Snowfall Depths

nacho libre · 03-03-2018 11:47pm #1

I've noticed a consistent theme in snow fall events i've read about over the years, and in this most recent one; there seems to be a discrepancy between snowfall depth recorded at offical stations and those that are recorded by weather enthusiasts and observers around the country.Is this because Met Eireann don't actually have enough weather stations around the country, or that there stations are not located in the prime areas to record the most snow depths?
Or do us, amateurs, simply measure our snow depths incorrectly?
I ask because the official readings from Gaoth Laidir for this event seemed a lot lower than i thought they would be given some of these areas were where most of the snow fell.

Agent_47 · 03-03-2018 11:59pm

what are the standards? Check daily?

We had 40 cm here in Navan to yesterday afternoon, cleared drive and it had a further 10 cm this morning but the accumulated snow around the cars was just 43 cm. I will take 50 cm for Navan based on the daily snow falls as obviously the weight and humidity affect the height of this snow, it was powdery at the start but was wet today with yesterday evenings fall.

BTW snow on my roof is dripping all day and evening with the thaw, don't think it will be a slow thaw.

Casualsingby · 04-03-2018 12:16am

Powder snow and wind has made it even harder to get an idea on depth IMO. Also, Dublin airport recorded almost 4 times precipitation as Casement yet Casement had a deeper snow depth throughout. Puzzling to me.

Donegal Storm · 04-03-2018 12:18am

As I said throughout I couldn't really give an accurate measurement of depth here at all. Theres a small car parking area here thats open on all sides so nothing to catch drifts and yet snow is twice as deep at one end as the other. Even at the height of the blizzard there were patches of almost bare concrete with knee deep snow a few steps away

I have no doubt I and a lot of others are measuring incorrectly but if drifting snow is discounted as inaccurate I don't see why an area thats constantly having snow blown off it is any more accurate

downthemiddle · 04-03-2018 12:48am

According to ME on RTE tonight Glenbride in West Wicklow had the greatest recorded depth with 67cm. The same area was one of those worst affected by the snow that started on 27th February 2001.:eek:

nacho libre · 04-03-2018 1:38am

downthemiddle wrote: »

According to ME on RTE tonight Glenbride in West Wicklow had the greatest recorded depth with 67cm. The same area was one of those worst affected by the snow that started on 27th February 2001.:eek:

I wonder is that place high up. It still is impressive, but I have in mind places at or close to sea level. I get it with this event it was hard to get accurate measurements because of the drifts, but even when reading about great snowfalls events of the past, the offical measurements seemed to be fairly low in comparison to what people at the time had measured in various parts of the country.Last December my folks and a neighbour said they measured six inches of snow from a frontal snow event back home, but i'm beginning to think it was an inaccurate measurement. Mine from December 2010 probably was too. There is obviously a bite more to it than just going out with a ruler to measure it on the tarmac.

ZX7R · 04-03-2018 1:48am

nacho libre wrote: »

I wonder is that place high up. It still is impressive, but I have in mind places at or close to sea level. I get it with this event it was hard to get accurate measurements because of the drifts, but even when reading about great snowfalls events of the past, the offical measurements seemed to be fairly low in comparison to what people at the time had measured in various parts of the country.Last December my folks and a neighbour said they measured six inches of snow from a frontal snow event back home, but i'm beginning to think it was an inaccurate measurement. Mine from December 2010 probably was too. There is obviously a bite more to it than just going out with a ruler to measure it on the tarmac.

Just did it a quick Google on how to measure snow depth, the weather network has an interesting right up about how to do it correctly, not as straightforward as I thought

Rodin · 04-03-2018 2:27am

downthemiddle wrote: »

According to ME on RTE tonight Glenbride in West Wicklow had the greatest recorded depth with 67cm. The same area was one of those worst affected by the snow that started on 27th February 2001.:eek:

I'll see your 67cm and raise you almost double....

wakka12 · 04-03-2018 2:28am

I think there was a lot of people posting how much there was in their area just kind of guessing . There was a lot of new posters in the forum who only had a passing interest in the weather. In my area of south east dublin it was like 11 or 12 inches with drifts up to like 1.5 feet I suppose but lots of my friends and neigours from same area saying things like can't believe theres 3 feet snow outside on the street, there just wasn't that much but I think the novelty of there being such vast amounts of snow led to people posting things like that from some parts of the country

I still do find it hard to believe 67cm was the highest though having seen pics from kildare of snow drifts the same height as cars..how could that be??

Rodin · 04-03-2018 2:30am

wakka12 wrote: »

I think there was a lot of people posting how much there was in their area just kind of guessing by eye. There was a lot of new posters in the forum who only had a passing interest in the weather. In my area of south east dublin it was like 11 or 12 inches with drifts up to like 1.5 feet I suppose but lots of my friends and neigours from same area saying things like can't believe theres 3 feet snow outside on the street, there just wasn't that much but I think the novelty of there being such vast amounts of snow led to people posting things like that from some parts of the country

I still do find it hard to believe 67cm was the highest though having seen pics from kildare of snow drifts the same height as cars..how could that be??

67cm is paltry

_Dara_ · 04-03-2018 6:45am

nacho libre wrote: »

I wonder is that place high up.

According to Google Maps, it's about 480-500m asl. So pretty high ground by Irish standards!

King of Spades · 04-03-2018 7:39am

I heard that Dunsany in Meath had the highest amount of snowfall of any official weather station.

Jpmarn · 04-03-2018 8:46am

Got about between 5 and 10 cm snow during the whole event over the past few days in my location outside Limerick city. The first snow was on Wednesday morning but had some daytime thawing. As of this Sunday morning the lying snow is nearly gone. It like that we weren't badly affected be this cold weather event. Glad it is over now. It is a busy time of the year for any dairy farmer.

M.T. Cranium · 04-03-2018 9:06am

Snow measurement is complicated especially when the observer has any evidence that liquid precipitation has also fallen during the same period. As I am only familiar with the official way to do the measurements in North America, I won't confuse people with what may be different operational procedures.

However, the 67 mm of liquid at Dunsany could mean one of four things:

(a) an automatic sensor detected 67 mm of melted snow but nobody knows what depth of snow that ever was.

(b) a human observer measured 67 cm of snow and was following a procedure for his/her class of station to state precip as 1/10 of snow depth.

(c) a human observer measured some unknown to us amount of snow (let's say 80.4 cm) and determined its water content (let's say it was 12.5:1) and calculated the precip was 67 mm (840/12.5).

(d) a human observer determined that there was x mm of rain and y cm of snow and did one of the two options above to derive the precip equivalent of the y cm of snow and added that to the x mm of rain.

Some variants are possible. You sometimes have no other option than to melt down a mess of slush in a rain gauge if rain and snow are falling together, and estimate how much of the liquid is rain, then assign a snowfall value to what was not rain, which more or less matches what snowfall was measured.

The one thing that might be different in my experience here and what is done there, is that snowfall for any given day is the sum of eight measurements made on a cleared level space (a board is used as a foundation), once each one is taken, the board is cleared off and measured again. So you can get a bit more snow in total than the actual depth (because some can settle, blow away, or partially melt). If it does that in the three hours that is not part of the calculation, you're stuck with that reduction. But in a good old fashioned snow storm, the accumulation is usually pretty close to the aggregated measurements.

There's a tendency for weather enthusiasts to overstate slightly but more veteran ones tend to be reliable. You have to keep in mind, airports are deliberately placed where heavy snow is not expected on a regular basis, and places where it is have other functions like being ski hills or farm fields. It is part of that evolution of land use that helps explain why airports often report less snow than most places around them. Having all those vehicles and airplanes trundling around is a bit of a deterrence to snow accumulation too.

Gaoth Laidir · 04-03-2018 9:48am

www.weather.us is a brilliant site. Not only does it give countless ECM parameters (not available anywhere else) but it also gives a huge array of observational data, including hourly snow depths. See here for the latest, and zoom in to click on individual station values over the past 4 hours. https://weather.us/observations/ireland/snow-depth/20180304-0800z.html

That only gives the depths, though. If you want a little more insight into what type of cover it is then it's easy to get from the hourly synop code. The latest synops for Ireland are here http://www.ogimet.com/ultimos_synops.php?lang=en&estado=Irel&fmt=html&Send=Send

e.g. Casement (03967). The snow depth group is the one beginning with 4 on the 333 line. It's in the format 4E'sss), where E' is the description of cover (see below) and sss is the depth in whole cm (except a value of 997 means <0.5 cm, 998 means "snow cover, not continuous", 999 means innacurate or not measureable).

AAXX 04071 03967 42350 80804 10019 20009 39754 49868 56013 886//
333 44014 81708 88709==

So above means 14 cm of uneven wet or compacted snow covering the whole ground.

0975

E´ State of the ground with snow or measurable ice cover

Code figure

0 - Ground predominantly covered by ice
1 - Compact or wet snow (with or without ice) covering less than one-half of the ground
2 - Compact or wet snow (with or without ice) covering at least one-half of the ground but ground not
completely covered
3 - Even layer of compact or wet snow covering ground completely
4 - Uneven layer of compact or wet snow covering ground completely
5 - Loose dry snow covering less than one-half of the ground
6 - Loose dry snow covering at least one-half of the ground but ground not completely covered
7 - Even layer of loose dry snow covering ground completely
8 - Uneven layer of loose dry snow covering ground completely
9 - Snow covering ground completely; deep drifts

Notes:
(1) The definitions in the code for E´ apply to an open representative area.
(2) In all instances, the highest code figures applicable shall be reported.
(3) In the above code table, whenever reference is made to ice, it also includes solid precipitation other than snow.

Casement's E' figure started off as 7 on Wednesday morning, then went to 8 on Friday as the drifting started, and is now back to 4. It never went to 9, which is a bit strange as drifts were present, though as MT said, drifting around an airport is not as severe as on places like roads, etc., where a 9 has definitely been warranted in some places this week. Not sure how deep is "deep", but there is a different synop group used in some countries that differentiates between drifts above or below "eye-level". Then that begs the question, whose eyes?

Macy0161 · 04-03-2018 9:52am

Very hard for me to tell here with the drifting. We had areas around the house with bare concrete and then up over the window sill literally around the corner!

The12thMan · 04-03-2018 11:40am

17cm here in southside of cork city

Alun · 04-03-2018 12:05pm

Was out and about yesterday on Bray Head and around some small back roads between Bray and Greystones. What struck me was the number of really seriously high drifts in random places. We'd be walking along a snow covered road, maybe only a few cms of compacted snow, then we'd come to a bend or a T junction and suddenly there'd be clear tarmac followed by drifts of 1-2m high blocking the road completely. It was the same up on Bray Head, a couple of hundred metres of either very little snow or even bare earth and then we'd be up to over our knees.

An Ri rua · 04-03-2018 12:32pm

wakka12 wrote: »

I think there was a lot of people posting how much there was in their area just kind of guessing . There was a lot of new posters in the forum who only had a passing interest in the weather. In my area of south east dublin it was like 11 or 12 inches with drifts up to like 1.5 feet I suppose but lots of my friends and neigours from same area saying things like can't believe theres 3 feet snow outside on the street, there just wasn't that much but I think the novelty of there being such vast amounts of snow led to people posting things like that from some parts of the country

I still do find it hard to believe 67cm was the highest though having seen pics from kildare of snow drifts the same height as cars..how could that be??

Rodin wrote: »

67cm is paltry

Snow FALL, not lying snow. I imagine that is the key to your collective conundrum.

Gaoth Laidir · 04-03-2018 12:43pm

King of Spades wrote: »

I heard that Dunsany in Meath had the highest amount of snowfall of any official weather station.

But there are no snow measurements there as it is a fully automatic station. Yes, it had the highest liquid equivalent of all stations, but I didn't see any measurements. Do you have a source? I think MT's (a) above is correct here.

RobertKK · 06-03-2018 4:40pm

I haven't a clue how much snow fell as the drifting was on a high scale, so there were near bare patches and then snow up to 2.5m to 3m deep.
I could say x amount fell but I know it would be totally false as I found it impossible, I believe my weather station didn't record all the liquid that fell as it was blown off that too.
I will just say a lot fell, it is more accurate for me to say that than x amount fell.

Elmer Blooker · 06-03-2018 5:36pm

Casualsingby wrote: »

Powder snow and wind has made it even harder to get an idea on depth IMO. Also, Dublin airport recorded almost 4 times precipitation as Casement yet Casement had a deeper snow depth throughout. Puzzling to me.

I must have received a similar amount as Dublin A. as it was a frontal event but I received a LOT more snow in Dec 2010 from streamers, like you I'm puzzled?
Does anyone have any theories why north Dublin got so little despite the readings at the airport?

patneve2 · 06-03-2018 6:14pm

Im really starting to think that the salt in the air blowing in on the strong E gale somewhat stunted the accumulations even a few km inland. Gusts were over 50kts at times. Add on a few very brief thaws here and there as well as strong winds and you get a messy picture. My 17.5 cm could have been at least 40. Also its logical to think that the gale not only blew falling snow far inland, but also a bit of lying snow resulting those massive drifts inland wiclow/dublin kildare meath etc.

wakka12 · 06-03-2018 6:23pm

patneve2 wrote: »

Im really starting to think that the salt in the air blowing in on the strong E gale somewhat stunted the accumulations even a few km inland. Gusts were over 50kts at times. Add on a few very brief thaws here and there as well as strong winds and you get a messy picture. My 17.5 cm could have been at least 40. Also its logical to think that the gale not only blew falling snow far inland, but also a bit of lying snow resulting those massive drifts inland wiclow/dublin kildare meath etc.

I believe that thawing effect was noticeable as far in as the centre of dublin. Im in milltown and it was noticeable to me. Icicles were falling off my eaves even during the peak of the storm which is what made me afraid the snow that night was rain. The significant accumulations made the thaw fairly unnoticeable though but it probably was significant
The sea thawing effect didn't seem to stop until at least west of terenure

I was kind of a bit disappointed tbh. The event in our area of Dublin was exceptional rather than historical like in west Dublin.

Elmer Blooker · 06-03-2018 7:22pm

wakka12 wrote: »

I believe that thawing effect was noticeable as far in as the centre of dublin. Im in milltown and it was noticeable to me. Icicles were falling off my eaves even during the peak of the storm which is what made me afraid the snow that night was rain. The significant accumulations made the thaw fairly unnoticeable though but it probably was significant
The sea thawing effect didn't seem to stop until at least west of terenure

I was kind of a bit disappointed tbh. The event in our area of Dublin was exceptional rather than historical like in west Dublin.

The temperature was always below zero in my parts when snow was falling ranging from -4.5c at the beginning of the cold spell to -0.6c when snow fell for the last time on Friday night/early Sat morning. There was brief thawing in the middle of the day on Friday, around 1.5c, but fell just below freezing in the afternoon when snow started to fall again. I wouldn't agree with your theory that thawing was taking place when snow was falling. Mysterious?

wakka12 · 06-03-2018 8:22pm

Elmer Blooker wrote: »

The temperature was always below zero in my parts when snow was falling ranging from -4.5c at the beginning of the cold spell to -0.6c when snow fell for the last time on Friday night/early Sat morning. There was brief thawing in the middle of the day on Friday, around 1.5c, but fell just below freezing in the afternoon when snow started to fall again. I wouldn't agree with your theory that thawing was taking place when snow was falling. Mysterious?

Many places across the country reported thaw while it was snowing on saturday morning/evening though?
It was snowing heavily on friday in my part of Dublin but I could literally see drips from my eaves and the icicles were all falling. On saturday there was no accumulation but it was still snowing and the thawing was very significant on saturday whilst it was snowing, and it was definitely snow

sryanbruen · 04-04-2018 1:40pm

Whilst not depths, I thought it would be worth a note to mention here.

The March 2018 monthly weather summary states the following:

Widespread heavy falls of drifting snow occurred on 1st, 2nd and 3rd, heaviest in the East and Southeast, with accumulations of up to 69 cm in the Wicklow mountains.

http://cli.met.ie/cli/bulletin/data/2018/03/sum_032018.pdf

arctictree · 04-04-2018 1:52pm

sryanbruen wrote: »

Whilst not depths, I thought it would be worth a note to mention here.

The March 2018 monthly weather summary states the following:

http://cli.met.ie/cli/bulletin/data/2018/03/sum_032018.pdf

There were 2M high drifts around here. Is that 69cm on the flat?

riffmongous · 04-04-2018 4:32pm

Drift data isn't very useful for short events though, it might be interesting to note them but they are so localised it doesn't really tell you very much, what's important is knowing how much liquid fell, and for this you need high frequency measurements like distrometers or sonic depth sensors (and they need to be really well sited). For longer time scales then it's no longer the depth of the snow but the snow water equivalent that needs to be measured.

Snowfall Depths

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