saturday, with temperatures only a few degrees above freezing at best, for many at or below 0C, perhaps slight recovery in far south. Less cold air arriving across southern areas on Sunday with temps perhaps reaching 6-7C, but still close to or a few degrees above freezing in the north.

Edited February 28, 2018 by Nick F

[West is Best]

Incredible.

Do we need to pinch ourselves reading Nick's message above?!

[PolarWarsaw]

17 minutes ago, West is Best said:

Incredible.

Do we need to pinch ourselves reading Nick's message above?!

I was thinking pinch wasn't strong enough to be honest. For those of us in the central, north and parts of East Midlands that have only seen a sugar coating from the odd shower, this looks like more of the same. 

Be nice to see if shift north and east a little so we can join in the fun. 

Absolutely superb post though Nick, easy to read, easy to understand. Thanks.

[matty40s]

9 minutes ago, PolarWarsaw said:

I was thinking pinch wasn't strong enough to be honest. For those of us in the central, north and parts of East Midlands that have only seen a sugar coating from the odd shower, this looks like more of the same. 

Be nice to see if shift north and east a little so we can join in the fun. 

Absolutely superb post though Nick, easy to read, easy to understand. Thanks.

some have, some havnt, my daughter 10 miles south of me has no lying snow, I have several inches and more falling now, Nottingham folk 10 miles North were moaning all day about getting nothing, now they are getting a pasting.

These set ups and accurate forecasting are not what the models are about. There is no way a model can forecast lake effect snow in the Uk accurately unlike the American great lakes where they have years of data to work with.

You have to take an overview of most of the models , binning the gfs, and use the fax charts to give an expectation, after that its nowcasting and lamp post watching.

[knocker]

Satellite at 2130 showing Emma and the warm front across northern Biscay (courtesy Dundee Satellite Receiving Station)

Edited February 28, 2018 by knocker

[Interitus]

3 hours ago, knocker said:

Out of interest had a quick look at the midday sounding at Albermarle. You wont see many midday soundings on the last day of Feb, in the UK

Ironicallly, the shallow depth of the troposphere and cold throughout limits the potential snowfall, compared to say the nor'easters of the US.

[Interitus]

17 hours ago, Interitus said:

The best indicator is from the 700mb omega chart, with uplift shown in orange and reds, sinking air in blue, the mountain ranges show as vertical motions perpendicular to the wind flow, the Welsh mountains, Pennines and Cumbrian fells stand out sharply

This part of the explanation was a bit unsatisfactory, as the observant will notice that the subsiding air appears to be collocated with the upland areas, and greatest uplift on the lee side. The Meteociel charts for that particular model don't include vertical velocity at lower levels so here is the lower resolution 700mb chart from the GFS which is broadly similar to the above -

and here is the vertical velocity at 925mb which shows the uplift and sinking motion much more where they might be expected (with marked subsidence for the west of Wales, including Carmarthenshire) -

The 925mb level is between 560-660 metres altitude at this time and the wind tracks the topography more closely than at the 2740-2800 metres at 700mb, and there is a phase shift between these levels. The idealised image below shows that with increasing altitude above the mountains, the surface uplift becomes less significant and the downwards flow shifts back from the lee side towards the summits. This is followed by a strong upwards motion denoted as the primary wave. Depending on the stability of the air, these waves may propagate tens or hundreds of kilometres down stream, but roughly speaking this primary wave is the situation in the 700mb images above -

Finally, here is a cross-section of a real example modeled from a windstorm - https://www.researchgate.net/publication/280832542_Case_study_and_numerical_simulations_of_the_November_19_2004_severe_windstorm_in_Central_Europe

Wind flow is from the left, and at lower altitudes the uplift/sinking motions (light/dark grey) are located as expected over the high ground. Higher up though the initial uplift is not present, with the sinking air over the upslope and summit, and a strong upward wave downstream.

Hopefully this clears up any confusion.

 

Edited March 1, 2018 by Interitus

[knocker]

Today the continuing evolution takes on another phase so best to start with a quick appraisal of where we stand this morning.

Currently the is a very severe frost with heavy snow showers still persisting, predominately still in the north/north east

But as can be seen from the above fax Emma is getting organized and by 1800 is in the Bay of Biscay moving north as are also the associated fronts with the upper and warm fronts having already encroached the south. In fact the 00 Herstmonceux sounding indicates the approaching front quite well at 600mb

These are the bare bones, and sets the scene for what is set to be a day of atrocious and dangerous weather in many areas of the UK today, Heavy snow showers will persist in the central belt of Scotland and further south into north east England with blizzard conditions in the strong wind giving further accumulations and feeling bitterly cold. further south snow showers will also figure, particularly in the east but not as concentrated bu also bitterly cold. Then we come to Emma and the fronts and these are already bringing snow to the south coast  This area of snow will then track north and west during the day with blizzard conditions in places in the very strong winds and producing large accumulations of snow, possibly 10-20 cm in many areas and double that on the moors.And remaining bitterly cold all day.

Overnight the showers will persist in the north with perhaps the snow in the south west easing but with a significant risk of freezing rain and with the strong winds persisting still feeling bitterly cold.

During Friday the squally showers will still persist in the north east with further snow and ice in the south west where the winds will ease somewhat but still feeling bitterly cold apart from Cornwall where the milder air has encroached.

 

Edited March 1, 2018 by knocker

[PompeyFC]

Does anyone know which site shows the north Atlantic / Europe pressure charts which updates hourly. Cannot remember the site name.

[knocker]

2 minutes ago, PompeyFC said:

Does anyone know which site shows the north Atlantic / Europe pressure charts which updates hourly. Cannot remember the site name.

Do you mean here?

http://meteocentre.com/analysis/map-surface.php?lang=en&area=eur

[Average Joe]

Just wanted to say thanks again to Knocker for his extremely informative and well written updates. For those very much in the minority such as myself who regularly read these pages simply to acquire accurate information as to the forecast itself, they really are greatly appreciated. 

[knocker]

Further to my post above the updated fax chart has EMMA 977mb just south of Ireland at 00 Saturday with the occlusion accompanied by snow nudging north over North Wales and the Midlands. The GFS is pretty much in agreement with the position of the front and snow but not the depth of the low.

So not being sure how much credence we can give to the GFS will stick to the Icon and during Saturday the snow showers will persist in the north with wintry showers further south and still feeling very cold in the strong wind but warmer air (relatively) has encroached in the south

For an overview of the where this going a quick glance at the 850mb anomaly and wind streams could well be good news for many people assuming the GFS is reading this correctly of course

 

[knocker]

Ths gfs does appear to be on it's own vis the depth and position of EMMA at T48

Thereafter the ecm does slowly introduce warmer air from the south

 

Edited March 1, 2018 by knocker