Statistically when is the coldest part of winter?

[damianslaw]

Would be good if anyone had the stats, number crunching to confirm when is on average the coldest part of the winter. I've read somewhere it is the first week of February. I'd expect the coldest core of the winter on average to be about 20 Jan - 10 Feb. 

Just like end July/early August tends to be the warmest part of the winter - helped in large part by very mild nights.

Always think late Jan/early Feb is the depths of winter, despite being some 6 weeks since the Winter Solstice. 

As the saying goes 'as the days lengthen the cold strengthens'..

Also chimes with Candlemas Day folklore on 2 Feb.. have half your hay still available to get through rest of winter - mid point between 21 Dec and 21 March.

[I remember Atlantic 252]

Just now, damianslaw said:

Would be good if anyone had the stats, number crunching to confirm when is on average the coldest part of the winter. I've read somewhere it is the first week of February. I'd expect the coldest core of the winter on average to be about 20 Jan - 10 Feb. 

Just like end July/early August tends to be the warmest part of the winter - helped in large part by very mild nights.

Always think late Jan/early Feb is the depths of winter, despite being some 6 weeks since the Winter Solstice. 

As the saying goes 'as the days lengthen the cold strengthens'..

Also chimes with Candlemas Day folklore on 2 Feb.. have half your hay still available to get through rest of winter - mid point between 21 Dec and 21 March.

the bold bit, maybe in Australia

[damianslaw]

5 minutes ago, I remember Atlantic 252 said:

the bold bit, maybe in Australia

Ha ha sorry winter on my mind!

[hillbilly]

Just had a brief lookand came up with the following.

Winters since 1970 based on the coldest temperature for each year there have been 15 days in December,18 in January and 15 in February.

Looking at the coldest temperatures recorded for each day of the year[torro] and counting days below -22 deg we have december9,January 14 and February 11.

I guess it does look like January is on that basis the coldest month but interestingly there is not any groupings around late January and early February.I would say that there are definately more colder days in the first half of January and also Februarys tally is mainly around mid month.This could change if i had time to look at a larger list of numbers.

Also interesting to note the 3 coldest temperatures recorded[since records began] all being -27.2 deg are recorded on December 30th,January 10th and February 11th.

Also noteworthy -23 deg has been recorded as early as November 14th and as late as February 18th although it was almost reached as late as March 14th.

I do see that there are two anomolys which gave a very out of place very cold spell mid November 1919 and a very late very cold spell mid March 1958 both of which can almost rank among the coldest spells at any time of winter.

[damianslaw]

Thanks for reply. First half of January and mid February then - mmm interesting. Mid Feb more likely to deliver cold anticyclonic conditions or easterlies compared to earlier in the winter so that makes sense, however, would have thought statistically second half of Jan and early Feb colder than first half of January, atlantic traditionally is a bit quieter, northerly and easterly outbreaks also likely to be more colder.

[Stargazer]

Here in Reading the university has a daily temperature record going back nearly 100 years. I remember seeing graphs somewhere, and in January and February the temperature bumps up and down a bit around a minimum of 2 and maximum of 8 - if I recall correctly the coldest individual day in their 1981-2010 record was 14 February, with around 0-7 average. The warmest day of the year by some way was 29 July.

[cheeky_monkey]

here stats wise the coldest part of winter is Mid Dec - Mid Jan..summer warmth tis early July - early August.

Edited February 1, 2021 by cheeky_monkey

[Penrith Snow]

Philip Eden in his 1996 book Weatherwise said the average coldest day is 14th January when the combination of solar input

and rapidly falling sea temperatures reach optimum levels for cold.

Any given synoptic situation will result in slightly colder weather in mid January than early January or early February 

My own observations over the years bears this out, the sun will melt snow on trees in early February but not mid January given a temperature below freezing.

Andy

[damianslaw]

1 hour ago, Penrith Snow said:

Philip Eden in his 1996 book Weatherwise said the average coldest day is 14th January when the combination of solar input

and rapidly falling sea temperatures reach optimum levels for cold.

Any given synoptic situation will result in slightly colder weather in mid January than early January or early February 

My own observations over the years bears this out, the sun will melt snow on trees in early February but not mid January given a temperature below freezing.

Andy

Yes that makes sense, mid Jan still close enough to the winter solstice to see little solar input, but also by then SST values have had time to cool markedly, likewise the continent.

By early February solar input does have a greater effect, however, the arctic is still cooling believe it or not, and northerlies I often think are colder in February and January, to an extent easterlies as well can be every bit as cold as in Jan think late Feb 2018.

I have a saying winter's back breaks in mid February, and I'm much happier when severe cold spells occur before then, optimum time is around 3rd week Jan that feels like the depths of winter, as we edge through first half of Feb there is that sense we are leaving true winter behind and moving into its latter stages.

I feel the same about summer, about 3rd week July is peak high summer for me and when I want heat, through first half of August there is that nagging feeling summer is on the wane, despite often very high temperatures.

I'm still in full winter mode until the third week in Feb, lets get a week of freezing cold in before that change happens!

[TheOgre]

I don’t think there is an exact coldest time in a mild climate. It can vary significantly. In 2010/11 December was the coldest but in 2018 early March brought the coldest temperatures. I’d say January is generally coldest inland and February along coasts but difficult to pin it down a a particular coldest week.

[Bradley in Kent]

Evening all,

I was thinking this today and looking at observations and stats, I'm going to throw in some complication! Before I start, think about percentiles, range and averages (mean, median and mode)

Daytime maximum temps:

The warmest 10 percentile of maximums in December are still relatively high owing to warm SSTs and high dew points. These 'warm days' cool away steadily to their lowest in early February before a sudden increase in late February when the sun gets to work. Typical conditions are during humid SW'ly winds in December and clear sunny days in late February.

The coldest 10 percentile of maximums are at their lowest point quite early around Christmas / NYE where solar input is low. These 'cold days' stay about the same until late February. Typical conditions are when you have freezing fog all day in early winter or keen Easterly winds later on in the season.

For the daytime maximum (all percentiles) the last day of February is the same as first day of December in terms of mean.

Nighttime minimum temps:

The warmest 10 percentile of minimums start quite high in December again due to warmer SSTs and higher dew points. These 'warm nights' are least warm mid-February and don't really get warmer again until mid-March. Typical conditions are with total cloud cover all night and windy. 

The coldest 10 percentile of minimums actually start off quite low in December and the lowest point again around Christmas / NYE. Like the coldest daytime temps, this is due to lower solar input and longer nights. These 'cold nights' then rise slightly mid-January and stay the same throughout the rest of winter and don't rise until March. Typical conditions are when there is no wind and clear skies.

Unlike daytime maxes, the average minimum temps end winter a lot lower than the beginning, despite having the coldest 10 percentile early. In fact it's not until late March when the minimums are higher than the 1st December!

To sum up:

Range and percentiles are key when talking about climate averages. Your coldest days and nights are likely to occur Christmas and New Year but this is also a time of year when you get your warmest days in winter too! 

As the season progresses, you lose the coldest coldest days, but the warmest days become less warm so on average (median) late January / early February is the coldest period. Or in other words, the range decreases through winter before widening up again in early March.

I rather enjoyed typing that out, hope you enjoyed reading it!

[shuggee]

On 21/01/2021 at 21:07, damianslaw said:

Would be good if anyone had the stats, number crunching to confirm when is on average the coldest part of the winter. I've read somewhere it is the first week of February. I'd expect the coldest core of the winter on average to be about 20 Jan - 10 Feb. 

Just like end July/early August tends to be the warmest part of the winter - helped in large part by very mild nights.

Always think late Jan/early Feb is the depths of winter, despite being some 6 weeks since the Winter Solstice. 

As the saying goes 'as the days lengthen the cold strengthens'..

Also chimes with Candlemas Day folklore on 2 Feb.. have half your hay still available to get through rest of winter - mid point between 21 Dec and 21 March.

It's in my mind too that first week of February is, on balance, the coldest part of winter. Thermal lag must have such a huge influence on our maritime climate. Interesting to read about Philip Eden's take however - a worthy weather statistician. More information needed, especially the last decade's stats. 

[damianslaw]

On 03/02/2021 at 19:18, Bradley in Kent said:

Evening all,

I was thinking this today and looking at observations and stats, I'm going to throw in some complication! Before I start, think about percentiles, range and averages (mean, median and mode)

Daytime maximum temps:

The warmest 10 percentile of maximums in December are still relatively high owing to warm SSTs and high dew points. These 'warm days' cool away steadily to their lowest in early February before a sudden increase in late February when the sun gets to work. Typical conditions are during humid SW'ly winds in December and clear sunny days in late February.

The coldest 10 percentile of maximums are at their lowest point quite early around Christmas / NYE where solar input is low. These 'cold days' stay about the same until late February. Typical conditions are when you have freezing fog all day in early winter or keen Easterly winds later on in the season.

For the daytime maximum (all percentiles) the last day of February is the same as first day of December in terms of mean.

Nighttime minimum temps:

The warmest 10 percentile of minimums start quite high in December again due to warmer SSTs and higher dew points. These 'warm nights' are least warm mid-February and don't really get warmer again until mid-March. Typical conditions are with total cloud cover all night and windy. 

The coldest 10 percentile of minimums actually start off quite low in December and the lowest point again around Christmas / NYE. Like the coldest daytime temps, this is due to lower solar input and longer nights. These 'cold nights' then rise slightly mid-January and stay the same throughout the rest of winter and don't rise until March. Typical conditions are when there is no wind and clear skies.

Unlike daytime maxes, the average minimum temps end winter a lot lower than the beginning, despite having the coldest 10 percentile early. In fact it's not until late March when the minimums are higher than the 1st December!

To sum up:

Range and percentiles are key when talking about climate averages. Your coldest days and nights are likely to occur Christmas and New Year but this is also a time of year when you get your warmest days in winter too! 

As the season progresses, you lose the coldest coldest days, but the warmest days become less warm so on average (median) late January / early February is the coldest period. Or in other words, the range decreases through winter before widening up again in early March.

I rather enjoyed typing that out, hope you enjoyed reading it!

Thanks. Surprised with the low means and maxima around Christmas and new year. I guess due to lack of solar input temps struggle to rise at that time of year. Absolute low means I would expect later in Jan or early Feb.

 

[Harry233]

For myself I would say the coldest part of winter is usually late January/early February. December isn’t usually overly cold although there is cold snaps but aside from 2009/2010 I can’t recall any other Decembers with any significant snow that’s lasted more than a couple of days I would even say March is snowier than December. Recently the years where I’ve recorded the most snow is around late January. I would say generally February is the Frostiest and calmest winter month however due to the days getting considerably longer there can be quite mild days like 2019 where I recorded freezing temperatures but also 15.C come the afternoon.

[damianslaw]

13 hours ago, Harry233 said:

For myself I would say the coldest part of winter is usually late January/early February. December isn’t usually overly cold although there is cold snaps but aside from 2009/2010 I can’t recall any other Decembers with any significant snow that’s lasted more than a couple of days I would even say March is snowier than December. Recently the years where I’ve recorded the most snow is around late January. I would say generally February is the Frostiest and calmest winter month however due to the days getting considerably longer there can be quite mild days like 2019 where I recorded freezing temperatures but also 15.C come the afternoon.

February can be one of the driest months in the Lake District. Indeed we are now entering the drier third of the year here, roughly lasting mid Feb to mid June, the dry season!