Yorkshire and E England regional discussion

[Craigers]

3 minutes ago, Scott Ingham said:

Yeah i wouldnt rule out settling snow from 12am as i put a few posts back but i think at this point it is extremely marginal

The spine of the band slips down the middle of Yorkshire is kind of an upgrade for me

[fazzafarrand]

4 minutes ago, LeeSnowFan said:

Above 200m

 

[LeeSnowFan]

All we can do is wait Scott and Craig have been pretty good lately so I follow them

[bazookabob]

Well I'm at 87m asl east of Leeds and I'm not really expecting any lying snow on Thursday, maybe some falling snow. However, if any people should be aware of how unpredictable snow can be, it should be us lot after last Friday! So I will be keeping an eye on things over the next 24-36hrs and hoping we can "do a Harrogate"!

[Winter Cold]

Hudson suggesting snow chances for all as Thursday goes on during look North just now.

He said milder over weekend though and temps looked too high for snow. Monday and Tuesday didn't reflect the model runs with a cold spell arriving from next week, he showed 5c. I want cold and snow!!!!!

Lol

[Craigers]

7 minutes ago, LeeSnowFan said:

All we can do is wait Scott and Craig have been pretty good lately so I follow them

Do you have a weather station mate? Usually helps alot in these situations.

Personal Weather Station Dashboard | Weather Underground

WWW.WUNDERGROUND.COM

---

Weather Underground provides local & long-range weather forecasts, weather reports, maps & tropical weather conditions for locations worldwide.

Its been fitted with a new sensor last year so its very reliable with dew points.

[Slysi100]

The Look North forecast was a little underwhelming tbh. Snow potentially for anywhere tomorrow and thurs, but emphasis on higher ground. More rain at the weekend and showed temps up to 7 degrees. Next week, temps around 5 degrees

[LeeSnowFan]

10 minutes ago, Craigers said:

Do you have a weather station mate? Usually helps alot in these situations.

Personal Weather Station Dashboard | Weather Underground

WWW.WUNDERGROUND.COM

---

Weather Underground provides local & long-range weather forecasts, weather reports, maps & tropical weather conditions for locations worldwide.

Its been fitted with a new sensor last year so its very reliable with dew points.

I use there app its good

[Kasim Awan]

 

Dew points & wet bulbs are a far more useful parameter than surface temperatures & 850s in this set ups. Get both of these values at 0 and the precipitation will be guaranteed snow in this set up. 850s are important but these largely following the 0C dewpoint & 0C wb lines, which also follow the 300m freezing line for low level snow. The frontal / triple point system here means there will be a fairly defined rain > snow gradient throughout representing the colder air of the eastern quadrant of the frontal system. It will be well defined because that's what fronts do, so I suspect a prognosis of a 200 mile gradient is way out, I expect the rain to snow gradient for places with the same altitude to be 20-30 miles. Anywhere within this cold quadrant will likely see a freezing altitude between 200 and 600 metres depending on precipitation intensity, see next. Use surface temps, i.e. local weather stations to track it's progress through Thursday.

As mentioned above even in the cold sector there is a base line freezing point of 600 metres with a 100 metre adiabatic temperature of 1.5C in the absence of evaporative cooling. So, elevations above 200m, once you're in the cold sector you don't need any evaporative cooling it's likely snow throughout. As @Scott Inghammentioned, for lower levels below about 200-250m elevation this needs to drop by a certain amount (say 1C) for snow as a guaranteed precipitation type. The extent to which this drops is dependent on the intensity of the precipitation. The Arome / Euro4 has far more patchy precipitation than the GFS/Arpege which would therefore limit the extent of evaporative cooling and lead to much more patchy low level accumulations of snow. This is why the Met Office bet of "patchy" 2-5cm to lower levels is very reaosnable at present, playing it safe somewhat I believe as some models have a much more widespread and well defined front like the Arpege which would bring the snow line down.

Again, going into a bit more technical why the precip intensity duration is needed. With temps of 1.5C and 2C at 100-200m the "wet bulb" temperature is 0C to 0.5C which means "given optimal evaporative cooling the temperature will drop to 0C to 0.5C", that is what the wet bulb temperature is. Higher humidities in the atmosphere prevent evporative cooling & lead to higher wet bulbs. As the cold, drier air comes in > the wet bulbs fall off > evapo cooling is more effective. However, in order to meet this effective evaporative cooling temperature we rely on steady state atmospheric conditions (steady precip). A non continuous precipitation will limit this and any breaks will ultimately bring a location back to square 1 on the evap cooling curve. So, you can see why the longevity is required for lower levels. All a case of monitoring the precipitation charts to see if the front is more defined > then more areas will realise their wet bulb evaporative cooling temperature & you can expect a widespread 3-10cm rather than the patchy 2-5cm the Met Office speak about. 

Edited January 12, 2021 by Kasim Awan

[Winter Cold]

Good GEFS tonight I think, here's South Yorkshire temps, falling away to only 1 or 2c next week so should be some snow chances. I think the TV forecasts are too broad brush and we'll do ok from the up coming spell:

 

[adrianh]

Models are all looking pretty decent both short and mid term and at least put us in with a chance of snowfall. Whether we get deep cold is another matter but its a million times better than last years horrific winter. 

The main model thread is such sombe reading with people keen to go looking for a West based NAO like some sort of bogeyman on every run

[Scott Ingham]

34 minutes ago, fazzafarrand said:

Above 200m

 

For them amounts.

Have you noticed hes atrached a snow depth chart which those comments relate to.

That chart shows 6cm at lower levels

[Craigers]

7 minutes ago, LeeSnowFan said:

I use there app its good

That one is in my back garden at 66m asl. So if that is showing -0.0c dew then all of barnsley will be snow

[Scott Ingham]

10 minutes ago, Kasim Awan said:

 

Dew points & wet bulbs are a far more useful parameter than surface temperatures & 850s in this set ups. Get both of these values at 0 and the precipitation will be guaranteed snow in this set up. 850s are important but these largely following the 0C dewpoint & 0C wb lines, which also follow the 300m freezing line for low level snow. The frontal / triple point system here means there will be a fairly defined rain > snow gradient throughout representing the colder air of the eastern quadrant of the frontal system. It will be well defined because that's what fronts do, so I suspect a prognosis of a 200 mile gradient is way out, I expect the rain to snow gradient for places with the same altitude to be 20-30 miles. Anywhere within this cold quadrant will likely see a freezing altitude between 200 and 600 metres depending on precipitation intensity, see next. Use surface temps, i.e. local weather stations to track it's progress through Thursday.

As mentioned above even in the cold sector there is a base line freezing point of 600 metres with a 100 metre adiabatic temperature of 1.5C in the absence of evaporative cooling. So, elevations above 200m, once you're in the cold sector you don't need any evaporative cooling it's likely snow throughout. As @Scott Inghammentioned, for lower levels below about 200-250m elevation this needs to drop by a certain amount (say 1C) for snow as a guaranteed precipitation type. The extent to which this drops is dependent on the intensity of the precipitation. The Arome / Euro4 has far more patchy precipitation than the GFS/Arpege which would therefore limit the extent of evaporative cooling and lead to much more patchy low level accumulations of snow. This is why the Met Office bet of "patchy" 2-5cm to lower levels is very reaosnable at present, playing it safe somewhat I believe as some models have a much more widespread and well defined front like the Arpege which would bring the snow line down.

Again, going into a bit more technical why the precip intensity duration is needed. With temps of 1.5C and 2C at 100-200m the "wet bulb" temperature is 0C to 0.5C which means "given optimal evaporative cooling the temperature will drop to 0C to 0.5C", that is what the wet bulb temperature is. Higher humidities in the atmosphere prevent evporative cooling & lead to higher wet bulbs. As the cold, drier air comes in > the wet bulbs fall off > evapo cooling is more effective. However, in order to meet this effective evaporative cooling temperature we rely on steady state atmospheric conditions (steady precip). A non continuous precipitation will limit this and any breaks will ultimately bring a location back to square 1 on the evap cooling curve. So, you can see why the longevity is required for lower levels. All a case of monitoring the precipitation charts to see if the front is more defined > then more areas will realise their wet bulb evaporative cooling temperature. 

Thank you mate.

@Cheese Rice  and @The PIT

This is what i was trying to say in a less technical way.

Forger 850s, forget snow guides.

This is a wet bulb and rain intensity set up.

All is different forecasts for snow are not that simplisitc

Edited January 12, 2021 by Scott Ingham

[Kasim Awan]

You are right every snow event has to be treated with a special consideration - the two important factors here are following of the cold air contours & then the precipitation intensity. The cold air to reach a baseline of 300m & intensity to lower this down. Depends on how widespread the precipitation rates of above 2mm per hour are, for the difference between the actual air temp & wet bulb temp (temp which will be reached after 3mm of rainfall within an hour). SO, if you are within the cold air mass > @ 60m, 1.8C & wb of 0.9C as a starting figure means you need a temp of 0.6C > 1.2C of cooling which is 1.8 - 0.9 = 0.9C so 1.2C/0.9C = 1.3 hours of 3mm per hour! Dew points will follow. Roughly !!

Edited January 12, 2021 by Kasim Awan

[Scott Ingham]

Just now, Kasim Awan said:

You are right every snow event has to be treated with a special consideration - the two important factors here are following of the cold air contours & then the precipitation intensity. The cold air to reach a baseline of 300m & intensity to lower this down. Depends on how widespread the precipitation rates of above 2mm per hour are, for the difference between the actual air temp & wet bulb temp (temp which will be reached after 3mm of rainfall within an hour). SO, if you are within the cold air mass > @ 60m, 1.8C & wb of 0.9C means you need a temp of 0.6C > 1.2C of cooling which is 1.8 - 0.9 = 0.9C so 1.2C/0.9C = 1.3 hours of 3mm per hour! Roughly !!

Brilliant.

Better said than i was trying to say without your expert snow forecast knowledge

[Craigers]

Its this cold at 7:38pm in my back garden!

vs 

Thats a bit out to me 

Edited January 12, 2021 by Craigers

[Jeremy Shockey]

Many thanks Kasim & Scott , really helpful stuff

[Sunny_AS]

Thanks for the info, to those on both sides of the analysis. What I like about the Yorkshire thread is everyone is respectful enough to agree to disagree. 

[Craigers]

Thanks to the people on this forum there is more usefulness to all ideas on the current charts opposed to the mad thread that its becoming ridiculous. Keep it up everyone, it certainly is becoming a great winter  

Edited January 12, 2021 by Craigers

[Arnie1965]

1 hour ago, Craigers said:

ECM 12Z UPGRADE ALERT 

bang in the sweet spot

 

[Winter Cold]

21 minutes ago, Craigers said:

Its this cold at 7:38pm in my back garden!

vs 

Thats a bit out to me 

Yes, same here. Meto have me at 2c predicted now to on the website and I'm reading 0.1c on my station, so a lot cooler.

Dew point currently -1 as well! 

[Adam lufc]

Were at -4c mo temps saying 1c. Have to laugh.

[Adam lufc]

Just now, Adam lufc said:

Were at -4c mo temps saying 1c. Have to laugh.

Sorry -3c

[Kasim Awan]

Again, you can see the "Base" freezing line of 500-600m in the North Sea indicated by the blue colours. Inland the freezing lines look very good, indicating that the evporative cooling conditions are met quite easily under the persistent moderate rainfall, bringing the freezing-line down to about 150m (snow to 10-50m). Indicates the potential for fairly widespread snow-conducive cooling if this slightly stronger & westerly track option is taken. Produces 1-6cm to lower levels fairly widely, with a greater precip intensity requirement on the coastal strip (0 to 8 miles from coast) due to an easterly developing, less likely that this will be met for those on the coast - have more a 2C starting point so need double the evap cooling requirements discussed above which is for 1C wet bulb reduction > here you need a 2C wet bulb reduction. So worse here.

Edited January 12, 2021 by Kasim Awan