Depressed Tmax and Tmin Temperatures – 7th to 10th Feb 12…

5 Feb

In association with the weekly outlook I highlighted the threat of temperatures become particularly low once again especially after Tuesday both by day and also by night across England and Wales.  Well there are interesting reasons for that and I wanted to give them a general discussion to highlight the reasons why.

For an example I have selected the last 72hr FAX chart which shows England and Wales beneath a ridge of high pressure (1036mb to 1040mb) with a weak Easterly flow around the southern flank of the ridge;

Areas of high pressure bring what are known as inversions.  Air within a region of high pressure sinks and warms as it does so which eventually creates an inversion.  This inversion can essentially trap cold air beneath it and especially during the winter months signal particularly cold temperatures at surface levels.  To help illustrate this find below a forecast sounding for Fairford in Central-Southern England for Wednesday (8th Feb) afternoon;

The inversion is evident on this image where the red line (air temperature) and blue line (dew point temperature) suddenly diverge and you can actually see the temperature (red line) suddenly rise/heading towards the right.  As I have highlighted it is beneath this region where cold air can ‘pool’ quite significantly during the winter months.  Also it is times like this when looking at 850mb temperatures don’t always tell the full story because the inversion can be below the 850mb temperature level, which in this example it is.  Generally 850mb temperatures are a good indicator as to what kind of air mass will be evident, whether it’s cold (850mb temps below -5C say) or whether it is warm like in summer when 850mb temperatures can rise to above 15C. 

So what does this all mean?.  Well in summary the combination of the high pressure and temperature inversion which is likely to develop across England and Wales combining with a weak and clearly cold air mass within the low levels of the atmosphere from off the near Continent, will herald another noteworthy spell where Maximum and Minimum temperatures are depressed.  Here’s the latest Tmax and Tmin temperatures from the GFS Det for Wednesday afternoon and then also Wednesday night into Thursday;

As can be seen at the moment Tmax are between say 0C and 3C at very most.  Not only that Tmin by the middle of the week are down to -5C to -7C generally, so in more rural and prone locations another -8C to -10C minimum temperature may be reached at times.

So, and finally, when looking at 850mb temperatures don’t always take what they are showing as gospel, as under certain circumstances they may well look uninspiring in terms of cold weather, but beneath the 850mb level (approx 5,000ft up in the air) it is a different story and can often be cold or even very cold at surface levels as this coming week will provide a perfect example of.

Wrap up warm, get Monday out of the way in particular and England and Wales are looking at a pretty cold week to say the least!.

Regards to all,



7 Responses to “Depressed Tmax and Tmin Temperatures – 7th to 10th Feb 12…”

  1. Paul c February 5, 2012 at 4:28 pm #

    Liking the new format for your extended thoughts. reads well on my phone.
    Many tks

  2. Paul February 5, 2012 at 4:59 pm #

    Cheers matt thankyou for the explanation.

    Paul S. (snowish) Burnley

  3. Lawrence February 5, 2012 at 5:31 pm #

    Hello Matt

    You may remember me from some dust ups years ago on UK.Sci. Weather. I just wanted to say how impressed I am by your progress and maturity that you show has a meteorologist and a man.

    Well done mate and I really sincerely mean that.

    All the best


    • Matt Hugo February 7, 2012 at 8:52 am #

      Hi Lawrence, yes I do remember you. Thanks for the comment, it is much appreciated after all these years. Clearly UK.Sci.Weather was something I found many years ago as a teenager in the late 90’s and into the year 2000 if I remember correctly and it did indeed end up quite unpleasant on there. I was certainly partially to blame myself and as ever we all do and say silly things when we’re younger and those days are long gone. I certainly don’t “take the bait” as easily as I did all those years ago, being 31 now life experiences have told me to do otherwise!.

      Again thanks for your comments, forecasting and meteorology was always something i’ve wanted to do and I do believe persistence and patience does pay off as I am now in a position I always wanted to be be all those years ago.

      Kind regards, Matt.

  4. Chris Armstrong February 5, 2012 at 8:55 pm #

    Great Blog Matt. I’m learning something here! Liking the cold Feb, after our mild Dec/Feb. Keep reporting cold to come 🙂

  5. (@weather_events) February 5, 2012 at 9:16 pm #

    An educational and insightful write-up Matt.. really looking forward to keeping up with your future blog posts!

  6. Chris Armstrong February 7, 2012 at 11:30 am #

    Great stuff Matt. My family and the local shopkeepers are always asking me if it is going to snow! This blog and your Twitter feed keeps me (and them) informed 🙂

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