johnholmes

Snowed here, just looks like a thin covering but it makes it the 3 rd day with snow in this cold spell, T=0.4 C after falling to -0.6 C earlier

What on earth is this all about? Areas of rain, sleet, and away from immediate coastal areas, snow, are expected to push north and east across the area later this evening and into the early hours of Sunday. Whilst not everywhere will see accumulating snow, some places will likely see 1-3 cm, with 5-10 cm possible over some hills and mountains of Wales, the Peak District and south Pennines. Ice will be an additional hazard. What should I do? Snowy, wintry weather can cause delays and make driving conditions dangerous. Keep yourself and others safe by planning your route, giving yourself extra time for your journey. Not needing to rush, reduces your risk of accidents, slips, and falls. Check for road closures or delays to public transport and amend plans if necessary. If you need to make a journey on foot or by bike, try to use pavements along main roads which are likely to be less slippery. If driving, make sure you have some essentials in your car in the event of any delays (e.g., warm clothing, food, water, a blanket, a torch, ice scraper/de icer, a warning triangle, high visibility vest and an in-car phone charger). Be prepared for weather warnings to change quickly: when a weather warning is issued, the Met Office recommends staying up to date with the weather forecast in your area. The warning is fine but why are Met issuing all the other words? Not their job or never was. What is the weather world coming too?

Thanks for that BW, an interesting read, I think at times the forecaster get unjustified criticism from folk on here

Dry and a bit mist at dawn, very cold with a low of -4.4C, the 2nd coldest night this year; yesterday was the coldest day of the year with a max of 0.6 C; only 1 night in the past 8 without at least a ground frost.

Fog returns after a very cold day, only about 3 or 4 hours above zero C, now -0.4 C in thick fog after a max of 0.6 C

On Tuesday ( 28/11) NOAA 8-14 is much the same as the previous one so a broad westerly is to be expected within that time frame; meridional still on the 6-10 Friday 1 December - Another look at NOAA and ECMWF NOAA 6-10 has no signal for blocking over the last 3 days or so and its 8-14 chart continues this. However the contour values arriving over the UK are about/a bit below average so although less cold than now, not mild by any means. A similar temperature level from the ECMWF output for a similar period to NOAA 6-10 day. The overall 500 mb pattern on both outputs is broadly westerly, a touch north of west at times. On the NOAA 6-10 and 8-14 you can see that the usual major trough around ne Canada is nothing like as deep as we usually see around the start of winter. The trough off western USA/Canada shows on the 6-10 but not really on the 8-14. So we see a generally westerly 500 MB flow over much of the chart extending into Europe with no signal for any marked European trough. This all suggests to me that whilst deep cold is unlikely in the 6-14 day period, neither is any really mild air, other than perhaps now and then for the far south of the UK. Snow probably confined to high ground from the Peak District north but on lower ground at times further north. Beyond 14 days then that is not for these charts. Climate Prediction Center - 6-10 Day 500mb Outlook WWW.CPC.NCEP.NOAA.GOV Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4965535

On Tuesday ( 28/11) NOAA 8-14 is much the same as the previous one so a broad westerly is to be expected within that time frame; meridional still on the 6-10 Friday 1 December - Another look at NOAA and ECMWF NOAA 6-10 has no signal for blocking over the last 3 days or so and its 8-14 chart continues this. However the contour values arriving over the UK are about/a bit below average so although less cold than now, not mild by any means. A similar temperature level from the ECMWF output for a similar period to NOAA 6-10 day. The overall 500 mb pattern on both outputs is broadly westerly, a touch north of west at times. On the NOAA 6-10 and 8-14 you can see that the usual major trough around ne Canada is nothing like as deep as we usually see around the start of winter. The trough off western USA/Canada shows on the 6-10 but not really on the 8-14. So we see a generally westerly 500 MB flow over much of the chart extending into Europe with no signal for any marked European trough. This all suggests to me that whilst deep cold is unlikely in the 6-14 day period, neither is any really mild air, other than perhaps now and then for the far south of the UK. Snow probably confined to high ground from the Peak District north but on lower ground at times further north. Beyond 14 days then that is not for these charts. Climate Prediction Center - 6-10 Day 500mb Outlook WWW.CPC.NCEP.NOAA.GOV

Meteorology is 3 dimensional not one dimensional; I was making a 3 dimensional comment.

The difficulty of milder air pushing dense cold air away is not myth it is meteorological fact. Was pre model days and still is. No one has found a way of solving this so far. How many days for deep cold to affect the milder air coming in, how dense the cold air both at the surface and the bottom 3-5,ooo ft. The direction in which a low approaches, some seem less likely to advance than from slightly different directions. It makes trying to forecast the arrival of genuinely mild air still almost as difficult as it was pre computer models. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4965369

The difficulty of milder air pushing dense cold air away is not myth it is meteorological fact. Was pre model days and still is. No one has found a way of solving this so far. How many days for deep cold to affect the milder air coming in, how dense the cold air both at the surface and the bottom 3-5,ooo ft. The direction in which a low approaches, some seem less likely to advance than from slightly different directions. It makes trying to forecast the arrival of genuinely mild air still almost as difficult as it was pre computer models.

Clear sky and dry with current low at -2.2 C; Last evening around 2230 a light snow shower covered the ground, less than 1 cm, but a white start to this morning

Not a return to 'mild' as in above normal temperatures for early December. An overall upper flow from north of west seems the most likely but no deep cold in the next week or 10 days in my view sorry no charts I'll try and drop some in later today.

Another slight air frost, low of -0.6 C, not sure if any ppn, nil showing in Davis, clear sky

No charts to show but worth remembering that prior to computers weather forecasters (me included) often moved milder air too quickly in to replace deep cold air. The huge and very complex weather models of today are often guilty of a similar error. Once deep cold is well organised then warm air finds it more difficult than the very complex hydrostatic equations would suggest. I'm not saying it will occur in this instance but depending on how long and how cold the air gets over the UK it is something to watch for. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4963399

No charts to show but worth remembering that prior to computers weather forecasters (me included) often moved milder air too quickly in to replace deep cold air. The huge and very complex weather models of today are often guilty of a similar error. Once deep cold is well organised then warm air finds it more difficult than the very complex hydrostatic equations would suggest. I'm not saying it will occur in this instance but depending on how long and how cold the air gets over the UK it is something to watch for.

Dry and mostly clear, some patchy CuSc especially on eastern side, patchy frost showing with current low at -0.9 C

A long long time ago but the surface chart was drawn up using surface data. The 500 mb chart was drawn up using 500 mb T-ph (Skew-T) data. The 'thickness' chart (DAM) charts was then arrived at by 'gridding' surface and 500 together on a 'light' table, lit from below a glass base. It was also possible to do this surface and DAM to get the 500 flow! This was done prior to computers arriving. In those days the DAM predicted chart, derived by the forecaster for T+24 usually formed the basis for the surface forecast for 24 hours ahead. On a few occasions it was possible to stretch the outlook (!) to 48 hours. Oh how times have changed! Sorry to go off topic Paul, rambling of a dinasaur Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4962274

A long long time ago but the surface chart was drawn up using surface data. The 500 mb chart was drawn up using 500 mb T-ph (Skew-T) data. The 'thickness' chart (DAM) charts was then arrived at by 'gridding' surface and 500 together on a 'light' table, lit from below a glass base. It was also possible to do this surface and DAM to get the 500 flow! This was done prior to computers arriving. In those days the DAM predicted chart, derived by the forecaster for T+24 usually formed the basis for the surface forecast for 24 hours ahead. On a few occasions it was possible to stretch the outlook (!) to 48 hours. Oh how times have changed! Sorry to go off topic Paul, rambling of a dinasaur

I may be wrong but that sounds odd to me. Things may well be rather different to when I drew weather charts up in the Met Office!

re LRD post Yes the 500 mb westerly flow is well south so little signal for any +ve heights in the Azores region. Happy to chat via messaging if you wish

The last two NOAA 8-14 500 mb anomaly charts now show a broad westerly flow into the UK and Europe. It is pretty rare that they are not showing the most likely outlook in that time scale. Climate Prediction Center - 8-14 Day 500mb Outlook WWW.CPC.NCEP.NOAA.GOV

Dry and cold with a mainly clear sky just now, temperature is still edging down, now on 1.7 C

Just looking at my usual charts to see if there are any signs of a major change in upper wavelength Monday (27 Nov) and a marked shift in the NOAA 8-14 chart issued Sunday evening. On Saturday(Friday evening) and it continued with the 6-10 meridional output. Last evening, Sunday, and it had totally changed, see chart. It is only one output and I always like to see at least 2 showing a similar pattern before suggesting it will be a valid chart. It is also supported to some extent by the ECMWF output for 2 nd- 6 th with a developing ridge bringing a less cold airmass over the UK by about day 3. The 850’s for example show the -5 C retreating north of Scotland in that time frame. Climate Prediction Center - 6-10 Day 500mb Outlook WWW.CPC.NCEP.NOAA.GOV

Raining with temperature on 3.8 C; rainfall total since midnight 8.4 C

Dry and with a lot of cloud, white patchy frost, cars and roofs with the current low on -0.8 C