WINTER WEATHER 2013/2014 - See Mod Note First Post

finnbob123 wrote: »

hey, ken love your weather reports but I see your in the irish news a lot lately http://www.irishexaminer.com/ireland/a-white-december-but-no-snow-on-christmas-day-243168.html and also got an email from electric Ireland supposedly quoting you.

Ah, mystery solved. I do remember that reporter and as you can see, I did not say a white December - that was her interpretation and her headline, not mine. It looks like Electric Ireland took something from her headline and used it to advertise.

<SNIP>
has anyone an idea of how long the winter will last or will it be like last year cold until nearly may.

Might rain a bit.

M.T. Cranium wrote: »

Might rain a bit.

This is how I like my weather forecasts, short and to the point!

Quiet atlantic storm season, good for easterly strength down the line?

tylercollins wrote: »

Keats. Ode on a Grecian Urn.

icesnowfrost wrote: »

Can anyone explain blocking and is blocking a good set up for cold

Very basic explanation for the scenario we want - cold - is that a high pressure forms north of Europe and blocks out low pressure systems coming in from the Atlantic, which bring warmer air with them. Instead, we ideally get easterlies, which blow in lovely freezing air from Siberia and can result in a snowfest.

What does Dec look like according to you method?

I saw a snow plough on the M50 about an hour ago, heading south bound from the finglas exit. I suspect its going down to the depot near the toll.

Spring Onion wrote: »

For us non-techies, does that mean lots of cold?

It's just a measure of whether the CFS is predicting higher or lower pressure to our north.
Air tends to circulate clockwise around high pressure, so when high pressure is just to our north the likelihood of easterly winds increases, which can bring cold polar/continental air over Ireland.

While the strength and positioning of the high pressure can causes differences in the weather that we experience here, in general, a trend towards high pressure to our north is a good thing for cold winter weather, and that's what the CFS has been showing.

This is my winter 2013-14 forecast for Ireland and the U.K., adapted here for Irish readers (you can see my U.K. version on Net-weather today).

The following forecast is based on the latest upgrade of my research model which attempts to discover and catalogue signals of natural variability on a wide variety of time scales.

In general terms, the winter forecast for the UK and Ireland is for milder than average conditions about two-thirds of the time, and colder than average about one-third of the time, in the main winter months of December, January and February. I could add that both November and March show similar outcomes in the research model output so whatever your preference for a winter season, this should apply, mild spells will tend to outnumber cold spells.

December looks particularly mild as well as early November, and mid to late February. January shows the greatest parity of mild and cold spells and may end up closer to long-term normal values. My IMT predictions with CET predictions in brackets for the various months at this early stage are

NOV 7.5 (7.2) -- about 1-2 above normal
DEC 6.3 (6.1) -- about 1-2 above normal
JAN 4.5 (3.8) -- close to normal or slightly below
FEB 5.2 (4.5) -- close to normal
MAR 6.3 (6.0) -- close to normal

Although I have mentioned mild as the dominant theme, the fact that January sees more equal chances of mild and cold may rescue the winter from the category of very mild and snow-free "modern winter" that often dominated in the period 1988 to 2007, and perhaps this will be more of an "average" winter as a result, so my estimation of wintry disruption potential is something like moderate or about five to ten days in total for most regions (of the UK and eastern Ireland, probably three to seven on average in western Ireland).

I'm expecting some rather lengthy intervals of very mild southwest flow and occasional heavy rainfalls and strong winds during parts of early November, much of December, late January and possibly into part of February although here I expect any mild spells to be more caused by southerly flow associated with European blocking. March by contrast may be dominated more by cold zonal flow patterns.

When it might turn colder (notably parts of mid to late November, and then first half of January) there could be some briefly severe winter conditions and a large-scale reversal of the dominant circulation to high-latitude blocking and northeast winds so that as usual sea-effect snow could provide most of the snowfall potential with perhaps one or two cyclonic storm events in a southerly jet position. My research output is not very encouraging on severity and some of this colder weather may be of the 2006 variety, cold and dry.

Given the overall set-up around the hemisphere, I am also going for a rather cold winter in eastern and central North America, and mild in far eastern Canada and on the west coast of North America inland to about the central plains and prairies. The preferred escape route for arctic air this winter will likely be western Hudson Bay to Great Lakes towards the southeast U.S. states. Note that this pattern places ridges near 110 W and 55 W which if you do the math places the next downstream ridge close to the Greenwich (0W) meridian. That would suggest a Bartlett or Euro-high pattern but with such an active jet stream expected it's more likely to become a fast stormy (SW) flow, so I have added the detail that at least one major windstorm is probable this winter. As readers of my forecasts know, I tend to favour northern maximum around full moon in Dec (16-17) and Jan (15-16) for wind storm potential with new moon a secondary peak. However, the new moon of 1 January is well timed to coincide with a circulation change and so that could turn out to be the stage for the strongest windstorm potential. The following new moon event on 30-31 Jan is also well timed from the trend in the model output.

Meanwhile the chances of a white Christmas seem rather low from this perspective, with a peak in temperatures right on the 25th in the research output, in fact Christmas Day is indicated as having the best chance of all dates this winter to set a record high temperature which would be 14 to 17 C in most regions. Not saying it will necessarily be that mild but above 12 would not surprise me at all given the strength of this mild signal (which then fades away rapidly by New Years).

The coldest days of the winter are indicated to be around 10-14 January which in context of an otherwise rather mild winter brings up an analogue with Jan 1987. It may then turn out to be a case of a bland winter with one very notable cold spell which will some in from the ledge anyway.

I should conclude by noting that the range of uncertainty in these seasonal forecasts is rather large and so these percentages indicate the assessed chances of the winter ending up in each of the 20% groupings based on all past cases:

MILDEST 20% (very mild) ... chance for 2013-14 is 26%
NEXT MILDEST 20% (mild) ... chance for 2013-14 is 33%
NEAR AVERAGE 20% ... chance for 2013-14 is 25%
COLDER 20% (cool) ... chance for 2013-14 is 13%
COLDEST 20% (very cold) ... chance for 2013-14 is 3%

The median probability places this winter around 34th mildest out of 100 cases.

Any chance MT might be completely wrong and it ends up being The Big Freeze again?!