Kasim Awan

Yes however on the GFS18Z it isn't a problem as the jet is eay South. West based is only a problem with a more north jet like on the ECM 00Z.

Hello Narnia, it's been a while.

Sorry I didn't look properly with -2.5 uppers it is full snow down to 550m so in intensity could be sleet down to 150-200m. Icon has the Kent streamer.

There is no sleet anywhere. DPs are around 3-4C. 200m+ in the SW earlier dps were close to 0C so there earlier.

Personally feel mixed about this morning's output. The models have further strengthened that concerning arm of the jet to our SW such that we are now seeing charts like these appear. Granted it improves but not an encouraging sign. Sometimes with medium range weather forecasting the best approach is not to take charts at face value and instead ask the question, what would occur if a blend of the indicated mechanisms occurred? Well, probably something like the ECM00Z which in itself still produces cold air and a lot of moisture nearby. It is very likely that the PV will push into Europe but how much resistance it meets from the South West is yet to be resolved. So the outcome may be more along the lines of a blend of the current scenarios indicated. It could also be on the favorable / less favorable side as the options of a potent NE blast and a complete shunt east of the PV section are still physically feasible. So any big conclusions can't really be drawn from this other than these options on the table. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4994499

That's the 00Z.

Personally feel mixed about this morning's output. The models have further strengthened that concerning arm of the jet to our SW such that we are now seeing charts like these appear. Granted it improves but not an encouraging sign. Sometimes with medium range weather forecasting the best approach is not to take charts at face value and instead ask the question, what would occur if a blend of the indicated mechanisms occurred? Well, probably something like the ECM00Z which in itself still produces cold air and a lot of moisture nearby. It is very likely that the PV will push into Europe but how much resistance it meets from the South West is yet to be resolved. So the outcome may be more along the lines of a blend of the current scenarios indicated. It could also be on the favorable / less favorable side as the options of a potent NE blast and a complete shunt east of the PV section are still physically feasible. So any big conclusions can't really be drawn from this other than these options on the table.

High resolution UKV confirms this ascertion for Monday with the presence of scattered convection beloe 10,000 feet resulting in showers falling as snow into surface cooled air. A freezing level below 500m and surface cooled air will almost always result in snow. A stronger easterly wind could be an issue here as without a cold surface a 500m secondary freezing level would be marginal. Two more points are the mixed phase precip boundary inlandward depends on wind speed and flurries well inland are possible due to convective mechanisms.

The first few flakes? Sunday Temperatures gradually reducing from supporting snow only >400m early on Sunday afternoon to scattered cooled pockets of ground level snow line due to surface cooling by late allowing some of the rogue flurries to fall as sleet / wet snow >50miles inland where showers interact with surface cold, where this cooling does not occur due to cloud etc rain/sleet more likely. Freezing levels around 500m with significant surface warming in the east initially leading to high wet bulb driven melting widely. Sunday night looks to bring a tight NNE wind which may produce a Kent clipper which would either be full snow or marginal dependent on depth of surface cold modulated by uppers influencing freezing level and wind speed which affect surface dew point layer. Stronger winds are an issue here. Potential for something interesting if it coincides with a cold sector and lightish winds as seen on ICON again which drops off uppers quickly into Monday early hours. -7/-9 850hpa core required so only a 25/30% chance as per current modelling. Combined with evaporative cooling could allow temporary ground level snow lines near the coast Kent etc. Also depends on this NNE wind being retained on output. Localized 2-6cm possible under best case scenario. Monday On Monday soundings improve where a 400m asl freezing level is enough in low dew point surface air 20-30 miles inland North of Essex for nocturnal wet snow showers and accumulation at night depends on precipitation though with daytime mixed wet precipitation. Nearer sea the long wind fetch North of Essex likely to result in near coastal warm layers. Few spots perhaps seeing a dusting at night Midlands Pennines East Wales. Note less precip in SE later Monday but also lower dew points so more likely to fall as snow near to coast Essex South so any rogue flurries will probably be a greater snow to rain ratio than further North. Bar the potential Kent clipper and perhaps some more organised very light precip Sunday night this is really only the odd shower. These will occur *as long as 500mb heights are kept below 556hpa*. Even if nothing appears on high res. My snow sense is a bit rusty for obvious reasons. Kasim ❄ Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4994100

The first few flakes? Sunday Temperatures gradually reducing from supporting snow only >400m early on Sunday afternoon to scattered cooled pockets of ground level snow line due to surface cooling by late allowing some of the rogue flurries to fall as sleet / wet snow >50miles inland where showers interact with surface cold, where this cooling does not occur due to cloud etc rain/sleet more likely. Freezing levels around 500m with significant surface warming in the east initially leading to high wet bulb driven melting widely. Sunday night looks to bring a tight NNE wind which may produce a Kent clipper which would either be full snow or marginal dependent on depth of surface cold modulated by uppers influencing freezing level and wind speed which affect surface dew point layer. Stronger winds are an issue here. Potential for something interesting if it coincides with a cold sector and lightish winds as seen on ICON again which drops off uppers quickly into Monday early hours. -7/-9 850hpa core required so only a 25/30% chance as per current modelling. Combined with evaporative cooling could allow temporary ground level snow lines near the coast Kent etc. Also depends on this NNE wind being retained on output. Localized 2-6cm possible under best case scenario. Monday On Monday soundings improve where a 400m asl freezing level is enough in low dew point surface air 20-30 miles inland North of Essex for nocturnal wet snow showers and accumulation at night depends on precipitation though with daytime mixed wet precipitation. Nearer sea the long wind fetch North of Essex likely to result in near coastal warm layers. Few spots perhaps seeing a dusting at night Midlands Pennines East Wales. Note less precip in SE later Monday but also lower dew points so more likely to fall as snow near to coast Essex South so any rogue flurries will probably be a greater snow to rain ratio than further North. Bar the potential Kent clipper and perhaps some more organised very light precip Sunday night this is really only the odd shower. These will occur *as long as 500mb heights are kept below 556hpa*. Even if nothing appears on high res. My snow sense is a bit rusty for obvious reasons. Kasim ❄

Typical from the ECM an absolute mid way point between the two solutions. That's day 9. Although there is a bit of a west based setting up the speed at which the PV lobe moves South out of the Arctic 192H to 216H is likely providing the forcing needed to overcome this, and still great retrogression. So on balance 2 positives and 1 negative.

It is a straight easterly under relatively high heights. From experience and the physics involved this flow generates widespread scatteredlight flurries with sparse very narrow but locally heavy streamers as opposed to troughs. Given the ICON usually underdoes convection it can be presumed that this streamer shown in the South East would be fairly active but localised. The streamer over the Channels shows what would happen if the flow was even further North. All depends on the latitude of the high and resultant amount of instability.

Admitted again and having op tomorrow so fingers crossed for the best.

Then we will see a rapid switch in the ensembles when / if the colder option is discounted which is why ensemble forecseting should always be done using a cluster approach. Means should never be used on their own always with a reference mean from a previous run to assess change. Also use the standard deviation plots on meteociel. 400m+ will probably have a few flakes in the wind even with no sferics always the case in these setups.

Not the mean mate but a few individual ensembles plus the issue of a stronger ridge through SW Mediterranean which is a known deflecter of cold. That's around 2c below average here.

I have to agree that we are now at a point where it wouldn't take much at all to shift the pattern too far NW.

By day 3-8C combined with those night temperatures is around 2C below average.

The GEFS showed the same delay and increase in 850s aswell which was a result of more ensemble members trending the pattern north.

It's mild air so wont bother. Only like long walks in the cold.

To say nothing has changed from yesterday is inaccurate, I have posted clear changes between yesterday and today's ensemble means, minor changes yes but affect the balance of the outlook slightly.

That's ugly and it's a real possibility.

Would be infuriating to end up with a faux cold bullseye low close to the UK with a huge arc of blocking from the Mid Atlantic to the pole but with these synoptics being so drawn out spatially, it is certainly possible.

That isn't west based that's a nice middle ground sensible looking chart.

Please post the charts or better a link I can't see on meteociel.

Day 14 then?