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icedust

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  1. I must apologise to many of you who regularly post on this forum. Until today, I have been thinking 'Why are all these people posting about 10 day forecasts as if the synoptics will bear any resemblance to these forecasts in 10 days time'. In fact , until today I would look at T+240 charts to find out what was NOT going to happen. How wrong I have been! And now all that has changed. In my tier 4 lockdown this morning I have done some verification from the Meteociel site. I chose the past 2 significant changes of types that involved cold weather over the UK. First the major develo
  2. Just had 6cm here in Macclesfield in an hour. The snow moving across the Pennines to much of NW England was completely not forecast this morning. So being an ex-met office forecaster I have had a look at the models based on midnight data to see what they should have forecast. Basically they failed, in spite of data being available to enable the snow to have been predicted. In short it was a warm front development in deep unstable air I show the 850mb and 700mb chart for 1500Z, from the Euro4 model using the midnight forecast data today. Preceded by the 500mb chart for 2
  3. Hi all 06Z Euro4 looks interesting for us Cheshire Folk, and nearby. Possible polar low development in the Liverpool Bay area tomorrow night. Note the very cold 500mb temp of -36C. A pre-requisite for Polar lows. But Euro4 was very poor last night for this morning's accumulations. So we will see.....
  4. Yep, extreme rainfall here in Macclesfield, so heavy that visibility was 50m briefly. A notable line squall moving east over the last few hours. Manchester Airport reported thunder and a gust of 75kn (86mph) at 1120, which I did not believe until the radar revealed the squall, so I am sure it was real.
  5. I was marooned in Devon (Hemyock) in February 1978. It snowed for 40 hours non-stop with an easterly gale. 20ft-30ft drifts. over 2ft level snow (but it could not be measured due to drifts). Said to be the worst blizzard of the 20th century for Devon (surpassed by 1891). All roads in Devon were said to be closed. M5 was empty. Princetown cut off for a week. And that was followed within 2 days of its ending with a rapid thaw. Let's hope this one is not as bad.
  6. Model chaos indeed. ECMWF, EURO4 and GFS are all predicting 850 temps above zero edging in to the SW and far south of England at around T+ 42 to T+48 . BUT at the same time the surface and 950mb temps well BELOW zero.: This is a forecasters' nightmare and could be (as our North American friends say) an 'ice storm' or freezing rain. It depends how deep that warm nose is forecast to be whether the snow melts into rain as it falls through this nose. Luckily all is back to some sort of normal by T+54 (by T+72 for ECMWF due to its only 24h
  7. There is a cruel irony in the answer - if you are into cold and snow. So often the Azores High is public enemy number one in preventing cold easterlies reaching the UK. But in 1991 it was an Azores High that was our friend and ridged northeast, after that major cold pool that gave snow in 1991 had passed , and prevented it from moving too far west. Now this year, and lets just assume for the moment that the forecasts are correct, there is a major upper LOW and surface low over - yes the Azores, quite the opposite to 1991. Our cold pool, forecast to move west over the next few days, is exp
  8. Who cares about Friday - yet - when there is all that potential energy you show above to come out before then. All snow. Help!
  9. That's a very interesting forecast tool. Not come across that before but it seems to have some physical sense, in that low dew points encourage cooling by evaporation, or sublimation, hence maintaining any snow that falls and reducing the melting into rain. As a forecaster for many years one obviously had to consider the many variables that affect snow or rain to occur in the UK. The hardest one to get right is the intensity of precipitation. In marginal conditions this makes all the difference. Heavy snow cools air as it melts and falls further down before turning all to rain. So that is wha
  10. Hi John, I remember you from my days in the Met Office. at Manchester (Andy Day). Just discovered this site. You are of course correct. 510dm lines are rare these days (Jan 1996 was a good one here in Macclesfield and 1991 (over 20cm)). Looking at the excellent graphics on weatheronline I see the phenomenal low temperatures at 500mb due for tomorrow. -46!!. and a sub 504 cold pool for Scotland. That has to mean thunder snow and horrendous conditions for some places, with the eastern side right up the UK getting really bad in many places.
  11. Polar Low? Re the possible polar low overnight/early tomorrow. Investigating the upper air it seems the trough is under a minimum of 500mb temperature (about minus 36) which is moving west under the otherwise undisturbed baroclinic flow. Baroclinic to those not in the jargon means thickness lines being advected, in this case cold advection slightly wobbling, maybe wobbling enough to generate the surface trough, not evident higher up. In short, a small area of increased instability moving west to southwest will pep up and merge the showers in this trough (may become a very small centre).
  12. Hi all. Had great fun following this brilliant forum last night. Just to introduce myself; I was senior forecaster at Manchester Weather Centre for 20 years, now retired. I think that it was definitely a polar low. It showed all the characteristics on the sat pics. Also, 'mature' polar lows do acquire frontal characteristics, there are many examples. As circulation develops around the low, warmer air is entrained, with cold air to the north coming down the west side and a sort of warm front/cold front pair develops. Hence the areas of rain last night were in the warm sector, with snow to th
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