Autumn 2018 - General discussion

JCX BXC

Possible Sleet in the forecast for Knock from 7am-10am tomorrow.

Oscar Bravo

A cool night.

9pm:
Mt Dillon 3 degrees
Casement 3 degrees
Gurteen 4
Ballyhaise 4
Athenry 4
Dunsany 4

Gonzo

very chilly night here already, feels baltic outside.

sryanbruen

sryanbruen wrote: »

The AO and NAO indexes still forecast to be on the negative side into early November with brief rises to neutral from time to time - can't always be consistently negative. This negative switch on the indexes will result in higher chances of blocking to the north sending the jet stream southwards.

There's a lot of talk right now about the chances of a cold November. I'll believe it when I see it, not confident on a cold November personally! My November forecast that I set in my Autumn forecast at the end of August was for a mild and possibly very wet November. No sign of overly mild conditions soon but there has been a trend of more unsettled weather.

Like I said in yesterday's post on a cold November, I'll believe it when I see it. The NAO is now forecast to go back positive in early November, a complete flip on what the GFS ensembles have been shown for a good few days now.

ECM 12z maybe very unsettled but it's not your straightforward zonal pattern. There'd be a lot of rain, similar in vein to November 2009, with low pressures getting stuck constantly around Ireland. There lies several areas of interest that I've put rings around in the ECM 12z chart below that need monitoring.

DOCARCH

Ballyhaise reporting 1c and sleet at 0700.

Pangea

https://imgur.com/a/enLKU22

Barnesmore Gap right now. Photo posted by a John Mc Donagh on Facebook

pauldry

Snow on Ben Bulben sleet in Sligo

km79

sryanbruen wrote: »

ECM 12z maybe very unsettled but it's not your straightforward zonal pattern. There'd be a lot of rain, similar in vein to November 2009, with low pressures getting stuck constantly around Ireland.

:eek:

Nice bit of snow on Nephin this morning.

DOCARCH

Looks like Irish Sea showers edging closer all the time to the Wicklow/Wexford coast.

Nice bit on Croagh Patrick too.

leahyl

It is BALTIC this morning!!!

hoody

pauldry wrote: »

Snow on Ben Bulben sleet in Sligo

Took this from Ballyshannon this morning

sryanbruen

https://twitter.com/Jimmy48carmen/status/1056141885272719360

https://twitter.com/Jimmy48carmen/status/1056149289112616961

Oscar Bravo

A white Croagh patrick today

Reckless Abandonment

Love that pic bravo

SleetAndSnow

Beautiful pictures guys!

Its cold here in Cork City with strong gusts of wind. Only about 5 degrees now but was 3/4 for the majority of the morning. Dry with sunny spells.

JCX BXC

2:30 knock airport: 3c and rain shower.

How Octobery.

m17

Inverness Scotland 27/10/18

m17

Tuam Co galway 27/10/18 13.22 temperature 4°C

Artane2002

Hail shower in Dublin 5, nearly looks like graupel. It's turning to rain now.

SleetAndSnow

still blue skies here in cork city but cold! Fire is lit

TECH85

sryanbruen wrote: »

This is going to be my forecast for Autumn 2018 because the day has come now for me to release it. I'm going to explain a couple of phenomena and their impact for the coming Autumn then give a summary of what my analogues had to say as a reminder for the Autumn and last but not least, my actual thoughts for the Autumn based on everything we've looked at including analogues and models.

The current state of the North Atlantic Ocean is a strange one with a large cold blob to the northeast of the North Atlantic but very warm over towards Newfoundland. The tropics are at about average levels. This combination of sea surface temperature anomalies leads to believe a positive North Atlantic Oscillation (NAO) is likely especially given the cold blob which was last seen in 2016 before this year and therefore, this means milder than average temperatures are more likely than below average. The tropics have significantly warmed up through the Summer compared to where it was in May which will lead to a ramp up in tropical developments. This can lead to quite big changes in the Atlantic to allow patterns to change such as the NAO. The latest ensembles are perfectly split on where the NAO will go in early September indicating the uncertainty and I think the warming of the tropics is aiding this uncertainty. However, in theory, you'd think a positive NAO is the most likely this Autumn. This will be highly unusual if it verifies because the NAO has already had a record breaking long run of positivity from April to August 2018.

ENSO is currently in neutral stages and I expect it to remain so through this Autumn with no significant deviations occurring. However, models like the CFSv2 are keen on El Nino to occur beginning in the Autumn. I am extremely dubious about this as the ocean has not shown its reaction towards El Nino. Therefore, with neutral levels, ENSO is not likely to have much impact this Autumn on the weather.

The Polar Vortex, which is the ribbon of air that surrounds the Arctic Circle disallowing cold air from filtering down into the mid-latitudes, is expected to be weak this Autumn by the CFS ensembles. In theory, this should mean that northern blocking would be more likely to occur with an increased chance of northerly or easterly incursions though not necessarily a cold or settled Autumn overall. With the state the North Atlantic Ocean is in, I would think easterlies are more likely than northerlies unless a massive shift takes place in the sea surface temperatures. This weakening of the Polar Vortex is theorised to aid the chances of a Canadian Warming occurring later in the Autumn into early Winter. A Canadian Warming is a type of Sudden Stratospheric Warming (SSW) which occurs over in Canada mainly during November or December. A November Canadian Warming has occurred in 1962, 1968, 1977 and 2000; all of which were followed by cold Winters. This type of event can also lead to some cold spells or snaps in November itself as such happened in 1962 teasing what was gonna come in 1962-63.

On model runs recently, the Siberian High has appeared and it is quite early to be seeing this form on European charts especially to its extent shown. As a result, the snow cover extent through Eurasia is expected to be faster than average through this Autumn. When this occurs, it can be a sign of some colder interludes during the Autumn season but this is most importantly the case for Winter time.

In terms of long range models, well there's strong confidence from them on a milder than average Autumn which I have to agree with personally. I agree because of the state of the North Atlantic Ocean and mild Autumns occur much much more often than cold. I don't think it'll be like Autumn 2011 or 2006 type mild conditions, I think it will be an unremarkably mild Autumn. The models are far more mixed on the rainfall aspect though most are going wetter than average which I agree with again for this Autumn. Positive NAO in Autumn especially later on (November) usually means wetter than average conditions.

My analogues showed the prospects of a mixed September, a settled October whilst a very wet November for Autumn 2018. In contrast to the models which are very strong on a mild Autumn, there didn't seem to be much of a signal for the temperatures from the analogues for this Autumn. Going by the 500mb height anomalies in the analogues, September is likely to be close to average to milder than average. October is likely to be close to average though this largely depends on the exact alignment of high pressure and the wind direction. November is interesting because there have been signals in some analogues for quite a cold November and the Beijing Climate Centre model showed the possibility of this too but unsettled. The unsettled nature combined with the colder than average conditions would give away to some early wintry weather potential. However, I see this as a very small possibility and I predict November to be a stormy, mild month with a lot of rain and strong winds.

In summary,

September - A fairly mild and mixed month. Likely to be on the relatively wetter than average side but no big deviation.
October - Settled and fairly mild again. Lot of quiet weather.
November - Very wet, mild and stormy. Plenty of gales and rain.

Remember long range forecasting is not to be relied upon and is just for fun.

So far , so right. As usual ;-)

m17

Corofin co galway 27/10/18

Timmyboy

Snow on the 'Reeks in Kerry this morning, Sunday, 28th October 2018.
First snow that I have seen this Autumn was yesterday morning that occured on Friday night (26th October 2018)

SleetAndSnow

20 past 9 (or 20 past 10 if the clocks hadn’t go back) and the cars outside are all still frosted over and it’s bitterly cold after just waking up in cork city.

Rhineshark

Lovely bright day on the south coast of Galway, but cold enough for a brass monkey to be starting to look a little pained. (About 4C)

m17

Tuam Co galway 28/10/18 10.32 temperature 5°C

Clonmel1000

In Santiago de Compostela for the weekend. Absolutely miserable day heavy frequent hail/graupel showers and biting cold. Thoroughly unpleasant but a beautiful city.

Tigerandahalf

Clonmel1000 wrote: »

In Santiago de Compostela for the weekend. Absolutely miserable day heavy frequent hail/graupel showers and biting cold. Thoroughly unpleasant but a beautiful city.

That Galician area had fabulous weather until a few days ago. It was in the 20s for most of Oct.