Weather

High pressure is now firmly in charge of our weather, although certainly for much of Yorkshire and Lincolnshire it’s been disappointingly cloudy.

 

A feed of moist northerly air around the periphery of the area of high pressure is to blame, with southern and western parts of the UK most favoured in these situations.

 

Nevertheless, the predominantly dry and settled conditions which were predicted around 10 days ago look set to continue well into next week.

 

It’s at this time of the year that climatologist Professor Lamb’s work is of interest.

 

He studied 100 years of weather patterns to determine whether any repeated themselves.

 

One of the patterns which Lamb discovered is called the ‘return of the westerlies’, during the second half of June.

 

It describes a resumption of an unsettled and changeable pattern of weather, with areas of low pressure and associated rain-bearing weather fronts spreading eastwards across the UK from the Atlantic.

 

This follows a period through late spring and early summer when westerly winds are at their weakest.

 

Some models are indicating a more unsettled westerly pattern at the very end of June and into the first week of July; although in forecast terms it’s still a long way off.

Comments

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  • Comment number 93. Posted by JaimeJ

    on 24 Jun 2014 14:37

    Heavy rain here where only light rain shower was forecast. High pressure system is breaking up now and it looks like lows will dominate for a while, though not with any particularly pronounced westerlies. Temperatures near normal or on cool side. All in all, a rather typical damp British summer in the making. Jet stream predicted to run well south of the British isles at first, then there's the possibility it will slam directly into us first week of July. What happened to that drought we were supposed to have?

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  • Comment number 92. Posted by QuaesoVeritas

    on 24 Jun 2014 07:50

    I've never fully understood the relationship between the daily summary and the daily detail on the MO 5 day web forecast.

    Here is a comparison between the current daily summaries and the actual daily range in the forecast for temperature at Albemarle:

    24/6/14 Daily summary max. 16c, min. 7c. Actual range max. 15c, min. 10c.
    25/6/14 Daily summary max. 16c, min. 9c. Actual range max. 15c, min. 8c.
    26/6/14 Daily summary max. 17c, min. 10c. Actual range max. 16c, min. 10c.
    27/6/14 Daily summary max. 16c, min. 10c. Actual range max. 14c, min. 10c.
    28/6/14 Daily summary max. 16c, min. 10c. Actual range max. 15c, min. 10c.

    As you can see, the daily summaries rarely tie in with the daily range and sometimes differ by 2c or more.

    When I asked the MO why this was, this is the explanation I received:

    "If by "detailed forecast" you mean the 3 hourly breakdown, these time steps, as I am sure we have explained before, are derived from our models of the atmosphere based on observations from around the world and across the UK. There is no manual editing or intervention and represent a snapshot for how the model predicts the weather or temperatures will behave at or near that place, at or near that time. This means that at any time between a 3 hour period, the maximum temperature for the day could exceed a snapshot temperature. "

    The MO seem to find this explanation perfectly acceptable. It was written before the MO changed to hourly forecasts for the first 2 days, but it still happens.
    What it doesn't explain is why there should be a difference between the hourly figures and the daily "snapshot" which would require "manual intervention".

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  • Comment number 91. Posted by QuaesoVeritas

    on 24 Jun 2014 07:46

    Raining here at the moment.
    There was rain at 11:00 in the forecast issued at 06;00 but there's none at all in the one issued at 07:00.

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  • Comment number 90. Posted by waikuku

    on 23 Jun 2014 17:46

    @86 . . . ""Snow also melts, refreezes, and new snow can fall on top. This makes it difficult to discern how much snow has fallen at different times or on different days." . . . Why would that be a problem if you are only using snow on the ground to measuring depth?"

    In terms of rainfall equivalent it doesn't, snow or other solid ppn in the gauge will be measured at intervals relevant to the observing/reporting station and then - if appropriate - added to the climatological records of such a station.

    For a snow cover/depth report, if several 'falls' had occurred since a previous observation then unless it was continually observed/recorded it would be difficult to apportion what depth had occurred at what time. Usually cover/depth is reported at 0900utc and records of snow lying refer to those observations. That doesn't mean depths and coverage cannot be recorded at other times and in certain winter weather it is useful to have regularly updated info.

    The water content of ppn lying on the ground will vary according to prevailing temperatures and humidity. For example, in cold sub-zero temps if you lifted a sample of lying snow, melted it and observed the water content it would be less than the same sample lifted in fog (100% humidity) and a temperature of zero and in turn that sample would dry out again if the temperature and prevailing humidity fell. (In my truncated post earlier today I referred to sublimation which is basically the drying out of snow on the ground and this occurs even with sub zero temps and is often why over a period of days without snow the snow seems to gradually disappear). Another reason why, if it is not in the gauge it would not be measured and added to rainfall stats.

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  • Comment number 89. Posted by newdwr54

    on 23 Jun 2014 16:50

    NOAA out for May 2014: warmest May on record: http://www.ncdc.noaa.gov/sotc/global/2014/5

    Though I see that April 2014 has been relegated from joint warmest to second warmest, behind 2010 in the latest NOAA reshuffle.

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  • Comment number 88. Posted by QuaesoVeritas

    on 23 Jun 2014 16:50

    NCDC figures posted.
    Global and NH down, SH up.
    Another record high for May.
    The main "hotspots" seem to be E.Europe, Canada and Australia, but again it's really the SH to blame.
    Not much coverage of the poles.
    http://www.ncdc.noaa.gov/sotc/service/global/map-blended-mntp/201405.gif

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  • Comment number 87. Posted by QuaesoVeritas

    on 23 Jun 2014 15:07

    Apparently "global warming" will cause more "stagnant atmospheric conditions" worsening air pollution.
    http://www.nature.com/news/air-quality-to-suffer-with-global-warming-1.15442
    This seems to contradict predictions of more "extreme weather".
    Of course it is based of computer models.

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  • Comment number 86. Posted by sjw62

    on 23 Jun 2014 10:17

    @82. waikuku

    "Snowfall on the ground is NOT measured for calculating rainfall - if it is not in the gauge it is not measured as rainfall."

    I stand corrected.

    One thing puzzles me though. In the blog I linked to earlier it says

    "Snow also melts, refreezes, and new snow can fall on top. This makes it difficult to discern how much snow has fallen at different times or on different days."

    Why would that be a problem if you are only using snow on the ground to measuring depth?

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  • Comment number 85. Posted by waikuku

    on 23 Jun 2014 08:29

    83 & 84

    Was related to sublimation rather than melt. . . .

    (oops apparently the blog police don't allow posting more frequently than 180 seconds - how bizarre!

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  • Comment number 84. Posted by waikuku

    on 23 Jun 2014 08:26

    83 QV - yes there was a bit more - I'll amend later if have time . . . .ta

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