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Ruling out March snow


J07

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Posted
  • Location: City of Gales, New Zealand, 150m ASL
  • Location: City of Gales, New Zealand, 150m ASL
Posted

Greetings all,

Seems that March snow is divisive.

Which camp will it be?

1) The sun is too strong for lying snow- and it's spring!

2) It can still snow in June and it's not unusual to get good falls in March or April.

I fall more towards the latter.

I am not old and yet I know that March snow is possible, and fairly common. The early 2000s we definitely got it- and April 1999 (or 2000, still can't remember which) was a classic. Big snow followed by sunny weather- and guess what? The legendary blistering heat of April sunshine failed to prevent the snow from prevailing throughout the day. Who'd have thunk it?!

I simply do not believe that the sun in March is strong. Strong *compared* with Feb and Jan, yes. But strong enough to preclude lying snow? I don't think so.

Looking at UV indices gives 1 across most of the country with some 2s floating around on clear, pollution free days. That's a cat's whisker, a tickle from a flower. I know that UV does not melt snow, but irradiance figures are harder to come by. It's natural to expect a correlation between UV and solar radiation though.

Furthermore:

SSTs are generally at their lowest,

We have not passed the equinox,

The UK is still in the coldest quarter of the year,

It's only spring according to our arbitrary calendar system.

Why the hurry for summer? Why can it not snow? I feel that it's all very reactionary, and highly dependent on people's feelings of the winter, the current weather and the long and short term prognoses. If there's no snow on the horizon, it's "roll on summer". If there's possible snow on the horizon, it's "yeah, I'm hoping for a bit, but after that I want Spring. And it doesn't matter anyway because it won't snow anyway. As usual. Since my location is the most snowless in the UK."

I'm sure it's fair to state that our seasons are becoming blended. My feelings are that it's hard to rule out anything at this time of the year.

Here is some interesting bits of information with regards to cold Spring snaps in NZ. Directly relevant to the UK? Not exactly. However, I have a point to make.

http://www.metservice.co.nz/default/index....tic=2004spring1

Spring 2004:

Started like this:

1 September. Heavy rain in northern and western parts, eg. 41.6mm at Westport in 24 hours to 10pm, including 20.6mm in 1 hour ending 9am. Foehn northwesterlies bring unusually mild temperatures to east of South Island, eg. 20°C in Kaikoura.

Severe cold snap in south

18-19 September 2004

A very cold south to southwest airstream spread over New Zealand 18-19 September, bringing winter-like conditions to many places, especially the south and east. Worst affected was the Southland and Otago hill country where hundreds of thousands of newly born lambs died due to the hypothermic effects of low temperatures, wet grounds and strong winds. Hence, this storm was labelled by some the "lamb killer".

On 18 September, a southwest change swept over the South Island, bringing heavy showers with hail to Southland and Otago, and snow to near sea level. At midday, Invercargill reported hail, 3°C and a southwest wind gusting to 85 km/hr. Highs reached only 7°C at Manapouri and 8°C at Queenstown. As the change went through Canterbury temperatures fell quickly. One hour falls included Timaru: 17 to 8°C (3pm), Le Bons Bay (Banks Peninsula): 15 to 4°C (4pm), and Christchurch: 16 to 8°C (4pm).

On the 19th, the south to southwest airstream became general over the whole country. Snow fell to near sea level at first in Southland and Otago, also Banks Peninsula, but the freezing level rose slowly through the day. Around 50cm snow accumulated in the Otago hill country, stranding trucks, with graders required to clear the way. There were further hail showers, notably in Invercargill, and southwesterlies reached gale force in coastal Southland and Otago. Temperatures only reached 6°C in Dunedin, and 7°C in Invercargill and Queenstown. Places sheltered from the south to southwest flow recorded severe frosts, eg. Timaru -4°C.

The North Island also suffered, with snow falling on the North Island high country. A major portion of I need to control my language, both the Desert Road and the section between Waiouru and Taihape, was closed by snow overnight 19-20 September. On the 19th, Waiouru recorded a high of just 5°C and Taupo 9°C. Also, a tornado was reported in the Wairarapa on the 19th.

This snap is notable for massive accumulations inland. 50cm in September is pretty big. Otago hill country is not all that high- in the region of 200m-400m ASL.

The freezing level rose throughout the day, so maybe not the best example to illustrate my point.

Next up,

Spring 2005:

http://www.metservice.com/default/index.php?static=2005spring1

Started like this:

1-3 September. Morning fogs in central and northern North Island. Flights disrupted at Auckland Airport (1st/2nd). Persistent fog in Taupo suppresses daytime high to 12°C but nearby Kawerau reaches 24°C (1st). An early season fire ban is placed in Canterbury and north & central Otago due to dry conditions (1st). Wet in Fiordland and Westland due to a stalled front.

Then, almost a year to the day!

http://' target="_blank">s.gifOver 19-20 September, a very cold south to southwest flow swept over New Zealand following the passage of the low. On the 19th, snow fell to sea level in Southland, Otago and Canterbury causing much disruption, including killing thousands of lambs by hypothermia. A small low formed just east of the South Island (see maps for the 19th) which intensified conditions over eastern Canterbury. In Christchurch, the snow there was the heaviest since 1992, with many roads and schools closed (about 7cm fell in the central city, 10cm at the Airport). Dunedin and Christchurch only managed highs of 5°C and Queenstown 4°C.

Also on the 19th, southwest winds reached gale force in many coastal places, and heavy showers with thunder and hail peppered northern and central districts, notably Hastings and Blenheim.

Overnight 19-20 September, the North Island bore the brunt of the cold snap, with snow falling as low as 300-400m in central and southern parts of the island. Four State Highways (including the Desert Road) were closed by snow in central regions, and the Rimutaka Road was also closed briefly. Dustings of snow were visible on some northern mountains on the 20th, eg. Mt Tarawera, Mt Pirongia and Mt Te Aroha.

Conditions slowly eased on the 20th, although it remained very cold, with Waiouru's high only 3°C.

It wasn't all bad news however, with ski-fields doing well out of the late-season snowstorm. Fresh snow on Coronet Peak allowed it to reopen for a time.

I realise there are many factors that influence snow fall (John Holmes pointed out a site the other day, it seems there's a lot to take into account).

However, two crucial ones that keep popping up in "March Snow" posts are:

1) Increasing air temperatures rule out snow

2) Strength of sun rules out lying snow

In the above cases:

1) Both Alexandra (Otago Hill Country) and Christchurch (Canterbury coast) average highs of 15C in September, significantly higher than most of the UK in March. Yet, cold snaps knocked down temperatures enough for snow, and decent accumulations to be fair!

2) Although I can't argue the point of solar irradiance, I can try a UV-analogue. UV in mid September in NZ ranges from 6/7 in the far North (never gets snow anyway) to 3-4 in the deep South. In other words, a fair old bit higher than the UK in March. Also, it's 10 degrees nearer the equator, which will naturally make the radiation from the sun greater. Yet, lying snow still came about!

Both NZ and the UK can and do get good cold snaps. Yet, if anything, the conditions at ground level in NZ are more marginal in Spring than they are in the UK (especially in Christchurch). It's my feeling that the two common arguments for improbability of snow in the UK in March are not really valid. I won't argue the point of what set-up is required and whether it is on the horizon, what I am saying is that the climate at this time of the year in the country still make it quite vulnerable to snow. All of this has happened before and all of this will happen again.

All comments welcome, even if it's to inform me of how awfully wrong I am.

  • Replies 11
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Posted

Haven't got time to read it in detail but what an excellent post <_<

Snow lying in April is possible in the UK even in the english midlands though i have to admit the chance of lying snow lasting does rapidly diminish the further into spring you get, top class post. :)

I know new zealands climate is similar to the UK`s but have you had the same amount of warming as we have had since 1988?

I dont think you have i think your summers and winters have been cooler than ours since then.

Posted
  • Location: City of Gales, New Zealand, 150m ASL
  • Location: City of Gales, New Zealand, 150m ASL
Posted
Haven't got time to read it in detail but what an excellent post :)

Snow lying in April is possible in the UK even in the english midlands though i have to admit the chance of lying snow lasting does rapidly diminish the further into spring you get, top class post. :)

I know new zealands climate is similar to the UK`s but have you had the same amount of warming as we have had since 1988?

I dont think you have i think your summers and winters have been cooler than ours since then.

Good point on the general warming. Pretty sure that NZ has not seen it to the degree of the UK. Having said that, the "catch-up" from the UK has not been great enough to overtake NZ. The rough guide is that NZ Winter = UK Spring (approximate national average temperature of 9C).

It has always been the case that there's a larger difference between the winters than between the summers. I'm not sure how that has changed since 1988. The average summer temperature for all of NZ is 16.6C. I have no idea what it is for UK summer.

Posted
  • Location: City of Gales, New Zealand, 150m ASL
  • Location: City of Gales, New Zealand, 150m ASL
Posted

Trying to find a better marker for "strength of sun", I have found that the total direct and scattered solar radiation in September at the locations mentioned is between 11 and 13 Megajoules per Square Metre.

Unfortunately, such information is not available for the UK (freely, anyway). By fudging my way through it using some theoretical model, and ignoring "inconvenient" terms, I came up with a value in the region of 1MJ m^-2 for a standard UK site. This doesn't sound right at all.

So I looked at fudging it in a way where I can actually keep track of my jam.

Just assuming radiation incident on a plane circle, which is parallel to the earth's surface at a given point.

The area of this circle comes out as being = pi * (r_a)^2 * sec ^2 ((latitude))

where r_a is the radius of the circle, were it directly incident to the solar radiation (ie at the equator). (for a quick case you would take this as 1, just left it in for book-keeping).

I think I got the trigonometry right.

Using latitudes of 52N and 42S, the area of the circle comes out as being larger in the UK by a factor of 1.45 over that in NZ. So the solar radiation is spread over a larger area, giving weaker sun. This is hardly groundbreaking stuff, it just suggests that I may have got my trig function correct in the equation.

In addition, compare the increased hours of sunshine in NZ, looking at 150-160 per month in September - call it 5 hours a day. In the Uk that would be more like 100-120, depending on location- call it 4 hours a day (though I suspect nearer to 3 for a snow-prone area).

Sticking it all together and you come out with:

Combining sunnier days with stronger sun between NZ and the UK and you find that in an average September day, total solar radiation would be 81% greater in the NZ locations.

Must admit, that's a fair bit more than I expected. But remember, my working was not the most precise- though good enough for a quick flick through the problem. One issue is that really I should have considered an ellipse, not a circle, but that would lead to geometry that would be too awkward.

Anyway, if lying snow can happen in NZ in September, then this evidence above suggests that the "UK March Sun Strength" argument appears to be weakened. This wouldn't be a real conclusion if I didn't recommend further study. So someone else should look at it if they have the time and interest ;)

Have attached scrawled diagram.

;)

post-7526-1205220686_thumb.jpg

Posted
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield
  • Weather Preferences: Any Extreme
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield
Posted

I wouldn't rule out Snow in March but when you consider in recent years Snow has been very rare in Dec Jan and Feb it's going to be even rarer in March. Plenty of light Snow around for us March 2006 but thats really the exception to the rule these days.

Posted
  • Location: Derbyshire Peak District. 290 mts a.s.l.
  • Weather Preferences: Anything extreme
  • Location: Derbyshire Peak District. 290 mts a.s.l.
Posted

A March with no lying snow is the exception rather than the rule here. The average number of mornings with lying snow in March, over the last 30 years, is 4 and ranges from 0 in 1991, 1997,2000, 2002 and 2003, to 14 in 1987; going back even further March 1970 produced 21 mornings with lying snow.

The frequency of March snowfall has certainly declined in the last 10 years or so, although March 2001 managed 11 mornings with snow lying and a fall of 16cm on the 21st; this was the last heavy snowfall in March here.

It's certainly true that a light snowfall in March is more likely to melt during the morning than in the winter months, firstly because the sun is stronger and also because it rises about 90 minutes earlier and therefore has more chance to 'do its work'. On the other hand if it snows with a very cold air mass in place even March sunshine has little effect, unless it's continuous.

The fact that snowfalls in March or April tend to be short lived affairs is probably a due to the fact that they tend to result from showers or from back edge snow as a cold front moves through, resulting in relatively small accumulations which are more easily disposed of by a sun which is rising early in the morning.

Prolonged heavy snow in a cold air mass is just as likely to stick as in mid-winter, as proved by the late April blizzards of 1981.

I'd say the frequency of March snowfall has declined less in recent years than that in January and February.

Posted
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield
  • Weather Preferences: Any Extreme
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield
Posted
A March with no lying snow is the exception rather than the rule here. The average number of mornings with lying snow in March, over the last 30 years, is 4 and ranges from 0 in 1991, 1997,2000, 2002 and 2003, to 14 in 1987; going back even further March 1970 produced 21 mornings with lying snow.

The frequency of March snowfall has certainly declined in the last 10 years or so, although March 2001 managed 11 mornings with snow lying and a fall of 16cm on the 21st; this was the last heavy snowfall in March here.

It's certainly true that a light snowfall in March is more likely to melt during the morning than in the winter months, firstly because the sun is stronger and also because it rises about 90 minutes earlier and therefore has more chance to 'do its work'. On the other hand if it snows with a very cold air mass in place even March sunshine has little effect, unless it's continuous.

The fact that snowfalls in March or April tend to be short lived affairs is probably a due to the fact that they tend to result from showers or from back edge snow as a cold front moves through, resulting in relatively small accumulations which are more easily disposed of by a sun which is rising early in the morning.

Prolonged heavy snow in a cold air mass is just as likely to stick as in mid-winter, as proved by the late April blizzards of 1981.

I'd say the frequency of March snowfall has declined less in recent years than that in January and February.

Also TM you have the advantage of 600ft over me. ;)

Posted
  • Location: City of Gales, New Zealand, 150m ASL
  • Location: City of Gales, New Zealand, 150m ASL
Posted
I wouldn't rule out Snow in March but when you consider in recent years Snow has been very rare in Dec Jan and Feb it's going to be even rarer in March. P

Can you really make this conclusion?

Posted
  • Location: Teesdale,Co Durham. 360m asl
  • Location: Teesdale,Co Durham. 360m asl
Posted
A March with no lying snow is the exception rather than the rule here. The average number of mornings with lying snow in March, over the last 30 years, is 4 and ranges from 0 in 1991, 1997,2000, 2002 and 2003, to 14 in 1987; going back even further March 1970 produced 21 mornings with lying snow.

The frequency of March snowfall has certainly declined in the last 10 years or so, although March 2001 managed 11 mornings with snow lying and a fall of 16cm on the 21st; this was the last heavy snowfall in March here.

It's certainly true that a light snowfall in March is more likely to melt during the morning than in the winter months, firstly because the sun is stronger and also because it rises about 90 minutes earlier and therefore has more chance to 'do its work'. On the other hand if it snows with a very cold air mass in place even March sunshine has little effect, unless it's continuous.

The fact that snowfalls in March or April tend to be short lived affairs is probably a due to the fact that they tend to result from showers or from back edge snow as a cold front moves through, resulting in relatively small accumulations which are more easily disposed of by a sun which is rising early in the morning.

Prolonged heavy snow in a cold air mass is just as likely to stick as in mid-winter, as proved by the late April blizzards of 1981.

I'd say the frequency of March snowfall has declined less in recent years than that in January and February.

Copley nearest Meto site to me 8 miles West and 110m lower, also recorded 11days of snow lying >50% but with a max depth 25cm. March 2006 had 11 days of snow lying aswell max depth only 10cm though.

A repeat of either month would be nice. Decent and prolonged snow cover isn't out the question.

Mark

Teesdale,Co Durham

Posted
  • Location: City of Gales, New Zealand, 150m ASL
  • Location: City of Gales, New Zealand, 150m ASL
Posted
North Island high country. A major portion of I need to control my language, both the Desert Road

!

I need the Netweather swear filter to grow a $%!^% brain!

Posted
  • Location: Inbhir Nis / Inverness - 636 ft asl
  • Weather Preferences: Freezing fog, frost, snow, sunshine.
  • Location: Inbhir Nis / Inverness - 636 ft asl
Posted

Snow is of course possible in March, there's no denying that. ;)

What I don't understand is why one of the most beloved snow events of the last 5 years (March 4 - 14, Depending on location in the UK), is able to be looked upon with fondness, but move that spell back ten days (to fall in line with what's coming) and everyone says: "urrrgh, I hate it."

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