South West England Cold Spell Discussion

[BristolBlizzard]

I hope we see a forecast like this sometime next week

[kaz]

Its only 2.4c here atm as well, in fact we've only dropped lower than 0c twice since this cold spell started in mid-December, i find it very odd im not sure if the sea has some involvement in this.

I've just watched the countryfile forecast and it looks amazing i've never seen or heard a forecaster saying "don't panic" in their forecast. However in regards to the cold front he said that it would be of rain and sleet the further south west you go, but it looks to me as if its cold enough for it fall as snow everywhere the uppers are way below -5c for Tuesday/Wednesday even if there was a warm sector it would still fall as snow surely.

=

hi last year it was -3 here and it fell as rain due to the dew point being +1 .. that seems to be what to look out for not ground temps.. We did get snow a few days later, so all not lost. i missed country file tonight as i was watching the darts. And yes your right sea temps do play a huge part in all the weather over the uk. I'm not sure how warm this warm sector is going to be but in my experance its good to have a warm (ish) sector this helps to trigger some ppn even better when you get a warm frount banging up against a cold one when this happends boom. Ive never seen charts like the ones we have seen over the last few days awsome to see. now time to sit glued to NW and have fun

kaz x

[littlemissy]

-3.4c .Not looking forward to the ice in the morning.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

I hope we can have a clear and calm night like this, with snowcover.

-4.7C now

[Somerset Squall]

-4.7C here, going to be a cold one!

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

-4.7C here, going to be a cold one!

Snap!!!

[LostInABlizzard]

-4C here right now. I went out for a walk but the dogs refused to join me so I came back in again !

[Thermohaline Conveyor]

I posted this on TWO earlier in relation to a very similar question.

"The latest 06Z GFS guidance soon to be updated with the 12Z release shows a Theta-e profile of +14 tied into the warm sector - which would lend an approximately 80% chance of snow to MSL under the assumption that PPN is moderate/heavy or prolonged for a period >30 minutes. Therefore ground above 100M or 75> would support a 98% chance of snowfall. Note the Theta-e +14 is only projected for Devon, Cornwall and the extreme coastal areas of Dorset at T+60 Tuesday 5th 18Z with cooler air still +12 slightly inland. The adjustment would take the 0oC isotherm down to 30M or less - basically to MSL. Through the period 5th January 18Z, 21Z, 00Z into 6th the Theta-e profile drops to +12 and +10 with the channel low projection simulating moderate to heavy PPN. This would almost certainly lead to snowfall inland across the South 1 mile or more away from the coast and it would only take 20 minutes or more of PPN falling near the coast at moderate intensity for the isotherm to lower 100M. It's all rather speculative of course at the minute because the specifics will change - but with a T850 BL wavering between -7/-8 and DP profiles in the region of 0 or -1 then it really does become less marginal than what one would assume. As for the far SW - I would imagine DP is a little higher - but snow to higher ground across Dartmoor would be likely and eventually after 30 minutes of PPN to lower levels being primarily transient - MSL snowfall would be possible. We await the 12Z to see if this channel low can verify 3/4 runs on GFS - also the 12Z NAE will be coming into resolution for this forecast period, at least the version we get will"

Although at first glance it would appear to be some-what complicated in nature - a good indicator of snowfall to the surface can be gauged by taking the Potential Equivalent (Theta-e) +14 as a marker. You do generally need to make some manual adjustments based on local variations such as surface tempertures projections, dew point and the topography (terrain) that is locally being forecast for - but a general rule of thumb is a theta-e gradient of +14 or Theta-WB +3 would deliver a 0oC isotherm to MSL (surface) in moderate intensity PPN events associated or tied into frontal systems that belong to a warm sector environment entrained in a depression. It's around 80% probability - ideally <12 Theta-e would indicate an almost perfect probability for PPN descending in hydrometeor form to turn to snow or a wintry varietal that will accumulate in nature. I often find that some-times the lower planetary layer of the atmosphere around 1000-850mb tends to have a high humidex profile - which again can hinder or slow down the transient nature or process of rain > snow. This is why, preferably in heavy PPN events it's advantageous to have a dry profile to enhance evaporative cooling induced by melting known as the isothermal melt layer. Anyway - current GFS 18Z guidance simulates Theta-e profiles T850 to be +14 tied into the warm sector - so you would assume that there is a warmer lower layer - so 100M isotherm could get eroded reasonably easy with a shower that is 10 minutes or more in length and of moderate intensity phasing.

Good to see some familiar faces on here.

[BristolBlizzard]

I posted this on TWO earlier in relation to a very similar question.

"The latest 06Z GFS guidance soon to be updated with the 12Z release shows a Theta-e profile of +14 tied into the warm sector - which would lend an approximately 80% chance of snow to MSL under the assumption that PPN is moderate/heavy or prolonged for a period >30 minutes. Therefore ground above 100M or 75> would support a 98% chance of snowfall. Note the Theta-e +14 is only projected for Devon, Cornwall and the extreme coastal areas of Dorset at T+60 Tuesday 5th 18Z with cooler air still +12 slightly inland. The adjustment would take the 0oC isotherm down to 30M or less - basically to MSL. Through the period 5th January 18Z, 21Z, 00Z into 6th the Theta-e profile drops to +12 and +10 with the channel low projection simulating moderate to heavy PPN. This would almost certainly lead to snowfall inland across the South 1 mile or more away from the coast and it would only take 20 minutes or more of PPN falling near the coast at moderate intensity for the isotherm to lower 100M. It's all rather speculative of course at the minute because the specifics will change - but with a T850 BL wavering between -7/-8 and DP profiles in the region of 0 or -1 then it really does become less marginal than what one would assume. As for the far SW - I would imagine DP is a little higher - but snow to higher ground across Dartmoor would be likely and eventually after 30 minutes of PPN to lower levels being primarily transient - MSL snowfall would be possible. We await the 12Z to see if this channel low can verify 3/4 runs on GFS - also the 12Z NAE will be coming into resolution for this forecast period, at least the version we get will"

Although at first glance it would appear to be some-what complicated in nature - a good indicator of snowfall to the surface can be gauged by taking the Potential Equivalent (Theta-e) +14 as a marker. You do generally need to make some manual adjustments based on local variations such as surface tempertures projections, dew point and the topography (terrain) that is locally being forecast for - but a general rule of thumb is a theta-e gradient of +14 or Theta-WB +3 would deliver a 0oC isotherm to MSL (surface) in moderate intensity PPN events associated or tied into frontal systems that belong to a warm sector environment entrained in a depression. It's around 80% probability - ideally <12 Theta-e would indicate an almost perfect probability for PPN descending in hydrometeor form to turn to snow or a wintry varietal that will accumulate in nature. I often find that some-times the lower planetary layer of the atmosphere around 1000-850mb tends to have a high humidex profile - which again can hinder or slow down the transient nature or process of rain > snow. This is why, preferably in heavy PPN events it's advantageous to have a dry profile to enhance evaporative cooling induced by melting known as the isothermal melt layer. Anyway - current GFS 18Z guidance simulates Theta-e profiles T850 to be +14 tied into the warm sector - so you would assume that there is a warmer lower layer - so 100M isotherm could get eroded reasonably easy with a shower that is 10 minutes or more in length and of moderate intensity phasing.

Good to see some familiar faces on here.

great post thanks

[Lynxus]

Nite all.

Just like to say, its -6.3 here

[Dorset_Weather]

Current temp here is -9.1c :cold:

Hope everyone has a safe trip back to work today.

[SteveB]

Coldest night of the Winter so far.

Temp -4.2C

[Iceberg]

If we take the shorter timeframe (NAE) model you can see that we have snow forecast for the SW in just 36 hrs now !.

Excellent post by TC above and it shows that most shouldn't really worry about whether it will fall as snow, (If your on the Cornwall SW coast then I hope your not expect snow).

Following on from this you then have the another bout of snow at 48 hrs just entering the SW from the east this time.

There is still plenty in the models for us after this but hopefully people will feel a bit more optimistic with a layer of snow on the ground.

[Rich_Clements]

flippin eck it's chilly outside

[dancing daisy]

Ian just just said significant snow risk going into the later part of the week on our local weather report!

He also said a bit of snow possible tomorrow, but patchy.

I look forward to seeing what he has to say on here later.

Right, out to work I go. I will miss you all! Gosh, a day without snow~watch.

[aspire27]

Ian just just said significant snow risk going into the later part of the week on our local weather report!

He also said a bit of snow possible tomorrow, but patchy.

I look forward to seeing what he has to say on here later.

Right, out to work I go. I will miss you all! Gosh, a day without snow~watch.

I think tomorrow we may see the odd sleety shower but thats about it.

As for the end of the week plenty of downgrades in the last model runs with everything going east, south east.

Please SW people dont get too excited.

Lots of winter sunshine and hard frosts this week i think.

[littlemissy]

-6.7c .Take care everyone.

[SteveB]

I think tomorrow we may see the odd sleety shower but thats about it.

As for the end of the week plenty of downgrades in the last model runs with everything going east, south east.

Please SW people dont get too excited.

Lots of winter sunshine and hard frosts this week i think.

Even I'm expecting snow tomorrow, so you should be in with a good shout. I must admit though, if we don't see snow tomorrow then it doesn't bode well for the rest of the week.

[aspire27]

Even I'm expecting snow tomorrow, so you should be in with a good shout. I must admit though, if we don't see snow tomorrow then it doesn't bode well for the rest of the week.

Well we will see. Have to watch that radar!

But im really not expecting anything. Maybe the odd sleety bit or rain around the coast (yes rain) in the morning then another fine and dry day. All I can say is enjoy the sunshine and frost. If your still off work have a nice walk in the sun!

[03jtrickey]

Wow. -3 last night. Coldest this year so far. What a cold spell.

[slinky1989]

Down to -6.4 here last night, and still going down!

[MP-R]

A perishingly cold night last night with a minimum of -7.0C, now foggy, earlier very foggy but gradually thinning with a temperature of -5.9C.

[Tuxedo]

Light flurries currently in Brislington Bristol....

[jethro]

Well, I can no longer whinge that it's not even cold around here; -6 last night, foggy too so everything is white with rime, all looks very pretty.

[03jtrickey]

Hmm just looked out the window and we have a shallow layer of freezing fog here. A thin layer of rime too. Perhaps it is keeping the temperature up a bit? Or maybe it's just Cheltenham's urban heat island.