notananorak

Snow can fall with a 5000ft temp of zero C. It entirely depends on the temp profile below there to the surface ( always assuming the profile above 5000ft has a lapse or is at least isothermal ). Warm frontal approach being a common example of this. Assuming a standard lapse ( in saturated air ) of around 2C per 1000ft then in unstable air -8 to -10C would be the cut-off for snow given average surface air dryness ( upper limit necessary for warm sea fetch ). The easterly mentioned above would have drier lower layers than a Pm flow ( and from memory had some WA aloft ). This an example of why the WBFL is more imprtant than the FL. Prolonged heavy snowfall can lower the snow level 3000ft (in a showery set-up this would require streaming).

Actually no - the wet-bulb temp is most significant. In the shade so long as there is a -ve wet-bulb then snow will not melt - the drier the air the more enhanced the effect. The reason that WBFL's are more important than just FL's in forecasting downward snow penetration. The evaporative cooling preservation holding back melting even in sun ( low angle ) other than against warmed surfaces. How often have you noticed frost/ice/snow unmelted in the shade when air temps are +3C? Down to very low dewpoint air.

Yes.

The UKMO model does not run beyond T144 ( at least it didn't 3 odd years ago before I retired ) and so the Met Medium Range F/c'er uses chiefly the GFS and EC Op runs and their ensembles to forecast beyond 6 days - hence the O/L forecast posted today, with the 3-5 day forecast consistent with their published Faxes. That shows that the northern blocking ( in MetO's opinion - confirmed to me by an inside source this am. ) is likely ( going to be ) robust enough to win sway even if the UKMO T120/144 comes off. For some reason they think their model is odds on at the mo. - maybe just because of its consistency/persistence over several runs.

As someone who was directly a victim of the MetO's rationalisation of its infrastructure during 2006 when it shrank back to Exeter, Belfast and Aberdeen I feel I have something to add to this thread. Forecasters at Aberdeen, as indeed I did elsewhere, had/have the authority to instigate warnings on their own initiative and have free input into the forecasting process at Exeter. The forecasters at Aberdeen, I can assure you, have their eyes on local weather and if the weather fit's the criteria for an NSWW then it will be issued. Remember the warnings are based on "disruption". Quote: "Also, the Met Office get night time minima for the Highland's embarrassingly wrong, very often. I actually disregard their predictions." Would these those shown on the BBC national charts? If that is the case then of course they are wrong unless you live near Glasgow, Inverness or Stornoway airports as those are the places that are forecast as a necessity within the Offices 11 cities Key Performance target - and the success of those forecasts is there for all to see here … http://www.metoffice.gov.uk/corporate/verification/city.html This thread is about the need for a Scottish MetO. In my opinion you have one already. Aberdeen ( at least in 2006 ) can and did provide considerable input into the warning and media side of things. What else do you want? The media will always distort the message for their ends and snow in London is a story whereas falling in Shetland is not. If there is not a warning for that snow there it is Aberdeen's fault NOT Exeter's.

When I worked for a certain organisation advising of snow/ice/frost, if anything the councils threw far too much salt on the roads. It would only take a mention of a risk of hoar frost and night after night they would grit - the roads becoming white wiith salt ( if they ever dried out ) - and they admitted this to me at that. The Highways Agency actually have/had a rule whereby roads had to be gritted every 24hrs if a frost was predicted. As for snow, throwing salt on it is really just a PR excercise to make the public think there is something being done. As a result people think that gritting ( rock salt ) is the answer that makes the problem of heavy snowfall go away. No - it helps but really only for relatively light falls. Heavy falls require it to be ploughed continuously until it's stopped falling and then driven on with the right skills and equipment ( winter/studded tyres ). When ever it snowed I would prefer to take the train/walk to work as even though I drove to the conditions some idiot would be up my backside or overtaking so I'm at serious risk anyway. BTW Re the non-use of salt in Canada. Salt does not work below temperatures of around -7C and so it would be no use in that climate anyway. The problem we have here is that traffic density is very great, snow driving skills are poor and ordinary roads tyres useless ( re last night A38 Devon ) - any sort of gradient stumps them. Hence road blocked and emergency services shut out. I fume when I hear stupid comments from people who should know better Re how countries with harsh winter climates carry on through winter. Well of course they do. They have too because it comes every year!